Apocalypse now or nigh impossible?

THE awful destructive power of Hurricane Katrina and the devastation it has wreaked on New Orleans seem to offer a graphic illustration of the threat posed by global warming.

Meanwhile, growing concern over the danger of avian flu jostles for media space with news of floods in central Europe and tension over Iranian nuclear ambitions.

In fact, hardly a day goes by without an article or news item about the latest catastrophe to threaten civilisation, whether it be global warming, pandemic, nuclear Armageddon or one of many other doomsday scenarios.

These are worrying times, as prophecies of doom that only recently appeared hypothetical or far-fetched suddenly seem close at hand. Is the end nigh?

Events like Hurricane Katrina or the spread of avian flu serve to remind us that disasters do strike. In fact, civilisation has been remarkably fortunate for millennia in avoiding catastrophe on a global, extinction-threatening level.

The history of civilisation has been characterised by a 9000-year period of comparative climate stability, and no civilisation has ever had to deal with a global-scale disaster. The last time such an event affected our species was 73,500 years ago, when a super-volcano erupted in Indonesia.

That cataclysm nearly wiped out mankind, and policy-makers and the general public alike should realise that similar threats, both natural and man-made, are not confined to the prehistoric past or the distant future, but pose a clear and present danger.

The problem is that there seem to be so many dangers. Some threaten to kill millions, others appear to endanger the existence of the entire planet. Some are purely hypothetical or wildly improbable, others appear to be at our very doorstep. It becomes a question of which doomsday scenario you should fear the most. Which scenarios are likely to happen, which will be genuinely catastrophic if they do come to pass, and which ones might we be able to avert?

Bird flu is a good example of the complexities involved in answering these questions. If bird flu infects a human host who also carries a normal influenza virus, the two germs could swap genes and create a deadly hybrid with the contagious power of normal human flu and the high mortality rate of bird flu.

Since no-one would have any immunity to this new virus, it could spread incredibly quickly and kill millions.

At the moment, there is little risk of this conversion happening in Britain. The wild birds carrying the avian flu virus are unlikely to reach our shores, and even if they do, and our poultry flocks catch it, few humans will be exposed.

Even if they are, good public health monitoring should mean that the virus has little chance to make the leap it needs to become a killer of humans on a pandemic scale.

In south-east Asia, where this strain of bird flu comes from, the story is different. There, millions of farmers live in close proximity with their birds, and there is much less public health monitoring. Only luck has so far prevented the lethal combination of circumstances that could set in motion a human-bird flu hybrid pandemic. Sooner or later, it is almost certain to happen - if not with the current strain, then with a similar one. When it does happen, will it mean the end of civilisation? History suggests otherwise. The Spanish flu pandemic of 1918 afflicted a world ravaged by war at a time when the anti-viral and vaccine technology we have today did not exist. Though it caused terrible loss of life, it did not bring down civilisation.

A bird flu pandemic might kill anywhere between 20 and 50 million people worldwide, but civilisation would endure. Global warming poses a much more serious threat to civilisation.

Hurricane Katrina illustrates exactly how. Global warming means more heat in the atmosphere and the oceans, which means more evaporation, more rainfall and more energy in the system all round. Combine these factors and you get wild weather - more torrential downpours, more floods and more hurricanes. Combine these with rising sea levels, and you get storm surges like the one that has flooded 80 per cent of New Orleans. The city is particularly vulnerable, since much of it lies below sea level, but in the near future the combination of storms and rising sea levels could affect many more coastal and low-lying cities, from New York to London.

This is just one of the potential impacts of global warming - others include droughts, killer heat waves, damage to global agriculture and mass extinctions.

But while global warming may be much more dangerous than avian flu, it is also within our power to do something about it. An avian flu pandemic is almost inevitable, but global warming could be checked by swift, concerted global action.

Unfortunately, at present this kind of action looks unlikely, so we can expect to see many more Hurricane Katrinas in the future.

The Doomsday Book: Scenarios for the End of the World by Joel Levy is published by Vision Paperbacks, priced 10.99