LONDON - Recession is set to cause the sharpest fall in world greenhouse gas emissions in 40 years, according to an estimate on Monday as world leaders gathered in New York to try to break deadlock on a new climate treaty.

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

It expressed hopes that the world would seize on the decline to shift to lower-carbon growth despite worries that governments might take 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, IEA chief economist Fatih Birol told Reuters.

World leaders are to meet at U.N. headquarters in New York on Tuesday for a one-day climate summit to try to unlock 190-nation 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 perhaps $100 billion a year to help the poor combat warming and adapt to changes such as rising seas or desertification.

Some experts expressed doubts that recession and falling industrial output could be a springboard to greener growth.

When politicians talk about the financial crisis everything is about returning to growth, which means higher emissions, said Paal Prestrud, director of the Center for International Climate and Environmental Research in Oslo.

We have to reduce emissions in a planned way to avoid social problems, not through recession, he said.


Eyes for Tuesday's summit are on China and the United States, the top emitters which account for more than 40 percent of the world total, 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 rest of the world that Washington is serious about cutting its emissions when it looks unlikely that the U.S. Senate will pass climate legislation by Copenhagen.

The U.N. talks are dangerously close to deadlock, European Commission President Jose Manuel Barroso was due to say later on Monday and challenge developing nations to do more in order to secure financial support from industrialized nations.

This may not be a simple negotiating stand-off that we can fix next year, according to notes for a speech in New York. It risks being an acrimonious collapse, delaying action against climate change perhaps for years.

British Prime Minister Gordon Brown opened the possibility of turning the December 7-18 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.

And the head of the U.N. Climate Change Secretariat said too much was at stake to let Copenhagen fail.

We are too close to an agreement now to fail at the last gate, said Yvo de Boer, head of the U.N. Climate Change Secretariat. A strong agreement at Copenhagen, to tackle climate change, will keep humanity in control of its destiny.

On September 24-25, leaders of the G20 will meet in Pittsburgh but Washington said that it would not include a major focus on how developed nations should provide financial support to developing nations to cope with climate change.