Projections of CMIP5 Models: Will They Ever Come Together?
Christensen, J.H. and Boberg, F. 2012. Temperature dependent climate projection deficiencies in CMIP5 models. Geophysical Research Letters 39: 10.1029/2012GL053650.
Analyzing the role of this difference as "a contributing factor for some models to project stronger regional warming than others," the two scientists found that "models with a positive temperature dependent bias tend to have a large projected temperature change," and that "these tendencies increase with increasing global warming level." In addition, they say that this situation "appears to be linked with the ability of models to capture complex feedbacks accurately," noting in particular that land-surface/atmosphere interactions are treated differently and with different degrees of realism among the various models they investigated, and that "soil moisture-temperature feedbacks are relevant for temperature extremes in a large fraction of the globe," consistent with their findings.
The unfortunate upshot of these observations, in the words of Christensen and Boberg, is that "accepting model spread as a way to portray uncertainty of the projection estimate may result in an overestimation of the projected warming and at the same time indicate little model agreement on the mean value." And they say that "a non-negligible part" of this sad state of affairs "is due to model deficiencies," which have yet to be overcome to the point that all model results come together and converge on a common projection.
So, will it ever happen? Will the convergence finally occur?