There, by threatening to isolate the US President, he achieved genuine progress in setting up a framework to negotiate a new agreement - a process that starts when environment ministers meet in Ottawa this weekend. His surprising willingness to bark at, if not bite, the "toxic Texan" incurred Mr Bush's anger; now the poodle has been brought to heel.
It is shameful, for he has betrayed his own beliefs. Whatever the rest of the country thought, he at least shared the President's views on Iraq, indeed held them first. By contrast, he has been loud in his support of the Kyoto process, despite Mr Bush's opposition to it, insisting, for example - in a major speech just a year ago - that "it can achieve results". He knows that his newly professed belief, which we report today, that science and technology will solve the problem is false: business, which wants certainty, is reluctant to adopt new, cleaner technology until the rules change. As its leaders constantly reiterate, they need governments to lay down legally binding requirements before they can justify the investment.
Mr Blair's volte-face may well reflect his abysmal failure to put his money where his mouth has so often been. Despite all his rhetoric, Britain now emits more carbon dioxide - the main cause of global warming - than when he took power. The truth is that he has consistently funked every substantial attempt to cut the pollution, starting with John Prescott's plans to introduce a sustainable transport policy back in 1997. It all adds up to a huge betrayal - and one for which future generations will rightly hold him to account.