London: Leading scientists have dismissed studies which say that global warming is a natural phenomenon connected with sunspots, rather than the result of the man-made emissions of carbon dioxide (CO2).
According to a report in The Independent, the researchers, all experts in climate or solar science, said that the scientific evidence continually cited by skeptics to promote the idea of sunspots being the cause of global warming is deeply flawed.
Studies published in 1991 and 1998 claimed to establish a link between global temperatures and solar activity – sunspots – and continue to be cited by climate skeptics.
However, problems with the data used to establish the correlation have been identified by other experts and the flaws are now widely accepted by the scientific community, even though the studies continue to be used to support the idea that global warming is “natural”.
The issue has gained new importance in the light of opinion polls showing that nearly one in two people now believe global warming is a natural phenomenon unconnected with CO2 emissions.
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 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.
According to Peter Laut, a former adviser to the Danish Energy Agency who first identified the flaws, there were practically no observations to support the idea that variations in sunspots played more than a minor role in global warming.
Laut’s analysis of the flaws is accepted by most scientists familiar with the research, including Paul Crutzen, an atmospheric chemist at the Max Planck Institute in Germany, who won a Nobel Prize for his work on understanding the hole in the ozone layer.
“There is definitely a problem (with these studies). Laut has really pinned it down but the (sunspot) argument keeps reappearing and its quite irritating.” Professor Crutzen said.
“I’ve looked into this quite closely and I’m on Laut’s side in terms of his analysis of the data,” said Professor Stefan Rahsmstorf, of Potsdam University.