The Future: Hotter Than We Think?

" ... it is likely that the future will be hotter than we think."

Torn, M. S., and J. Harte (2006), Missing feedbacks,asymmetric 
uncertainties, and the underestimation of future warming. 
Geophysical Research Letters, 33, L10703, doi:10.1029/2005GL025540.

Received 19 December 2005; revised 17 March 2006; accepted 24 March 
2006; published 26 May 2006.

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 ice core information and general circulation model 
(GCM) climate sensitivity, finding that the warming of 1.5-4.5 C 
associated with anthropogenic doubling of CO2 is amplified to 1.6-6.0 
C 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.


"One study estimated that more than half (59 percent) of 1598 species 
exhibited measurable changes in their phenologies and/or 
distributions over the past 20 to 140 years .... high proportion of 
species responding to recent, relatively mild climate change (global 
average warming of 0.6 C)."

Parmesan, Camille. ' Ecological and Evolutionary Responses to Recent 
Climate Change.' Annual Review of Evolution, Ecology, and 
Systematics. 2006. 37: 637-69
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