Scientists, including a Nobel Prize-winner, have rounded on studies used by climate sceptics to show that global warming is a natural phenomenon connected with sunspots, rather than the result of the man-made emissions of carbon dioxide.
The researchers have said that the scientific evidence continually cited by sceptics to promote the idea of sunspots being the cause of global warming is deeply flawed.
Many sceptics who accept that global temperatures have risen in recent decades suggest it is part of the climate's natural variability and could be accounted for by normal variations in the activity of the Sun. Powerful support for this idea came in 1991 when Eigil Friis-Christensen, director of the Danish National Space Centre, published a study showing a remarkable correlation between global warming and the length of sunspot cycles.
A further study published in 1998 by Mr Friis-Christensen and his colleague Henrik Svensmark suggested a possible explanation for the warming trend with a link between solar activity, cosmic rays and the formation of clouds.
However, many scientists now believe both of these studies are seriously flawed, and that when errors introduced into the analysis are removed, the correlations disappear, with no link between sunspots and global warming.
Peter Laut, a former adviser to the Danish Energy Agency who first identified the flaws, said there were practically no observations to support the idea that variations in sunspots played more than a minor role in global warming.
Professor Stefan Rahsmstorf, of Potsdam University, agreed: “I've looked into this quite closely and I'm on Laut's side in terms of his analysis of the data.”
Some scientists believe the flaws are so serious that the papers should be at least retracted.