Climate Science Documents
Soil organic matter turnover is governed by accessibility not recalcitrance
Mechanisms to mitigate global climate change by sequestering carbon (C) in different ‘sinks’ have been proposed as at least temporary measures. Of the major global C pools, terrestrial ecosystems hold the potential to capture and store substantially increased volumes of C in soil organic matter (SOM) through changes in management that are also of benefit to the multitude of ecosystem services that soils provide. This potential can only be realized by determining the amount of SOM stored in soils now, with subsequent quantification of how this is affected by management strate- gies intended to increase SOM concentrations, and used in soil C models for the prediction of the roles of soils in future climate change. An apparently obvious method to increase C stocks in soils is to augment the soil C pools with the longest mean residence times (MRT). Computer simulation models of soil C dynamics, e.g. RothC and Century, partition these refractory constituents into slow and passive pools with MRTs of centuries to millennia. This partition- ing is assumed to reflect: (i) the average biomolecular properties of SOM in the pools with reference to their source in plant litter, (ii) the accessibility of the SOM to decomposer organisms or catalytic enzymes, or (iii) constraints imposed on decomposition by environmental conditions, including soil moisture and temperature. However, con- temporary analytical approaches suggest that the chemical composition of these pools is not necessarily predictable because, despite considerable progress with understanding decomposition processes and the role of decomposer organisms, along with refinements in simulation models, little progress has been made in reconciling biochemical properties with the kinetically defined pools. In this review, we will explore how advances in quantitative analytical techniques have redefined the new understanding of SOM dynamics and how this is affecting the development and application of new modelling approaches to soil C. Keywords: C isotopes, decomposition, recalcitrance, soil C models, soil microorganisms, soil organic matter
Interactive influences of ozone and climate on streamflow of forested watersheds
The capacity of forests to mitigate global climate change can be negatively influenced by tropospheric ozone that impairs both photosynthesis and stomatal control of plant transpiration, thus affecting ecosystem productivity and watershed hydrology. We have evaluated individual and interactive effects of ozone and climate on late season streamflow for six forested watersheds (38–970 000 ha) located in the Southeastern United States. Models were based on 18–26 year data records for each watershed and involved multivariate analysis of interannual variability of late season streamflow in response to physical and chemical climate during the growing season. In all cases, some combination of ozone variables significantly improved model performance over climate-only models. Effects of ozone and ozone 9 climate interactions were also consistently negative and were proportional to variations in actual ozone exposures, both spatially across the region and over time. Conservative estimates of the influence of ozone on the variability (R2) of observed flow ranged from 7% in the area of lowest ozone exposure in West Virginia to 23% in the areas of highest exposure in Tennessee. Our results are supported by a controlled field study using free-air concentration enrichment methodology which indicated progres- sive ozone-induced loss of stomatal control over tree transpiration during the summer in mixed aspen-birch stands. Despite the frequent assumption that ozone reduces tree water loss, our findings support increasing evidence that ozone at near ambient concentrations can reduce stomatal control of leaf transpiration, and increase water use. Increases in evapotranspiration and associated streamflow reductions in response to ambient ozone exposures are expected to episod- ically increase the frequency and severity of drought and affect flow-dependent aquatic biota in forested watersheds. Regional and global models of hydrologic cycles and related ecosystem functions should consider potential interactions of ozone with climate under both current and future warmer and ozone-enriched climatic conditions. Keywords: climate, drought enhancement, forest water use, ozone, streamflow
Hydrology, forests and precipitation recycling: a reply to van der Ent et al
We warmly welcome the debate our article on the relationship between forest cover and water yield has inspired.....We read with general satisfaction their view that: ‘Ellison et al. (2012a) [have] initiated an important shift in thinking of forests as water suppliers, instead of mere water users’.On the other hand, we regret that we are required to point out and correct a number of misplaced criticisms and misrepresentations of our work. climate change adaptation, ecosystem services, forests, precipitation recycling, water yield
CO2 emissions from land-use change affected more by nitrogen cycle, than by the choice of land-cover data
The high uncertainty in land-based CO2 fluxes estimates is thought to be mainly due to uncertainty in not only quantifying historical changes among forests, croplands, and grassland, but also due to different processes included in calculation methods. Inclusion of a nitrogen (N) cycle in models is fairly recent and strongly affects carbon (C) fluxes. In this study, for the first time, we use a model with C and N dynamics with three distinct historical reconstructions of land-use and land-use change (LULUC) to quantify LULUC emissions and uncertainty that includes the integrated effects of not only climate and CO2 but also N. The modeled global average emissions including N dynamics for the 1980s, 1990s, and 2000–2005 were 1.8 ` 0.2, 1.7 ` 0.2, and 1.4 ` 0.2 GtC yr␣1, respectively, (mean and range across LULUC data sets). The emissions from tropics were 0.8 ` 0.2, 0.8 ` 0.2, and 0.7 ` 0.3 GtC yr␣1, and the non tropics were 1.1 ` 0.5, 0.9 ` 0.2, and 0.7 ` 0.1 GtC yr␣1. Compared to previous studies that did not include N dynamics, modeled net LULUC emissions were higher, particularly in the non tropics. In the model, N limitation reduces regrowth rates of vegetation in temperate areas resulting in higher net emissions. Our results indicate that exclusion of N dynamics leads to an underestimation of LULUC emissions by around 70% in the non tropics, 10% in the tropics, and 40% globally in the 1990s. The differences due to inclusion/exclusion of the N cycle of 0.1 GtC yr␣1 in the tro- pics, 0.6 GtC yr␣1 in the non tropics, and 0.7 GtC yr␣1 globally (mean across land-cover data sets) in the 1990s were greater than differences due to the land-cover data in the non tropics and globally (0.2 GtC yr␣1). While land-cover information is improving with satellite and inventory data, this study indicates the importance of accounting for different processes, in particular the N cycle. Keywords: carbon cycle, carbon emissions, land-use change, model, nitrogen cycle
Annual plants change in size over a century of observations
Abstract Studies have documented changes in animal body size over the last century, but very little is known about changes in plant sizes, even though reduced plant productivity is potentially responsible for declines in size of other organisms. Here, I ask whether warming trends in the Great Basin have affected plant size by measuring specimens preserved on herbarium sheets collected between 1893 and 2011. I asked how maximum and minimum temperatures, precipitation, and the Pacific Decadal Oscillation (PDO) in the year of collection affected plant height, leaf size, and flower number, and asked whether changes in climate resulted in decreasing sizes for seven annual forbs. Species had contrasting responses to climate factors, and would not necessarily be expected to respond in parallel to climatic shifts. There were generally positive relationships between plant size and increased minimum and maximum temperatures, which would have been predicted to lead to small increases in plant sizes over the observation period. While one species increased in size and flower number over the observation period, five of the seven species decreased in plant height, four of these decreased in leaf size, and one species also decreased in flower production. One species showed no change. The mechanisms behind these size changes are unknown, and the limited data available on these species (germination timing, area of occupancy, relative abundance) did not explain why some species shrank while others grew or did not change in size over time. These results show that multiple annual forbs are decreasing in size, but that even within the same functional group, species may have contrasting responses to similar environmental stimuli. Changes in plant size could have cascading effects on other members of these communities, and differential responses to directional change may change the composition of plant communities over time.
Post-clearcut dynamics of carbon, water and energy exchanges in a midlatitude temperate, deciduous broadleaf forest environment
Clearcutting and other forest disturbances perturb carbon, water, and energy balances in significant ways, with corre- sponding influences on Earth’s climate system through biogeochemical and biogeophysical effects. Observations are needed to quantify the precise changes in these balances as they vary across diverse disturbances of different types, severities, and in various climate and ecosystem type settings. This study combines eddy covariance and micrometeo- rological measurements of surface-atmosphere exchanges with vegetation inventories and chamber-based estimates of soil respiration to quantify how carbon, water, and energy fluxes changed during the first 3 years following forest clearing in a temperate forest environment of the northeastern US. We observed rapid recovery with sustained increases in gross ecosystem productivity (GEP) over the first three growing seasons post-clearing, coincident with large and relatively stable net emission of CO2 because of overwhelmingly large ecosystem respiration. The rise in GEP was attributed to vegetation changes not environmental conditions (e.g., weather), but attribution to the expan- sion of leaf area vs. changes in vegetation composition remains unclear. Soil respiration was estimated to contribute 44% of total ecosystem respiration during summer months and coarse woody debris accounted for another 18%. Evapotranspiration also recovered rapidly and continued to rise across years with a corresponding decrease in sensi- ble heat flux. Gross short-wave and long-wave radiative fluxes were stable across years except for strong wintertime dependence on snow covered conditions and corresponding variation in albedo. Overall, these findings underscore the highly dynamic nature of carbon and water exchanges and vegetation composition during the regrowth following a severe forest disturbance, and sheds light on both the magnitude of such changes and the underlying mechanisms with a unique example from a temperate, deciduous broadleaf forest. Keywords: carbon balance, evapotranspiration, forest disturbance and regrowth, forest management, net ecosystem productivity
Mountain landscapes offer few opportunities for high-elevation tree species migration
Climate change is anticipated to alter plant species distributions. Regional context, notably the spatial complexity of climatic gradients, may influence species migration potential. While high-elevation species may benefit from steep cli- mate gradients in mountain regions, their persistence may be threatened by limited suitable habitat as land area decreases with elevation. To untangle these apparently contradictory predictions for mountainous regions, we evalu- ated the climatic suitability of four coniferous forest tree species of the western United States based on species distri- bution modeling (SDM) and examined changes in climatically suitable areas under predicted climate change. We used forest structural information relating to tree species dominance, productivity, and demography from an exten- sive forest inventory system to assess the strength of inferences made with a SDM approach. We found that tree spe- cies dominance, productivity, and recruitment were highest where climatic suitability (i.e., probability of species occurrence under certain climate conditions) was high, supporting the use of predicted climatic suitability in examin- ing species risk to climate change. By predicting changes in climatic suitability over the next century, we found that climatic suitability will likely decline, both in areas currently occupied by each tree species and in nearby unoccupied areas to which species might migrate in the future. These trends were most dramatic for high elevation species. Cli- matic changes predicted over the next century will dramatically reduce climatically suitable areas for high-elevation tree species while a lower elevation species, Pinus ponderosa, will be well positioned to shift upslope across the region. Reductions in suitable area for high-elevation species imply that even unlimited migration would be insufficient to offset predicted habitat loss, underscoring the vulnerability of these high-elevation species to climatic changes. Keywords: climate change, demography, dominance, forest inventory and analysis, productivity, suitability, tree species, upslope migration
Divergent phenological response to hydroclimate variability in forested mountain watersheds
Mountain watersheds are primary sources of freshwater, carbon sequestration, and other ecosystem services. There is significant interest in the effects of climate change and variability on these processes over short to long time scales. Much of the impact of hydroclimate variability in forest ecosystems is manifested in vegetation dynamics in space and time. In steep terrain, leaf phenology responds to topoclimate in complex ways, and can produce specific and measurable shifts in landscape forest patterns. The onset of spring is usually delayed at a specific rate with increasing elevation (often called Hopkins’ Law; Hopkins, 1918), reflecting the dominant controls of temperature on greenup timing. Contrary with greenup, leaf senescence shows inconsistent trends along elevation gradients. Here, we present mechanisms and an explanation for this variability and its significance for ecosystem patterns and services in response to climate. We use moderate-resolution imaging spectro-radiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data to derive landscape-induced phenological patterns over topoclimate gradients in a humid temperate broadleaf forest in southern Appalachians. These phenological patterns are validated with different sets of field observations. Our data demonstrate that divergent behavior of leaf senescence with elevation is closely related to late growing season hydroclimate variability in temperature and water balance patterns. Specifically, a drier late growing season is associated with earlier leaf senescence at low elevation than at middle elevation. The effect of drought stress on vegetation senescence timing also leads to tighter coupling between growing season length and ecosystem water use estimated from observed precipitation and runoff generation. This study indicates increased late growing season drought may be leading to divergent ecosystem response between high and low elevation forests. Landscape-induced phenological patterns are easily observed over wide areas and may be used as a unique diagnos- tic for sources of ecosystem vulnerability and sensitivity to hydroclimate change. Keywords: drought deciduousness, hydroclimate variability, landscape phenology, MODIS NDVI, topoclimate gradient
Trend changes in global greening and browning: contribution of short-term trends to longer-term change
Field observations and time series of vegetation greenness data from satellites provide evidence of changes in terres- trial vegetation activity over the past decades for several regions in the world. Changes in vegetation greenness over time may consist of an alternating sequence of greening and/or browning periods. This study examined this effect using detection of trend changes in normalized difference vegetation index (NDVI) satellite data between 1982 and 2008. Time series of 648 fortnightly images were analyzed using a trend breaks analysis (BFAST) procedure. Both abrupt and gradual changes were detected in large parts of the world, especially in (semi-arid) shrubland and grass- land biomes where abrupt greening was often followed by gradual browning. Many abrupt changes were found around large-scale natural influences like the Mt Pinatubo eruption in 1991 and the strong 1997/98 El Nin ̃o event. The net global figure – considered over the full length of the time series – showed greening since the 1980s. This is in line with previous studies, but the change rates for individual short-term segments were found to be up to five times higher. Temporal analysis indicated that the area with browning trends increased over time while the area with greening trends decreased. The Southern Hemisphere showed the strongest evidence of browning. Here, periods of gradual browning were generally longer than periods of gradual greening. Net greening was detected in all biomes, most conspicuously in croplands and least conspicuously in needleleaf forests. For 15% of the global land area, trends were found to change between greening and browning within the analysis period. This demonstrates the importance of accounting for trend changes when analyzing long-term NDVI time series. Keywords: GIMMS NDVI, global greening and browning, gradual and abrupt change detection, time series analysis, trend breaks
