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A puzzling discovery has raised a question mark over the Sun's impact on climate change and could provide ammunition for sceptics, it was revealed today.
Until now it has been assumed that less activity from the Sun equates to less warming of the Earth.
But the new research, which focuses on a three-year snapshot of time between 2004 and 2007, suggests the opposite may be true.
As solar activity waned at the end of one of the Sun's 11-year cycles, the new data show the amount of energy reaching the Earth at visible wavelengths rose rather than fell.
Scientists believe it may also be possible that during the next up-turn of the cycle, when sun activity increases, there might be a cooling effect at the Earth's surface.
A further twist arises from the fact that over the past century, overall solar activity has been increasing.
If the new findings apply to long as well as short time periods, this could translate into a small degree of cooling rather than the slight warming effect shown in existing climate models. It would effectively turn received wisdom on its head.
Sceptics are likely to say the results further undermine the reliability of climate change science, especially with regard to solar effects.
Professor Joanna Haigh, from Imperial College London, who led the study, said: 'These results are challenging what we thought we knew about the Sun's effect on our climate.