Economist Sir Nicholas Stern has told MPs he is encouraged by the progress being made around the world to tackle climate change.
Sir Nicholas praised EU proposals
India and China had to be persuaded to do more but the scientific arguments were gaining ground in the US.
And the EU had set more ambitious targets for carbon reduction than expected, he added.
Sir Nicholas suggested in a report last year that global warming could shrink the global economy by 20%.
But taking action now would cost just 1% of the world's gross domestic product every year, his 700-page study said.
Asked if action being taken around the world was urgent enough. the former chief economist of the World Bank said: "I think it is moving strongly in the right direction."
But he added: "Whether it will get far enough, soon enough I don't know."
He told the Commons environmental audit committee it did not matter "whether you are optimistic or pessimistic" about climate change, the "crucial thing" was to have the right policies in place.
He stressed the importance of international action but said Britain had a role to play in persuading other countries to cut emissions.
And he praised the EU's Strategic Energy Review, published last week, which said Europe should cut its greenhouse gas emissions by at least 20% by 2020, and try to persuade other countries to follow suit.
Sir Nicholas said this "showed a level of ambition higher than we might have expected".
He also praised Californian governor Arnold Schwarzenegger, recently re-elected on a pledge to cut emissions by 80%.