HR: 08:45h
AN: GC11A-04    [Abstracts]
TI: Constraints on Climate Sensitivity From the Observed Seasonal Cycle
AU: * Knutti, R
EM: knutti@ucar.edu
AF: NCAR, P.O. Box 3000, Boulder, CO 80307 United States
AU: Meehl, G A
EM: meehl@ucar.edu
AF: NCAR, P.O. Box 3000, Boulder, CO 80307 United States
AU: Allen, M R
EM: atmmra@atm.ox.ac.uk
AF: Oxford University, Atmospheric, Oceanic and Planetary Physics, Parks Road, Oxford, OX1 3PU United Kingdom
AB: Estimates of impacts as well as adaptation and mitigation strategies related to anthropogenic climate change require a precise understanding of the anticipated changes as well as the uncertainties associated with it. Long-term uncertainty in future warming is dominated by the uncertainty in climate sensitivity. The range of climate sensitivity was based on expert opinion only for many years, and only recently a few new methods were suggested to objectively quantify its uncertainty. Here we use a multi-thousand member ensemble from climateprediction.net, a distributed computing experiment where versions of a general circulation climate model are run with multiple parameter perturbations. We apply a neural network to establish a relation between climate sensitivity and the amplitude of the seasonal cycle in regional temperature. Most models with high sensitivities are found to overestimate the seasonal cycle compared to observations. A probability density function for climate sensitivity is then calculated from the present day seasonal cycle in observational and reanalysis datasets. Subject to a number of assumptions on the models and datasets used, we find that climate sensitivity is very unlikely to be either below about 2 K or above about 6 K, with the best agreement found for sensitivities between 3 and 3.5 K. This confirms the range of values suggested by most AOGCMs, and is considerably narrower than probabilistic estimates derived from the observed 20th century warming.
DE: 1626 Global climate models (3337, 4928)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 6309 Decision making under uncertainty
SC: Global Climate Change [GC]
MN: Fall Meeting 2005