The International Energy Agency said output of carbon dioxide, the commonest greenhouse gas from burning fossil fuels, would fall by about 2.6% this year, amid a tumble in industrial activity.

It hoped the world would seize on the decline to shift to lower-carbon growth, despite fears governments might use it as an excuse for inaction.

“This fall in emissions and in investment in fossil fuels will only have meaning with agreement in Copenhagen which provides a low-carbon signal to investors,” said IEA chief economist Fatih Birol.

World leaders are meeting at UN headquarters in New York today for a one-day climate summit to try to unlock negotiations on a new deal to combat global warming due to be agreed in Copenhagen in December.

Negotiations among 190 nations are stalled over how to share out curbs to 2020 between rich and poor and on how to raise $100 billion (£62bn) a year to help the poor combat warming and adapt to changes such as

rising seas or desertification.

China and the US, the top emitters which account for more than 40% of the world total, are being urged to help spur the Copenhagen talks.

Chinese President Hu Jintao is due to unveil plans to tackle global warming at the summit.

Speculation focuses on goals for curbing “carbon intensity” – the amount of emissions per unit of economic output – but stopping short of absolute cuts in emissions.

And President Barack Obama will have to persuade the world that Washington is serious about cutting emissions when it looks unlikely that the US Senate will pass

climate legislation this year.

Jose Manuel Barroso, Euro-pean Commission President, reckons the UN talks are “dangerously close to deadlock” and he challenged

developing nations to do more in order to secure financial support from industrialised nations.

According to notes for his speech in New York, Barroso said: “This may not be a simple negotiating stand-off that we can fix next year.

“It risks being an acrimonious collapse, delaying action against climate change perhaps for years.”

Prime Minister Gordon Brown opened the possibility of turning the Copenhagen talks – due to be a meeting of environment ministers – into a summit of world leaders.

“If it is necessary to clinch the deal, I will personally go to Copenhagen to achieve it – and I will be urging my fellow leaders to do so too,” Brown wrote in an article in Newsweek magazine.