Nature 360, 328 - 330 (26 November 1992); doi:10.1038/360328a0

Solar cycle length, greenhouse forcing and global climate

P. M. Kelly & T. M. L. Wigley

Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK

THE recent rise in global-mean surface air temperature is widely thought to be the result of increasing atmospheric concentrations of greenhouse gases^1–3, but there are discrepancies between the predicted response of the atmosphere to this radiative forcing and the observed temperature changes^1–5. Solar irradiance fluctuations have been proposed as a possible explanation for these discrepancies, and various solar properties (for example, radius⁶, smoothed sunspot number⁷ or cycle length⁸) have been suggested as proxies for solar irradiance variations in the absence of direct data. Here we model the effects of a combination of greenhouse and solar-cycle-length forcing and compare the results with observed temperatures. We find that this forcing combination can explain many features of the temperature record, although the results must be interpreted cautiously; even with optimized solar forcing, most of the recent warming trend is explained by greenhouse forcing.

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