The findings, published in the journal Nature, could help conservationists do a better job of saving the endangered great apes and might provide insights into human health.

"In terms of evolution, the orangutan genome is quite special among great apes in that it has been extraordinarily stable over the past 15 million years," Richard Wilson of Washington University in St. Louis, the genomics expert who oversaw the study, said in a statement.

"This compares with chimpanzees and humans, both of which have experienced large-scale structural rearrangements of their genome that may have accelerated their evolution."

Devin Locke and colleagues sequenced DNA from two species of orangutans, the intelligent, reddish-colored great apes found only in the deepest forests of Indonesia and Malaysia.

Their two closest cousins -- humans and chimpanzees -- both have very rapidly evolving genomes. Chimps, especially, have been undergoing genetic change.

This change is driven in part by stretches of DNA called "alu" sequences. Locke has an analogy for them.

"In any novel, there are thousands, if not tens of thousands, of certain words like 'the' and 'and,'" he said in a telephone interview.

"Alus are high-copy repeats. They make up over 10 percent of the human genome sequence. They are important for shaping genomes and they have also been implicated in moving sequences around the genome and lubricating the machinery."

DEFINING HUMANS

This is important for defining what makes a human being on the genetic level because the human gene map is puny compared to some other species, with only around 20,000 active genes.

Genetics experts realize it is not how many genes a species has that really matters, but what the body does with them. Comparing humans with our closest relatives can help show what makes us unique.

Locke and his team found that orangutans have relatively few alu sequences.

He does not believe that contributed to the rapid decline of orangutans, which are endangered. There are about 7,000 orangutans in Sumatra and 40,000 to 50,000 on Borneo.

"If humans didn't populate the area, orangutans would be fine," Locke said. "They are being forced into areas that humans find unsuitable for cultivation."

The first 10 years of the millennium proved to be the hottest decade since records began in the 19th century, it said.

"The main signal is that the warming trend continues and is being strengthened year after year," WMO Secretary-General Michel Jarraud told a news conference.

"The trend, unfortunately, will continue for a number of years but the amplitude will depend on the amount of greenhouse gases released," the Frenchman added. "It will depend on action taken to minimize the release of greenhouse gases."

Jarraud said the latest data should convince doubters about the growing evidence for man-made climate change. "If they look at it in an unbiased way, it should convince them, or hopefully a few of them, that the skeptical position is untenable."

2010 was also marked by further melting of Arctic ice -- in December its extent was at its lowest on record, the WMO said -- and by extreme weather, including Russia's heatwave and devastating floods in Pakistan.

Rising temperatures, already about 0.8 degree Celsius above pre-industrial times, mean the world will struggle to limit warming to below 2 degrees Celsius, a target agreed by almost 200 nations at U.N. talks last month in Mexico.

Many experts see 2C as a threshold for dangerous climate change, like more heatwaves, droughts, floods and rising seas.

"We have to act very fast and strongly" to limit emissions, said Bob Ward, of the Grantham Research Institute on Climate Change and Environment at the London School of Economics and Political Science.

He noted that many skeptics say global warming has stopped because of no new records since 1998, when temperatures were boosted by a strong El Nino event that warms the Pacific.

"But they cannot explain away the fact that nine of the 10 warmest years have occurred since 2000," he said.

"Data received by the WMO show no statistically significant difference between global temperatures in 2010, 2005 and 1998," the United Nations body, which compiles its ranking from data provided by British and U.S. agencies, said in a statement.

Data from British institutes on Wednesday showed last year was the world's second warmest behind 1998, while the other two main groups tracking global warming, based in the United States, said 2010 was tied for the hottest on record.

Over the 10 years from 2001 to 2010, global temperatures have averaged 0.45 degrees Celsius (0.83 degrees Fahrenheit) above the 1961-1990 average and are the highest ever recorded for a 10-year period since climate records began, WMO said.

The difference between the three hottest years was less than the margin of uncertainty in comparing the data, according to WMO, whose assessment is based on climate data from land-based weather and climate stations, ships, buoys and satellites.

The fight against global warming suffered a setback in the wake of the financial crisis, slowing funding for renewable energy projects and knocking momentum from international efforts to agree a climate deal to succeed the Kyoto Protocol in 2013.

(Additional reporting by Alister Doyle in Oslo; Editing by Jonathan Lynn and Janet Lawrence)