Don't blame the Sun

The theory that the Sun, not human activity, is responsible for most of the warming of the Earth in the past century has been debated for many years. According to that theory, the Sun has increased in brightness, and the brightening accounts for most of the warming. A new study puts the theory to rest.

Astrophysicists Peter Foukal of Heliophysics, Inc., in Nahant, Massachusetts, and Hendrik C. Spruit, of the Max Planck Institute for Astrophysics in Garching, Germany, together with two colleagues, analyzed records of variation in solar luminosity caused by changing dark and bright areas on the Sun--sunspots and faculae.

The team began by examining twenty-five recent years of precise solar-luminosity records gathered by radiometers on spacecraft. To peer further back in time, they scrutinized historical records of sunspots and faculae from the past century, as well as isotope ratios in the Greenland and Antarctic ice sheets, which register changes in solar activity for the past 1,000 years. They correlated those data with reconstructions of how temperatures have varied in the Northern Hemisphere during the past millennium, giving a fine-grained picture of the effects of changes in the Sun's brightness on climate.

The Sun did get brighter during the past 200 years, they discovered, but only by about 0.04 percent. That variation, they conclude, is far too small to have contributed substantially to the accelerated global warming observed since the mid-1970s. Although other solar traits--variable ultraviolet rays or solar winds, for instance--may yet be discovered to play a role, people burning fossil fuels are responsible for the bulk of the recent warming. (Nature)

COPYRIGHT 2006 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning