Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming
Historical evidence shows that atmospheric greenhouse
gas (GhG) concentrations increase during periods of
warming, implying a positive feedback to future climate
change. We quantified this feedback for CO2 and CH4 by
combining the mathematics of feedback with empirical icecore
information and general circulation model (GCM)
climate sensitivity, finding that the warming of 1.5 –4.5C
associated with anthropogenic doubling of CO2 is amplified
to 1.6– 6.0C warming, with the uncertainty range deriving
from GCM simulations and paleo temperature records.
Thus, anthropogenic emissions result in higher final GhG
concentrations, and therefore more warming, than would be
predicted in the absence of this feedback. Moreover, a
symmetrical uncertainty in any component of feedback,
whether positive or negative, produces an asymmetrical
distribution of expected temperatures skewed toward higher
temperature. For both reasons, the omission of key positive
feedbacks and asymmetrical uncertainty from feedbacks, it
is likely that the future will be hotter than we think.
Citation: Torn, M. S., and J. Harte (2006), Missing feedbacks,
asymmetric uncertainties, and the underestimation of future
warming.
Publication Date: 2006
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