Thirteen of the warmest years recorded have occurred within the last decade and a half, proving that global warming is a reality, the UN's World Meteorological Organisation said on Tuesday.

The year 2011 caps a decade that ties the record as the hottest ever measured, the WMO said in a provisional report on climate trends and extreme weather events, unveiled at UN climate talks in Durban.

"Our science is solid and it proves unequivocally that the world is warming and that this warming is due to human activities," WMO Secretary-General Michel Jarraud said in a statement, adding that policy makers should take note of the findings.

"Concentrations of greenhouse gases in the atmosphere have reached new highs and are very rapidly approaching levels consistent with a 2 to 2.4 Celsius rise in average global temperatures."

Scientists believe that any rise above the 2.0 threshold could trigger far-reaching and irreversible changes over land and in the seas.

The 2002-2011 period equals 2001-2010 as the warmest decade since 1850, the report said.

2011 ranks as the 10th warmest year since 1850, when accurate measurements began.

This was true despite a cooling La Nina event -- one of the strongest in 60 years -- that developed in the tropical Pacific in the second half of 2010 and continued until May 2011.

The report noted that the cyclical climate phenomenon, which strikes every three to seven years, helped drive extreme weather events including drought in east Africa, islands in the equatorial Pacific and the southern United States.

While La Nina, and its meteorological cousin El Nino, are not caused by climate change, rising ocean temperatures caused by global warming may affect their intensity and frequency, scientists say.

Average surface temperatures over land were above long-term averages in most regions.

"There is no single country that has reported 2001-2010 mean temperatures that are colder than their national long-term average from 1961-1990," WMO Deputy Secretary General R.D.J. Lengoasa told journalists in Durban, citing a forthcoming review of weather trends over the last ten years.

For 95 percent of 80 countries that had submitted relevant data, 2001-2010 was the warmest decade on record, he added.

Forty percent had seen national heat records broken in 2001-2010, as compared to 15 percent in the 1991-2000 period, and 10 percent in the 1981-1990 period.

"Urgent action is needed to prevent the worst climate change scenarios in the coming decades," Lengoasa said.

Sea ice in the Arctic shrank to its second lowest surface area after 2007, and has reached record levels of thinness.

Extreme weather events in 2011 -- some influenced by La Nina -- hit regions unevenly.

In eastern Africa, where agriculture is almost entirely rain-fed, severe drought affected many countries, especially Kenya, Somalia and parts of Ethiopia.

Some 13 million people required emergency aid, according to the UN Office for Coordination of Humanitarian Affairs (OCHA).

In East Asia, rainfall during the 2011 monsoon season was far above average, with Thailand and Laos most affected. Floods claimed nearly 1,000 lives across Thailand, Cambodia and Myanmar.

Fourteen weather-climate events in the United States each caused at least one billion dollars in losses.

In central and south America, rainfall exceeding 200 millimetres (eight inches) in a few hours left at least 900 dead in the mountains north of Rio de Janeiro, one of the deadliest natural disasters in Brazil's history.

For the second year in a row, Pakistan saw severe flooding, though more localised -- in the south -- than in 2010.

A separate report also released Tuesday showed that Pakistan, Guatemala and Colombia were the countries worst hit in 2010 by extreme weather events.

Over a 20-year span, Bangladesh, Myanmar and Honduras were shown to be most vulnerable to Nature's violent outbursts, said the report, by European NGO Germanwatch.