Global average climate forcing and temperature response since 1750

Estimates are made for the period since 1750 of the major radiative forcing factors thought to be important in climate change. Analysis of these emphasizes the role of biospheric CO2 release and increasing methane up to the early twentieth century. Fossil fuel burning had a minor role until the mid-twentieth century, with the relatively small effects of fossil fuel CO2 being cancelled by sulphate aerosols from the same source. It is shown that, by using reasonable estimates of the contributions by greenhouse gases and anthropogenic and volcanic aerosols, a simple box-diffusion climate model simulates many features of the observed record of global climate change as estimated from both instrumental and glacier data. This is achieved without including either variations in solar intensity over this period or internal variability-which recent discussions of the topic have suggested are needed-but including forcing by volcanic aerosols, which these studies neglected. Three different estimates of forcing by volcanic aerosols are considered; although the volcanic aerosols substantially improve the model's fit to the observations, the validation does not show any one estimate to be clearly superior. The temperature record is shown to be consistent with the climate sensitivity obtained with three-dimensional models. (C) 1998 Royal Meteorological Society.