Henrik Svensmark, Professor in the Division of Solar System Physics at the Danish National Space Institute in Copenhagen, says cosmic radiation thrown out by the sun deflects the particles that cause clouds to form in the atmosphere.
As this solar activity increases, it means less clouds form and so less sun is reflected away from the Earth by them.
This then increases the temperature of the planet – Mr Svensmark says patterns in global temperature rising and falling over the last several hundred years match trends in solar irradiance more closely than they correlate with greenhouse gas emissions.
He said: “There’s no doubt that carbon dioxide is also affecting climate but it looks as if the climate sensitivity to carbon dioxide is probably smaller because the sun is also part of what’s going on.”
The physicist adds he does not believe the world is heading towards disaster because the data doesn’t suggest floods, droughts or hurricanes are actually increasingly in frequency or severity.