The Debate Heats Up

For the first time, researchers have shown a strong correlation between solar activity and fluctuations in the earth's temperature. And the study has convinced some proponents of the greenhouse-warming theory that sunspot activity is at least in part responsible for the rise in global temperatures they believe has occurred over the last century.

Eigil Friis-Christensen and Knud Lassen of the Danish Meteorological Institute compared the records of the earth's temperature for the last 130 years with records of sunspot activity and found that when the intervals between peaks in sunspot abundance began shortening at the end of the last century, the earth began to warm. When the sunspot cycle began lengthening around 1940, the temperature peaked and began falling. And when the solar-cycle length started getting shorter again in the '60s, the planet's temperature began climbing. In fact, there was a 0.95 correlation coefficient between the two curves.

Keith Shine, an atmospheric scientist at the University of Reading, told Science that if the figures are correct, "We have to change our view of climate fundamentally. It's an incredible correlation; it would imply that almost nothing else is important in the climate system." Almost all of the 0.5-degree Celsius warming of the last century is accounted for by the sunspot cycle theory.

Critics caution that the temperature records are unreliable, going back only 130 years or so and covering well only land masses of the Northern hemisphere. (These facts did not seem so important when greenhouse skeptics raised them to question whether the supposed global warming had even occurred.)

But even James Hansen of the Goddard Institute for Space Studies, a very vocal proponent of the greenhouse theory, is impressed by the Danish study. He told The New York Times, "My gut feeling…is that they're at least partly right."