Behind the Science Cyclone climate link rejected
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28 February 2010
RESEARCH by hurricane scientists may force the UN climate panel to retract its claims that greenhouse gas emissions have caused an increase in the number of tropical storms.
The benchmark 2007 report by the Intergovernmental Panel on Climate Change said an increase in cyclone-force storms since 1970 was probably caused by climate change.
It followed some of the most damaging tropical storms in history, such as Hurricane Katrina, which hit New Orleans, and Hurricane Dennis, which struck Cuba, both in 2005.
The IPCC added that the world could expect a big increase in such storms over the 21st century unless greenhouse gas emissions were controlled. The warning helped turn hurricanes -- also known as cyclones or typhoons -- into one of the most widely cited threats posed by global warming, with politicians including British Energy Secretary Ed Miliband and former Us vice-president Al Gore describing them as a growing threat to humanity.
The cover of some editions of Mr Gore's latest book, Our Choice, even depicts a world beset by super-cyclones as a warning of what might happen if carbon emissions keep rising.
However, the latest research, just published in the Nature Geoscience journal, paints a very different picture.
It suggests the rise in cyclone frequency since 1995 was part of a natural cycle and that several similar previous increases have been recorded, each followed by a decline.
It draws on computer modelling to predict that the most likely impact of global warming will be to reduce the frequency of tropical storms. The research predicts a fall of up to 34 by 2100.
It does, however, suggest that when tropical storms occur they could become stronger, with average wind speeds rising by 2100.
A tropical cyclone is a tropical depression of sufficient intensity to produce sustained gale force winds of at least 63 km/h.
A "severe tropical cyclone" produces sustained hurricane force winds of at least 118 km/h.
"We have come to substantially different conclusions from the IPCC," said Chris Landsea, a scientist at the American government's National Hurricane Centre, who co-authored the report.
He added: "Hurricanes are much less sensitive to temperature increase than the IPCC report suggested. There are a lot of legitimate concerns about climate change but hurricanes are not among them."
