More than 500m people travel for leisure each year. Our mass migrations wreak havoc on the environment. Among the most severe environmental effects of international travel are the carbon emissions belched from aeroplanes at high altitudes, which contribute directly to global warming. At ground level, logging of forests and mining of coral reefs for materials to build resorts have devastated wildlife; the development of beach fronts has led to the disappearance of wetlands; safari trails have interfered with hunting habits and the availability of quarry; and the boom development of popular tourist cities has increased urban pollution. From the Polar regions to Yellowstone National Park to the Lake District, tourism has supplied vast quantities of litter and debris, adversely affecting wildlife and polluting landscapes.

Is there an alternative? Eco-tourism's commercial practitioners claim that is what they offer. They work with local people to conserve fragile ecosystems, support endangered species and habitats, preserve indigenous cultures and develop sustainable local economies.

But the basic notion behind eco-tourism is a pragmatic one - where there's a public will, there's a market. Many travellers would rather their trip abroad had a minimal effect on the environment and culture of the country they're visiting, and the past two decades have seen a substantial expansion in eco-tourism.

Next year is to be the International Year of Eco-tourism, and in May 2002 Quebec will host an international Summit meeting, convened by the United Nations Environment Programme (UNEP) and the World Tourism Organisation (WTO). David de Villiers, Deputy Secretary General of the WTO, believes that, "sustainable development is the only way forward to guarantee the long-term viability of tourism businesses."

Travel operators offering eco-friendly holidays aim not only to reduce the ill effects of tourism (eg by booking with hotels that recycle waste and use environmentally-friendly utility systems, and minimising use of damaging forms of transport), but also they aim to "respect the indigenous" - accept the locals' right to privacy and respect their local customs and their very difference.

These are all commendable aims. The trouble starts when eco-tour operators - profit-making companies as they are - suggest that their particular brand of 'cleaned up and enlightened' tourism can positively enhance the regions it alights upon. This leads to a high moral tone, an implied suggestion that by wandering around the Galapagos Islands on an eco-tour the tourist is performing an equal good to a summer's worth of sweaty conservation work. Organisations such as the National Audubon Society, a US eco-tourism group, argue that tourism can be a "powerful tool favoring environmental conservation," by "enhancing public awareness of environmentally sensitive areas." Conservation International, a "private, non-profit organisation" suggests that eco-tourism can be "both an effective conservation tool and a successful community development model."

But tourism is, essentially and inescapably, environmentally destructive. An Oxford-based ecological 'footprinting' company, Best Foot Forward, points out that a return flight from London to Brazil uses 2,391kg of carbon. This means in this one trip a traveller uses twice the average annual carbon emissions of an average African (1,200kg), and half the average annual carbon emissions per person globally (4,000kg). An average Briton, who takes one or two trips abroad, emits 9,000kgs of carbon a year. If everyone in the world emitted this much carbon, we would need two and a half planets to support us all.

The impacts of global warming have been and will continue to be worst felt in poor, developing regions, through increased incidents of drought, flooding and freak weather. Any short-term 'development' of these countries through tourism must be set against the catastrophic effects already seen and still anticipated from global warming.

There is no such thing, in real terms, as eco-tourism. If we travel, we should do so in the knowledge that our tourism brings with it environmental damage. We travel for our enjoyment, because we can, because it is increasingly cheap to do so. We should not delude ourselves that are performing an altruistic social service.