Sunspot activity may be a primary factor in climate fluctuations, according to Willie Soon, a researcher affiliated with the Harvard-Smithsonian Center for Astrophysics and the Harvard College Observatory, who offered the hypothesis in an interview with TG Daily, an online news source.

Although many climatologists have cited increases in carbon dioxide as the primary cause of the temperature increases associated with global warming, Soon maintained that solar radiation from sunspots also has a great effect.

“The sun is a great driving force to climate change,” Soon said in an interview with The Crimson yesterday, adding that most observed climate data could be explained by fluctuations in solar radiation.

Sunspots—pockets of magnetism on the sun’s surface—generate high levels of energy, which then heat the Earth’s atmosphere.

Soon told TG Daily that the lack of additional energy resulting from a decrease in sunspots is directly responsible for colder temperatures experienced in recent years.

He said that, as of last week, there had been sunspots on only 11 days this year, and there were only 99 days with visible sunspots last year—the second-lowest total since 1911.

Brian F. Farrell, a Harvard meteorology professor, acknowledged a connection between sunspot activity and temperatures on the Earth, but cited other research showing that sunspots only account for an overall temperature change of a tenth of a degree centigrade.

Farrell did acknowledge that there could have been larger temperature effects caused by sunspots in the past.

“A strong correlation between the amount of radioactive carbon and temperature from ice cores has shown that solar activity can affect temperature,” Farrell said.

He cautioned that the link was “a hypothesis...[that] does not have firm scientific grounding.”

But Soon said that there have been much greater temperature fluctuations due to sunspots in the past and that proponents of global warming need to consider the effects of sunspot activity on global temperatures.