Increasing soil methane sink along a 120-year afforestation chronosequence is driven by soil moisture
Upland soils are important sinks for atmospheric methane (CH4), a process essentially driven by methanotrophic bacteria. Soil CH4 uptake often depends on land use, with afforestation generally increasing the soil CH4 sink. How- ever, the mechanisms driving these changes are not well understood to date. We measured soil CH4 and N2O fluxes along an afforestation chronosequence with Norway spruce (Picea abies L.) established on an extensively grazed subal- pine pasture. Our experimental design included forest stands with ages ranging from 25 to >120 years and included a factorial cattle urine addition treatment to test for the sensitivity of soil CH4 uptake to N application. Mean CH4 uptake significantly increased with stand age on all sampling dates. In contrast, CH4 oxidation by sieved soils incu- bated in the laboratory did not show a similar age dependency. Soil CH4 uptake was unrelated to soil N status (but cattle urine additions stimulated N2O emission). Our data indicated that soil CH4 uptake in older forest stands was driven by reduced soil water content, which resulted in a facilitated diffusion of atmospheric CH4 into soils. The lower soil moisture likely resulted from increased interception and/or evapotranspiration in the older forest stands. This mechanism contrasts alternative explanations focusing on nitrogen dynamics or the composition of methano- trophic communities, although these factors also might be at play. Our findings further imply that the current dramatic increase in forested area increases CH4 uptake in alpine regions. Keywords: afforestation, alpine regions, chronosequence, fertilization, methane oxidation, nitrous oxide, Norway spruce, soil moisture regime
Rethinking species’ ability to cope with rapid climate change
Ongoing climate change is assumed to be exceptional because of its unprecedented velocity. However, new geophysical research suggests that dramatic climatic changes during the Late Pleistocene occurred extremely rapid, over just a few years. These abrupt climatic changes may have been even faster than contemporary ones, but relatively few continent-wide extinctions of species have been documented for these periods. This raises questions about the ability of extant species to adapt to ongoing climate change. We propose that the advances in geophysical research challenge current views about species’ ability to cope with climate change, and that lessons must be learned for modelling future impacts of climate change on species. Keywords: adaptation, biodiversity, dispersal, extinction, habitat fragmentation, phenotypic plasticity, rapid climate change
Biogenic vs. geologic carbon emissions and forest biomass energy production
n the current debate over the CO2 emissions implications of switching from fossil fuel energy sources to include a substantial amount of woody biomass energy, many scientists and policy makers hold the view that emissions from the two sources should not be equated. Their rationale is that the combustion or decay of woody biomass is simply part of the global cycle of biogenic carbon and does not increase the amount of carbon in circulation. This view is frequently presented as justification to implement policies that encourage the substitution of fossil fuel energy sources with biomass. We present the opinion that this is an inappropriate conceptual basis to assess the atmospheric greenhouse gas (GHG) accounting of woody biomass energy generation. While there are many other environmental, social, and economic reasons to move to woody biomass energy, we argue that the inferred benefits of biogenic emissions over fossil fuel emissions should be reconsidered. Keywords: bioenergy emissions, biogenic carbon, carbon debt, forest biomass, greenhouse gas accounting
The outcome is in the assumptions: analyzing the effects on atmospheric CO2 levels of increased use of bioenergy from forest biomass
Recently, several studies have quantified the effects on atmospheric CO2 concentration of an increased harvest level in forests. Although these studies agreed in their estimates of forest productivity, their conclusions were contradictory. This study tested the effect of four assumptions by which those papers differed. These assump- tions regard (1) whether a single or a set of repeated harvests were considered, (2) at what stage in stand growth harvest takes place, (3) how the baseline is constructed, and (4) whether a carbon-cycle model is applied. A main finding was that current and future increase in the use of bioenergy should be studied considering a series of repeated harvests. Moreover, the time of harvest should be determined based on economical principles, thus taking place before stand growth culminates, which has implications for the design of the baseline scenario. When the most realistic assumptions are used and a carbon-cycle model is applied, an increased harvest level in forests leads to a permanent increase in atmospheric CO2 concentration. Keywords: atmosphere, bioenergy, carbon, climate change, Faustmann, impulse response functions
Mineral soil carbon fluxes in forests and implications for carbon balance assessments
Forest carbon cycles play an important role in efforts to understand and mitigate climate change. Large amounts of carbon (C) are stored in deep mineral forest soils, but are often not considered in accounting for global C fluxes because mineral soil C is commonly thought to be relatively stable. We explore C fluxes associated with forest management practices by examining existing data on forest C fluxes in the northeastern US. Our findings demonstrate that mineral soil C can play an important role in C emissions, especially when considering inten- sive forest management practices. Such practices are known to cause a high aboveground C flux to the atmo- sphere, but there is evidence that they can also promote comparably high and long-term belowground C fluxes. If these additional fluxes are widespread in forests, recommendations for increased reliance on forest biomass may need to be reevaluated. Furthermore, existing protocols for the monitoring of forest C often ignore mineral soil C due to lack of data. Forest C analyses will be incomplete until this problem is resolved. Keywords: carbon accounting, deep soil mineral carbon, Forest carbon pool assessments, forest soil, stand level carbon dynamics
Methane emissions from sheep pasture, measured with an open-path eddy covariance system
Methane (CH4) is an important greenhouse gas, contributing 0.4–0.5 W m␣2 to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measure- ments of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH4, using the newly developed LI-COR LI-7700 open-path methane analyser, to measure field-scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m␣2 s␣1, whereas those in the afternoon were above 100 nmol m␣2 s␣1, and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photo- synthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60–277, year 2010), cumulative methane fluxes were 0.34 mol CH4 m␣2, equating to 134.3 g CO2 equivalents m␣2. By comparison, a carbon dioxide (CO2) sink of 819 g CO2 equivalents m␣2 was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off-site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH4 emissions per head of livestock as 7.4 kg CH4 sheep␣1 yr␣1, close to the published IPCC emission factor of 8 kg CH4 sheep␣1 yr␣1. Keywords: agriculture, carbon sink, closed path, CO2 flux, global warming potential, grassland, grazing, grazing system
Temperature-growth divergence in white spruce forests of Old Crow Flats, Yukon Territory, and adjacent regions of northwestern North America
We present a new 23-site network of white spruce ring-width chronologies near boreal treeline in Old Crow Flats, Yukon Territory, Canada. Most chronologies span the last 300 years and some reach the mid-16th century. The chro- nologies exhibit coherent growth patterns before the 1930s. However, since the 1930s, they diverge in trend and exhibit one of two contrasting, but well-replicated patterns we call Group 1 and Group 2. Over the instrumental per- iod (1930–2007) Group 1 sites were inversely correlated with previous-year July temperatures while Group 2 sites were positively correlated with growth-year June temperatures. At the broader northwestern North America (NWNA) scale, we find that the Group 1 and Group 2 patterns are common to a number of white spruce chronolo- gies, which we call NWNA 1 and NWNA 2 chronologies. The NWNA 1 and NWNA 2 chronologies also share a sin- gle coherent growth pattern prior to their divergence (ca. 1950s). Comparison of the NWNA 1/NWNA 2 chronologies against gridded 20th-century temperatures for NWNA and reconstructed northern hemisphere sum- mer temperatures (AD 1300–2000) indicates that all sites responded positively to temperature prior to the mid-20th century (at least back to AD 1300), but that some changed to a negative response (NWNA 1) while others maintained a positive response (NWNA 2). The spatial extent of divergence implies a large-scale forcing. As the divergence appears to be restricted to the 20th century, we suggest that the temperature response shift represents a moisture stress caused by an anomalously warm, dry 20th-century climate in NWNA, as indicated by paleoclimatic records. However, because some sites do not diverge and are located within a few kilometres of divergent sites, we specu- late that site-level factors have been important in determining the susceptibility of sites to the large-scale drivers of divergence. Keywords: boreal treeline, dendroclimatology, divergence, Old Crow Flats, ring-width, white spruce, Yukon Territory
Fragmentation and thermal risks from climate change interact to affect persistence of native trout in the Colorado River basin
Impending changes in climate will interact with other stressors to threaten aquatic ecosystems and their biota. Native Colorado River cutthroat trout (CRCT; Oncorhynchus clarkii pleuriticus) are now relegated to 309 isolated high- elevation (>1700 m) headwater stream fragments in the Upper Colorado River Basin, owing to past nonnative trout invasions and habitat loss. Predicted changes in climate (i.e., temperature and precipitation) and resulting changes in stochastic physical disturbances (i.e., wildfire, debris flow, and channel drying and freezing) could further threaten the remaining CRCT populations. We developed an empirical model to predict stream temperatures at the fragment scale from downscaled climate projections along with geomorphic and landscape variables. We coupled these spa- tially explicit predictions of stream temperature with a Bayesian Network (BN) model that integrates stochastic risks from fragmentation to project persistence of CRCT populations across the upper Colorado River basin to 2040 and 2080. Overall, none of the populations are at risk from acute mortality resulting from high temperatures during the warmest summer period. In contrast, only 37% of populations have a ! 90% chance of persistence for 70 years (simi- lar to the typical benchmark for conservation), primarily owing to fragmentation. Populations in short stream frag- ments <7 km long, and those at the lowest elevations, are at the highest risk of extirpation. Therefore, interactions of stochastic disturbances with fragmentation are projected to be greater threats than warming for CRCT populations. The reason for this paradox is that past nonnative trout invasions and habitat loss have restricted most CRCT popula- tions to high-elevation stream fragments that are buffered from the potential consequences of warming, but at risk of extirpation from stochastic events. The greatest conservation need is for management to increase fragment lengths to forestall these risks. Keywords: climate change, cutthroat trout, fragmentation, multiple stressors, native fish, stream temperature model, stream warming
Comparing carbon sequestration in temperate freshwater wetland communities
High productivity and waterlogged conditions make many freshwater wetlands significant carbon sinks. Most wet- land carbon studies focus on boreal peatlands, however, with less attention paid to other climates and to the effects of hydrogeomorphic settings and the importance of wetland vegetation communities on carbon sequestration. This study compares six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: an isolated depressional wetland site connected to the groundwater table, and a riverine flow-through wetland site that receives water from an agricultural watershed. Three cores were extracted in each community and analyzed for total carbon content to determine the soil carbon pool. Sequestration rates were determined by radiometric dating with 137Cs and 210Pb on a set of composite cores extracted in each of the six communities. Cores were also extracted in uplands adjacent to the wetlands at each site. Wetland communities had accretion rates ranging from 3.0 to 6.2 mm yr␣1. The depressional wetland sites had higher (P < 0.001) organic content (146 ± 4.2 gC kg␣1) and lower (P < 0.001) bulk density (0.55 ± 0.01 Mg m␣3) than the riverine ones (50.1 ± 6.9 gC kg␣1 and 0.74 ± 0.06 Mg m␣3). The soil carbon was 98–99% organic in the isolated depressional wetland communities and 85–98% organic in the riv- erine ones. The depressional wetland communities sequestered 317 ± 93 gC m␣2 yr␣1, more (P < 0.01) than the river- ine communities that sequestered 140 ± 16 gC m␣2 yr␣1. The highest sequestration rate was found in the Quercus palustris forested wetland community (473 gC m␣2 yr␣1), while the wetland community dominated by water lotus (Nelumbo lutea) was the most efficient of the riverine communities, sequestering 160 gC m␣2 yr␣1. These differences in sequestration suggest the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets. Keywords: 137Cs, 210Pb, carbon accumulation, Gahanna Woods, Nelumbo lutea, Old Woman Creek, Phragmites australis, Quercus palustris, wetland community, wetland hydrgeomorphology
Linking forest fires to lake metabolism and carbon dioxide emissions in the boreal region of Northern Quebec
Natural fires annually decimate up to 1% of the forested area in the boreal region of Que ́bec, and represent a major structuring force in the region, creating a mosaic of watersheds characterized by large variations in vegetation structure and composition. Here, we investigate the possible connections between this fire-induced watershed heterogeneity and lake metabolism and CO2 dynamics. Plankton respiration, and water–air CO2 fluxes were measured in the epilimnia of 50 lakes, selected to lie within distinct watershed types in terms of postfire terrestrial succession in the boreal region of Northern Que ́ bec. Plankton respiration varied widely among lakes (from 21 to 211lgCL1day1), was negatively related to lake area, and positively related to dis- solved organic carbon (DOC). All lakes were supersaturated in CO2 and the resulting carbon (C) flux to the atmosphere (150 to over 3000 mg C m2 day1) was negatively related to lake area and positively to DOC concentration. CO2 fluxes were positively related to integrated water column respiration, suggesting a biological component in this flux. Both respiration and CO2 fluxes were strongly negatively related to years after the last fire in the basin, such that lakes in recently burnt basins had significantly higher C emissions, even after the influence of lake size was removed. No significant differences were found in nutrients, chlorophyll, and DOC between lakes in different basin types, suggesting that the fire-induced watershed features influence other, more subtle aspects, such as the quality of the organic C reaching lakes. The fire-induced enhancement of lake organic C mineralization and C emissions represents a long-term impact that increases the overall C loss from the landscape as the result of fire, but which has never been included in current regional C budgets and future projections. The need to account for this additional fire-induced C loss becomes critical in the face of predictions of increasing incidence of fire in the circumboreal landscape. Keywords: boreal, carbon dioxide flux, climate, forest fire, lakes, organic carbon, plankton respiration, watershed
Climate change, income and happiness: An empirical study for Barcelona
The present article builds upon the results of an empirical study exploring key factors which determine life satisfaction in Barcelona. Based on a sample of 840 individuals we first look at the way changes in income, notably income reductions, associated with the current economic situation in Spain, affect subjective well-being. Income decreases which occur with respect to one year ago have a negative effect on happiness when specified in logarithmic terms, and a positive one when specified as a dummy variable (and percentage change). The divergence in results is discussed and various explanations are put forward. Both effects are however temporary and do not hold for a period longer than a year, probably for reasons of adaptation and a downward adjustment of reference consumption and income levels. Next, we examine the implications of experiencing forest fires and find a lasting negative effect on life satisfaction. Our results suggest that climate policy need not reduce happiness in the long run, even when it reduces income and carbon-intensive consumption. Climate policy may even raise life well- being, if accompanied by compensatory measures that decrease formal working hours and reference consumption standards, while maintaining employment security.
