It pains me to write this. I marched with the best of them last year on the Stop the War rally through the cold streets of London, and at that time my hatred of the Bush'n'Blair "axis of evil" knew no bounds. I still feel the same about Bush. But I now see new dangers, and as a result, new opportunities in politics this side of the Atlantic. It may be time, I suggest reluctantly, to move on, and to offer Tony Blair one last chance to earn our support.
The importance of Iraq can be overstated. Compared to other wars, relatively few people have been killed. In the Democratic Republic of Congo, there were no "embedded" journalists to watch while rebel armies committed cannibalism, raped thousands, and recruited children as young as seven for military service. An estimated four million people lost their lives, against 10,000 or so civilian casualties in the invasion of Iraq. Moreover, some good has come out of the Iraq campaign: most Iraqis, despite mixed feelings about the humiliation of military occupation, remain grateful - according to a recent BBC poll - for the removal of Saddam Hussein's tyranny.
Continual attacks on Blair from the left can lead only to more bitterness and cynicism. Instead, we should invite Blair to rise to a new challenge. This one, if he meets it, would give him the place in history that he craves so much.
In 2005, Britain will assume the presidencies of both the G8 and the EU. No 10 has already indicated that it wants to make climate change and Africa - including the UN Millennium Development Goal of halving world poverty by 2015 - the two big themes of the presidency. The growing impacts of global warming, from drowning Pacific islands to disappearing Alpine glaciers, create added urgency on the first issue, as does the recent report that a quarter of the earth's species might become extinct by 2050 because of climate change. Yet the Kyoto Protocol is increasingly imperilled by lack of Russian ratification.
On the second issue, only slow progress has been made towards meeting the UN targets for 2015, which include achieving universal primary education; reducing child mortality by two-thirds; reducing maternal mortality by three-quarters; and stopping the spread of Aids and malaria. At the current pace, according to the UN, sub-Saharan Africa will not meet the goals for poverty until 2147, nor those for child mortality until 2165.
Ministers and their advisers are always casting around for a "big idea" that might stand out against the usual stream of targets that are forgotten almost as soon as they are announced. Yet a single big idea - one that could solve the twin crises of global poverty and global warming - is already in circulation, and rapidly gaining steam in policy-making circles. First proposed by the London-based Global Commons Institute more than a decade ago, "contraction and convergence" (C&C) is now being taken seriously: Geoff Mulgan and David Miliband, the current and former heads of the No 10 policy unit, have both highlighted the idea publicly. More explicit support has come from Sir John Harman, chairman of the Environment Agency, Sir John Houghton, the UK's most eminent climatologist, and the MPs' environmental audit and international development committee. C&C aims to move gradually to a position where global greenhouse-gas emissions are reduced to sustainable levels but where every human being has an equal right to consume fossil fuels. So rich countries would "contract" their emissions, while the poorest could increase theirs, so that both sides ultimately "converge" on per capita equality.
C&C's biggest selling point is that it offers a science-based framework with reliable outcomes at the end of a process that must stretch for decades into the future. Although Kyoto is a good first step, there is no long-term planning: nothing else on the table can tell us with certainty where we will end up in 2050 or 2100.
C&C gets back to first principles. First, it asks how much climate change we are prepared to tolerate, and pins this to a specific, scientifically valid commitment, mandating an upper limit to the concentration of greenhouse gases in the atmosphere. (The current level is the highest on earth in more than 420,000 years.)
Once this "cap" has been agreed, it implies a budget for the remaining emissions of greenhouse gases as fossil fuels are phased out. No longer will the atmosphere be a free-for-all dumping ground. This budget must be divided up fairly among the world's population - nothing less will be acceptable to the countries of the south, which will rightly be suspicious of any treaty that might freeze their development. It is like food rationing during the Second World War - with a limited amount of atmosphere to go round, sacrifices will be accepted only if they are fairly shared.
A frequent objection to C&C is that America will never sign up to a global agreement based on equity. But opposing fairness will be a difficult negotiating position to sustain, and the US objection to Kyoto - that developing countries are not given targets - is tackled head on by a C&C regime where everyone has a converging target. Indeed, the US spoke in favour of C&C at the original Kyoto negotiations, saying it could be the basis of the next agreement.
Moreover, if the US or any other western country wants to go on consuming more than its fair share, that's fine - but it will have to pay for the privilege. C&C distributes atmospheric ownership rights fairly, and you can't use what you don't own. This is a quantum shift. Suddenly we are away from aid - where the rich condescendingly give a few pennies to the poor - and into trade, with hard-nosed commercial bargaining for mutual benefit. The rich will have to buy "emissions rights" from the poor - recognising the "ecological debt" we already owe for a century of fossil fuel-based growth, and generating potentially billions a year in revenue flows to the south.
So carbon trading could eventually bridge the yawning income gap that has opened up with globalisation, bringing the Millennium Development Goals out of the conference circuit for the first time and into the realms of practical possibility. There is no reason why income generated from carbon trading should not be earmarked specifically for providing access to safe water to the 1.1 billion people who currently lack it, for getting the 115 million young children who are currently excluded from school into lessons and for helping developing countries pay for clean generation of power.
But C&C needs a champion. Someone who can sell it to the EU. Someone who can go on to build an alliance between the EU and the south. Someone who can recruit the recalcitrant Americans, with a new president at the helm, one hopes. What better role for Blair?
Britain already has one of the most far-sighted climate change policies in the world. The UK's Kyoto commitment of 12.5 per cent reductions in carbon emissions by 2012 is one of the toughest in the EU, and the government's long-term target of 60 per cent reductions by 2050 is exactly what climate scientists and environmentalists alike have long been calling for. Meanwhile, the renewables sector is booming, again partly due to sustained government support. Although the wind-power industry is still behind that of Germany and Spain, capacity is expected to triple over the next two years, with much of the growth coming from huge offshore developments.
I have heard from several different sources that Blair is strongly committed to tackling climate change, and believes it poses the greatest long-term threat to humankind. At a speech to mark the launch of last year's white paper on energy, Blair said global poverty and climate change were "just as devastating in their potential impact" as weapons of mass destruction and terrorism. "There can be no genuine security," Blair rightly asserted, "if the planet is ravaged by climate change."
The man often pilloried as George Bush's poodle has never wavered in his opposition to American intransigence on global warming, even telling Congress last June (during his "history will forgive us for the Iraq war" speech): "Climate change, deforestation and the voracious drain on natural resources cannot be ignored. So America must listen as well as lead."
It now seems that Blair hopes some of the political capital he gained with his support of US policy on Iraq might be spent on shifting its policy on climate. Indeed, the energy white paper sets "as a key objective of . . . foreign policy" a 60 per cent cut in emissions throughout the developed world by 2050.
Blair's presidency of the G8 in 2005 could provide a forum for serious discussions on climate and poverty, assuming the PM can use his political capital to avoid a US veto. As I write, the forces of civil society are gathering for street demonstrations around the summit that could generate the same momentum as the Jubilee campaign in 2000. I would guess that almost all these people were alienated by the Iraq war, and many have turned away from what they see as repeated betrayals by new Labour. Yet they could - and should - be Labour's core support base. All it needs is for Blair to show commitment and vision. Then, having turned from a warmonger into a champion of the poor and the planet, he may find even the war's strongest opponents ready to forgive him for Iraq.
Mark Lynas's High Tide: news from a warming world, is just published by Flamingo. www.marklynas.org