Leading article: Global warming and the need for all of us to act now to avoid catastrophe

Even total cataclysm cannot be ruled out. It is time for national governments to confront the crisis head on

Marches will take place today in more than 30 countries around the globe in a collective effort to persuade our political representatives to take urgent action over the greatest single threat to natural life on this planet: man-made global warming. It is to be hoped their message is heeded because we are rapidly approaching the point of no return.

The scientific evidence that runaway climate change has become a reality is now irrefutable. Due to the rapidly increasing carbon content of our atmosphere, more of the sun's heat is being trapped by our planet. The 10 hottest years since records began have all occurred since 1990. As a result, the polar ice caps are melting at an unprecedented rate and sea levels are rising.

In the short term, our planet will endure stronger storms, floods, heatwaves and droughts. This will have terrible consequences for millions of species of plants and animals. Already the rhythms of the natural world are being disrupted. And, for the first time, humans are now under threat. Hundreds of people are being evacuated from an atoll in the the South Pacific because of rising water levels. And the fishing grounds of the Inuit people of Alaska are disappearing. Developing countries are likely to be next to feel the pain. The Sahel region and southern Africa are likely to dry substantially. This will mean more famine and more violent competition for natural resources. Finally, it will be the turn of those of us who live in rich countries to face the reality of climate change. No one will be immune.

Even total cataclysm cannot be ruled out. Scientists are beginning to talk of massive "climate shifts". Strange patterns in the Gulf Stream were revealed this week. The strength of the current has slowed by some 30 per cent. This is likely to be a result of melting Arctic ice caps releasing huge quantities of fresh water into the oceans. It is generally assumed that climate change will mean a hotter climate. But if the Gulf Stream were to "switch off", it would mean Britain being plunged into sub-zero temperatures.

It is time for national governments - particularly in the developed world - to confront the problem head on. This will require drastic cuts in each nation's greenhouse emissions. Governments must demand greater energy conservation from industry. And action must be taken to curtail emissions from transport. That means extensive investment in the development of alternative fuels and the taxation of air flights. The must also be radical measures to preserve the C0 ₂-absorbing forests of the world, preferably along the lines of last week's proposal by Papua New Guinea that rich countries should be forced to offset their pollution by paying developing countries to preserve their green spaces. The merit of this mechanism is that it would harness the self-interest of the West for the good of the planet.

But most importantly, the world's governments must agree on binding curbs on emissions. Without explicit targets for each nation, there will be no real pressure on governments to do so. The free market will never do the job on its own. That is the assumption that lies behind the United Nations Climate Change Conference that began in Montreal last week, where 189 nations are meeting to agree on a replacement for the Kyoto protocol.

But the sad truth is that Kyoto never really got off the ground. It was ratified by 140 countries, but not by the US, which is responsible for a quarter of global pollution. There has undoubtedly been movement at a local level in the US in recent years. Some prominent senators have woken up to the imminence of the danger. But the blinkered Bush administration still shows no signs of doing so. The US delegates told the Montreal conference on Monday that America is not interested in discussing new multilateral commitments on cutting emissions and prefers to put its faith in new clean energy technologies.

This is a shameful abnegation of responsibility. If America, the supposed leader of the free world, cannot be persuaded to commit itself unequivocally to reducing emissions, what hope is there of persuading a growing giant like China to do so? President Bush has branded Kyoto an economic straitjacket. But he should consider the cost of repairing New Orleans, devastated by Hurricane Katrina. The US - along with the rest of the world - can expect many more climate-related disasters in future.

But it is not just governments that have a responsibility. Individuals must act too. By opting to cycle or walk, instead of driving everywhere, we can all do something to reduce emissions. If more of us turned off electrical devices when not in use and recycled our waste properly, our societies would be hugely less energy inefficient. If populations become greener, it will send a potent message to our political representatives. There can be a revolution in attitudes from the bottom up.

We all face this looming era of climactic unpredictability together. The window of opportunity for intervention is closing rapidly. A failure to act now will not be forgiven by future generations.