Potential of geoengineering highly uncertain
1st paragraph: Despite having the knowledge and tools to dial back greenhouse gas emissions from fossil fuel burning and land-use change, humanity seems on track to continue with business as usual, concludes Geoengineering the climate: Science, governance and un- certainty, a report from the U.K.’s Royal Society. The report emphasizes that emissions reductions re- main the first priority for mitigating global warming, but geoengineering could play a role as a tool of last resort in the face of a future climate crisis. And so, we’d better learn something about it.
Classification of Climate Change-Induced Stresses on Biological Diversity
Conservation actions need to account for and be adapted to address changes that will occur under global climate change. The identification of stresses on biological diversity (as defined in the Convention on Biological Diversity) is key in the process of adaptive conservation management. We considered any impact of climate change on biological diversity a stress because such an effect represents a change (negative or positive) in key ecological attributes of an ecosystem or parts of it. We applied a systemic approach and a hierarchical framework in a comprehensive classification of stresses to biological diversity that are caused directly by global climate change. Through analyses of 20 conservation sites in 7 countries and a review of the literature, we identified climate-change-induced stresses. We grouped the identified stresses according to 3 levels of biological diversity: stresses that affect individuals and populations, stresses that affect biological communities, and stresses that affect ecosystem structure and function. For each stress category, we differentiated 3 hierarchical levels of stress: stress class (thematic grouping with the coarsest resolution, 8); general stresses (thematic groups of specific stresses, 21); and specific stresses (most detailed definition of stresses, 90). We also compiled an overview of effects of climate change on ecosystem services using the categories of the Millennium Ecosystem Assessment and 2 additional categories. Our classification may be used to identify key climate-change-related stresses to biological diversity and may assist in the development of appropriate conservation strategies. The classification is in list format, but it accounts for relations among climate-change-induced stresses. Keywords: adaptation, conservation, strategies,adaptive management,climatechange,conservation planning, conservation targets, hierarchical framework, threats to biological diversity
Higher Hydroclimatic Intensity with Global Warming
Because of their dependence on water, natural and human systems are highly sensitive to changes in the hydrologic cycle. The authors introduce a new measure of hydroclimatic intensity (HY-INT), which integrates metrics of precipitation intensity and dry spell length, viewing the response of these two metrics to global warming as deeply interconnected. Using a suite of global and regional climate model experiments, it is found that increasing HY-INT is a consistent and ubiquitous signature of twenty-first-century, greenhouse gas– induced global warming. Depending on the region, the increase in HY-INT is due to an increase in precipitation intensity, dry spell length, or both. Late twentieth-century observations also exhibit dominant positive HY-INT trends, providing a hydroclimatic signature of late twentieth-century warming. The authors find that increasing HY-INT is physically consistent with the response of both precipitation intensity and dry spell length to global warming. Precipitation intensity increases because of increased atmospheric water holding capacity. However, increases in mean precipitation are tied to increases in surface evaporation rates, which are lower than for atmospheric moisture. This leads to a reduction in the number of wet days and an increase in dry spell length. This analysis identifies increasing hydroclimatic intensity as a robust integrated response to global warming, implying increasing risks for systems that are sensitive to wet and dry extremes and providing a potential target for detection and attribution of hydroclimatic changes.
Relationship between fire, climate oscillations, and drought in British Columbia, Canada, 1920–2000
Climate oscillations such as El Nin ̃o–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are known to affect temperature and precipitation regimes and fire in different regions of the world. Understanding the relationships between climate oscillations, drought, and area burned in the past is required for anticipating potential impacts of regional climate change and for effective wildfire-hazard management. These relationships have been investigated for British Columbia (BC), Canada, either as part of national studies with coarse spatial resolution or for single ecosystems. Because of BC’s complex terrain and strong climatic gradients, an investigation with higher spatial resolution may allow for a spatially complete but differentiated picture. In this study, we analyzed the annual proportion burned– climate oscillation–drought relationships for the province’s 16 Biogeoclimatic Ecosystem Classification (BEC) zones. Analyses are based on a digital, spatially explicit fire database, climate oscillation indices, and monthly precipitation and temperature data with a spatial resolution of 400 m for the period 1920–2000. Results show that (1) fire variability is better related to summer drought than to climate oscillations, and that (2) fire variability is most strongly related to both, climate oscillations and summer drought in southeastern BC. The relationship of area burned and summer drought is strong for lower elevations in western BC as well. The influence of climate oscillations on drought is strongest and most extensive in winter and spring, with higher indices being related to drier conditions. Winter and spring PDO and additive winter and spring PDO ENSO indices show BC’s most extensive significant relationship to fire variability. Western BC is too wet to show a moisture deficit in summer that would increase annual area burned due to teleconnections. Keywords: area burned, aridity index, Canada, ENSO, PDO, wildfire
GLOBAL WARMING AND FISH MIGRATIONS
Ocean temperatures are expected to rise over the next decades. This is likely to affect the distribution of fish stocks between the exclusive economic zones (EEZs) of different countries. Such changes are likely to be triggered as temperatures rise beyond certain threshold levels, and they are likely to be irregular because temperatures are likely to vary around a rising trend. The paper looks at the case where temperature changes would displace a fish stock out of the EEZ of one country and into the EEZ of another, with a transition period in which the stock is shared. It is examined how this might affect the risk of extinction and degree of overfishing, under different cost scenarios and different assumptions about how countries react to observed changes in the distri- bution of the stock between their economic zones.
Climate change and the world economy: short-run determinants of atmospheric CO2
Volcanic eruptions, the El Nin ̃ o Southern oscillation (ENSO), world population, and the world economy are the four variables usually discussed as influencing the short-run changes in CO2 atmospheric levels through their influence on CO2 emissions and sinks. Using proper procedures of detrending, we do not find any observable relation between the short-term growth of world population and the increase of CO2 concentrations. Results suggest that the link between volcanic eruptions, ENSO activity, and CO2 concentrations may be confounded by the coincidence of the Pinatubo eruption with the breakdown of the economies of the Soviet Bloc in the early 1990s. Changes in world GDP (WGDP) have a significant effect on CO2 concentrations, so that years of above-trend WGDP are years of greater rise of CO2 concentrations. Measuring WGDP in constant US dollars of 2000, for each trillion WGDP deviates from trend, the atmospheric CO2 concentration has deviated from trend, in the same direction, about half a part per million.
Timing of climate variability and grassland productivity
Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and high- intensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing. Konza | net primary production | streamflow | critical climate periods
The Influence of Climate, Soils, Weather, and Land Use on Primary Production and Biomass Seasonality in the US Great Plains
Identifying the conditions and mechanisms that control ecosystem processes, such as net primary production, is a central goal of ecosystem ecology. Ideas have ranged from single limiting-resource theories to colimitation by nutrients and climate, to simulation models with edaphic, climatic, and competitive controls. Although some investigators have begun to consider the influence of land-use practices, especially cropping, few studies have quantified the impact of cropping at large scales relative to other known controls over ecosystem processes. We used a 9-year record of produc- tivity, biomass seasonality, climate, weather, soil conditions, and cropping in the US Great Plains to quantify the controls over spatial and temporal patterns of net primary production and to esti- mate sensitivity to specific driving variables. We considered climate, soil conditions, and long-term average cropping as controls over spatial patterns, while weather and interannual cropping varia- tions were used as controls over temporal vari- ability. We found that variation in primary production is primarily spatial, whereas variation in seasonality is more evenly split between spatial and temporal components. Our statistical (multi- ple linear regression) models explained more of the variation in the amount of primary produc- tion than in its seasonality, and more of the spatial than the temporal patterns. Our results indicate that although climate is the most important variable for explaining spatial patterns, cropping explains a substantial amount of the residual variability. Soil texture and depth con- tributed very little to our models of spatial vari- ability. Weather and cropping deviation both made modest contributions to the models of temporal variability. These results suggest that the controls over seasonality and temporal variation are not well understood. Our sensitivity analysis indicates that production is more sensitive to climate than to weather and that it is very sen- sitive to cropping intensity. In addition to iden- tifying potential gaps in out knowledge, these results provide insight into the probable long- and short-term ecosystem response to changes in climate, weather, and cropping. Key words: primary production; carbon; land use; agriculture; climate; weather; soil; seasonality; cropping; grassland; US Great Plains.
SOME REFLECTIONS ON CLIMATE CHANGE, GREEN GROWTH ILLUSIONS AND DEVELOPMENT SPACE
Many economists and policy makers advocate a fundamental shift towards “green growth” as the new, qualitatively-different growth paradigm, based on enhanced material/resource/energy efficiency and drastic changes in the energy mix. “Green growth” may work well in creating new growth impulses with reduced environmental load and facilitating related technological and structural change. But can it also mitigate climate change at the required scale (i.e. significant, absolute and permanent decline of GHG emissions at global level) and pace? This paper argues that growth, technological, population-expansion and governance constraints as well as some key systemic issues cast a very long shadow on the “green growth” hopes. One should not deceive oneself into believing that such evolutionary (and often reductionist) approach will be sufficient to cope with the complexities of climate change. It may rather give much false hope and excuses to do nothing really fundamental that can bring about a U-turn of global GHG emissions. The proponents of a resource efficiency revolution and a drastic change in the energy mix need to scrutinize the historical evidence, in particular the arithmetic of economic and population growth. Furthermore, they need to realize that the required transformation goes beyond innovation and structural changes to include democratization of the economy and cultural change. Climate change calls into question the global equality of opportunity for prosperity (i.e. ecological justice and development space) and is thus a huge developmental challenge for the South and a question of life and death for some developing countries (who increasingly resist the framing of climate protection versus equity).
GREEN-TREE RETENTION IN HARVEST UNITS: BOON OR BUST FOR BIODIVERSITY?.pdf
etween trees and man there is a rift in the perception of time, and forest managers have no choice but to yield to the pace of the trees. This can make innovations in forest management difficult to evaluate. Nonetheless, innovation is key to meeting society’s changing expectations. It is not just timber anymore. Biodiversity, recreation, aesthetics, and clean water all share top billing with a sustainable crop of timber. And although novel silvicultural strategies are being promoted to meet these complex demands, without the benefit of time, it is difficult to know exactly how well they will achieve their goals.
Greenhouse Gassed: Carbon Dioxide Spells Indigestion for Food Chains
The author closes with a quote from a biologist who asks who will be chasing wild ungulates with nutrition supplements. CO2 is a fertilizer, with side effects. Plants may grow more rapidly, but at the cost of their nutritional value. Hessman interviews researchers studying this effect on a range of animals from insects to mammals.
High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years
The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.
Climate effects of global land cover change
When changing from grass and croplands to forest, there are two competing effects of land cover change on climate: an albedo effect which leads to warming and an evapotranspiration effect which tends to produce cooling. It is not clear which effect would dominate. We have performed simulations of global land cover change using the NCAR CAM3 atmospheric general circulation model coupled to a slab ocean model. We find that global replacement of current vegetation by trees would lead to a global mean warming of 1.3°C, nearly 60% of the warming produced under a doubled CO2 concentration, while replacement by grasslands would result in a cooling of 0.4°C. It has been previously shown that boreal forestation can lead to warming; our simulations indicate that mid- latitude forestation also could lead to warming. These results suggest that more research is necessary before forest carbon storage should be deployed as a mitigation strategy for global warming.
