Johann Hari: Now that everyone's moving to the city...

A significant shift of humanity from the country to the cities could be an environmental victory

Long after the names of Bush and Blair and Brown are forgotten and the ephemera of our little lives have crumbled into old newsprint, this decade - the Noughties - will mark one of the greatest shifts in human history.

As Professor Mike Davis puts it, "Sometime in the next year, a woman will give birth in the Lagos slum of Ajegunle, a young man will flee his village in west Java for the bright lights of Jakarta, or a farmer will move his impoverished family into one of Lima's innumerable pueblos jóvenes.

The exact event is unimportant, and it will pass entirely unnoticed. Nonetheless, it will constitute a watershed in human history, comparable to the Neolithic or Industrial Revolutions. For the first time, the urban population of the earth will outnumber the rural."

Humanity has just stopped being a country-dwelling species. The incredible experiment that began in 4000 BC in Ur, Iraq - when tens of thousands of people began to huddle together for safety and business and company - just hit its logical endgame. We all live in Ur now, and it has happened in a history-flash. As recently as 1800, only 3 per cent of human beings lived in cities; in my lifetime, it will hit 70 per cent.

Most people, when they hear this, feel a low sense of sadness. They imagine a peaceful Pochahontas past of people living in tune with nature, ruptured by the roaring concrete confusion of the city.

Yet before I register all the complex practical problems this new reality tosses out - and there are many - I have an underlying gut reaction that cries exactly the opposite. I have never found a city I didn't fall in love with, and I've been to some of the worst: Baghdad, Kinshasa, Gaza City, Hull. Every city every day is a swirling, whirling mix of people forced to find a way to live together or die trying, an ongoing experiment using the most interesting raw material of all - humanity. If I'm not part of it, if I have not been shoe-horned into a tiny space with at least seven million other people, I feel lost and alone.

Every day in London I spot at least one amazing human cocktail: I was just driven by a super-smart Somalian minicab driver whose family back home lives under shariah law, but who now works in Soho transporting transsexuals, transvestites and girls in tiny belt-skirts. And you tell me I should be in Keswick looking at a lake that is really just an immense puddle?

And, in parallel, I have never been to a patch of countryside I didn't detest. I have never found a lake district that didn't bore me into a semi-coma, a Swiss alp that didn't make me pine for some polluted air, an Arizonan desert that didn't make me want to hail a taxi to the nearest town. Go back two generations, and all my family were subsistence farmers living "in tune with nature". It was a life of back-breaking tedium that left them all dead by 40. I want to keep the green belt buckled far from me.

Every political value I like - cosmopolitanism, the mixing of peoples, intellectualism - was cradled and nurtured in the city. Every political value I hate - inwardness, prudishness, a longing for stasis, a dislike of "book-learners" or Jews or gays - is nurtured in the wide open plains of the countryside.

The French Revolution or the Nazis, Stonewall or the Taliban, Dostoyevsky or Tolstoy, Coronation Street or Emmerdale: who could choose the intellectual children of the countryside over the fruits of the city? Who would not strangle Wordsworth with one of his accursed daffodils in order to get to W H Auden, sitting in one of the dives on 52nd Street, uncertain and afraid?

At first glance, there is one glaring exception. Isn't environmentalism - a political philosophy that has never been more necessary as runaway global warming trashes our habitat - the product of the countryside?

But the figures reveal something fascinating. Which part of Britain do you suppose has the lowest carbon emissions per head of population? Dorset? The Welsh Valleys? The Highlands? The Department for the Environment has discovered it is London. The average Londoner makes half the contribution to global warming of an average Cornwaller. She also uses half the electricity, and one-third of the petrol. She is, in short, far greener.

This is true of city-dwellers all over the world. It's because they are far more likely to use public transport than a private car, and there are other huge economies of scale: my heating also warms my whole apartment block, rather than leaking into the sky.

It's a startling fact that if every American brought their carbon emissions down to the level of the average Manhattanite, the US would soar past the Kyoto targets and become the greenest country in the developed world. A significant shift of humanity from the country to the cities could actually be an environmental victory rather than an environmental disaster.

But only a Panglossian fool could unequivocally celebrate the way urbanisation is happening today. The most bleak symbol of this unplanned exodus is Cairo's City of the Dead, where one million bitterly poor people have taken over the ancient Mamluk tombs and live among the graves in a walled island next to clotted motorways. They sleep in the Pharaonic vaults and hang their washing between the gravestones. But even they are actually fairly lucky, since their housing is structurally safe. Compare that to the tin slums that have built up on the hills surrounding Caracas in Venezuela, where a heavy rain can simply wash away homes and children to a muddy grave. In 1999, more than 10,000 people died in a single flash-flood.

These disasters aren't the result of urbanisation itself, but of urbanisation uncoordinated and unaided by government. If a government stands limp and passive in the face of drastic and chaotic change, then a mudslide into one disaster or another is guaranteed. One of the tragedies of the past decade is that this global rush to the cities has coincided with a period when the International Monetary Fund was demanding poor world governments become limp and passive.

The one billion people who are now living unhelped in new slum-cities are monuments to this market fundamentalism. The new populist movements rising in Latin America - from Hugo Chavez to Evo Morales - are largely a backlash of the slums screaming for help.

But still millions flock to the cities, and not just for economic reasons. When you hear of 2006's shift in the history of our species, don't pine for some mythical Arcadia. Think of the intellectual, social and sexual freedom these people will find now they can choose from a pool of millions to interact with, rather than being trapped with the stale hundreds chance happens to have dropped into their claustrophobic village. And think of the carbon they won't belch into the atmosphere.

Like Burt Lancaster at the end of Sweet Smell of Success, I can only sniff these statistics and mutter, "I love this dirty town."

j.hari@independent.co.uk