Johann Hari: New Orleans is a frightening glimpse of the future

It is the poor and the weak who are invariably swept away first by climate change
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We may have just witnessed a global warming 9/11 at the heart of the United States. A million American refugees from the weather, the transformation of New Orleans into a New Atlantis: is this the face of climate change?

As the South wades through the aftermath of its soggy apocalypse, a Category Three debate is tearing through the world of climatology as scientists try to figure out what role (if any) the rapid warming of the world played in Hurricane Katrina.

At first glance, this might seem like a distasteful bout of environmental ambulance-chasing. Hurricanes happened before man-made climate change, and they will happen long after the last lump of coal and the last drop of oil have been burned. But there is an emerging scientific consensus that global warming is making hurricanes more intense and more destructive. It turns out that Katrina fits into a pattern that scientists and greens have been trying to warn us about for a long time.

Ruth Curry, research specialist at Woods Hole Oceanographic Institute, explains the facts. "Ocean and atmospheric circulation is the engine of a hurricane, but heat is the fuel. In order to form, a hurricane must have an ocean temperature of at least 80 degrees [fahrenheit] down to a depth of 164 feet. If that isn't there, the hurricane dies out. But at the moment, sea surface temperatures all over the tropics are running at 1.8 to 3.6 degrees above normal because of global warming. So when the other factors line up to cause a storm, a warmer ocean makes it last longer and be more destructive."

The likely effect on Katrina? She was a baby hurricane when she was first glanced off the coast of South Florida, blowing along at Category One. But then she hit the blistering, fossil-fuel-warmed sea surface temperatures in the Gulf of Mexico and became supercharged to Category Five. Yet it's hard to prove a definitive link.

Even when a person smokes for 50 years and dies of lung cancer, a doctor cannot definitively say the patient died because of her puffing: there's always a slim possibility she would have contracted the disease anyway. All we can do is point to a general pattern - and it's some pattern.

Check out, for example, the research of Professor Kerry Emanuel of the Massachusetts Institute for Technology. He had been a sceptic about the capacity of global warming to affect hurricanes when he began a detailed study of the data, but he was shocked to discover that hurricanes have increased in length and strength by 50 per cent since the mid-1970s - in line with rising sea temperatures.

So take a good look at the pictures of New Orleans. Unless we change our petro-holic societies, they are pictures of our future. It's not only the weather you should watch in the watery footage: it's the way the poor and the weak are invariably swept away first by climate change.

The rich white people of the South had the cash and the cars to get out of town the moment warnings were issued. And they knew their houses and property were well insured, so even if everything were swept away, they would not be left facing penury. The people left in the path of the hurricane were those who felt they had no choice but to stay and guard their meagre belongings.

All the disasters caused by global warming are having this lop-sided social impact. Here in Western Europe, we have been rich enough to deal this year with the driest summer on record at the cost of only a few deaths, mostly from forest fires. In sub-Saharan Africa, however, hotter summers and the changing El Nino cycle are contributing to crop failure, famine and starvation. The rich can protect themselves, the poor can't: it's an old story, but global warming is making it the story of the 21st century.

And there is another dark symbol in the "Cat On A Wet Tin Roof" landscape of New Orleans today. Mass looting in the face of a climate disaster seems incomprehensible at first - did the looters want to drown wearing Armani and a Gucci watch? But the world's oil companies are doing precisely the same thing, and on a far larger scale.

While we all face a catastrophe caused by the burning of fossil fuels, they are still - at our behest - seizing the world's oil supplies and flogging them off for private profit. Right now, they are trying to prevent Americans from joining the scientific dots. They are sending their shiny spokesmen on to CNN and Fox News to reassure everyone that only Mad Greens and purveyors of Junk Science believe in "the unproven theory" of global warming. The Republican and Democrat senators they have bought are dismissing the evidence of a link to extreme weather events as "madness".

Storm? What storm?