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  • A wake-up call for Washington

The political effect on the United States of its failure to anticipate Hurricane Katrina's full impact will hopefully generate a more considered attitude to the threat of climate change.

One side-effect of the tsunami that swept across the Indian Ocean last December was to act as a wake-up call for government officials who were still dragging their feet over protecting their communities from the impacts of global warming.

Even though the two phenomena are not linked, the destruction caused by sea level surges as far away as Somalia and the Seychelles spurred political action, for example in changing regulations for coastal development, in a way that no amount of scientific research could ever have done.

With luck, the same may become true of Hurricane Katrina. Environment groups and liberal politicians across the world have been quick to draw the conclusions that the force of the hurricane that struck New Orleans and other parts of the Gulf of Mexico last week was a direct result of human induced climate change. Many claimed the same was true of other recent exceptional weather conditions, such as the fatal floods that have inundated parts of Europe this summer.

Sceptics have responded — correctly — that there is no hard scientific proof that climate change is to blame. They point out that there have been many other equally destructive hurricanes in the past, such as those that hit New Orleans in the 1950s and 1960s.

Indeed, there is strong evidence to suggest that, following several years that have been relatively quiet on the hurricane front, an increase in storms was to be expected as little more than the result of a natural 30-year cycle in hurricane intensity.

But that misses the point. Whatever the sceptics may argue, the case linking climate change — and its potentially destructive effects, particularly in the developing world — both to violent storms and to human activity is now accepted by most of the experts in the field.

To ignore this conclusion is now a political, rather than a scientific, act. Just as the Bush administration's decisions have been to ignore warnings of the potential perils facing New Orleans and the surrounding regions.

Scientific arguments

In fact, those who suggest a link between climate change and hurricanes have some important scientific arguments of their side. The most obvious ones lie in the dynamics of hurricanes themselves. These are easily triggered once ocean temperatures rise above 30 degrees Celsius, stimulated by the interaction between warm wet air close to the surface, and the cooler air above it.

This process does not need man-made global warming to induce it; and to that extent president Bush and his political allies are correct to state that hurricanes remain a natural disaster. But clearly, the warmer the oceans become, the more likely these conditions are to prevail.

A paper published last month in Nature, for example, by a group of US climatologists, headed by Kerry Emanuel at the Massachusetts Institute of Technology, argued that the numbers of major storms occurring both in the Atlantic and the Pacific have grown in both duration and intensity by about 50 per cent since the 1970s.

The researchers suggest a potential link to the fact that average global temperatures rose by more than one degree Celsius during this period.

Similar claims were made by another climatologist, Kevin Trenberth, head of the climate analysis section of the US National Center for Atmospheric Research in Boulder, Colorado.

Writing in the journal Science earlier this year, he argued that even if the frequency of hurricanes and typhoons does not increase as the oceans warm, their intensity is likely to (see Science 308, 1753; 2005).

In particular, Trenberth argued that higher sea surface temperatures in the Atlantic Ocean and increased water vapour in the lower atmosphere — caused by global warming — are to blame for the past decade's intense storms.

Although Emanuel and colleagues have expressed scepticism about whether the observed global warming is the result of increased carbon emissions, rather than just natural variability in climate cycles, Trenberth has been less reluctant to draw the link. Yet this is now the majority view within the scientific community, as expressed through the consensus on the Intergovernmental Panel on Climate Change.

Political damage

It is already clear that the Bush administration has inflicted significant political damage on itself by refusing to take either warnings of the storm threat to New Orleans — or calls for adequate preventive action — sufficiently seriously.

Official statements about the unpredictability of such events are disingenuous. There have been plenty of studies in recent years outlining not only the physical threats resulting from hurricanes, but also the inadequacy of the city's systems of levees — embankments raised to protect the low-lying city from floods.

Last year, for example, shortly after New Orleans narrowly avoided another Category 5 storm — Hurricane Ivan — scientists at Louisiana State University were predicting that the levees would have failed if the city had been hit directly.

Yet despite this and other warnings, the Bush administration has, as is now widely known, been seeking major cuts in funding for levee reconstruction and maintenance.

It is unthinkable that these cuts will not be reversed in Washington. Faced with claims that a short-sighted focus on national security issues following the events of 11 September 2001 has blinded it to many other more pressing issues, the Bush administration is now engaged in a damage limitation exercise.

But if history is not to repeat itself in New Orleans, it is essential that a substantial part of this is a renewed commitment to adequate prevention. And this means more than just additional technical fixes, such as strengthened levees. Equally important — like the planning for redevelopment that has been taking place around the Indian Ocean since the tsunami — is the need for a broader reassessment of strategies for coastal development. 

Preventive action

Researchers at Louisiana State University, for example, have been arguing for several years that in the long term, the best way of mitigating the threat to New Orleans would be to restore the barrier reefs and marshlands that lie in the delta between the city and the Gulf of Mexico.

Their arguments have striking resonance with those claiming that the damage caused by the tsunami was much worse than it might have been because mangrove forests that had previously protected coastlines had been destroyed (see Mangrove forests 'can reduce impact of tsunamis').

Similarly, much of last year's loss of life caused by Hurricane Jeanne in Haiti was made significantly worse by the effects of intense logging and the fact that many of the communities most badly affected had been built on vulnerable hillsides (see Haiti's lessons for managing the global environment). 

The rain brought by the hurricane rapidly washed away much of the remaining soil and clogged the rivers with debris, destroying houses and communities as it rushed down hillsides.

The lessons of Haiti, of the tsunami and of Hurricane Katrina are surprisingly close. All act as dramatic and painful reminders that, whatever humanity's technological ingenuity, the potentially destructive impact of the forces of nature must remain as high a political priority as concerns over national security.

Furthermore each provides evidence that although, on the one hand, this ingenuity has provided us with many defences against these forces, at the same time it has also – unwittingly – helped in some circumstances to magnify their impact.

If the broader lessons of the tsunami are now, thanks to Hurricane Katrina, at least being absorbed in Washington, it will have been a small silver lining to the catastrophe that hit New Orleans last week.

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