Satellite data sheds new light on solar cycle

The sun may warm the Earth more during waning solar cycles, new satellite data has shown.

Last Updated: Oct 07, 2010, 10:05 AM IST

London: The sun may warm the Earth more during waning solar cycles, new satellite data has shown, turning scientific understanding on its head and helping to explain extreme local weather patterns, scientists said.

But scientists said the findings did not undermine the case for man-made global warming through greenhouse gas emissions.

The heat and light of the sun waxes and wanes over a roughly 11-year period. Scientists had thought it warmed the Earth more during peaks of activity, for example as measured by the number of spots visible in the sun`s atmosphere.

But new satellite data showed that, in fact, from 2004-2007 as the cycle waned, more light reached the Earth`s surface. It was only high frequency, ultraviolet light -- which hardly reaches the Earth`s surface -- that faded.

That means the sun warmed the Earth more during that declining cycle, a new and counter-intuitive finding.

"It`s quite intriguing, it`s suggesting the solar influence is completely opposite to expectations," said Imperial College London`s Joanna Haigh, lead author of the paper titled "An influence of solar spectral variations on radiative forcing of climate," to be published in the journal Nature on Thursday.

The authors underlined that the findings were only for a three-year period, more proof was needed and could be provided if light at the Earth`s surface fell when the sun becomes more active again, as expected in the next year or so.

Bureau Report