Vertical structure of warming consistent with an upward shift in the middle and upper troposphere

Warming in climate-change simulations reaches a local maximum in the tropical upper troposphere, as expected from approximately moist-adiabatic lapse rates in the tropical troposphere. But an assumption of moist-adiabatic lapse rates does not capture differences between the vertical profile of tropical warming in different models, and it is not applicable to the mean stratification of the extratropics. A promising alternative is to consider the response of tropospheric temperatures to global warming as involving an upward shift. We have previously introduced the vertical-shift transformation (VST) in which atmospheric variables shift vertically in a manner consistent with the moist primitive equations. Here, we use the VST to relate the vertical profile of warming to the climatological temperature profile in simulations from the Coupled Model Intercomparison Project 5 (CMIP5) and in observations. The VST captures much of the intermodel scatter in the ratio of upper- to middle-tropospheric warming in both the extratropics and tropics of simulations from CMIP5. Application of the VST to observed climatological temperatures yields warming ratios that are in the range of what is obtained from the model climatological temperatures, although biases in some model climatologies lead to substantial errors when shifted upwards. Radiosonde temperature trends are consistent with an upward shift in recent decades in the Northern Hemisphere, with less-robust results in the Southern Hemisphere.