finding 15.3 : key-finding-15-3

While climate models incorporate important climate processes that can be well quantified, they do not include all of the processes that can contribute to feedbacks, compound extreme events, and abrupt and/or irreversible changes. For this reason, future changes outside the range projected by climate models cannot be ruled out (very high confidence). Moreover, the systematic tendency of climate models to underestimate temperature change during warm paleoclimates suggests that climate models are more likely to underestimate than to overestimate the amount of long-term future change (medium confidence).

This finding is from chapter 15 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: The key finding is based on the IPCC AR5 WG1 Chapter 9,a46eaad1-5c17-46f7-bba6-d3fee718a092 as well as systematic paleoclimatic model/data comparisons.

Description of evidence base: This key finding is based on the conclusions of IPCC AR5 WG1,f03117be-ccfe-4f88-b70a-ffd4351b8190 specifically Chapter 9;a46eaad1-5c17-46f7-bba6-d3fee718a092 the state of the art of global models is briefly summarized in Chapter 4: Projections of this report. The second half of this key finding is based upon the tendency of global climate models to underestimate, relative to geological reconstructions, the magnitude of both long-term global mean warming and the amplification of warming at high latitudes in past warm climates (e.g., Salzmann et al. 2013;828c7c4c-3dcf-4865-b21f-a6ad1fcedca1 Goldner et al. 2014;35038076-c098-424d-892a-8ba6a87bf142 Caballeo and Huber 2013;9f061a0a-e32d-417f-8404-c5ad0d4b01f4 Lunt et al. 201297079544-53fc-496d-b8fc-871be0681b33).

New information and remaining uncertainties: The largest uncertainties are structural: are the models including all the important components and relationships necessary to model the feedbacks and if so, are these correctly represented in the models?

Assessment of confidence based on evidence: There is very high confidence that the models are incomplete representations of the real world; and there is medium confidence that their tendency is to under- rather than over-estimate the amount of long-term future change.

This finding was derived from figure -.2: Confidence / Likelihood

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