Skeptical Science

Post image for Climate Models: “Epic Failure” or “Spot on Consistent” with Observed Warming?

NASA scientist Roy Spencer recently posted on his Web site some startling graphs produced by John Christy, his colleague at the University of Alabama in Huntsville. The graph immediately below compares the linear-trend temperature projections of 73 climate models with the linear trend of observed temperatures for the bulk tropical atmosphere during 1979-2012.


The 73 models are part of the fifth phase of the Coupled Model Intercomparison Project (CMIP-5), a collaborative effort of 20+ modeling groups to inform the IPCC’s forthcoming Fifth Assessment Report (AR5). The Project’s three main objectives are to “evaluate how realistic the models are in simulating the recent past,” “provide projections of future climate change” out to 2035 and 2100, and “understand some of the factors responsible for differences in model outputs” such as different estimates of feedback effects.

Christy’s graph reveals what Spencer calls an “epic failure” of the models to match the actual behavior of the tropical atmosphere. Models that overestimate recent warming are likely to overestimate future warming as well.

Of course, observational systems may have biases and errors, but that is an implausible explanation for the mismatch. The observations come from two satellite and four radiosonde (weather balloon) datasets, which all independently give “virtually identical trends.”

What about the subset of U.S.-designed models — do they get the trend right? Nope. Take a gander at the next graph.


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