Satellite Temperature Measurements - Reconciliation With Climate Models

Reconciliation With Climate Models

Climate model results summarized by the IPCC in their third assessment show overall good agreement with the satellite temperature record. In particular both models and satellite record show a global average warming trend for the troposphere (models range for TLT/T2LT 0.6 - 0.39°C/decade; avg 0.2°C/decade) and a cooling of the stratosphere (models range for TLS/T4 -0.7 - 0.08°C/decade; avg -0.25°C/decade).

There remain, however, differences in detail between the satellite data and the climate models used.

Globally, the troposphere is predicted by models to warm about 1.2 times more than the surface; in the tropics, the troposphere should warm about 1.5 times more than the surface. Most climate models used by the IPCC in preparation of their third assessment show a slightly greater warming at the TLT level than at the surface (0.03°C/decade difference) for 1979-1999 while GISS and Hadley Centre surface station network trends are +0.161 and +0.160 °C/decade respectively, the lower troposphere trends calculated from satellite data by UAH and RSS are +0.140 °C/decade and +0.148 °C/decade. The expected trend in the lower troposphere, given the surface data, would be around 0.194 °C/decade.

This greater global average warming in the troposphere compared to the surface (present in the models but not observed data) is most marked in the tropics. CCSP SAP 1.1 chapter 5 says:

"In the tropics, surface temperature changes are amplified in the free troposphere. Models and observations show similar amplification behavior for monthly and interannual temperature variations, but not for decadal temperature changes. Tropospheric amplification of surface temperature anomalies is due to the release of latent heat by moist, rising air in regions experiencing convection."

Although all the datasets show the expected tropospheric amplification at seasonal and annual timescales it is still debated whether or not the long term trends are consistent with the expected moist adiabatic lapse rate amplification due to difficulty of producing homogenized datasets, some satellite temperature reconstruction are consistent with the expected amplification while others are not.