An article in Science written by Richard A. Kerr (1996) summarizes recent evidence linking earth temperature fluctuations more strongly than previously thought to fluctuations in output of the sun. The IPCC report suggests that solar fluctuations are very small compared to greenhouse gas forcing. But Daniel Cayan and Warren White of Scripps Institute of Oceanography find fluctuations in ocean temperatures that match the fluctuations in solar output due to sunspots (decreases in solar energy) and faculae, or bright spots (increases in solar energy). Plots of surface temperature and total solar irradiance over the last 400 years show remarkable similarity. But the magnitude of the fluctuation in energy levels is not enough, in itself, to cause such a large change in temperature, so scientists are looking for some kind of amplification mechanism. Evidence suggests that about three-fourths of the warming that brought the earth out of the Little Ice Age in the late 1600s could have been due to solar brightening. Since 1860, it is estimated that brightening accounted for about half of the warming but only about one third since 1970. The remainder during these latter periods are presumably due to greenhouse gas increases.

If these finding withstand further scrutiny, they may suggest that climate models have overpredicted greenhouse warming over the last 130 years by more than previously thought.

Kerr, Richard A., 1996: A new dawn for sun-climate links. Science 271, 1360-1361.