The US is now the only obstacle to a successful agreement at Copenhagen on tackling climate change, says Lord Stern, author of the influential report on the economics of climate change in 2006.
Speaking at the London School of Economics (LSE) this week, Stern said he was still optimistic a deal could be reached at Copenhagen.
'We've got an idea of the targets we need to achieve and the areas we need action on to achieve those. We can see the technologies coming through and we know enough about them to get started.
'The only thing missing is the political will to go to Copenhagen and collaborate.
'I think the problem now lies with the United States,' he said.
A summary of the main points of his speech:
To have a 'reasonable chance' of avoiding a global temperature rise of more than 2C, Stern says we require annual emissions to be cut to no more than 20 gigatonnes by 2050.
He says carbon levels are likely to reach 50 gigatonnes in 2010 but must drop to 44 gigatonnes by 2020, 35 gigatonnes by 2030 and be under the 20 gigatonnes limit by 2050.
Key action areas
Stern says the key areas we need to act on are; energy efficiency, low-carbon technologies and deforestation.
'We are never going to get to that 20 gigatonnes level without zero-carbon electricity,' he said.
He highlighted the falling capital cost of solar power and said China was already a leader in solar research and development.
While China has given no specific figure on the extent of its planned greenhouse gas reductions, Stern says there is 'no doubt that it will'.
'China has committed to notable reductions and when a Chinese leader says "notable" he means it. China does not embark on plans unless it understands how it can be done and that is why it will take a little while for China to come up with numbers.'
'There is no other country in the world that has as strong a team as Obama's on science. The problem is US politics and can they deliver enough in time.
'The Waxman-Markey bill is a step forward and will bring the US by 2020 down to where they were in 1990. But it won't be there in time for Copenhagen.
'No-one wants to argue that the US doesn't have a great deal to do but at the same time we have to understand the constraints of US politics,' he said.
'Can we grow and de-carbonise growth? Yes, we can with the right type of policies', says Stern.
'We are likely to set off a process of growth that is as dynamic as any we've seen in economic history precisely because the innovation and investment and change that is necessary is so strong and covers the whole economy.
'The transition to a low-carbon economy over the next four decades, if we get our policies right, will be among the most dynamic periods of growth in human history. And when we get there it will be more energy secure, quieter, cleaner, safer and more biodiverse.'
'If you look at the kind of intentions that are on the table now, based on announced policies from the EU, China, Japan, India and what the US has on the cards with Waxman-Markey, if you put all those together we may be reducing from business as usual levels to around 48/49 gigatonnes of carbon by 2020.
'So we have about 4/5 gigatonnes to go to get under 44 gigatonnes by 2020. We don't have far to go. It is possible. What it needs is very strong and enlightened leadership and strong pressure from those who aren't leaders.'
LSE International Growth Centre