You batter your head against the door until you begin to wonder whether it is a door at all. Suddenly it opens, and you find yourself flying through space. The superstores' green conversion is astonishing, wonderful, disorientating. If Tesco and Wal-Mart have become friends of the earth, are there any enemies left?These were the most arrogant of the behemoths. They have trampled their suppliers, their competitors and even their regulators. They have smashed local economies, broken the backs of the farmers, forced their contractors to drive down wages, shrugged off complaints with a superciliousness born of the knowledge that they were unchallengeable. For them, it seemed, there was no law beyond the market, no place too precious to be destroyed, no cost they could not pass on to someone else.
We environmentalists developed a picture of the world that seemed to be repeatedly confirmed by experience. Big corporations destroy the environment. They are the enemies of society. The bigger they become, the less they can be constrained by democracy or consumer power. The politics of scale permit them to bully governments, tear up standards, and reshape the world to suit them. We also recognised that this was a dialectical process. As businesses began to operate globally, so could the campaigns against them. By improving global communications and ensuring that we could all speak their language, they helped us to confront them more effectively.
But hardly anyone believed that change could happen so fast. Through the 80s and 90s, they brushed us off like dust. Then, as a result of powerful campaigns against sweatshops in the US and Europe, some of the big clothing and sports retailers broke ranks. Soon after that, the energy companies started announcing big investments in renewable technologies (though not, unfortunately, any corresponding disinvestments in fossil fuel). But the supermarkets have shifted faster than anyone else. Environmental campaigners are partly responsible (listen to how the superstore bosses keep name-checking the green pressure groups); even so, their sudden conversion leaves us reeling.
Embarrassingly, for those of us who have scorned the idea of corporate social responsibility, some of these companies now claim to be setting higher standards than any government would dare to impose on them. Marks and Spencer, for example, has promised to become carbon neutral, to cease sending waste to landfill by 2012, and to stop stocking any fish, wood or paper that has not been sustainably sourced. Tesco promises to attach a carbon label to all its goods. Wal-Mart now says it will run its US stores entirely on renewable energy.
These standards, moreover, are rather higher than those the British government sets for itself. M&S has pledged to use carbon offsets (paying other people to make cuts on its behalf) only as "a last resort". The government uses them as a first resort. Could it be true, as the neoliberals insist, that markets can do more to change the world than governments? If so, it reflects democratic failure as much as market success. Held back by forces both real and imagined, politicians have failed to confront the environmental crisis, just as they have failed to tackle inequality, or to challenge the power of the White House, the media barons, the corporations and the banks. The choice between two rival brands of margarine appears to have become more meaningful than the choice between Labour and the Conservatives.
It is also true to say that The Wal-Mart Effect is a real one. When a huge company changes course, the impact is felt all over the world. One positive decision by the leviathan rumbles more widely than a thousand decisions by its smaller competitors. But those of us who have fought for the environment and against big business have not yet become redundant. There is plenty to celebrate in the recent announcements and plenty to suspect.
Tesco, for example, has made some bold commitments, to which it might eventually be held. At the moment they are weeviled with contradictions and evasions. In his speech on Thursday, the company's chief executive, Sir Terry Leahy, spoke of the sophisticated new refrigeration techniques that Tesco will use, which will allow it to reduce its consumption of climate changing gases called hydrofluorocarbons. But at no point did he mention an environmental technology called the door. How can you claim your stores are sustainable if the fridges and freezers don't have doors?
Tesco's press officer was unable to tell me whether the energy savings the company has promised (50% per square metre by 2010) will be independently audited. If not, the promise is worthless - a company can make any claim it likes if there is no outside body to hold it to account.
Leahy announced that he would respond to one of the biggest complaints of the green groups by cutting the distance Tesco's products travel, especially by air. He would also switch some of the chain's road freight (he did not say how much) to rail. But he said nothing about reducing the journeys made by his customers. Shopping accounts for 20% of car journeys in the UK, and 12% of the distance covered. By closing their out-of-town stores and replacing them with warehouses and deliveries, the supermarket chains could reduce the energy costs of their buildings and (according to government figures) cut the transport emissions caused by shopping by 70%.
Today, the Competition Commission publishes the initial results of its inquiry into the market dominance of the superstores. One of the issues it is investigating is the "land bank" accumulated by Tesco - a huge portfolio of sites on which the company appears to be sitting until it can obtain planning permission. Many of them are out of town. If Tesco develops them, it will drag even more cars on to the road. Out-of-town shopping is incompatible with sustainability.
So, perhaps, is the sheer scale of the business. Wal-Mart and Tesco can change the world at the stroke of a pen, but one decision they will not make voluntarily is to relax their grip on local economies. It will always be harder for small businesses to work with a global behemoth than with the local baker or butcher; Tesco's economy will continue to favour the big, distant supplier over the man down the road. And what of the sense of community that independent small shops help to foster, which encourages people to make their friends close to home? If love miles are the most intractable cause of climate change, we need to start cultivating as much community spirit as we can.
But there is a bigger contradiction than this, which has been overlooked by the supermarkets and by many of their critics. "The green movement," Leahy tells us, "must become a mass movement in green consumption." But what about consuming less? Less is the one thing the superstores cannot sell us. As further efficiencies become harder to extract, their growth will eventually outstrip all their reductions in the use of energy. This is not Tesco's problem alone: the green movement's alternatives still lack force.
The big retailers are competing to convince us that they are greener than their rivals, and this should make us glad. But we still need governments, and we still need campaigners.
George Monbiot