Warming fuels rise in tropical storms
By Rosslyn Beeby (Science & Environment Reporter), The Canberra Times, 27/12/2008
Warming ocean temperatures are creating more violent storms across the Earth's tropics, new research has found.
Sophisticated infra-red satellite technology has detected an increase in ''thunderheads'' towering cumulus clouds formed by the rising of warm moist air over tropical oceans.
A study by the United States National Aeronautics and Space Administration estimates if current global warming trends continue, the frequency of severe tropical storms and their devastating impacts on developing countries will increase by 6 per cent in the next decade.
The United Nations environment program has also warned the rate of extreme weather disasters is increasing, with the social and economic costs of storm and flood damage exceeding those caused by major earthquakes.
The agency says in 2008, the largest number of significant natural disasters were weather-related, with the global damage bill topped by Cyclone Nargis, which left a trail of wreckage across Burma in May. The cyclone killed more than 84,500 people and caused massive uninsured economic losses estimated at about $US4 billion ($A5.8 billion).
According to UN figures, while the frequency of earthquakes has increased by 50 per cent in the past 30 years, natural disasters caused by extreme weather have increased by 350 per cent.
NASA's satellite data, gathered over a five-year period from its Aqua spacecraft, shows more thunderheads are forming over the world's tropical oceans as a result of climate change.
These spectacular anvil-headed clouds can rise to heights of 8km, forming electrically charged storm supercells that generate torrential rain, hail and high winds.
The NASA study found these storm clouds were becoming more common as ocean temperatures rose, with a 1 degree Celsius increase in ocean surface temperatures triggering a 45 per cent increase in thunderhead formation.
Senior climate scientist Hartmut Aumann said the results would help improve climate models by establishing a link between global warming and the frequency and intensity of severe tropical storms.
''Clouds and rain have been the weakest link in climate prediction. The interaction between the daytime warming of the sea surface under clear-sky conditions and increases in the formation of low clouds, high clouds and, ultimately, rain is very complicated,'' he said.
A NASA satellite with sophisticated infra-red equipment designed to track formation of these deep-convection storm clouds usually detects about 6000 a day.
''The high clouds in our observations typically at altitudes of 20km and higher present the greatest difficulties for current climate models, which aren't able to resolve cloud structures smaller than about 250 kilometres in size,'' Dr Aumann said.
At present, thunderheads cover only 1 per cent of the world's tropical oceans, but generate more than 25 per cent of rain falling in that region.
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