It has been believed that the Sun’s activity waxes and wanes over an 11-year cycle and that when its activity wanes, the overall amount of radiation reaching the Earth decreases.

Now, the new study by researchers from Imperial College London and the University of Colorado found that as solar activity decreased, the amount of light and heat reaching the Earth rose rather than fell, causing the planet to become warmer.

The researchers, who looked at the Sun’s activity over the period 2004-2007 when it was in a declining part of a cycle, said a decline in the Sun’s activity does not always mean that the Earth becomes cooler.

Its impact on melting polar ice caps, and drying up rivers could therefore have been exaggerated by conventional climate models during the period, the Telegraph reported.

The scientists also believe it may also be possible that during the next upturn of the cycle, when solar activity increases, there might be a cooling effect at the Earth’s surface.

While this may support climate change sceptics’ arguments in the short term, long term analysis suggests it actually provides further evidence that the heating of the planet is more than a natural, cyclical phenomenon, they said.

Over the past century, overall solar activity has been increasing and should therefore cool the Earth, yet global temperatures have increased.

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.

“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.

“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.” The research, published in the journal Nature, is based on data from a satellite called SORCE (Solar Radiation and Climate Experiment) that has been measuring the sun’s energy output at X-ray, ultraviolet, visible, and near-infrared wavelengths.

Denying that their findings would fuel scepticism about climate change research, Professor Haigh said: “I think it doesn’t give comfort to the climate sceptics at all.

“It may suggest that we don’t know that much about the Sun. It casts no aspersions at all upon the climate models.” Professor Brian Hoskins, the Director of the Grantham Institute for Climate Change at Imperial College London, said: “We know that the Earth’s climate is affected both by human activity and by natural forces and today’s study improves our understanding of how the Sun influences our climate.

“Studies like this are vital for helping us to create a clear picture of how our climate is changing and through this, to work out how we can best protect our planet.”"