Posted on 22 Jan 2010
New Orleans could find itself in the path of more Katrina-level storms, according to research led by Morris Bender of the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey.
Bender says the most violent storms are expected to be concentrated in the west Atlantic, putting the Bahamas and the southeast coast of the US at risk.
According to Bender and his team, "Our results suggest that a significant anthropogenic (man-made) increase in the frequency of very intense Atlantic hurricanes may emerge from the background climate variability in the latter half of the 21st century, despite a projected decrease in the overall number of hurricanes."
Despite the smaller number of storms, the destructive potential of powerful cyclones meant hurricanes were likely to inflict more damage than they do today, says the team.
To date Category Three to Five storms have accounted for 86% of all damage in the US caused by hurricanes, said the scientists.
The new forecast predicts an increase in potential damage of around 30% in the 21st century.
Claims that global warming has already affected hurricane activity are not borne out by the models, the researchers said.
Previous climate simulations have pointed to an increase in hurricane intensity, but the new study involves a "sharper" picture of atmospheric changes than any seen before.
The scientists used a technique of transferring data from "fuzzy" climate models to ones of increasing resolution. In the end they were able to predict which hurricanes would develop into moderate Category Three and more powerful Category Four and Five storms.
The model, reported in the journal Science, showed an 18% decline in the number of hurricanes, but by the end of the 21st century, Category Four and Five storms with maximum wind speeds of more than 134mph doubled in frequency.
A three-fold increase was seen in the occurrence of "super-hurricanes" with winds above 145mph.
The findings support the theory that as ocean temperatures rise, the extra water vapour driven into the atmosphere can intensify existing storms and inhibit the formation of new ones.
In the real world, hurricanes have doubled in number over the past 25 years. According to the simulations, global warming should have caused a slight decline over this period.
The impact of global warming on hurricanes is likely to be felt in years to come, said the scientists. Currently, its effect would still be masked by natural variations in hurricane activity.