Only the United States and Canada experienced cooler conditions than average, the World Meteorological Organisation said, although Alaska had the second-warmest July on record.
In central Africa and southern Asia, this will probably be the warmest year, but overall, 2009 will "be about the fifth-warmest year on record," said Michel Jarraud, secretary-general of the WMO.
The agency also noted an extreme heat wave in India in May and a heat wave in northern China in June. It said parts of China experienced their warmest year on record, and that Australia so far has had its third-warmest year. Extremely warm weather was also more frequent and intense in southern South America.
The decade 2000-2009 "is very likely to be the warmest on record, warmer than the 1990s, than the 1980s and so on," Jarraud told a news conference, holding a chart with a temperature curve pointing upward. The second warmest decade was the 1990s.
The current decade has been marked by dramatic effects of warming.
In 2007-2009, the summer melt reduced the Arctic Ocean ice cap to its smallest extent ever recorded. In the 2007-2009 International Polar Year, researchers found that Antarctica is warming more than previously believed. Almost all glaciers worldwide are retreating.
Meanwhile, such destructive species as jellyfish and bark-eating beetles are moving northward out of normal ranges, and seas expanding from warmth and glacier melt are encroaching on low-lying island states.
If 2009 ends as the fifth-warmest year, it would replace the year 2003. According to the US space agency NASA, the other warmest years since 1850 have been 2005, 1998, 2007 and 2006. NASA says the differences in readings among these years are so small as to be statistically insignificant.
The U.N. agency reported that the global combined sea surface and land surface temperature for the January-October 2009 period is estimated at 0.44degC above the 1961-1990 annual average of 14degC, with a margin of error of plus or minus 0.11degC. Final data will be released early in 2010.
Negotiators at the two-week talks in Copenhagen turned yesterday to "metrics," ''gas inventories" and other dense technicalities, as delegates worked to craft a global deal to rein in carbon dioxide and other greenhouse gases and stem climate change.
Governments, meanwhile, jockeyed for position leading up to the finale late next week, when more than 100 national leaders, including President Barack Obama, will converge on Copenhagen for the final days of bargaining.
In a series of reports beginning in the 1990s, the Intergovernmental Panel on Climate Change, a UN-sponsored scientific network, has warned that unless the world is weaned away from fossil fuels to greener sources of energy, the Earth will face the consequences of ever-rising temperatures: the extinction of plant and animals, the flooding of coastal cities, more extreme weather, more drought and the spread of tropical diseases.
Some governments have reacted slowly to the warnings because of concerns over the cost to business and consumers of converting economies to new energy sources, the influence of "old energy" industries on policy, and the reluctance of societies to change their ways.
Although temperatures have fluctuated up and down in the eons before record-keeping, as determined by tree rings, ice cores and other evidence, the causes were natural. The difference now is that they are being driven up by human activity, that modern civilization has many more coastal cities and needs to feed far more people, and that scientists believe humans can head off such dangerous warming.
On Monday, when the conference opened, the Obama administration gave the talks a boost by announcing steps that could lead to new US emissions controls that don't require the approval of the US Congress.
The US Environmental Protection Agency said scientific evidence clearly shows that greenhouse gases "threaten the public health and welfare of the American people" and that the pollutants - mainly carbon dioxide from burning fossil fuels - should be reduced, if not by Congress then by the agency responsible for enforcing air pollution.
As Congress considers the first US legislation to cap carbon emissions, the EPA finding will enable the Obama administration to act on greenhouse gases without congressional action, potentially imposing federal limits on climate-changing pollution from cars, power plants and factories.
The announcement gave Obama a new card in what is expected to be tough bargaining next week at the climate conference. In preparation, Obama met with former Vice President Al Gore, who won a Nobel for his climate change efforts, at the White House on Monday.
European climate change officials welcomed the US move.
"This is meaningful because it is yet a sign that the Americans have more to offer. My evaluation is that the U.S. can offer much more," EU environment spokesman Andreas Carlgren told reporters in Stockholm.
Yvo de Boer, UN climate chief, said the EPA finding gives Obama "something to fall back on."
"I think that will boost people's confidence" at the Copenhagen talks in the Americans' ability to offer more, he said.
The European Union has pledged to reduce greenhouse gas emissions by 20 percent by 2020, compared with 1990, and is considering raising that to 30 percent if other governments also aim high. EU leaders will have an opportunity to make such a move at an EU summit this Thursday and Friday in Brussels.
In Britain, Prime Minister Gordon Brown urged fellow Europeans to raise their bid on reducing greenhouse gas emissions to pressure the US and others to offer more at Copenhagen.
"We've got to make countries recognise that they have to be as ambitious as they say they want to be. It's not enough to say 'I may do this, I might do this, possibly I'll do this.' I want to create a situation in which the European Union is persuaded to go to 30 percent," Brown was quoted as saying by Britain's Guardian newspaper.
The EU had called for a stronger bid by the Americans, who thus far have pledged emissions cuts much less ambitious than Europe's. The U.S. has offered a 17 percent reduction in emissions from their 2005 level - comparable to a 3-4 percent cut from 1990 levels.
Whether the prospect of EPA action will satisfy such demands - and what China may now add to its earlier offer - remains to be seen. And success in the long-running climate talks hinges on more than emissions reductions. Most important, it requires commitments of financial support by rich countries for poor nations to help them cope with the impact of a changing climate.
Swedish negotiator Anders Turesson said the US 17 percent reductions "are insufficient and we hope more would come out of that."
He suggested the US buy more carbon credits on the international market, where emissions reductions by developing countries can be credited and sold to the industrialised world.