How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006
To distinguish between simultaneous natural and anthropogenic impacts on surface temperature, regionally as well as globally, we perform a robust multivariate analysis using the best available estimates of each together with the observed surface temperature record from 1889 to 2006. The results enable us to compare, for the first time from observations, the geographical distributions of responses to individual influences consistent with their global impacts. We find a response to solar forcing quite different from that reported in several papers published recently in this journal, and zonally averaged responses to both natural and anthropogenic forcings that differ distinctly from those indicated by the Intergovernmental Panel on Climate Change, whose conclusions depended on model simulations. Anthropogenic warming estimated directly from the historical observations is more pronounced between 45°S and 50°N than at higher latitudes whereas the model-simulated trends have minimum values in the tropics and increase steadily from 30 to 70°N.
Reduction of spring warming over East Asia associated with vegetation feedback
Over East Asia, surface air temperature displays a significant increasing trend particularly in early months of the year for the period of 1982 – 2000. Warming per decade is strongest in late winter, 1.5°C in February and 1.1°C in March, but is significantly reduced in spring, 0.4°C in April and 0.1°C in May. During the analysis period, the reduced temperature increase from late winter to spring is found to be in contrast with the increased vegetation greenness derived from the satellite-measured leaf area index over the domain. We examined this inverse relationship using two climate model experiments— coupled with and without a dynamic vegetation model. In both experiments, strong warming in winter is relatively well reproduced, but weak warming in spring is observed only in the coupled experiment. Analysis of the surface energy budget indicates that weaker spring warming results from an evaporative cooling effect due to the increased vegetation greenness. Over East Asia, the vegetation-evaporation feedback, therefore, may produce seasonal asymmetry in the warming trend.
Rising temperature depletes soil moisture and exacerbates severe drought conditions across southeast Australia
Over the past decade the southern catchments of the Murray Darling Basin (MDB), responsible for much of Australia’s agricultural output, have experienced a severe drought (termed the ‘‘Big Dry’’) with record high temperatures and record low inflow. We find that during the Big Dry the sensitivity of soil moisture to rainfall decline is over 80% higher than during the World War II drought from 1937 – 1945. A relationship exists between soil moisture and temperature independent of rainfall, particularly in austral spring and summer. Annually, a rise of 1°C leads to a 9% reduction in soil moisture over the southern MDB, contributing to the recent high sensitivity. Since 1950, the impact from rising temperature contributes to 45% of the total soil moisture reduction. In a warming climate, as the same process also leads to an inflow reduction, the reduced water availability can only be mitigated by increased rainfall. Other implications for future climate change are discussed.
Declining annual streamflow distributions in the Pacific Northwest United States, 1948–2006
Much of the discussion on climate change and water in the western United States centers on decreased snowpack and earlier spring runoff. Although increasing variability in annual flows has been noted, the nature of those changes is largely unexplored. We tested for trends in the distribution of annual runoff using quantile regression at 43 gages in the Pacific Northwest. Seventy-two percent of the stations showed significant (a = 0.10) declines in the 25th percentile annual flow, with half of the stations exceeding a 29% decline and a maximum decline of 47% between 1948 and 2006. Fewer stations showed statistically significant declines in either median or mean annual flow, and only five had a significant change in the 75th percentile, demonstrating that increases in variance result primarily from a trend of increasing dryness in dry years. The asymmetric trends in streamflow distributions have implications for water management and ecology well beyond those of shifted timing alone, affect both rain and snow-dominated watersheds, and contribute to earlier timing trends in high- elevation watersheds.
Observed relation between evapotranspiration and soil moisture in the North American monsoon region
Soil moisture control on evapotranspiration is poorly understood in ecosystems experiencing seasonal greening. In this study, we utilize a set of multi-year observations at four eddy covariance sites along a latitudinal gradient in vegetation greening to infer the ET-q relation during the North American monsoon. Results reveal significant seasonal, interannual and ecosystem variations in the observed ET-q relation directly linked to vegetation greening. In particular, monsoon-dominated ecosystems adjust their ET-q relation, through changes in unstressed ET and plant stress threshold, to cope with differences in water availability. Comparisons of the observed relations to the North American Regional Reanalysis dataset reveal large biases that increase where vegetation greening is more significant. The analysis presented here can be used to guide improvements in land surface model parameterization in water-limited ecosystems.
Impact of reduced Arctic sea ice on Greenland ice sheet variability in a warmer than present climate
A global climate model with interactive vegetation and a coupled ice sheet-shelf component is used to test the response of the Greenland ice sheet (GIS) to increased sea surface temperatures (SSTs) and reduced sea ice (SI) cover during the mid-Pliocene warm period (∼3 Ma) as reconstructed from proxy records. Seasonally open water in the Arctic and North Atlantic are shown to alter regional radiation budgets, storm tracks, and moisture and heat advection into the Greenland interior, with increases in temperature rather than precipitation dominating the ice sheets response. When applied to an initially glaciated Greenland, the presumed warm, ice-free Pliocene ocean conditions induce rapid melting of nearly the entire ice sheet and preclude a modern-like GIS from (re)growing, regardless of orbital forcing. The sensitivity of Greenland to imposed Pliocene ocean conditions may have serious implications for the future response of the ice sheet to continued warming in the Arctic basin.
Climate commitment in an uncertain world
Climate commitment—the warming that would still occur given no further human influence—is a fundamental metric for both science and policy. It informs us of the minimum climate change we face and, moreover, depends only on our knowledge of the natural climate system. Studies of the climate commitment due to CO2 find that global temperature would remain near current levels, or even decrease slightly, in the millennium following the cessation of emissions. However, this result overlooks the important role of the non‐CO2 greenhouse gases and aerosols. This paper shows that global energetics require an immediate and sig- nificant warming following the cessation of emissions as aerosols are quickly washed from the atmosphere, and the large uncertainty in current aerosol radiative forcing implies a large uncertainty in the climate commitment. Fundamental constraints preclude Earth returning to pre‐industrial temperatures for the indefinite future. These same constraints mean that observations are currently unable to eliminate the possibility that we are already beyond the point where the ultimate warming will exceed dangerous levels. Models produce a narrower range of climate commitment, but under- sample observed forcing constraints.
Changes in winter precipitation extremes for the western United States under a warmer climate as simulated by regional climate models
We find a consistent and statistically significant increase in the intensity of future extreme winter precipitation events over the western United States, as simulated by an ensemble of regional climate models (RCMs) driven by IPCC AR4 global climate models (GCMs). All eight simulations analyzed in this work consistently show an increase in the intensity of extreme winter precipitation with the multi-model mean projecting an area-averaged 12.6% increase in 20-year return period and 14.4% increase in 50-year return period daily precipitation. In contrast with extreme precipitation, the multi-model ensemble shows a decrease in mean winter precipitation of approximately 7.5% in the southwestern US, while the interior west shows less statistically robust increases.
Quantifying the negative feedback of vegetation to greenhouse warming: A modeling approach
Several climate models indicate that in a 2 × CO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation down‐regulation to reduce plant’s photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2 × CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous simulations with elevated CO2. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6°C. Compared to previous studies, these results imply that long term negative feedback from CO2‐induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.
Space observations of inland water bodies show rapid surface warming since 1985
Surface temperatures were extracted from nighttime thermal infrared imagery of 167 large inland water bodies distributed worldwide beginning in 1985 for the months July through September and January through March. Results indicate that the mean nighttime surface water temperature has been rapidly warming for the period 1985–2009 with an average rate of 0.045 ± 0.011°C yr−1 and rates as high as 0.10 ± 0.01°C yr−1. Worldwide the data show far greater warming in the mid‐ and high latitudes of the northern hemisphere than in low latitudes and the southern hemisphere. The analysis provides a new independent data source for assessing the impact of climate change throughout the world and indicates that water bodies in some regions warm faster than regional air temperature. The data have not been homogenized into a single unified inland water surface temperature dataset, instead the data from each satellite instrument have been treated separately and cross compared. Future work will focus on developing a single unified dataset which may improve uncertainties from any inter‐satellite biases.
Interdependence of groundwater dynamics and land-energy feedbacks under climate change
Climate change will have a significant impact on the hydrologic cycle, creating changes in freshwater resources, land cover and land–atmosphere feedbacks. Recent studies have investigated the response of groundwater to climate change but do not account for energy feedbacks across the complete hydrologic cycle1,2. Although land-surface models have begun to include an operational groundwater-type component3–5, they do not include physically based lateral surface and subsurface flow and allow only for vertical transport processes. Here we use a variably saturated groundwater flow model with integrated overland flow and land-surface model processes6–8 to examine the interplay between water and energy flows in a changing climate for the southern Great Plains, USA, an important agricultural region that is susceptible to drought. We compare three scenario simulations with modified atmospheric forcing in terms of temperature and precipitation with a simulation of present-day climate. We find that groundwater depth, which results from lateral water flow at the surface and subsurface, determines the relative susceptibility of regions to changes in temperature and precipitation. This groundwater control is critical to understand processes of recharge and drought in a changing climate.
The Myth of Smart Growth
“Smart growth” is an urban growth management strategy that applies planning and design principles intended to mitigate the impacts of continued growth. If properly applied, these principles represent a positive contribution to new urban development. However, the rhetoric of “smart growth” is that population levels and growth rates are not the problem; it’s merely a matter of how we grow. According to the “smart growth” program, if we are less wasteful and more efficient in our urban growth, we can keep growing and everything will work out fine. The “smart growth” approach is fundamentally pro-growth and does not envision an end to growth or a need to end growth. “Smart growth” is cast as a comprehensive solution, whereas it is merely a potential means of modestly reducing the environmental, social, and economic impacts of continued growth while failing to address its inevitable consequences. The “smart growth” formula has been used to discount and transform legitimate public concerns about the amount and pace of growth into a discussion about how we should best continue growing.
Wildfire, Wildlands, and People: Understanding and Preparing for Wildfire in the Wildland-Urban Interface: Gen. Tech. Rep. RMRS-GTR-299. Fort Collins, CO. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 36 p.
Fire has historically played a fundamental ecological role in many of America’s wildland areas. However, the rising number of homes in the wildland-urban interface (WUI), associated impacts on lives and property from wildfire, and escalating costs of wildfire management have led to an urgent need for communities to become “fire-adapted.” We present maps of the conterminous United States that illustrate historical natural fire regimes, the wildland-urban interface, and the number and location of structures burned since 1999. We outline a sampler of actions, programs, and community planning and development options to help decrease the risks of and damages from wildfire. Key Words: wildfire, community planning, fire-adapted, wildland-urban interface, defensible space
WATER, CLIMATE CHANGE, AND FORESTS Watershed Stewardship for a Changing Climate
Water from forested watersheds provides irreplaceable habitat for aquatic and riparian species and supports our homes, farms, industries, and energy production. Secure, high-quality water from forests is fundamental to our prosperity and our stewardship responsibility. Yet population pressures, land uses, and rapid climate change combine to seriously threaten these waters and the resilience of watersheds in most places. Forest land managers are expected to anticipate and respond to these threats and steward forested watersheds to ensure the sustained protection and provision of water and the services it provides. Effective, constructive watershed stewardship requires that we think, collaborate, and act. We think to understand the values at risk and how watersheds can remain resilient, and we support our thinking with knowledge sharing and planning. We collaborate to develop common understandings and goals for watersheds and a robust, durable capacity for response that includes all stakeholders and is guided by science. We act to secure and steward resilient watersheds that will continue to provide crucial habitats and water supplies in the coming century by implementing practices that protect, maintain, and restore watershed processes and services.
Assessing potential climate change effects on vegetation using a linked model approach
We developed a process that links the mechanistic power of dynamic global vegetation models with the detailed vegetation dynamics of state-and-transition models to project local vegetation shifts driven by projected climate change. We applied our approach to central Oregon (USA) ecosystems using three climate change scenarios to assess potential future changes in species composition and community structure. Our results suggest that: (1) legacy effects incorporated in state-and-transition models realistically dampen climate change effects on vegetation; (2) species-specific response to fire built into state-and- transition models can result in increased resistance to climate change, as was the case for ponderosa pine (Pinus ponderosa) forests, or increased sensitivity to climate change, as was the case for some shrublands and grasslands in the study area; and (3) vegetation could remain relatively stable in the short term, then shift rapidly as a consequence of increased disturbance such as wildfire and altered environmental conditions. Managers and other land stewards can use results from our linked models to better anticipate potential climate-induced shifts in local vegetation and resulting effects on wildlife habitat.
Global temperature change
We conclude that global warming of more than 1°C, relative to 2000, will constitute ‘‘dangerous’’ climate change as judged from likely effects on sea level and extermination of species. climate change El Niños global warming sea level species extinctions
State of the Wild: PERSPECTIVE OF A CLIMATOLOGIST
“Animals are on the run. Plants are migrating too.”1 I wrote those words in 2006 to draw attention to the fact that climate change was already under way. People do not notice climate change because it is masked by day-to-day weather fluctuations, and we reside in comfortable homes. Animals and plants, on the other hand, can survive only within certain climatic conditions, which are now changing. The National Arbor Day Foundation had to redraw its maps for the zones in which tree species can survive, and animals are shifting to new habitats as well. Are these gradual changes in the wild consistent with dramatic scientific assessments of a crystallizing planetary emergency? Unfortunately, yes. Present examples only hint at the scale of the planetary emergency that climate studies reveal with increasing clarity.
