Climate model fidelity and projections of climate change

Abstract

[1] Relative entropy, which is a measure of the difference between two probability distributions, has been calculated for the simulations of the climate of the 20th century from 13 climate models and the observed surface air temperature during the past 100 years. This quantity is used as a measure of model fidelity: a small value of relative entropy indicates that a given model's distribution is close to the observed. It is found that there is an inverse relationship between relative entropy and the sensitivity of the model to doubling of the concentration of CO 2 . The models that have lower values of relative entropy, hence have higher fidelity in simulating the present climate, produce higher values of global warming for a doubling of CO 2 . This suggests that the projected global warming due to increasing CO 2 is likely to be closer to the highest projected estimates among the current generation of climate models. Citation: Shukla, J.,

Oceanic influences on recent continental warming

“…Reliable assessments of these contributing factors depend critically on reliable estimations of natural climate variability, either from the observational record or from coupled climate model simulations without anthropogenic forcings. Several recent studies suggest that the observed SST variability may be misrepresented in the coupled models used in preparing the IPCC's Fourth Assessment Report, with substantial errors on interannual and decadal scales (e.g., Shukla et al 2006, DelSole, 2006Newman 2007;Newman et al 2008). There is a hint of an underestimation of simulated decadal SST variability even in the published IPCC Report (Hegerl et al 2007, FAQ9.2 Figure 1).…”

Present‐day interannual variability of surface climate in CMIP3 models and its relation to future warming

“…In general, this relation is negative as found for other skill metrics (e.g. by Shukla et al, 2006), however in most cases small and not significant if the models with the worst IAV representation (mainly the models 'g', 'i', 'j' and 'h'; see above) are omitted. One exception is the extratropical summer where a significant negative relation (r ∼ −0.5) between the model's ability to represent extratropical IAV and extratropical temperature change is found.…”

“…Some studies (e.g. Shukla et al, 2006) found relations between model fidelity and temperature changes in the future with the 'better' models indicating significantly larger temperature changes in climate projections at least on the global scale.…”

Information Theory and Dynamical System Predictability

“…The problem of global warming projection was considered from the current perspective by [87]. They used the divergence between the equilibrium distribution of various models and the present observed climate/equilibrium distribution as a measure of the veracity of a particular model.…”