Influence of Sunspots on Global Mean Surface Temperature

The influence of variations in solar activity on earth's surface temperature is a key question in climate-change attribution. On the basis of natural cyclic sea surface temperatures and the annual mean daily sunspot number as a proxy for variability in solar influence on the energy retained by the planet, a predictive equation derived from well-understood physical principles proves capable of reproducing observed anomalies in annual global mean surface temperature since before 1900 with 90% accuracy (R 2 = 0.9049). This accuracy results even where a zero-contribution from changes in greenhouse-gas concentrations is assumed. Here we show that the cumulative influence of the unusually elevated solar activity in the 64 years 1941–2005, as calculated using the time-integral of sunspot number anomalies (with a proxy factor) might have been a primary cause of the global warming observed through 2001. After 2001 the low solar activity is consistent with the observed flat average global temperature trend. The physically-based predictive equation, with the widely-projected decline in solar activity, moderated by the substantial effective thermal capacitance of the planet, especially the oceans, projects a downtrend steeper than 0.1K/decade.