Stormy weather is linked with rising sea surface temperature which causes more frequent and fierce hurricanes, according to a study published in Nature Thursday.
Researchers of University College London, Britain, have quantified, for the first time, the contribution of sea warming to the increase in hurricane activity, and found that local sea surface warming was responsible for around 40 percent of the rise in number of storms between 1996 and 2005, compared to the 1950-2000 average, in the North Atlantic, according to the magazine.
The number of North Atlantic hurricanes has been above normal in 9 of the last 11 years, reaching a peak in 2005, a record number of 15 hurricanes formed between June and December 2005, making it the most active hurricane season on record.
Mark Saunders and Adam Lea of the university used a statistical model to disentangle the two main hurricane predictors -- sea surface temperature and near-surface trade wind speed. These two variables together explain about 80 percent of the variance observed in tropical Atlantic hurricane activity between 1965 and 2005.
Their result indicates that a 0.5 degree Celsius increase in August-September sea surface temperature should result in an average 40 percent increase in hurricane activity, a measure including both number and severity of storms.
In the tropical North Atlantic, sea surface temperatures in the 1996-2005 period were 0.27 degree Celsius above average, the highest ten-year anomaly since records began in 1950.
It is widely accepted that rising sea surface temperatures play the main role in the hurricane formation. Hurricanes can only form from pre-existing atmospheric disturbances in regions where sea surface temperatures exceed 26 degree Celsius.
Computer models suggest that sea surface temperatures in the Atlantic hurricane-forming region could warm by 2 degree Celsius by 2100.
If these waters warm by 2 degree Celsius by 2100, maximum wind speeds of hurricanes could increase by 63 percent, with damage from hurricanes rising in proportion to the cube of the wind speed.
The warmer the water, the more moisture and energy is available for intense storms to develop, the study showed.
The proportion of storms that hit the land versus those that stay at sea is unlikely to change, but the area of ocean surface warm enough to form hurricanes is likely to expand, making more coastline susceptible to these storms, according to the researchers.
(China Daily February 1, 2008)
