Natural and Anthropogenic Causes of Recent Climate Change

Abstract

Previous workers have examined atmospheric vertical temperature andreport anthropogenic influence on climate. However, none of theseconsidered the influence of natural forcing factors which may havebeen an influence on surface temperatures. Two issues are addressedhere. Firstly, whether the observed tropospheric warming might beexplained by solar forcing and the observed stratospheric coolingby the effects of ozone depletion. Secondly, whether greenhouse gasesand sulphate aerosols provide a complete explanation of observedchanges. In this paper, the method of optimal fingerprinting is employedto show that previous results of greenhouse gas influence on temperatureare robust to the inclusion of solar forcing. We also show, in adiagnostic tailored for the 11-year solar cycle, that we can detectthe influence of the solar cycle in recent vertical temperature structureand that the HadCM2 GCM may be underestimating the amplitude of thesolar signal by a factor of 2 to 3.