Sea-level and salinity fluctuations during the Paleocene–Eocene thermal maximum in Arctic Spitsbergen
Palaeoenvironmental manifestations of the Paleocene–Eocene thermal maximum (PETM; ~ 56 Ma) are relatively well documented in low- to mid-latitude settings and at high southern latitudes, but no documented high northern latitude sites record the entire hyperthermal event. We present high-resolution multi-proxy records from a PETM succession on Spitsbergen in the high Arctic (palaeolatitude ~75 °N). By comparing our results with those from Integrated Ocean Drilling Program Site 302-4A, we document regional palaeoenvironmental variations in the expression of the PETM, with evidence for major differences in basin- margin vegetation and water column oxygen depletion. Sedimentological, palynological and geochemical data demonstrate a pre-PETM sea level rise in Spitsbergen before the −4‰ δ13CTOC excursion, which culminated in maximum flooding during the peak of the event. The appearance of the dinoflagellate cyst Apectodinium before the onset of the carbon isotope excursion (CIE) corroborates that environmental change in the Arctic had begun prior to the CIE. Sedimentological and palynological evidence indicate that elevated terrestrial runoff resulted in water column stratification, providing further evidence for an intensification of the hydrological cycle during the PETM. Keywords: abrupt/rapid climate change, PETM, paleoecology, sedimentology, Spitsbergen, Arctic
Carbon Dynamics of the Forest Sector
Main points: The basic ecosystem science behind carbon dynamics in forests is relatively straightforward (really!).This science doesn’t seem to be applied very routinely in the policy arena. This mismatch is undermining the potential of the forest sector in helping to mitigate greenhouse gases in the atmosphere
Putting the Heat on Tropical Animals
Tropical animals may be particularly vulnerable to climate warming. First paragraph: Impacts of climate warming in the tropics— the cradle of biodiversity—are often predicted to be small relative to those in temperate regions (1, 2), because the rate of climate warming in the tropics is lower than at higher latitudes (3). Yet, predictions based only on the magnitude of climate change may be misleading. Models that include organismal physiology suggest that impacts of climate warming may be more severe in the tropics than in temperate regions.
Biodiversity management in the face of climate change: A review of 22 years of recommendations
Climate change creates new challenges for biodiversity conservation. Species ranges and ecological dynamics are already responding to recent climate shifts, and current reserves will not continue to support all species they were designed to protect. These problems are exacerbated by other global changes. Scholarly articles recommending measures to adapt conservation to climate change have proliferated over the last 22 years. We systematically reviewed this literature to explore what potential solutions it has identified and what consensus and direction it provides to cope with climate change. Several consistent recommendations emerge for action at diverse spatial scales, requiring leadership by diverse actors. Broadly, adaptation requires improved regional institutional coordination, expanded spatial and temporal perspective, incorporation of climate change scenarios into all planning and action, and greater effort to address multiple threats and global change drivers simultaneously in ways that are responsive to and inclusive of human communities. However, in the case of many recommendations the how, by whom, and under what conditions they can be implemented is not specified. We synthesize recommendations with respect to three likely conservation pathways: regional planning; site-scale management; and modification of existing conservation plans. We identify major gaps, including the need for (1) more specific, operational examples of adaptation principles that are consistent with unavoidable uncertainty about the future; (2) a practical adaptation planning process to guide selection and integration of recommendations into existing policies and programs; and (3) greater integration of social science into an endeavor that, although dominated by ecology, increasingly recommends extension beyond reserves and into human-occupied landscapes.
Opposing plant community responses to warming with and without herbivores
If controls over primary productivity and plant community composition are mainly environmental, as opposed to biological, then global change may result in large-scale alterations in ecosystem structure and function. This view appears to be favored among investigations of plant biomass and community responses to experimental and observed warming. In far northern and arctic ecosystems, such studies predict increasing dominance of woody shrubs with future warming and emphasize the carbon (C)-sequestration potential and consequent atmospheric feedback potential of such responses. In contrast to previous studies, we incorporated natural herbivory by muskoxen and caribou into a 5-year experimental investigation of arctic plant community response to warming. In accordance with other studies, warming increased total community biomass by promoting growth of deciduous shrubs (dwarf birch and gray willow). However, mus- koxen and caribou reduced total community biomass response, and responses of birch and willow, to warming by 19%, 46%, and 11%, respectively. Furthermore, under warming alone, the plant community shifted after 5 years away from graminoid-dominated toward dwarf birch-dominated. In contrast, where herbivores grazed, plant community composition on warmed plots did not differ from that on ambient plots after 5 years. These results highlight the potentially important and overlooked influences of vertebrate herbivores on plant community response to warming and emphasize that conservation and management of large herbivores may be an important component of mitigating ecosystem response to climate change. arctic climate change global warming herbivory species interactions
Extent and scale of local adaptation in salmonid fishes: review and meta-analysis
What is the extent and scale of local adaptation (LA)? How quickly does LA arise? And what is its underlying molecular basis? Our review and meta-analysis on salmonid fishes estimates the frequency of LA to be B55–70%, with local populations having a 1.2 times average fitness advantage relative to foreign populations or to their perfor- mance in new environments. Salmonid LA is evident at a variety of spatial scales (for example, few km to41000 km) and can manifest itself quickly (6–30 generations). As the geographic scale between populations increases, LA is generally more frequent and stronger. Yet the extent of LA in salmonids does not appear to differ from that in other assessed taxa. Moreover, the frequency with which foreign salmonid populations outperform local populations (B23– 35%) suggests that drift, gene flow and plasticity often limit or mediate LA. The relatively few studies based on candidate gene and genomewide analyses have identified footprints of selection at both small and large geographical scales, likely reflecting the specific functional properties of loci and the associated selection regimes (for example, local niche partitioning, pathogens, parasites, photoperiodicity and seasonal timing). The molecular basis of LA in salmonids is still largely unknown, but differential expression at the same few genes is implicated in the convergent evolution of certain phenotypes. Collectively, future research will benefit from an integration of classical and molecular approaches to understand: (i) species differences and how they originate, (ii) variation in adaptation across scales, life stages, population sizes and environmental gradients, and (iii) evolutionary responses to human activities.
ECONOMICS IN A FULL WORLD
The global economy is now so large that society can no longer safely pretend it operates within a limitless ecosystem. Developing an economy that can be sustained within the finite biosphere requires new ways of thinking
Detection and Attribution of Streamflow Timing Changes to Climate Change in the Western United States
This article applies formal detection and attribution techniques to investigate the nature of observed shifts in the timing of streamflow in the western United States. Previous studies have shown that the snow hy- drology of the western United States has changed in the second half of the twentieth century. Such changes manifest themselves in the form of more rain and less snow, in reductions in the snow water contents, and in earlier snowmelt and associated advances in streamflow ‘‘center’’ timing (the day in the ‘‘water-year’’ on average when half the water-year flow at a point has passed). However, with one exception over a more limited domain, no other study has attempted to formally attribute these changes to anthropogenic increases of greenhouse gases in the atmosphere. Using the observations together with a set of global climate model simulations and a hydrologic model (applied to three major hydrological regions of the western United States—the California region, the upper Colorado River basin, and the Columbia River basin), it is found that the observed trends toward earlier ‘‘center’’ timing of snowmelt-driven streamflows in the western United States since 1950 are detectably different from natural variability (significant at the p , 0.05 level). Furthermore, the nonnatural parts of these changes can be attributed confidently to climate changes induced by anthropogenic greenhouse gases, aerosols, ozone, and land use. The signal from the Columbia dominates the analysis, and it is the only basin that showed a detectable signal when the analysis was performed on individual basins. It should be noted that although climate change is an important signal, other climatic processes have also contributed to the hydrologic variability of large basins in the western United States.
Biophysical and Biogeochemical Responses to Climate Change Depend on Dispersal and Migration
Different species, populations, and individuals disperse and migrate at different rates. The rate of movement that occurs in response to changes in climate, whether fast or slow, will shape the distribution of natural ecosystems in the decades to come. Moreover, land-use patterns associated with urban, suburban, rural, and agricultural development will complicate ecosystem adaptation to climate change by hindering migration. Here we examine how vegetation’s capacity to disperse and migrate may affect the biophysical and biogeochemical characteristics of the land surface under anthropogenic climate change. We demonstrate that the effectiveness of plant migration strongly influences carbon storage, evapotranspiration, and the absorption of solar radiation by the land surface. As a result, plant migration affects the magnitude, and in some cases the sign, of feedbacks from the land surface to the climate system. We conclude that future climate projections depend on much better understanding of and accounting for dispersal and migration. Keywords: vegetation–climate feedback, global change, carbon storage, evapotranspiration, surface radiation
Effective Enforcement in a Conservation Area
There are two primary approaches to wildlife conservation, the generation of economic benefits from wildlife to local communities, so that protecting wildlife is in their interest, and the enforcement of protected areas. Outside of protected areas, community- based conservation must be the cornerstone of protection (1). However, within protected areas there is debate as to whether enforcement can maintain wildlife and even whether protected areas as wildlife reserves are realistic or morally justified (2). Here, we present the history of illegal harvesting in Serengeti National Park (SNP), Tanzania; estimate the amount of antipoaching activity by park staff; and show how the level of funding for antipoaching has affected the trends in abundance of three severely affected species: African buffalo, elephant, and black rhino.
Beaver (Castor canadensis) mitigate the effects of climate on the area of open water in boreal wetlands in western Canada
Shallow open water wetlands provide critical habitat for numerous species, yet they have become increasingly vulnerable to drought and warming temperatures and are often reduced in size and depth or disappear during drought. We examined how temperature, precipitation and beaver (Castor canadensis) activity influenced the area of open water in wetlands over a 54- year period in the mixed-wood boreal region of east-central Alberta, Canada. This entire glacial landscape with intermittently connected drainage patterns and shallow wetland lakes with few streams lost all beaver in the 19th century, with beaver returning to the study area in 1954. We assessed the area of open water in wetlands using 12 aerial photo mosaics from 1948 to 2002, which covered wet and dry periods, when beaver were absent on the landscape to a time when they had become well established. The number of active beaver lodges explained over 80% of the variability in the area of open water during that period. Temperature, precipitation and climatic variables were much less important than beaver in maintaining open water areas. In addition, during wet and dry years, the presence of beaver was associated with a 9-fold increase in open water area when compared to a period when beaver were absent from those same sites. Thus, beaver have a dramatic influence on the creation and maintenance of wetlands even during extreme drought. Given the important role of bea- ver in wetland preservation and in light of a drying climate in this region, their removal should be considered a wetland disturbance that should be avoided. Beaver Castor canadensis Drought East-central Alberta Elk Island National Park Mixed-wood boreal Wetland conservation
The Three Horsemen of Riches: Plague, War, and Urbanization in Early Modern Europe
How did Europe escape the “Iron Law of Wages?” We construct a simple Malthusian model with two sectors and multiple steady states, and use it to explain why European per capita incomes and urbanization rates increased during the period 1350–1700. Productivity growth can only explain a small fraction of the rise in output per capita. Population dynamics—changes of the birth and death schedules—were far more important determinants of steady states. We show how a major shock to population can trigger a transition to a new steady state with higher per-capita income. The Black Death was such a shock, raising wages substantially. Because of Engel’s Law, demand for urban products increased, and urban centers grew in size. European cities were unhealthy, and rising urbanization pushed up aggregate death rates. This effect was reinforced by diseases spread through war, financed by higher tax revenues. In addition, rising trade also spread diseases. In this way higher wages themselves reduced population pressure. We show in a calibration exercise that our model can account for the sustained rise in European urbanization as well as permanently higher per capita incomes in 1700, without technological change. Wars contributed importantly to the “Rise of Europe”, even if they had negative short-run effects. We thus trace Europe’s precocious rise to economic riches to interactions of the plague shock with the belligerent political environment and the nature of cities. Key words: Malthus to Solow, Long-run Growth, Great Divergence, Epidemics, Demographic Regime
How wide is a stream? Spatial extent of the potential ‘‘stream signature’’ in terrestrial food webs using meta-analysis
The magnitude of cross-ecosystem resource subsidies is increasingly well recognized; however, less is known about the distance these subsidies travel into the recipient landscape. In streams and rivers, this distance can delimit the ‘‘biological stream width,’’ complementary to hydro-geomorphic measures (e.g., channel banks) that have typically defined stream ecosystem boundaries. In this study we used meta-analysis to define a ‘‘stream signature’’ on land that relates the stream-to-land subsidy to distance. The 50% stream signature, for example, identifies the point on the landscape where subsidy resources are still at half of their maximum (in- or near-stream) level. The decay curve for these data was best fit by a negative power function in which the 50% stream signature was concentrated near stream banks (1.5 m), but a non-trivial (10%) portion of the maximum subsidy level was still found .0.5 km from the water’s edge. The meta-analysis also identified explanatory variables that affect the stream signature. This improves our understanding of ecosystem conditions that permit spatially extensive subsidy transmission, such as in highly productive, middle-order streams and rivers. Resultant multivariate models from this analysis may be useful to managers implementing buffer rules and conservation strategies for stream and riparian function, as they facilitate prediction of the extent of subsidies. Our results stress that much of the subsidy remains near the stream, but also that subsidies (and aquatic organisms) are capable of long-distance dispersal into adjacent environments, and that the effective ‘‘biological stream width’’ of stream and river ecosystems is often much larger than has been defined by hydro-geomorphic metrics alone. Limited data available from marine and lake sources overlap well with the stream signature data, indicating that the ‘‘signature’’ approach may also be applicable to subsidy spatial dynamics across other ecosystems. Key words: aquatic subsidies; dispersal; distance; food webs; insects; meta-analysis; stream.
