Leading article: The bells of New Orleans toll for the whole planet

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In the event, even a dramatic change of heart on Kyoto by President Bush would have been too late to save New Orleans - though heeding calls to raise the levees, rather than slashing spending on them, might well have done. The world's natural systems have massive time-lags built into them - so that the warming we are seeing now reflects the pollution of decades ago. But, by the same token, his success in holding up global action on climate change - and his persistent refusal to tackle the United States' overwhelming contribution to it - is storing up even greater disasters for the future.

No one can honestly say whether or not Katrina was caused by global warming, but there is widespread agreement that continued warming will bring even more vicious hurricanes in future. Worse, top scientists meeting in Exeter earlier this year concluded that the world has probably only a decade to bring the emissions under control if we are to avoid such unthinkable disasters as the failure of the Gulf Stream. As the United States blocks progress, these crucial years tick by.

Much of the problem lies in those time-lags. If pollution caused immediate disasters we would move heaven and earth to cut it. Because it does not, reasons can always be found for delay, often encouraged by the most polluting industries. It is easy for them to produce - usually highly inflated - reckonings of what it would cost, in cash and jobs, to change. These are easily countered - study after study shows that addressing global warming would produce more prosperity not less - but even false warnings of imminent pain often carry more weight.

New Orleans can change that. There can no longer be any cause for doubt of the horrendous cost - in both lives and hard cash - that neglect will cause. Even before last week there were many signs that the American public, industry, and even much of the Republican Party was parting company with the President on this issue; the deep - and well deserved - political damage that the disaster has done him will surely accelerate the process. But not just America needs to head the warning. The bells of New Orleans toll for all of us - and Katrina must prove a turning point for us all.