The study is an overview of work into one of the scariest yet also one of the least understood aspects of climate change.

Known in the Atlantic as hurricanes and in eastern Asia as typhoons, tropical storms are driven by the raw fuel of warm seas, which raises the question about what may happen when temperatures rise as a result of greenhouse gases.

Tom Knutson and colleagues from the UN's World Meteorological Organisation (WMO) looked at peer-reviewed investigations that have appeared over the past four years, when the issue began to hit the headlines. Their benchmark for warming is the "A1B" scenario, a middle-of-the-road computer simulation which predicts a global average surface temperature rise of 2.8 degrees Celsius (5.4 degrees Fahrenheit) over the 21st century.

"It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged," says the paper. But storms could have more powerful winds -- an increase of between two and 11 percent -- and dump more water, it warns.

 SOURCE : YAHOO NEWS

Rainfall could increase by 20 percent within 100 kilometres (62 miles) of the eye of the storm.

In addition, some storm basins will "more likely than not" see a big increase in the frequency of high-impact storms.

The overview calls for an effort to fill in some big gaps in knowledge, including the variability of cyclones in the past and how global warming will affect storm behaviour in specific regions.

It is published online by Nature Geoscience, a journal of Britain's Nature Publishing Group.

The findings broadly concur with those of the UN's panel of climate scientists, which in a 2007 report said it was "likely" that tropical cyclones would become more intense this century, with heavier rainfall and stronger wind speeds.

However, the panel said it was less confident in concluding whether the number of cyclones would decrease.