How many tree species are there in the Amazon and how many of them will go extinct?
New roads, agricultural projects, logging, and mining are claiming an ever greater area of once-pristine Amazonian forest. The Millennium Ecosystems Assessment (MA) forecasts the extinction of a large fraction of Amazonian tree species based on projected loss of forest cover over the next several decades. How accurate are these estimates of extinction rates? We use neutral theory to estimate the number, relative abundance, and range size of tree species in the Amazon metacommunity and estimate likely tree-species ex- tinctions under published optimistic and nonoptimistic Amazon scenarios. We estimate that the Brazilian portion of the Amazon Basin has (or had) 11,210 tree species that reach sizes >10 cm DBH (stem diameter at breast height). Of these, 3,248 species have population sizes >1 million individuals, and, ignoring possible climate-change effects, almost all of these common species persist under both optimistic and nonoptimistic scenarios. At the rare end of the abundance spectrum, however, neutral theory predicts the existence of 5,308 species with <10,000 individuals each that are expected to suffer nearly a 50% extinction rate under the nonop- timistic deforestation scenario and an 37% loss rate even under the optimistic scenario. Most of these species have small range sizes and are highly vulnerable to local habitat loss. In ensembles of 100 stochastic simulations, we found mean total extinction rates of 20% and 33% of tree species in the Brazilian Amazon under the optimistic and nonoptimistic scenarios, respectively. Amazonian tree diversity neutral theory tropical tree extinction
How complex do models need to be to predict dispersal of threatened species through matrix habitats?
Persistence of species in fragmented landscapes depends on dispersal among suitable breeding sites, and dispersal is often influenced by the ‘‘matrix’’ habitats that lie between breeding sites. However, measuring effects of different matrix habitats on movement and incorporating those differences into spatially explicit models to predict dispersal is costly in terms of time and financial resources. Hence a key question for conservation managers is: Do more costly, complex movement models yield more accurate dispersal predictions? We compared the abilities of a range of movement models, from simple to complex, to predict the dispersal of an endangered butterfly, the Saint Francis’ satyr (Neonympha mitchellii francisci). The value of more complex models differed depending on how value was assessed. Although the most complex model, based on detailed movement behaviors, best predicted observed dispersal rates, it was only slightly better than the simplest model, which was based solely on distance between sites. Consequently, a parsimony approach using information criteria favors the simplest model we examined. However, when we applied the models to a larger landscape that included proposed habitat restoration sites, in which the composition of the matrix was different than the matrix surrounding extant breeding sites, the simplest model failed to identify a potentially important dispersal barrier, open habitat that butterflies rarely enter, which may completely isolate some of the proposed restoration sites from other breeding sites. Finally, we found that, although the gain in predicting dispersal with increasing model complexity was small, so was the increase in financial cost. Furthermore, a greater fit continued to accrue with greater financial cost, and more complex models made substantially different predictions than simple models when applied to a novel landscape in which butterflies are to be reintroduced to bolster their populations. This suggests that more complex models might be justifiable on financial grounds. Our results caution against a pure parsimony approach to deciding how complex movement models need to be to accurately predict dispersal through the matrix, especially if the models are to be applied to novel or modified landscapes. Key words: capture–mark–recapture; connectivity; dispersal; habitat fragmentation; matrix habitat; Neonympha mitchellii francisci; restoration; spatially explicit individual-based simulation model.
Reframing Environmental Messages to be Congruent with American Values
Prior research has explored the relationship between values, attitudes about environmental issues, and pro-environmental behavior. These studies have shown a consistent pattern of results — individuals who value self-transcendent life goals tend to care more about environmental problems, favor environmental protection over economic growth, and engage in more proenvironmental behavior. In contrast, indi- viduals who value self-enhancing life goals tend to hold more egoistic concerns about environmental issues, tend to favor economic growth over environmental protection, and tend to engage in fewer environmental behaviors. Research on American values suggests that overall, people in the U.S. tend to hold strong self-enhancing values. These self- enhancing values have largely been considered incongruous with the values that lead to environmental concern and to environmental behavior. In this paper, we synthesize the past research on the relationship between values and environmen- tal behavior. Lessons from the Biodiversity Project are used to illustrate efforts to create effective value-based environmental messages. Keywords: values, environmental attitudes, proenvironmental behavior, value-based messages
Physically based assessment of hurricane surge threat under climate change
Storm surges are responsible for much of the damage and loss of life associated with landfalling hurricanes. Understanding how global warming will affect hurricane surges thus holds great interest. As general circulation models (GCMs) cannot simulate hurricane surges directly, we couple a GCM-driven hurricane model with hydrodynamic models to simulate large numbers of synthetic surge events under projected climates and assess surge threat, as an example, for New York City (NYC). Struck by many intense hurricanes in recorded history and prehistory, NYC is highly vulnerable to storm surges. We show that the change of storm climatology will probably increase the surge risk for NYC; results based on two GCMs show the distribution of surge levels shifting to higher values by a magnitude comparable to the projected sea-level rise (SLR). The combined effects of storm climatology change and a 1 m SLR may cause the present NYC 100-yr surge flooding to occur every 3–20 yr and the present 500-yr flooding to occur every 25–240 yr by the end of the century.
The increasing intensity of the strongest tropical cyclones
Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere1–4. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. To quantify and determine the significance of these trends, we use quantile regression. Quantile regression as employed here is a method to estimate the change (trend) in lifetime-maximum wind speed quantile as a function of year. A quantile is a point taken from ntensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.36 0.09 m s21 yr21 (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.
Atlantic hurricanes and climate over the past 1,500 years
Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decade1. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise2–5. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around AD 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Nina-like climate conditions and relative tropical Atlantic warmth.
Coupling snowpack and groundwater dynamics to interpret historical streamflow trends in the western United States
A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. During the last century in the western United States, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter and a decline in the summer. Previous work has identified elevation as it relates to snowpack dynamics as the primary control on streamflow sensitivity to warming. But along with changes in the timing of snowpack accumulation and melt, summer streamflows are also sensitive to intrinsic, geologically mediated differences in the efficiency of landscapes in transforming recharge (either as rain or snow) into discharge; we term this latter factor drainage efficiency. Here we explore the conjunction of drainage efficiency and snowpack dynamics in interpreting retrospective trends in summer streamflow during 1950–2010 using daily streamflow from 81 watersheds across the western United States. The recession constant (k) and fraction of precipitation falling as snow (Sf) were used as metrics of deep groundwater and overall precipitation regime (rain and/or snow), respectively. This conjunctive analysis indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in western United States are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain-dominated watersheds as well. These empirical findings support both theory and hydrologic modelling and have implications for how streamflow sensitivity to warming is interpreted across broad regions. KEY WORDS streamflow trend; hydrologic processes; groundwater processes; climate; warming
Land cover effects on runoff patterns in eastern Piedmont (USA) watersheds
Physiography and land cover determine the hydrologic response of watersheds to climatic events. However, vast differences in climate regimes and variation of landscape attributes among watersheds (including size) have prevented the establishment of general relationships between land cover and runoff patterns across broad scales. This paper addresses these difficulties by using power spectral analysis to characterize area-normalized runoff patterns and then compare these patterns with landscape features among watersheds within the same physiographic region. We assembled long-term precipitation and runoff data for 87 watersheds (first to seventh order) within the eastern Piedmont (USA) that contained a wide variety of land cover types, collected environmental data for each watershed, and compared the datasets using a variety of statistical measures. The effect of land cover on runoff patterns was confirmed. Urban-dominated watersheds were flashier and had less hydrologic memory compared with forest-dominated watersheds, whereas watersheds with high wetland coverage had greater hydrologic memory. We also detected a 10–15% urban threshold above which urban coverage became the dominant control on runoff patterns. When spectral properties of runoff were compared across stream orders, a threshold after the third order was detected at which watershed processes became dominant over precipitation regime in determining runoff patterns. Finally, we present a matrix that characterizes the hydrologic signatures of rivers based on precipitation versus landscape effects and low-frequency versus high-frequency events. The concepts and methods presented can be generally applied to all river systems to characterize multiscale patterns of watershed runoff. KEY WORDS watershed hydrology; power spectral analysis; hydrologic signatures; fluvial landscape ecology; hydrologic memory
How and Why Do Insects Migrate?
Countless numbers of insects migrate within and between continents every year, and yet we know very little about the ultimate reasons and proximate mechanisms that would explain these mass movements. Here we suggest that perhaps the most important reason for insects to migrate is to hedge their reproductive bets. By spreading their breeding efforts in space and time, insects distribute their offspring over a range of environmental conditions. We show how the study of individual long-distance movements of insects may contribute to a better understanding of migration. In the future, advances in tracking methods may enable the global surveillance of large insects such as desert locusts.
THE INSURANCE VALUE OF BIODIVERSITY IN THE PROVISION OF ECOSYSTEM SERVICES
From the text: In the face of uncertainty, diversity provides insurance for risk-averse economic agents. For example, investors in financial markets diversify their asset portfolio in order to hedge their risk; firms diversify their activities, products or services when facing an uncertain market environment; farmers traditionally grow a variety of crops in order to decrease the adverse impact of uncertain environmental and market conditions. In this paper, I argue that biological diversity plays a similar role: it can be interpreted as an insurance against the uncertain provision of ecosystem services, such as biomass production, control of water run-off, pollination, control of pests and diseases, nitrogen fixation, soil regeneration, etc. Such ecosystem services are generated by ecosystems and are used by utility- maximizing and risk-averse economic agents (Daily [1997], Millennium Ecosystem Assessment [2005]).
TRUST, CULTURE, AND COOPERATION: A Social Dilemma Analysis of Pro-Environmental Behaviors
Social dilemmas require a choice between cooperation, or sacrificing for the greater good, and self-interest. One commonly studied social dilemma is environmental conservation. Previous work suggests that trust predicts cooperation in the form of environmental protection. We contend that this view ignores cultural factors. Building on prior cross-cultural research, we predict an interaction between strength of social ties and trust on cooperation. Findings from General Social Survey data indicate that low trust levels found in the U.S. South (a collectivist culture) renders trust ineffective at promoting environmental protection. However, trust predicts cooperation in nonsouthern regions (which are more individualist), where trust levels are higher.
Emergence of a mid-season period of low floral resources in a montane meadow ecosystem associated with climate change
Summary. 1. Shifts in the spatial and temporal patterns of flowering could affect the resources available to pollinators, and such shifts might become more common as climate change progresses. 2. As mid-summer temperatures have warmed,we found that a montane meadow ecosystem in the southern Rocky Mountains of the United States exhibits a trend toward a bimodal distribution of flower abundance, characterized by a mid-season reduction in total flower number, instead of a broad, unimodal flowering peak lasting most of the summer season. 3. We examined the shapes of community-level flowering curves in this system and found that the typical unimodal peak results from a pattern of complementary peaks in flowering among three distinct meadow types (dry, mesic and wet) within the larger ecosystem. However, high mid-summer temperatures were associated with divergent shifts in the flowering curves of these individual meadow types. Specifically, warmer summers appeared to cause increasing bimodality in mesic habitats, and a longer interval between early and late flowering peaks in wet and dry habitats. 4. Together, these habitat-specific shifts produced a longer mid-season valley in floral abundance across the larger ecosystem in warmer years. Because of these warming-induced changes in flowering patterns, and the significant increase in summer temperatures in our study area, there has been a trend toward non-normality of flowering curves over the period 1974–2009. This trend reflects increasing bimodality in total community-wide flowering. 5. The resulting longer periods of low flowering abundance in the middle of the summer season could negatively affect pollinators that are active throughout the season, and shifts in flowering peaks within habitats might create mismatches between floral resources and demand by pollinators with limited foraging ranges. 6. Synthesis. Early-season climate conditions are getting warmer and drier in the high altitudes of the southern Rocky Mountains. We present evidence that this climate change is disrupting flowering phenology within and among different moisture habitats in a sub-alpine meadow ecosystem, causing a mid-season decline in floral resources that might negatively affect mutualists, especially pollinators. Our findings suggest that climate change can have complex effects on phenology at small spatial scales, depending on patch-level habitat differences.
Thermal legacies: transgenerational effects of temperature on growth in a vertebrate
Transgenerational plasticity (TGP), a generalisation of more widely studied maternal effects, occurs whenever environmental cues experienced by either parent prior to fertilisation results in a modification of offspring reaction norms. Such effects have been observed in many traits across many species. Despite enormous potential importance—particularly in an era of rapid climate change—TGP in thermal growth physiology has never been demonstrated for vertebrates. We provide the first evidence for thermal TGP in a vertebrate: given sufficient time, sheepshead minnows adaptively program their offspring for maximal growth at the present temperature. The change in growth over a single generation (c. 30%) exceeds the single-generation rate of adaptive evolution by an order of magnitude. If widespread, transgenerational effects on thermal performance may have important implications on physiology, ecology and contemporary evolution, and may significantly alter the extinction risk posed by changing climate. Keywords Cyprinodon variegatus, ecological epigenetics, maternal effects, sheepshead minnow.
