Tuesday, September 4, 2007

Global warming linked to stronger hurricanes

Global warming might not be increasing the number of hurricanes in the Atlantic Basin, but there is evidence to suggest it is making the storms stronger.

Speaking to the attendees of the Chamber of Commerce luncheon earlier this month, Cayman Islands Senior Manager for Meteorological Services Fred Sambula said the formation of no individual tropical cyclone could be attributed to global warming.

“So far, there is no reason to believe climate change is affecting tropical cyclone activity,” he said.

There has been increased numbers of tropical cyclones in the Atlantic Basin in recent years – as evidenced by the record year of 2005 – however the increase cannot be directly attributed scientifically to global warming.

A naturally occurring and cyclical event called the Atlantic Multi–decadal Oscillation has been cited as the most likely cause of the recent increase, especially when coupled with other factors known to increase Atlantic Basin cyclone activity, like the La NiƱa phenomenon in the Pacific Ocean.

The effect of climate change on global tropical cyclone activity was a topic for discussion at the World Meteorological Organisation’s Sixth International Workshop on Tropical Cyclones held in Costa Rica last November, Mr. Sambula said.

A position statement put out by the participants after the workshop pointed out that there seems to be an exception to the relationship between global warming and tropical cyclone frequency in the tropical North Atlantic, where many of the Atlantic Basin storms are formed.

The WMO’s statement said surface temperatures in the tropical North Atlantic Ocean are well established as one of the factors impacting the number of tropical cyclones. Evidence has shown that increasing sea surface temperatures are at least partly caused by global warming.

Because of technological advances and changing reporting techniques, it is difficult to accurately compare hurricane frequency on a historical basis.

Mr. Sambula explained why just counting the numbers of storms recorded now as compared to years past could be misleading. He pointed to the percentages of recorded hurricanes or tropical storms that made landfall before and after the advent of satellites.

Prior to satellite observation of the oceans, 77 per cent of all tropical cyclones made landfall, as opposed to 58 per cent after satellite observation. That disparity could not be possible, Mr. Sambula indicated.

“It seems that before satellite, we were missing a lot of storms that stayed out to sea,” he said.

Between 1900 and 1964, Mr. Sambula estimates two to three tropical cyclones a year went unrecorded because they did not make landfall anywhere.

Prior to satellite, tropical cyclones at sea were primarily recorded by ship reports.

The rise in sea surface temperatures is more clearly affecting tropical cyclones in a different way.

“What we have seen is that when these things do form, they are stronger,” Mr. Sambula said.

One study that was discussed at the WMO workshop showed that between 1975 and 2004 there was a 100 per cent increase in the proportion of major Category 4 and Category 5 hurricanes. Another study showed a small positive trend amounting to about 10 per cent in the frequency of Category 4 and 5 hurricanes over the past 20 years.

The effects of global warming could also be felt in other ways in the Cayman Islands. Arctic polar ice has melted to record lows this summer, and it is now thought there will be no summer ice at all possibly as early as 2030.

Melting polar ice and glaciers could then cause a rise in sea levels, something the low–lying Cayman Islands cannot afford.

There are conflicting scientific opinions as to how much the polar melting would affect sea levels in places like the Caribbean. Some scientists predict a large increase in sea levels resulting from the polar melting, enough to swamp some major cities in the United States and elsewhere.

“There are some islands in the Maldives that have been lost because of rising waters,” Mr. Sambula said.

It wouldn’t take that kind of rise to be dangerous for the Cayman Islands.

“Places like Cayman that are low are at risk to any rise in sea level,” Mr. Sambula said. “If you get storm surge and the sea is already higher, you’re going to get that much more surge.”

Mr. Sambula said the climate is changing quickly.

“Never has there been such a rapid change as in this period of global warming because of the burning of fossil fuels.”

Mr. Sambula thinks all governments should factor global warming and climate change into their long–term planning.

He also thinks the Cayman Islands needs to start thinking now about how to mitigate against rising sea levels.

“I think government should have a scientific policy advisor to consider things like this,” he said

Source: Cayman Islands

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