The relationship between atmospheric water vapor and temperature in simulations of climate change

Atmospheric moisture (Q) and temperature (T) relationships simulated by two general circulation models (GCMs) and that of a recent operational analysis are intercompared. The GCMs represent two important stages of model development, with the earlier one using a simplistic convective adjustment scheme and the more recent one employing a more physically‐realistic convective parameterization. While the models agree in some fundamental qualitative aspects of the Q‐T relationship, they differ quantitatively in the correlations of Q with T, and in the vertical dependencies of moistening to increasing CO2. As the sophistication of convective parameterizations has increased, model sensitivity to changes in atmospheric CO2 has decreased markedly. This study indicates the reduction in sensitivity is primarily due to a reduction in simulated moisture amount along with changes in vertical distributions. While the more recent model shows clear signs of improvements, there is also indication that it may have underestimated the Q‐T correlations, leading to a somewhat lower climate sensitivity with increasing CO2.