Thirteen of the warmest years recorded have occurred within the last decade and a half, 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, South Africa.
"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 on Earth 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 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 droughts in east Africa, islands in the central equatorial Pacific and the southern United States.
It also aggravated flooding in southern Africa, eastern Australia and southern Asia.
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.
Over northern Russia January to October temperatures were about 4.0 Celsius (7.2 Fahrenheit) above average in places. Nearby Finland had its hottest summer in 200 years.
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 -- included, by region:
EAST AFRICA: In a region where agriculture is almost entirely rain-fed, severe drought affected many countries through most of 2011, especially in northern Kenya, western Somalia and some parts of Ethiopia.
Some 13 million people required emergency aid, according to the UN Office for Coordination of Humanitarian Affairs (OCHA).
Starting in October, many of the same areas were overwhelmed by flood-provoking rains.
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.
Severe flooding, exacerbated by high tides, affected many parts of Bangkok for several weeks from mid-October, causing economic damage of several billion dollars.
NORTH AMERICA: Fourteen weather-climate events in the United States each caused at least one billion dollars in losses.
Extreme drought affected a large swath of the south, especially Texas, where rainfall for the first 10 months of the year was a record 56 percent below normal.
Temperatures in the Lone Star state were also exceptionally hot, 3.0 C (5.4 F) above long-term averages.
Some northern and central states, by contrast, saw record rainfall, leading to severe flooding, as did areas hit by Hurricane Irene in August and Tropical Storm Lee the next month.
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.
Central America experienced major flooding in October -- an astounding 1,513 millimetres (60.5 inches) of rain fell in Huizucar, El Salvador over 10 days. Guatemala, Nicaragua, Honduras and Costa Rica were also hit.
SOUTH ASIA: For the second year in a row, Pakistan saw severe flooding, though more localised -- in the south -- than in 2010. It was the wettest monsoon season on record for the province of Sindh.
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