A search for human influences on the thermal structure of the atmosphere

Abstract

Several recent studies have compared observed changes in near-surface temperature with patterns of temperature change predicted by climate models in response to combined forcing by carbon dioxide and anthropogenic sulphate aerosols. These results suggest that a combined carbon dioxide + sulphate aerosol signal is easier to identify in the observations than a pattern of temperature change due to carbon dioxide alone. This work compares modelled and observed patterns of vertical temperature change in the atmosphere. Results show that the observed and model-predicted changes in the mid- to low troposphere are in better accord with greenhouse warming predictions when the likely effects of anthropogenic sulphate aerosols and stratospheric ozone reduction are incorporated in model calculations, and that the level of agreement increases with time. This improved correspondence is primarily due to hemispheric-scale temperature contrasts. If current model-based estimates of natural internal variability are realistic, it is likely that the level of time-increasing similarity between modelled and predicted patterns of vertical temperature change is partially due to human activities.