A Little More than Sunspots

Gavin Schmidt and Michael Mann at Real Climate do a takedown of the oil industry-funded experts who assert the increased global temperatures are purely solar driven.

To do so, they do an analysis of this recent review in Nature (by P. Foukal1, C. Fröhlich, H. Spruit and T. M. L. Wigley, Nature 443, 161-166(14 September 2006) | doi:10.1038/nature05072) concerning just this effect. Given in abstract but graphically supplemented:

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.

Which is the nice careful, way scientists say: it sure as Hell doesn't look like brightness is driving the temperature increase, but yeah, it might be something we can't measure.

Now that's a reality-based statement.