The theory relies on a presumed relationship between solar radiation and sunspots, dark patches that periodically erupt on the solar surface. In the current issue of Science magazine, Eigil Friis-Christensen and Knud Lassen of the Danish Meteorological Institute show a striking relationship between sunspot activity and global temperature over the 130-year period for which accurate climate records exist. (Technically, the relationship is not with the appearance of sunspots as such, but with a mathematical abstraction representing the length of the sunspot cycle at a given time. Sunspot activity varies over a 9- to 13-year period and the shorter cycles are associated with higher temperatures on Earth.)
Unfortunately, the data that would conclusively prove the sunspot connection-direct satellite measurements of solar radiation itself–exist only for the last dozen years, not long enough to draw conclusions. It will probably take several decades before the evidence is in. Meanwhile, we can all watch the thermometer.
