The good news from America

Most environmentalists are indeed leftists who support the redistribution of wealth and believe in a

I'm in a darkened room, my face plastered with make-up, somewhere in Manhattan. With powerful lights on all sides, all I can see is the camera lens. My earpiece crackles and the first interviewer comes through, from a TV station in Minnesota. First the pleasantries, then the lead-in to the question: "Some scientists say this global warming is just another natural cycle . . ."

Welcome to the US climate-change debate. I was a guest of National Geographic, which has produced a 90-minute documentary film based on my book Six Degrees. Certainly, there was interest: I spent an exhausting 12 hours a day on the phone and on camera in a wide variety of radio and TV stations nationwide. I fielded callers on West Coast phone-ins, spoke to drivetime DJs in Midwestern cities and spent an hour webchatting on a social networking site. Every time, the same question came up: "Some scientists say . . ."

The answer is easy, but that is not the point. While scepticism about climate change is now a minority view - and in most interviews, once the obligatory question was out of the way, we had fascinating discussions - it is clearly a deep-seated social and political phenomenon, tapping in to a complex well of psychological fears and anxieties. One of the most persistent seems to be the identification of climate-change concerns with a "liberal" political viewpoint. You can see how this happened. Most environmentalists are indeed leftists who support the redistribution of wealth and think a simpler lifestyle would be better for all. Conservatives had nowhere to go. For them, global warming could not exist. The divide became rigid under the Bush adminis tration, whose rejectionist approach to climate change confirmed that you could be either an environmentalist or a conservative, but not both.

This may come to be seen as a grave strategic error by the right. By spending years in anti-scientific denial, this lobby has lost the chance to set the international negotiating agenda and advance free-market proposals for tackling greenhouse-gas emissions. Instead of wasting time arguing that nothing need be done about global warming, conservative economists should have been using their expertise to design trading systems to manage the problem efficiently and in a growth-oriented way. In the meantime, the general public got used to the idea that tackling carbon emissions was about piety and self-sacrifice rather than about being successful or aspirational.

This is why John McCain has been important. Despite being an out-and-out conservative on economic and social issues, he has a track record of advancing efforts to promote global warm- ing mitigation. In 2003, he and the Democratic senator Joe Lieberman introduced the first ever climate bill in the Senate. The legislation was voted down, but helped set the agenda for the great shift in US public opinion that has taken place since.

This is why the virtual coronation of John McCain as Republican presidential candidate is so important. Whoever wins the election (both Barack Obama and Hillary Clinton have policies on climate that are tougher than McCain's), there will be a decisive shift in US policy. Business is already preparing for a mandatory, US-wide "cap and trade" system; states such as California are competing to be the first to design it.

With Bush history, a new administration will be in place by the time the negotiating process launched in Bali completes in December 2009 in Copenhagen. Scientifically speaking, this is probably the world's last chance to set a long-term emissions-reduction path that will keep the planet within the target of a 2°C increase in warming. With the Americans onside, it will be possible to get that deal.

For the first time in years, I am optimistic.