It's completely counter-intuitive, but it now seems that increased solar activity actually leads to cooling on Earth.
As the sun's activity waxes and wanes over an 11-year cycle, the overall amount of radiation reaching Earth rises and falls accordingly. But a new study from Imperial College London and the University of Colorado, published in Nature, shows that the decline in solar activity between 2004 and 2007 was actually associated with an increase in warming.
Contrary to expectations, the amount of energy reaching Earth at visible wavelengths increased rather than decreased as the sun's activity declined, causing the warming effect.
The researchers believe it's possible that the inverse is also true, and that increased solar activity tends to cool, rather than warm, Earth. And as overall solar activity has been increasing over the past century, the researchers believe it is possible that during this period, the sun has been contributing a small cooling effect, rather than a small warming effect as had previously been thought.
"These results are challenging what we thought we knew about the Sun's effect on our climate. However, they only show us a snapshot of the Sun's activity and its behaviour over the three years of our study could be an anomaly," says lead author professor Joanna Haigh of Imperial College London.
"We cannot jump to any conclusions based on what we have found during this comparatively short period and we need to carry out further studies to explore the Sun's activity, and the patterns that we have uncovered, on longer timescales. However, if further studies find the same pattern over a longer period of time, this could suggest that we may have overestimated the sun's role in warming the planet, rather than underestimating it."