A U.N. climate deal due to be agreed in Copenhagen at talks from December 7-18 may fall short of a legally binding treaty, according to the United Nations.

If Copenhagen fails to live up to hopes of a strong pact to slow global warming, what are the reasons and who risks blame? The following are some of the candidates:

ECONOMIC DOWNTURN - Recession distracted focus from climate change after the world agreed in Bali, Indonesia, in 2007 to work out a new U.N. pact by December 2009. Rich nations have put billions of dollars into green growth as part of recovery packages but, when unemployment at home is high, find it hard to promise extra money for developing countries. The slowdown in industrial output means a brief fix -- greenhouse gas emissions are likely to fall by as much as 3 percent this year, according to the International Energy Agency.

UNITED STATES - Many delegates at U.N. talks have given up hope that the United States, the number two emitter after China, will agree legislation to cap carbon emissions before Copenhagen. The United States is the only industrialized nation outside the Kyoto Protocol for cutting greenhouse emissions until 2012. Many countries welcomed President Barack Obama's promises of doing more to fight climate change when he took office in January but hoped for swifter action.

RICH-POOR DIVIDE - Developing nations accuse the rich of repeatedly failing to keep promises of more aid. Few developed countries live up to a target agreed by the U.N. General Assembly in 1970 to give 0.7 percent of their gross domestic product in development aid. Other plans, such as the Agenda 21 environmental development plan agreed in 1992, have fallen short.

DEVELOPED NATIONS - Most rich nations are promising cuts in greenhouse gas emissions well short of the 25-40 percent below 1990 levels by 2020 that one scenario by the U.N. Climate Panel indicates are needed to avert the worst of climate change. Overall cuts promised by developed nations total between 11 and 15 percent. Best offers by countries including Japan, the European Union, Australia and Norway would reach the range.

CHINA, INDIA AND OTHER MAJOR DEVELOPING NATIONS - More than 90 percent of the growth in emissions between now and 2030 is set to come from developing nations -- with almost 50 percent from China alone, U.S. climate envoy Todd Stern said this week. No country holds the fate of the earth more in its hands than China. Not one, he said. China and India say they are slowing the growth of emissions but need to give priority to raising living standards by burning more energy -- as industrialized nations have done for 200 years.

POLLUTERS - Some big industries are reluctant to embrace deep cuts in carbon dioxide, fearing they will lose a competitive edge.

THE WEATHER - 2008 was the 10th warmest year since records began in the mid-19th century. The warmest was 1998, when a strong El Nino event in the eastern Pacific disrupted weather worldwide. That has led some to argue that global warming is slowing even though the U.N.'s World Meteorological Organization says a long-term warming trend is intact.

THE PUBLIC - People have been slow in changing lifestyles to use less carbon. Simple choices like taking more public transport, using less heating or air conditioning, even changing lightbulbs can help if millions of people act.