Will climate change make tropical cyclones – known as hurricanes in the Atlantic basin – more frequent or powerful in the future? And has this trend already begun? Some scientists argue that warmer oceans will provide more energy to fuel tropical storms, while others say that the hotter temperatures will create areas of stronger wind shear, which will inhibit the formation of tropical storms.

Right now the consensus view is that it is too early to say if global warming has already brought about a detectable change in the number and nature of tropical storms – the changes seen so far are still within the bounds of natural variability. However, advances in climate modelling are enabling researchers to be more confident about forecasting what the future might hold.

Global climate models are thought to be relatively credible at predicting the broad-scale climate changes that we might expect, but lack the resolution to pick out small-scale features like tropical storms. Meanwhile, high-resolution hurricane models can forecast the growth and path of tropical storms, but would require much greater computer power or eons of time to simulate the large samples of storms required for climate-change studies.

To overcome the mismatch between these kinds of models Tom Knutson, from the US National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, and colleagues used a technique known as downscaling. Taking the average atmosphere and ocean conditions forecast for the end of the century by 18 different climate models, they transferred them into a detailed hurricane model to discover what kind of impact these new conditions might have.

The team estimates that the number of category 4 and 5 hurricanes in the Atlantic basin could double by the end of the century, causing around 30% more damage in the US. The largest increase is projected to occur in the Western Atlantic, north of 20°N, which would threaten areas like Hispaniola, the Bahamas and the southeast coast of the US.

So why these changes? Warmer oceans and increased wind shear will both play a significant role it seems. "We project areas of increased vertical wind shear, which will act to decrease the overall number of tropical cyclones," Knutson told environmentalresearchweb. "However, the tropical storms that survive their transit through this region of increased shear, will enter a region of higher potential intensity, so that those 'survivors', though fewer in number, can reach higher intensity levels."

This result is supported by a new assessment report by a World Meteorological Organization expert group, which projects a decrease globally in the overall number of tropical storms, of between 6 and 34%, but an increase in the intensity of the storms that do form, of between 2 and 11%. In addition, they see an increase of around 20% in the rainfall rate within 100 km of the storm centre.

Most likely we are already committed to at least some of these climate changes, and even if the models are wrong and these increased numbers of intense hurricanes fail to emerge in the future, Knutson and his colleagues believe that society still needs to work harder at minimizing the damage hurricanes cause. One year after hurricane Katrina, one of the costliest and deadliest storms ever to hit the US, 10 eminent hurricane scientists including Kerry Emanuel, from Massachusetts Institute of Technology, along with Knutson, wrote, "the…urgent problem of our lemming-like march to the sea requires immediate and sustained attention. We call upon leaders of government and industry to undertake a comprehensive evaluation of building practices, and insurance, land use, and disaster relief policies that currently serve to promote an ever-increasing vulnerability to hurricanes." Four years later they still stand by those views.