Twenty-five Climate Models Can't All Be Wrong … Or Can They?

From the NIPCC report:

As seemingly never-ending work on developing and improving climate models progresses, there is also a seemingly never-ending set of assessments of how that work is progressing; and the study of Maloney et al. (2014) is one of the most recent such assessments, wherein its 31 authors provide a summary of projected twenty-first-century North America (NA) climate changes, as spewed out by 25 updated state-of-the-art climate and Earth system models used in CMIP5, i.e., phase 5 of the Coupled Model Intercomparison Project, focusing largely on the representative concentration pathway 8.5 (RCP8.5) in a core set of 17 CMIP5 models. So what did they learn? 

In terms of what most people would describe as shortcomings (or maybe even failures), they say (1) “the sign of mean precipitation changes across the southern United States is inconsistent among the models, as is the annual mean precipitation change in the core NA monsoon region,” (2) the models “also disagree on snow water equivalent changes on a regional basis, especially in transitional regions where competing effects occur because of greater snowfall and warming temperatures,” (3) “the western United States is characterized by large inter-model variability in changes in the number of frost days,” (4) “substantial inter-model spread exists for projections of how ENSO teleconnection changes will affect precipitation and temperature variability in western NA,” (5) “projected changes in seasonal mean Atlantic and east Pacific tropical cyclone activity are inconsistent among models, which disagree on the sign and amplitude of changes in environmental factors that modulate tropical cyclone activity,” (6) “models have substantial difficulties in simulating the historical distribution of persistent drought and wet spells,” and (7) “model success in producing historical climate has little bearing on regional projections,” as demonstrated previously by Pierce et al. (2009). Perhaps most important of all, however, is the 31 researchers’ conclusion that “even areas of substantial agreement among models may not imply more confidence that projections are correct, as common errors or deficiencies in model parameterizations may provide false confidence in the robustness of future projections.”

Reference

Maloney, E.D., Camargo, S.J., Chang, E., Colle, B., Fu, R., Geil, K.L., Hu, Q., Jiang, X., Johnson, N., Karnauskas, K.B., Kinter, J., Kirtman, B., Kumar, S., Langenbrunner, B., Lombardo, K., Long, L.N., Mariotti, A., Meyerson, J.E., Mo, K.C., Neelin, J.D., Pan, Z., Seager, R., Serra, Y., Seth, A., Sheffield, J., Stroeve, J., Thibeault, J., Xie, S.-P., Wang, C., Wyman, B. and Zhao, M. 2014. North American climate in CMIP5 experiments: Part III: Assessment of Twenty-First-Century Projections. Journal of Climate 27: 2230-2270.

NAmerClim_in_CMIP5_part3 (PDF)

Additional Reference

Pierce, D.W., Barnett, T.P., Santer, B.D. and Gleckler, P.J. 2009. Selecting climate models for regional climate change studies. Proceedings of the National Academy of Sciences USA 106: 8441-8446.