Don't Blame Sun for Global Warming, Study Says

Brian Handwerk
for National Geographic News
September 13, 2006

Sunspots alter the amount of energy Earth gets from the sun, but not enough to impact global climate change, a new study suggests.

The sun's role in global warming has long been a matter of debate and is likely to remain a contentious topic.

Solar astronomer Peter Foukal of Heliophysics, Inc., in Nahant, Massachusetts, points out that scientists have pondered the link between the sun and Earth's climate since the time of Galileo, the famous 17th-century astronomer.

"There has been an intuitive perception that the sun's variable degree of brightness—the coming and going of sunspots for instance—might have an impact on climate," Foukal said.

Foukal is lead author of a review paper on sunspot intensity appearing in tomorrow's issue of the journal Nature.

He says that most climate models—including ones used by the Intergovernmental Panel on Climate Change—already incorporate the effects of the sun's waxing and waning power on Earth's weather (related images: our stormy star).

But, Foukal said, "this paper says that that particular mechanism [sunspots], which is most intuitive, is probably not having an impact."

Sunspot Impact Simply Too Small

Sunspots are magnetic disturbances that appear as cooler, dark patches on the sun's surface. The number of spots cycles over time, reaching a peak every 11 years.

The spots' impact on the sun's total energy output is easy to see.

"As it turns out, most of the sun's power output is in the visible range—what we see as brightness," said Henk Spruit, study co-author from the Max Planck Institute for Astrophysics in Garching, Germany.

"The sun's brightness varies only because of the blemishes that are also visible directly on pictures: the dark patches called sunspots and the minute bright points called faculae. In terms of brightness changes, in large part, what you see is what you get."

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