Can forest management be used to sustain water-based ecosystem services in the face of climate change?
Forested watersheds, an important provider of ecosystems services related to water supply, can have their structure, function, and resulting streamflow substantially altered by land use and land cover. Using a retrospective analysis and synthesis of long-term climate and streamflow data (75 years) from six watersheds differing in management histories we explored whether streamflow responded differently to variation in annual temperature and extreme precipitation than unmanaged watersheds. We show significant increases in temperature and the frequency of extreme wet and dry years since the 1980s. Response models explained almost all streamflow variability (adjusted R2 . 0.99). In all cases, changing land use altered streamflow. Observed watershed responses differed significantly in wet and dry extreme years in all but a stand managed as a coppice forest. Converting deciduous stands to pine altered the streamflow response to extreme annual precipitation the most; the apparent frequency of observed extreme wet years decreased on average by sevenfold. This increased soil water storage may reduce flood risk in wet years, but create conditions that could exacerbate drought. Forest management can potentially mitigate extreme annual precipitation associated with climate change; however, offsetting effects suggest the need for spatially explicit analyses of risk and vulnerability.
Ecological extinction and evolution in the brave new ocean
The great mass extinctions of the fossil record were a major creative force that provided entirely new kinds of opportunities for the subsequent explosive evolution and diversification of surviving clades. Today, the synergistic effects of human impacts are laying the groundwork for a comparably great Anthropocene mass extinction in the oceans with unknown ecological and evolutionary consequences. Synergistic effects of habitat destruction, overfishing, introduced species, warming, acidification, toxins, and massive runoff of nutrients are transforming once complex ecosystems like coral reefs and kelp forests into monotonous level bottoms, transforming clear and productive coastal seas into anoxic dead zones, and transforming complex food webs topped by big animals into simplified, microbially dominated ecosystems with boom and bust cycles of toxic dinoflagel- late blooms, jellyfish, and disease. Rates of change are increasingly fast and nonlinear with sudden phase shifts to novel alternative community states. We can only guess at the kinds of organisms that will benefit from this mayhem that is radically altering the selective seascape far beyond the consequences of fishing or warming alone. The prospects are especially bleak for animals and plants compared with metabolically flexible microbes and algae. Halting and ultimately reversing these trends will require rapid and fundamental changes in fisheries, agricultural practice, and the emissions of green- house gases on a global scale.
Climate Change Challenges and Opportunities for Global Health
Editorial: Journal of the American Medical Association. Health is inextricably linked to climate change. It is important for clinicians to understand this relationship in order to discuss associated health risks with their patients and to inform public policy. To provide new US-based temperature projections from downscaledclimate modeling and to review recent studies on health risks related to climate change and the cobenefits of efforts to mitigate greenhouse gas emissions. We searched PubMed from 2009 to 2014 for articles related to climate change and health, focused on governmental reports, predictive models, and empirical epidemiological studies. Of the more than 250 abstracts reviewed, 56 articles were selected. In addition, we analyzed climate data averaged over 13 climate models and based future projections on downscaled probability distributions of the daily maximum temperature for 2046-2065. We also compared maximum daily 8-hour average with air temperature data taken from the National Oceanic and Atmospheric Administration National Climate Data Center. By 2050, many US cities may experience more frequent extreme heat days. For example, New York and Milwaukee may have 3 times their current average number of days hotter than 32°C (90°F). The adverse health aspects related to climate change may include heat-related disorders, such as heat stress and economic consequences of reduced work capacity; and respiratory disorders, including those exacerbated by fine particulate pollutants, such as asthma and allergic disorders; infectious diseases, including vectorborne diseases and water-borne diseases, such as childhood gastrointestinal diseases; food insecurity, including reduced crop yields and an increase in plant diseases; and mental health disorders, such as posttraumatic stress disorder and depression, that are associated with natural disasters. Substantial health and economic co-benefits could be associated with reductions in fossil fuel combustion. For example, the cost of greenhouse gas emission policies may yield net economic benefit, with health benefits from air quality improvements potentially offsetting the cost of US carbon policies. Evidence over the past 20 years indicates that climate change can be associated with adverse health outcomes. Health care professionals have an important role in understanding and communicating the related potential health concerns and the cobenefits from reducing greenhouse gas emissions.
Climate Change Puts Children in Jeopardy
From the text: Experts several years ago sounded the alarm on climate change’s potential harm to human health in the years to come. But the impact on a particularly vulnerable group—children—has not received a great deal of attention.
Historical Evaluation and Future Prediction of Eastern North American and Western Atlantic Extratropical Cyclones in the CMIP5 Models during the Cool Season
Extratropical cyclone track density, genesis frequency, deepening rate, and maximum intensity distributions over eastern North America and the western North Atlantic were analyzed for 15 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) for the historical period (1979–2004) and three future periods (2009–38, 2039–68, and 2069–98). The cyclones were identified using an automated tracking algorithm applied to sea level pressure every 6 h. The CMIP5 results for the historical period were evaluated using the Climate Forecast System Reanalysis (CFSR). The CMIP5 models were ranked given their track density, intensity, and overall performance for the historical period. It was found that six of the top seven CMIP5 models with the highest spatial resolution were ranked the best overall. These models had less un- derprediction of cyclone track density, more realistic distribution of intense cyclones along the U.S. East Coast, and more realistic cyclogenesis and deepening rates. The best seven models were used to determine projected future changes in cyclones, which included a 10%–30% decrease in cyclone track density and weakening of cyclones over the western Atlantic storm track, while in contrast there is a 10%–20% increase in cyclone track density over the eastern United States, including 10%–40% more intense (,980 hPa) cyclones and 20%–40% more rapid deepening rates just inland of the U.S. East Coast. Some of the reasons for these CMIP5 model differences were explored for the selected models based on model generated Eady growth rate, upper-level jet, surface baroclinicity, and precipitation.
Carbon Sequestration in Two Created Riverine Wetlands in the Midwestern United States
Wetlands have the ability to accumulate significant amounts of carbon (C) and thus could provide an effective approach to mitigate greenhouse gas accumulation in the atmosphere. Wetland hydrology, age, and management can affect primary productivity, decomposition, and ultimately C sequestration in riverine wetlands, but these aspects of wetland biogeochemistry have not been adequately investigated, especially in created wetlands. In this study we investigate the ability of created freshwater wetlands to sequester C by determining the sediment accretion and soil C accumulation of two 15-yr-old created wetlands in central Ohio—one planted and one naturally colonized. We measured the amount of sediment and soil C accumulated over the parent material and found that these created wetlands accumulated an average of 242 g C m-2 yr-1, 70% more than a similar natural wetland in the region and 26% more than the rate estimated for these same wetlands 5 yr before this study. The C sequestration of the naturally colonized wetland was 22% higher than that of the planted wetland (267 ± 17 vs. 219 ± 15 g C m-2 yr-1, respectively). Soil C accrual accounted for 66% of the aboveground net primary productivity on average. Open water communities had the highest C accumulation rates in both wetlands. This study shows that created wetlands can be natural, cost-effective tools to sequester C to mitigate the effect of greenhouse gas emissions.
Synthesis of Knowledge of Extreme Fire Behavior: Volume I for Fire Managers
The National Wildfire Coordinating Group definition of extreme fire behavior (EFB) indicates a level of fire behavior characteristics that ordinarily precludes methods of direct control action. One or more of the following is usually involved: high rate of spread, prolific crowning/spotting, presence of fire whirls, and strong convection column. Predictability is difficult because such fires often exercise some degree of influence on their environment and behave erratically, sometimes dangerously. Alternate terms include “blow up” and “fire storm.” Fire managers examining fires over the last 100 years have come to understand many of the factors necessary for EFB development. This work produced guidelines included in current firefighter training, which presents the current methods of predicting EFB by using the crown fire model, which is based on the environmental influences of weather, fuels, and topography. Current training does not include the full extent of scientific understanding. Material in current training programs is also not the most recent scientific knowledge. National Fire Plan funds have sponsored newer research related to wind profiles’ influence on fire behavior, plume growth, crown fires, fire dynamics in live fuels, and conditions associated with vortex development. Of significant concern is that characteristic features of EFB depend on condi- tions undetectable on the ground, relying fundamentally on invisible properties such as wind shear or atmospheric stability. Obviously no one completely understands all the factors contributing to EFB because of gaps in our knowledge. These gaps, as well as the limitations as to when various models or indices apply should be noted to avoid application where they are not appropriate or warranted. This synthesis will serve as a summary of existing extreme fire behavior knowledge for use by fire managers, firefighters, and fire researchers. The objective of this project is to synthesize existing EFB knowledge in a way that connects the weather, fuel, and topographic factors that contribute to development of EFB. This synthesis will focus on the state of the science, but will also consider how that science is currently presented to the fire management community, including incident commanders, fire behavior analysts, incident meteorologists, National Weather Service office forecasters, and firefighters. It will seek to clearly delineate the known, the unknown, and areas of research with the greatest potential impact on firefighter protection.
Fire and Fish Dynamics in a Changing Climate: Broad- and Local-Scale Effects of Fire-Induced Water Temperature Changes on Native and Nonnative Fish Communities
Fire is a key natural disturbance that affects the distribution and abundance of native fishes in the Rocky Mountain West. In the absence of migratory individuals from undisturbed portions of a watershed, persistence of native fish populations depends on the conditions of the post-fire stream environment. Stream temperatures typically warm after fire, and remain elevated until riparian vegetation recovers. An additional threat to native species is that nonnative fishes have invaded many waters, and these species tolerate or prefer warmer water temperatures. Thus, forecasting the long-term effects of fire on native fish populations requires an understanding of fire dynamics (size, distribution, frequency, and severity), the extent and location of changes in riparian forest structure and time to recovery, changes in stream temperatures associated with these forest changes, and how native and nonnative fish respond to changes in water temperature. To perform spatially explicit simulation modeling that examined the relations among fire disturbance, stream temperature, and fish communities, we upgraded and then linked the fire-forest succession model FireBGCv2 to a stream temperature model to project changes in water temperature in the East Fork Bitterroot River basin in Montana under an array of climate and fire management scenarios. Model projections indicated that although climate led to increases in fire severity, frequency, or size, water temperature increases at the basin scale were primarily a consequence of climate-driven atmospheric warming rather than changes in fire regime. Consequently, variation in fire management—fuel treatment or fire suppression—had little effect at this scale, but assumed greater importance at the scale of riparian stands. By revisiting a large number of previously sampled sites in the East Fork Bitterroot River basin in Montana, we evaluated whether bull trout persistence and other native and nonnative fish distributions were related to temperature changes associated with fire and recent climatic trends. Although fires were related to marked increases in summer water temperatures, these changes had a positive effect (westslope cutthroat trout) or a negligible effect (bull trout) on the abundance and distribution of native fish species, whereas the abundance of nonnative brook trout markedly declined in some instances. Fire-related changes in factors other than the thermal regime may have contributed to these patterns. In contrast, at the scale of the entire basin we observed an upward-directed contraction in the distribution of bull trout that was unrelated to fire. We concluded that this may be a response to temperature increases related to climate change.
Ecological Effects of Prescribed Fire Season: A Literature Review and Synthesis for Managers
Prescribed burning may be conducted at times of the year when fires were infrequent historically, leading to concerns about potential adverse effects on vegetation and wildlife. Historical and prescribed fire regimes for different regions in the continental United States were compared and literature on season of prescribed burning synthesized. In regions and vegetation types where considerable differences in fuel consumption exist among burning seasons, the effects of prescribed fire season appears, for many ecological variables, to be driven more by fire-intensity differences among seasons than by phenology or growth stage of organisms at the time of fire. Where fuel consumption differs little among burning seasons, the effect of phenology or growth stage of organisms is often more apparent, presumably because it is not overwhelmed by fire-intensity differences. Most species in ecosystems that evolved with fire appear to be resilient to one or few out-of-season prescribed burn(s). However, a variable fire regime including prescribed burns at different times of the year may alleviate the potential for undesired changes and maximize biodiversity.
Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States
We investigate the impact of climate change on wildfire activity and carbonaceous aerosol concentrations in the western United States. We regress observed area burned onto observed meteorological fields and fire indices from the Canadian Fire Weather Index system and find that May–October mean temperature and fuel moisture explain 24–57% of the variance in annual area burned in this region. Applying meteorological fields calculated by a general circulation model (GCM) to our regression model, we show that increases in temperature cause annual mean area burned in the western United States to increase by 54% by the 2050s relative to the present day. Changes in area burned are ecosystem dependent, with the forests of the Pacific Northwest and Rocky Mountains experiencing the greatest increases of 78 and 175%, respectively. Increased area burned results in near doubling of wildfire carbonaceous aerosol emissions by midcentury. Using a chemical transport model driven by meteorology from the same GCM, we calculate that climate change will increase summertime organic carbon (OC) aerosol concentrations over the western United States by 40% and elemental carbon (EC) concentrations by 20% from 2000 to 2050. Most of this increase (75% for OC and 95% for EC) is caused by larger wildfire emissions with the rest caused by changes in meteorology and for OC by increased monoterpene emissions in a warmer climate. Such an increase in carbonaceous aerosol would have important consequences for western U.S. air quality and visibility.
