RESEARCHERS have found the waxing and waning of the sun affects our planet’s temperature in exactly the opposite way scientists had thought. The work suggests, counterintuitively, that when the sun is at the dimmest point of its 11-year solar cycle, as it was in December 2009, it warms the Earth most, and vice versa.

“When I first saw the results I thought we had done the calculations wrong,” said the physicist Prof Joanna Haigh, at Imperial College London, who led the research just published in the journal Nature. While they only had three years of satellite data so far, Haigh said the discovery could have far-reaching consequences.

“If further studies find the same pattern over a longer period of time, [then] we may have overestimated the sun’s role in warming the planet,” she said.

The rethink comes from a better understanding of how mixture of light emitted by the sun changes as its intensity shifts. The revelation also helps explain some seemingly strange regional climate phenomena, such as how Europe can have very cold winters at a time when the world as a whole is warming.

Some climate change sceptics have suggested the changes in the sun’s brightness can explain the global warming seen over the past century.

But Haigh said: “It does not give comfort to climate sceptics at all.” If the sun warmed the Earth less when it was at the solar maximum, then the reverse was also true, she said: “You can’t have it one way and not the other.” In addition, she said, the warming influence of rising greenhouse gases in the atmosphere, emitted by human activities, was at least 10 times greater than changes in the strength of the sun.

Prof Mike Lockwood, a solar physicist at the University of Reading, England, said: “We don’t have any reason at the moment to change our overall view of the contributions of changing solar radiation to climate change, not on a global scale, but there is quite a lot of evidence coming forward that these changes do matter on a regional scale and particularly to us here in Europe.”

That is because the sun’s intensity plays a crucial role at mid-latitudes by controlling the jet stream winds, which in turn govern weather, he said. Changes to the jet stream are responsible for extremely cold European winters, such as the last one, and also the conditions which caused the volcanic ash cloud from the Eyjafjallajokull volcano to blow southwards and ground flights in April and May.

—The Guardian, London