Comparison of solar variability effects with the surface radiative forcing of CO2

In this paper we provide a comparison of the change in the solar flux with the surface forcing from greenhouse gases, particularly that of carbon dioxide which is increasing in the atmosphere due to fossil fuel combustion processes. This comparison shows that the maximum changes in the clear sky solar flux since the time of the approximate onset of the industrial period is comparable to the corresponding carbon dioxide surface forcing. In comparison with the forcing from all of the other major greenhouse gases combined, the solar contribution may be about 20-60% as strong. This comparison indicates that over the past few hundred years, the surface temperature change impact from solar variability can rival that from the anthropogenic increase in greenhouse gases. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.