A Test of the Tropical 200- to 300-hPaWarming Rate in Climate Models

by R. McKitrick and J. Christy, July 6, 2018 in AGU100

Overall climate sensitivity to CO2
doubling in a general circulation model results from a complex
system of parameterizations in combination with the underlying model structure. We refer to this as the modelsmajor hypothesis, and we assume it to be testable. We explain four criteria that a valid test should meet: measurability, specificity, independence, and uniqueness. We argue that temperature change in the
tropical 200- to 300-hPa layer meets these criteria. Comparing modeled to observed trends over the past
60 years using a persistence-robust variance estimator shows that all models warm more rapidly than
observations and in the majority of individual cases the discrepancy is statistically significant. We argue that
this provides informative evidence against the major hypothesis in most current climate models.