Addressing Monday's special informal session of the United Nations General Assembly on climate change UN secretary general Ban Ki-moon said aptly that "today, the time for doubt has passed". He called on world leaders to take unprecedented action on the issue, since inaction will be far more costly in the long term.
That he should speak so confidently and urgently speaks volumes about the scientific consensus that has emerged this year on how human activity causes global warming. It is now an urgent task to ensure a political consensus follows on reducing carbon emissions and finding new substitute technologies. This week's top-level meetings in New York and Washington must prepare the way.
The major policy cleavage on how best to tackle global warming divides European leaders from the Bush administration in the United States. Mr Bush did not attend Monday's special meeting in which many of his European counterparts participated. He does not accept the European commitment to mandatory cuts in carbon emissions nor the plans to trade them, thereby putting a real obstacle in front of such a worldwide regime.
Instead Mr Bush has convened a meeting in Washington this week bringing together 16 of the world's highest carbon emitters responsible for 80 per cent of emissions to explore voluntary reductions and how technological change can help achieve them.
China, India, Brazil and Mexico are to attend this meeting. It can serve a useful purpose if it helps overcome the other major division in these negotiations - between the most developed states responsible for the highest proportion of carbon emissions and the huge developing ones which aspire to grow in wealth but are willing to limit their emissions through technology transfers. The Bush administration now accepts that the negotiations must be conducted through the United Nations - another of this year's breakthroughs.
All eyes are now on the Bali summit in December where talks on a successor regime to the Kyoto Protocol will start. The Europeans are determined to see them finish at Copenhagen in 2009 and quite correctly insist that binding reduction targets must play a central role. They face a challenging task in holding their own group together and giving a lead to other states over that time. By then a new US president will have taken office and world public opinion, which polls show strongly supports radical action, will have had more time to exert itself politically.
Before the Bali meeting the UN's Intergovernmental Panel on Climate Change will issue its final synoptic report on humanity's responsibility for global warming and what can be done about it. This will complete a quite remarkable exercise in scientific analysis and international co-operation. The series of reports from the IPCC this year has coincided with extreme weather events throughout the world which can plausibly be related to global warming. Political leaders have now to absorb these lessons and take preventive action.