ABSTRACT: We examine tropospheric temperature trends of 67 runs from 22 ‘Climate of the 20th Century’ model simulations and try to reconcile them with the best available updated observations (in the tropics during the satellite era). Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs. These conclusions contrast strongly with those of recent publications based on essentially the same data. Copyright 2007 Royal Meteorological Society

1. Introduction

A panel convened by the National Research Council (2000) found for the satellite era (since 1979) ‘[a]pparently conflicting surface and tropospheric temperature trends’ that could not be reconciled, with the Earth’s surface warming faster than the lower troposphere. The panel concluded, after considering possible systematic errors that ‘[a] substantial disparity remains.’ From a study of several independent observational datasets Douglass et al. (2004b) confirmed that the disparity was real and arose mostly in the tropical zone. Also, Douglass et al. (2004a) showed that three state-of-the-art General Circulation Models (GCMs) predicted a temperature trend that increased with altitude, reaching a maximum ratio to the surface trend (‘amplification’ factor R) as much as 1.5–2.0 at a pressure (altitude) about 200–400 hPa. This was in disagreement with observations, which showed flat or decreasing amplification factors with altitude.