CLAIMS that increased solar activity is the cause of global warming — rather than man-made greenhouse gases — have been comprehensively disproved by a detailed study of the sun. Scientists have delivered the final blow to the theory that recent global warming can be explained by variations in the natural cycles of the sun — a favourite refuge for climate sceptics who dismiss the influence of greenhouse gas emissions.
An analysis of the records of every major attribute of the sun that has been measured over the decades — such as sunspot cycles and magnetic fields — shows that since 1985 solar activity has decreased significantly while global warming has continued to increase.
“In 1985, the sun did a U-turn in every respect. It no longer went in the right direction to contribute to global warming,” said Mike Lockwood of the Rutherford Appleton Laboratory in Chilton, Oxfordshire.
“We think it’s almost completely conclusive proof that that the sun does not account for the recent increases in global warming that we have seen. There is almost no way out of that conclusion,” he said.
The study, published in the journal Proceedings of the Royal Society, shows there is no doubt that solar activity over the past 20 years has run in the opposite direction to global warming and therefore cannot explain rises in average global temperatures.
Dr Lockwood and his colleague, Claus Frohlich, of the World Radiation Centre in Davos Dorf, Switzerland, have produced the most powerful counter argument to suggestions that current warming is part of the natural cycle of solar activities.
“There is considerable evidence for solar influence on earth’s pre-industrial climate and the sun may well have been a factor in post-industrial change in the first half of the last century,” the scientists wrote.
However, since about 1940 there has been no evidence to suggest that increases in global average temperatures were caused by solar activity rather than greenhouse gases.
“Our results show that the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified,” the two scientists said.
The theory that past changes in solar activity may have explained some changes in the climate before the industrial revolution is not in dispute.
In previous centuries, for instance, notably between about 1420 and 1570 when the Vikings had to abandon their Greenland settlements, solar minima corresponded with unusually cool weather, such as the “little ice age” of the 17th century when the Thames froze over.
However, climate sceptics have exploited this to dispute the idea that man-made emissions of carbon dioxide are now responsible for global warming. In a recent Channel 4 programme in the UK, The Great Global Warming Swindle, for example, the rise in solar activity over the latter half of the 20th century was erroneously presented as perfectly matching the rise in global average temperatures.
Dr Lockwood said that he was “outraged” when he saw the documentary because of the way the programme makers had used graphs of temperature rises and sunspot cycles that were cut off in the 1980s when the two trends went in the opposite direction.
“The trouble is that the theory of solar activity and climate was being misappropriated to apply to modern-day warming. The sceptics were taking perfectly good science and bringing it into disrespect,” he said.
There is some evidence to suggest that variations in solar activity has contributed to climate changes in pre-industrial times, and there may well be evidence to suggest that it continued up to the 1940s, but no evidence after this period, he said.
