The Environment Secretary, Margaret Beckett, speaking to the Avoiding Dangerous Climate Change conference in London this week, said these changes "are already built into the system". A battalion of the world's leading climatologists have been outlining what this will mean. An increase in world temperatures of just 2-30 Celsius - which is now on course to happen within my lifetime - will cause "irreversible damage to the Amazon rainforest, leading to its collapse."
But we no longer have to look to the future for victims of man-made climate change. In the summer of 2003, we suffered an environmental 11 September right here in Europe. Over 3,000 people - mostly pensioners and the sick - died in a heatwave that brought the highest temperatures in Europe for 500 years. Scientists at the Met Office and Oxford University have found that "more than half of the risk of 2003-like extreme European summers is attributable to human influences on the climate system."
This is hard to accept. The collapse of the Amazon? Rising sea levels? It sounds like a hackneyed late-night B-movie. I was so freaked out when I heard this, I decided to turn to the climate-change sceptics. They insist the news of anthropogenic (man-made) climate change is "a scam" and "a green myth". I wanted this to be true; it makes the future look so much brighter.
So I talked to dozens of distinguished climatologists seeking confirmation - and I have to tell you: it's not good news. They all agreed: the sceptics have no more scientific credibility than the people who insisted for decades that there was no relationship between smoking and lung cancer. There is legitimate dispute about the extent of climate change, but - as one climatologist told me off the record - "find me a scientist who denies the link between the actions of man and the changes in the climate, and I'll find you money from the oil, gas and energy companies."
This evidence is hard for us to absorb because it thwacks up against some deeply ingrained human assumptions. As the environmentalist Bill McKibben explains, "Our first problem is that we tell time badly. We are evolved to think of the earth as changing with infinite slowness. But it is now speeding up - by a factor of 60, according to some models. It is changing in rapid, dangerous and profound ways because there is an unprecedented amount of greenhouse gases in the atmosphere. Our systems haven't adjusted to this fact.
"Our second problem is that our sense of scale is awry," he continues. "We're used to thinking of people as small and the world as large, but in our lifetimes the opposite has become true. Human beings have not existed on this scale before. There are so many of us that we now dwarf nature."
So nature is no longer an independent force - something that is done to us. It is increasingly something we do to ourselves.
What was George Bush doing while his closest ally Tony Blair was at least honestly laying out the "scary" evidence for "catastrophic climate change"? Given that Bush leads the most powerful country in the world, what did he have to say about the biggest issue in the world? In his State of the Union address this week, he dedicated 60 seconds to the environment. He did not mention climate change, although he said he would support research into the creation of clean hydrogen-powered cars. They might emerge a few decades from now. By then, there will have been many more environmental 11 Septembers, some within the US itself. But - to be fair - Bush also offered another solution to this disaster. He promised "a modernised electricity grid."
Houston, we have a problem. The US emits a quarter of the world's greenhouse gases, despite containing only 4 per cent of its population - and, worse, the Bush administration is committed to scrapping all international environmental agreements to bring this under control. The administration is deeply enmeshed with the corporations who pump out junk science on the issue; most of the time, it is hard to tell where Halliburton ends and Bush begins.
Tony Blair often says that Bush "isn't doing enough" on climate change, but the reality is that he's doing too much - in entirely the wrong direction. Let's look at how Bush has dismantled environmental protections within the US itself. It would be too controversial actually to abolish domestic environmental laws outright, so Bush has adopted a different tactic. He has stuffed all the government's environmental agencies with men obedient to polluter's agenda.
For example, the US Department of the Interior regulates the mining industry, one of the dirtiest and most environmentally dangerous forms of business. So who did Bush appoint as Number Two in the department, with special responsibility for mining? A man called J Steven Grilles - better known as Old King Coal. Grilles has spent his life working and lobbying for Big Energy interests, including Shell, Texaco, Chevron, Arch Coal and the National Mining Association. He once said it was his ambition to "turn out the lights" on the very idea of regulating energy companies.
The Prime Minister says he is trying to persuade the Bush administration to co-operate on climate change. Yet there are huge structural reasons why the Bush administration - and Democratic administrations before them - are behaving this way, and no amount of Blair charm will overcome it. Energy corporations have largely bought the American political process by giving massive donations to both parties. Is Bush really going to suddenly, magically defy them? Worse, these corporations have skewed American public opinion about the seriousness of this issue by smearing the US press with bogus "scientific" reports that create the impression climate change is a "controversial" issue.
In his role as president of the G8 later this year, I suspect Blair will squeeze a few green drops of rhetoric - and maybe even a mini-policy or two - from Bush. There has been talk of coaxing the US into a "Kyoto lite", even though (as Blair admits) the full-fat Kyoto agreement is woefully inadequate, returning us only to the already dangerous emissions levels of 1990.
My anxiety is that many people will hear about this agreement, sigh, relax, and assume that climate change is being dealt with. In fact, we need a radical change in direction, not tiny steps - and I fear that in his efforts to coax the Bush administration, Blair might simply end up green-washing the White House. We must all remember that every major politician - including our own Prime Minister - has so far failed to offer policies that acknowledge the magnitiude of this problem.
Climatologists have spent the past week calmly, clearly telling us that it is five minutes to an environmental midnight. It is time to look at the clock.