15 July 2007The Australian / The Sunday Times
At present hurricanes, originating far out in the Atlantic, blow westwards towards the Caribbean and America's Gulf coast, and leave Europe's coastline unscathed.
Now scientists warn that climate change means that the Mediterranean is warming up so much it stores enough heat to trigger the formation of its own hurricanes.
They say this will have important implications for the safety of resorts, residents and holidaymakers.
"We have detected for the first time a risk of tropical cyclone (hurricane) development over the Mediterranean based on anthropogenic (man-made) climate change," said Miguel Gaertner, lead researcher at the environmental sciences faculty of the University of Castilla-La Mancha in Toledo, Spain.
Such a change would have serious implications for tourism, raising the prospect that hotels, campsites and resorts would need to develop hurricane shelters, evacuation plans and other protective measures similar to those on America's Gulf coast.
Hurricanes form far out in the tropical Atlantic. Few reach land and hardly any reach Europe.
Recently, however, researchers found hurricanes forming where they had never been seen before. In 2004 Cyclone Catarina became one of the very few ever to form in the South Atlantic, hitting the coast of Brazil.
Then, in 2005 Hurricane Vince formed around Madeira, an area that had never before produced such storms.
It even struck Spain - another first.
The same year also saw New Orleans overwhelmed by Hurricane Katrina and the American Gulf coast hit by Hurricane Rita, the fourth-most intense Atlantic hurricane ever recorded.
Hurricane researchers were shocked and have since put huge efforts into predicting how future climate change might alter patterns of hurricane formation.
In a paper in Geophysical Research Letters, Gaertner described how he gathered data from these unusual storms. He combined the information with data about long-term changes in water temperature across the Atlantic to create detailed computer models of future trends covering a range of sea temperature rises.
So far, scientists agree, the surface layers of the Atlantic and Mediterranean have warmed by about 0.6C, with most of that change happening since 1970. Some predict a further 2C-3C warming by 2050.
Gaertner's computer models showed a general increase in storm intensity with some scenarios predicting hurricanes.
"Some observed cyclones over the Mediterranean have already shown partially tropical characteristics," said Gaertner.
His findings fit with another recent study by America's National Academy of Sciences. It showed a powerful link between rising ocean temperatures in the key hurricane breeding grounds of the Atlantic and Pacific and an increase in the intensity of such such storms.
"The increases in sea surface temperature in these hurricane breeding grounds cannot be explained by natural processes alone," said Tom Wigley, of the National Center for Atmospheric Research (NCAR), in Boulder, Colorado.
"The best explanation for these changes has to include a large human influence."
Water temperature plays a vital role in the formation and growth of hurricanes.
They need an upper layer of water at least 100ft deep with a temperature above 79F before they can grow. Once such a layer forms it can release heat extremely quickly, providing the energy that fuels the resulting storm.
Kevin Trenberth, head of the climate analysis section of NCAR, said climate change would bring stronger storms to the Mediterranean although its land-locked geography meant it would seldom be possible for them to become hurricanes.
He said: "The scientific record shows global warming is raising sea-surface temperatures. Observation and theory suggest that hurricanes are becoming more intense as the earth warms."