Density stratification in an estuary with complex geometry: Driving processes and relationship to hypoxia on monthly to inter-annual timescales
The density field in Narragansett Bay (NB), a northeast U.S. estuary with complex geometry that suffers hypoxia, is described and related to driving factors using monthly means from time series observations at 9 sites during late spring to early fall 2001–2009. Stratification (deep-shallow density difference) is dominated by salinity and strongest (4–7 kg m␣3 in late spring) near rivers in the north and east. Shallow horizontal density gradients are about 0.2 kg m␣3 km␣1; deep densities have minor spatial and seasonal variations. Geographic structure in density, and its inter-annual anomalies, is weaker than expected based on the complex geometry and large size relative to the internal deformation radius. Inter-annual variability is primarily driven by river flow and weakly influenced by winds, contrasting nearby systems (Chesapeake Bay, Long Island Sound), likely due to reduced fetch and/or unfavorable alignment with prevailing winds. Stratification response to river flow follows 2/3 power scaling despite that the theory omits important NB attributes (complex geometry, depth-varying horizontal gradients). Contrasting other systems (Delaware Bay, San Francisco Bay), horizontal gradients are at least as responsive to river forcing as theoretical 1/3 power scaling; depth-dependent horizontal gradients or finite basin constraint of intrusion length may be responsible. Bay-wide inter-annual variations in seasonal hypoxia correlate with late spring stratification, though stratification peaks in the north and east with hypoxia most severe in the north and west. Long-term response of stratification, and thus its role in hypoxia, to climate-driven increases in river flow and temperatures will be dominated by the former.
Effects of irrigation on global climate during the 20th century
Various studies have documented the effects of modern‐day irrigation on regional and global climate, but none, to date, have considered the time‐varying impact of steadily increasing irrigation rates on climate during the 20th century. We investigate the impacts of observed irrigation changes over this century with two ensemble simulations using an atmosphere general circulation model. Both ensembles are forced with transient climate forcings and observed sea surface temperatures from 1902 to 2000; one ensemble includes irrigation specified by a time‐varying data set of irrigation water withdrawals. Early in the century, irrigation is primarily localized over southern and eastern Asia, leading to significant cooling in boreal summer (June–August) over these regions. This cooling spreads and intensifies by century’s end, following the rapid expansion of irrigation over North America, Europe, and Asia. Irrigation also leads to boreal winter (December–February) warming over parts of North America and Asia in the latter part of the century, due to enhanced downward longwave fluxes from increased near‐surface humidity. Precipitation increases occur primarily downwind of the major irrigation areas, although precipitation in parts of India decreases due to a weaker summer monsoon. Irrigation begins to significantly reduce temperatures and temperature trends during boreal summer over the Northern Hemisphere midlatitudes and tropics beginning around 1950; significant increases in precipitation occur in these same latitude bands. These trends reveal the varying importance of irrigation‐climate interactions and suggest that future climate studies should account for irrigation, especially in regions with unsustainable irrigation resources.
The 2010 Pakistan Flood and Russian Heat Wave: Teleconnection of Hydrometeorologic Extremes
In this paper, we present preliminary results showing that the two record setting extreme events during 2010 summer, i.e., the Russian heat wave/wild fires and Pakistan flood were physically connected. We find that the Russian heat wave was associated with the development of an extraordinary strong and prolonged extratropical atmospheric blocking event, and excitation of a large-scale atmospheric Rossby wavetrain spanning western Russia, Kazakhstan, and northwestern China/Tibetan Plateau region. The southward penetration of upper level vorticity perturbations in the leading trough of the Rossby wave was instrumental in triggering anomalously heavy rain events over northern Pakistan and vicinity in mid-to-late July. Also shown are evidences that the Russian heat wave was amplified by a positive feedback through changes in surface energy fluxes between the atmospheric blocking pattern and an underlying extensive land region with below- normal soil moisture. The Pakistan heavy rain events were amplified and sustained by strong anomalous southeasterly flow along the Himalayas foothills and abundant moisture transport from the Bay of Bengal in connection with the northward propagation of the monsoonal intraseasonal oscillation. This is a preliminary PDF of the author-produced manuscript that has been peer-reviewed and accepted for publication. Since it is being posted so soon after acceptance, it has not yet been copyedited, formatted, or processed by AMS Publications. This preliminary version of the manuscript may be downloaded, distributed, and cited, but please be aware that there will be visual differences and possibly some content differences between this version and the final published version.
BOTANY AND A CHANGING WORLD: INTRODUCTION TO THE SPECIAL ISSUE ON GLOBAL BIOLOGICAL CHANGE
The impacts of global change have heightened the need to understand how organisms respond to and influence these changes. Can we forecast how change at the global scale may lead to biological change? Can we identify systems, processes, and organisms that are most vulnerable to global changes? Can we use this understanding to enhance resilience to global changes? This special issue on global biological change emphasizes the integration of botanical information at different biological levels to gain perspective on the direct and indirect effects of global change. Contributions span a range of spatial scales and include both ecological and evolutionary timescales and highlight work across levels of organization, including cellular and physiological processes, individuals, populations, and ecosystems. Integrative botanical approaches to global change are critical for the eco- logical and evolutionary insights they provide and for the implications these studies have for species conservation and ecosys- tem management. Key words: community dynamics; flowering phenology; functional traits; global biological change; invasive species; land-use patterns; plant–microbial interactions; species interactions.
Identifying the World’s Most Climate Change Vulnerable Species: A Systematic Trait-Based Assessment of all Birds, Amphibians and Corals
Climate change will have far-reaching impacts on biodiversity, including increasing extinction rates. Current approaches to quantifying such impacts focus on measuring exposure to climatic change and largely ignore the biological differences between species that may significantly increase or reduce their vulnerability. To address this, we present a framework for assessing three dimensions of climate change vulnerability, namely sensitivity, exposure and adaptive capacity; this draws on species’ biological traits and their modeled exposure to projected climatic changes. In the largest such assessment to date, we applied this approach to each of the world’s birds, amphibians and corals (16,857 species). The resulting assessments identify the species with greatest relative vulnerability to climate change and the geographic areas in which they are concentrated, including the Amazon basin for amphibians and birds, and the central Indo-west Pacific (Coral Triangle) for corals. We found that high concentration areas for species with traits conferring highest sensitivity and lowest adaptive capacity differ from those of highly exposed species, and we identify areas where exposure-based assessments alone may over or under-estimate climate change impacts. We found that 608–851 bird (6–9%), 670–933 amphibian (11– 15%), and 47–73 coral species (6–9%) are both highly climate change vulnerable and already threatened with extinction on the IUCN Red List. The remaining highly climate change vulnerable species represent new priorities for conservation. Fewer species are highly climate change vulnerable under lower IPCC SRES emissions scenarios, indicating that reducing greenhouse emissions will reduce climate change driven extinctions. Our study answers the growing call for a more biologically and ecologically inclusive approach to assessing climate change vulnerability. By facilitating independent assessment of the three dimensions of climate change vulnerability, our approach can be used to devise species and area- specific conservation interventions and indices. The priorities we identify will strengthen global strategies to mitigate climate change impacts.
Drought, disease, defoliation and death: forest pathogens as agents of past vegetation change
The temperate and boreal forests of Europe and North America have been subject to repeated pathogen (fungal disease and phytophagus insect) outbreaks over the last 100 years. Palaeoecology can, potentially, offer a long-term perspective on such disturbance episodes, providing information on their triggers, frequency and impact. Mid-Holocene declines in Tsuga and Ulmus pollen dominate the Quaternary literature on forest pathogens, yet the role of pathogens, and even the presence of pathogenic fungal diseases, during these events has yet to be established. Pathogen-focused research strategies, informed by the sequence of events documented in modern outbreaks, and undertaken at high temporal resolution using a multi-proxy approach, are required. It is argued that forest pathogens are likely to have been significant agents of past vegetation change, even in cases where climate change was the primary stress factor.
Plant species richness: the world records
Questions: The co-existence of high numbers of species has always fascinated ecologists, but what and where are the communities with the world records for plant species richness? The species–area relationship is among the best-known patterns in community ecology, but does it give a consistent global pattern for the most saturated communities, the global maxima? Location: The world. Methods: We assembled the maximum values recorded for vascular plant species richness for contiguous areas from 1 mm2 up to 1 ha. We applied the power function to relate maximal richness to area and to make extrapolations to the whole Earth. Results: Only two community types contain global plant species maxima. The maxima at smaller spatial grain were from oligotrophic to mesotrophic, managed, semi-natural, temperate grasslands (e.g. 89 species on 1 m2), those at larger grains were from tropical rain forests (e.g. 942 species on 1 ha). The maximum richness values closely followed a power function with z = 0.250: close to Pres- ton’s ‘canonical’ value of 0.262. There was no discernable difference between maxima using rooted presence (i.e. including only plants rooted in the plot) vs shoot presence (i.e. including any plant with physical cover over the plot). How- ever, shoot presence values must logically be greater, with the curves flattening out at very small grain, and there is evidence of this from point quadrats. Extrap- olating the curve to the terrestrial surface of the Earth gave a prediction of 219 204 vascular plant species, surprisingly close to a recent estimate of 275 000 actual species. Conclusions: Very high richness at any spatial grain is found only in two particular habitat/community types. Nevertheless, these high richness values form a very strong, consistent pattern, not greatly affected by the method of sampling, and this pattern extrapolates amazingly well. The records challenge ecologists to consider mechanisms of species co-existence, answers to the ‘Paradox of the Plankton’. Biodiversity; Canonical hypothesis; Macroecology; Oligo- to mesotrophic grassland; Paradox of the Plankton; Power function; Rooted presence; Scale dependence; Shoot presence; Spatial grain; Spatial scale; Species–area relation; Tropical rain forest;
Trade-in to trade-up
Nature reserves and protected areas enjoy sacred status in conservation — which translates into a ‘do not touch’ attitude. But selling off some of the less worthy of them would pay conservation dividends.
Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise
Terrestrial plants remove CO2 from the atmosphere through photo- synthesis, a process that is accompanied by the loss of water vapour from leaves1. The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon2. Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange3. We find a substantial increase in water-use effi- ciency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various compet- ing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO2 fertilization effect. The results suggest a partial closure of stomata1—small pores on the leaf surface that regulate gas exchange—to maintain a near- constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegeta- tion, which may require a reassessment of the role of stomatal con- trol in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation–climate models.
Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America
Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Nin ̃o-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies recon- structed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subconti- nental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those re- gions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades. Atlantic Multidecadal Oscillation El Nino Southern Oscillation fire history network ocean warming Pacific Decadal Oscillation
Stream biodiversity: The ghost of land use past
The influence of past land use on the present- day diversity of stream invertebrates and fish was investigated by comparing watersheds with different land-use history. Whole watershed land use in the 1950s was the best predictor of present-day diversity, whereas riparian land use and watershed land use in the 1990s were comparatively poor indicators. Our findings indicate that past land-use activity, particularly agriculture, may result in long-term modifications to and reductions in aquatic diversity, regardless of reforestation of riparian zones. Preservation of habitat fragments may not be sufficient to maintain natural diversity in streams, and maintenance of such biodiversity may require conservation of much or all of the watershed.
Climatic Impact of Tropical Lowland Deforestation on Nearby Montane Cloud Forests
Tropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields and thus the TMCF environment. Landsat and Geostationary Operational Environmental Satellite imagery show that deforested areas of Costa Rica’s Caribbean lowlands remain relatively cloud-free when forested regions have well-developed dry season cumulus cloud fields. Further, regional atmospheric simulations show that cloud base heights are higher over pasture than over tropical forest areas under reasonable dry season conditions. These results suggest that land use in tropical lowlands has serious impacts on ecosystems in adjacent mountains.
Long-Distance Dispersal of Plants
Long-distance dispersal (LDD) of plants poses challenges to research because it involves rare events driven by complex and highly stochastic processes. The current surge of renewed interest in LDD, motivated by growing recognition of its critical importance for natural populations and communities and for humanity, promises an improved, quantitatively derived understanding of LDD. To gain deep insights into the patterns, mechanisms, causes, and consequences of LDD, we must look beyond the standard dispersal vectors and the mean trend of the distribution of dispersal distances. ‘‘Nonstandard’’ mechanisms such as extreme climatic events and generalized LDD vectors seem to hold the greatest explanatory power for the drastic deviations from the mean trend, deviations that make the nearly impossible LDD a reality.
Saturation of the Southern Ocean CO2 Sink Due to Recent Climate Change
Based on observed atmospheric CO2 concentration and an inverse method, we estimate that the Southern Ocean sink of CO2 has weakened between 1981 and 2004 by 0.08 PgC/y per decade relative to the trend expected from the large increase in atmospheric CO2. This weakening is attributed to the observed increase in Southern Ocean winds resulting from human activities and projected to continue in the future. Consequences include a reduction in the efficiency of the Southern Ocean sink of CO2 in the short term (~25 years) and possibly a higher level of stabilization of atmospheric CO2 on a multicentury time scale.
