Scientists discovered that a decline in solar activity did not lead to an expected cooling of the Earth, a bizarre finding that many think will have repercussions for climate change models.

The Sun is known to go through 11-year cycles where activity waxes and wanes. Scientists theorized that during waning phases, the amount of radiation that reaches Earth is far less.

A new study was carried out between 2004 and 2007 during a solar waning phase. Researchers found that the amount of energy in the ultraviolet part of the energy spectrum fell. But, contrary to popular belief in the science community, radiation in the visible part of the energy spectrum increased, instead of declining, which caused a warming effect.

The study is important because of a debate over how much global warming can be attributed to Man or to natural causes.

Climate specialists say that warming is largely due to man-made greenhouse gases. But skeptics say that this is a flawed notion, and point out that Earth has known periods of cooling and warming due to variations in the Sun’s output.

“These results are challenging what we thought we knew about the Sun's effect on our climate,” said lead author Joanna Haigh, a professor at Imperial College London.

“However, they only show us a snapshot of the Sun's activity and its behavior over the three years of our study could be an anomaly,” said Haigh, who is also a member of the Grantham Institute for Climate change.

Haigh said that if the Sun turned out to have a warming effect during its waning phase, it might also turn out to have a cooling effect during the waxing phase.

If that is the case, greenhouse gases would be more to blame than thought for the noticeable rise in global temperatures over the past 100 years.

It’s important not to jump to any conclusions “based on what we have found” in the short study period, said Haigh. “We need to carry out further studies to explore the Sun's activity, and the patterns that we have uncovered, on longer timescales,” she added.

The study is published in Nature, the weekly British science journal.