HAVANA, Sep 22 (IPS) - The devastation wrought by hurricanes Gustav, Hanna and Ike in the Caribbean has fuelled concern about the effects of global warming on the formation and intensity of tropical storms, an issue that has divided the scientific community and is causing alarm among island nations and coastal communities.

While the debate continues among climate experts, international bodies are studying the economic and social effects of the catastrophes caused by cyclones in the Caribbean basin, with the aim of designing and implementing adaptation measures to help countries cope with natural disasters.

"Over the next few years, we will continue to have active hurricane seasons, unless an El Niño episode happens, which brings a drop in activity in the Atlantic in any given year," José Rubiera, the head of the national forecast centre of Cuba’s Institute of Meteorology, told IPS.

"El Niño" and "La Niña" are the extreme phases of the oceanic-atmospheric phenomenon known as the "El Niño Southern Oscillation" (ENSO), which takes place in the equatorial region of the Pacific ocean every two to seven years, affecting different regions around the world to varying degrees, and especially South America.

La Niña is characterised by an atypical cooling of the surface waters of the ocean and an increase in the winds blowing east to west at the equator. The better known El Niño is the opposite: warmer surface waters and weaker winds.

"We will certainly continue to see intense hurricanes, associated with the heating up of the waters of the Atlantic ocean," said Rubiera.

Rising sea temperatures favour the formation of tropical storms. Some experts say the increased concentration of greenhouse gases has contributed -- to what extent is still under debate in academic circles -- to the heating up of the oceans by 0.5 degrees Celsius.

But there is no consensus on what impact the rise in temperature has had on the frequency or intensity of hurricanes.

In 2005, U.S. scientists Judith Curry at Georgia Tech and Kerry Emmanuel at MIT published studies that reported an increase in the intensity of tropical cyclones worldwide since 1970, parallel to the phenomenon of the heating up of the oceans. However, the annual average number of storms had remained steady, they said.

"There has been an increase in Atlantic tropical storm frequency since 1995, related to the 25- to 30-year cycles of hurricane activity, as has occurred at other periods during the 19th and 20th centuries," said Rubiera.

"In other parts of the world, the frequency of cyclone formation has not increased," he said.

"But the intensity of tropical storms is quite another matter: there does seem to be an increase in the number of intense hurricanes of categories 3, 4 and 5 (the maximum level on the Saffir-Simpson scale)," the expert said.

Between 1952 and 2000, Cuba was hit by only one near-category 3 hurricane, Flora, in 1963, in which over 1,000 people were killed in the eastern part of the island. But in the period from 2000 to 2008, six high-intensity cyclones have pounded this Caribbean country, the most recent, Ike, traversing virtually the whole island from east to west.

The Saffir-Simpson scale classifies hurricanes according to their sustained wind speeds, from 119 kilometres per hour (category 1) to over 250 kilometres per hour (category 5). In addition to gusting winds, waves and storm surges (above-normal sea levels caused by high winds piling up coastal water), torrential rain and tornadoes are the main causes of the destruction wrought by hurricanes.

"An interesting point is that this scale is quadratic, so that a category 2 hurricane does not cause twice as much damage as a category 1, but four times as much. A category 3 hurricane does not cause three times as much damage as a category 1, but nine times as much, and so on," Rubiera wrote in an article published in Enfoques magazine, produced by the IPS bureau in Cuba.

In the last few years the Caribbean region has been battered with particular ruthlessness by the devastating power of hurricanes.

In 2004, Grenada, a small English-speaking Caribbean island nation of approximately 90,000 people, suffered damages estimated at 889 million dollars, more than twice the country’s gross domestic product (GDP) in 2003, from the onslaught of hurricane Ivan.

Hurricanes Gustav and Ike caused estimated losses in Cuba of five billion dollars, including the destruction of more than 63,000 homes and the devastation of close to 100,000 hectares of crops, in a country with a serious housing deficit and where the agriculture industry is unable to feed its 11.2 million people. But only seven people were killed.

According to the official state newspaper Granma, the combined action of both hurricanes has been "the most devastating in the history of these meteorological phenomena in Cuba, in terms of the magnitude of the material damages caused."

The situation is even worse in the impoverished Caribbean nation of Haiti, which was lashed by tropical storm Hanna, as well as hurricanes Fay, Gustav and Ike, leaving a death toll variously reported as over 300 (by the national civil protection unit) or over 600 (the official government figure) and an estimated one million homeless.

The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) has launched an appeal for 108 million dollars for emergency relief and recovery efforts in Haiti.

"The fact is there is a cumulative effect, with new meteorological phenomena impacting on areas that have not yet fully recovered," says a report titled "El cambio climático en América Latina y el Caribe" (Climate Change in Latin America and the Caribbean), published by the United Nations Environment Programme (UNEP) in 2006.

Another document, published by the Economic Commission for Latin America and the Caribbean (ECLAC) in August 2006, called for the adoption of simultaneous mitigation and adaptation measures against natural disasters in the region, in the face of daunting climate forecasts for the coming years.

"We have to strike a balance between the urgent provision of shelters and roofs for the vulnerable population, and rebuilding houses and roofs with the strength and stability to withstand future hurricanes," Susan McDade, resident coordinator of the United Nations System in Cuba, told IPS.

"The challenge is to rebuild with higher quality standards and not just replace houses with others that will continue to be vulnerable to natural disasters. This will require coordination of the international community and working with the Cuban authorities," McDade said.