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.
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. But scientists said the findings did not undermine the case for man made global warming through greenhouse gas emissions.
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.
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.
“Its 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.
Skeptics of the theory of man made climate change have long argued that variation in solar activity could explain a warming Earth, rather than rising greenhouse gas emissions. The average amount of heat and light the sun pumps out has increased slightly over the past 150 years.
“It doesn’t give comfort to the climate skeptics at all,” said Haigh. “It may suggest that we don’t know that much about the sun.”
But climate scientists say that increase is only about one tenth of the warming effect of rising greenhouse gas emissions, which have helped cause global average temperatures to rise by more than 0.7 degrees Celsius since pre-industrial times.