James Hansen, the world's pre-eminent climate scientist, said any agreement likely to emerge from the negotiations would be so deeply flawed that it would be better to start again from scratch.
''I would rather it not happen if people accept that as being the right track because it's a disaster track,'' said Dr Hansen, who heads the NASA Goddard Institute for Space Studies, in New York. ''The whole approach is so fundamentally wrong that it is better to reassess the situation. If it is going to be the Kyoto-type thing then [people] will spend years trying to determine exactly what that means.''
Dr Hansen, in repeated appearances before Congress beginning in 1989, has done more than any other scientist to educate politicians about the causes of global warming and to prod them into action to avoid its most catastrophic consequences.
But he vehemently opposes the carbon market schemes - in which permits to pollute are bought and sold - which are seen by the European Union and other governments as the most efficient way to cut emissions and move to a new, clean-energy economy.
Dr Hansen is also fiercely critical of Barack Obama - and even Al Gore, who won a Nobel peace prize for his efforts to get the world to act on climate change - saying politicians have failed to meet what he regards as the moral challenge of our age.
In Dr Hansen's view, dealing with climate change allows no room for the compromises that rule the world of elected politics. ''This is analogous to the issue of slavery faced by Abraham Lincoln or the issue of Nazism faced by Winston Churchill,'' he said. ''On those kind of issues you cannot compromise. You can't say: 'Let's reduce slavery; let's find a compromise and reduce it 50 per cent or reduce it 40 per cent.'''
He added: ''We don't have a leader who is able to grasp it and say what is really needed. Instead we are trying to continue business as usual.''
Dr Hansen's journey from climate scientist to activist accelerated in the last years of the Bush administration. A reluctant public speaker, he says he was forced into the public realm by the increasingly clear looming spectre of droughts, floods, famines and drowned cities indicated by the science.
Dr Hansen has emerged as a leading campaigner against the coal industry.
He has irked some environmentalists by espousing a direct carbon tax on fuel use. Some see that as a distraction from rallying support in the US Congress for emissions trading - legislation that is on the table.
He is scathing of that approach. ''This is analogous to the indulgences that the Catholic Church sold in the Middle Ages. The bishops collected lots of money and the sinners got redemption. Both parties liked that arrangement despite its absurdity. That is exactly what's happening.
''We've got the developed countries who want to continue more or less business as usual and then these developing countries who want money, and that is what they can get through offsets.''
Guardian News & Media