Nature, 14 September 2006
Small variations in the Sun's power output, or luminosity, attract attention and controversy because of their possible implications for climate change. The changes arise from dark (sunspot) and bright (faculae) structures on the solar disk during the 11-year sunspot cycle. Since 1978 it has been possible to track these accurately with satellites, showing a variation of 0.07%. Foukal et al. review recent advances in our understanding of solar luminosity change and its effects on the energy balance on Earth. They conclude that solar brightening is unlikely to have had a significant effect on climate change since the seventeenth century. More speculative climate changes related to the Sun's ultraviolet light and magnetized plasma output are not yet ruled out, but are hard to quantify due to the complex interactions involved. The cover shows the structures responsible for the luminosity variations.
P. Foukal, C. Fröhlich, H. Spruit and T. M. L. Wigley
Nature 443, 161-166(14 September 2006) | doi:10.1038/nature05072
Variations in solar luminosity and their effect on the Earth's climate
Variations in the Sun's total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century. Additional climate forcing by changes in the Sun's output of ultraviolet light, and of magnetized plasmas, cannot be ruled out. The suggested mechanisms are, however, too complex to evaluate meaningfully at present.