The world is getting hotter, with 2011 one of the warmest years on record, and humans are to blame, a report by the World Meteorological Organisation (WMO) said on Tuesday.
It warned increasing global average temperatures were expected to amplify floods, droughts and other extreme weather patterns.
"Our science is solid and it proves unequivocally that the world is warming and that this warming is due to human activities," WMO Deputy Secretary-General Jerry Lengoasa told reporters in Durban, where almost 200 nations are gathered for U.N. climate talks.
The WMO report was released to coincide with U.N. climate talks which run until Dec. 9 in Durban aimed at trying to reach agreement on cutting planet-warming greenhouse gas emissions.
Prospects for a meaningful agreement appear bleak with the biggest emitters the United States and China unwilling to take on binding cuts until the other does first. Major players Japan, Canada and Russia are unwilling to extend commitments that expire next year and the European Union is looking at 2015 as a deadline for reaching a new global deal.
There has been an emerging surge of support for an EU plan to have a new global deal reached by 2015 and in force by 2020 that includes countries not bound by the Kyoto Protocol.
"Not only the EU but other countries share the same goal in one way or another," chief Japanese climate envoy Masahiko Horie told a news conference.
Japan is looking at a single, comprehensive legal document. Horie did not say Japan was on board with the European Union but signalled that Tokyo agreed with the principles of the plans laid out by Brussels.
The WMO, part of the United Nations, said the warmest 13 years of average global temperatures have all occurred in the 15 years since 1997. That has contributed to extreme weather conditions which increase the intensity of droughts and heavy precipitation across the world, it said.
"Global temperatures in 2011 are currently the tenth highest on record and are higher than any previous year with a La Nina event, which has a relative cooling influence," it said
This year, the global climate was influenced heavily by the strong La Nina, a natural phenomenon usually linked to extreme weather in Asia-Pacific, South America and Africa, which developed in the tropical Pacific in the second half of 2010 and continued until May 2011.
One of the strongest such events in 60 years, it was closely associated with the drought in east Africa, islands in the central equatorial Pacific and the United States, as well as severe flooding in other parts of the world.
The WMO report said the extent of Arctic sea ice in 2011 was the second lowest on record, and its volume was the lowest.
It said the build-up of greenhouse gases put the world at a tipping point of irreversible changes in ecosystems.
"Concentrations of greenhouse gases in the atmosphere have reached new highs," WMO Secretary-General Michel Jarraud said in a separate statement.
"They are very rapidly approaching levels consistent with a 2-2.4 degree Centigrade rise in average global temperatures which scientists believe could trigger far reaching and irreversible changes in our Earth, biosphere and oceans."
Russia experienced the largest variation from average, with its northern parts seeing January to October temperatures about 4 degrees C higher in several places, it said.
U.N. scientists said in a separate report this month an increase in heat waves is almost certain, while heavier rainfall, more floods, stronger cyclones, landslides and more intense droughts are likely across the globe this century as the Earth's climate warms.
The Organisation for Economic Cooperation and Development said global average temperatures could rise by 3-6 degrees Celsius by the end of the century if governments failed to contain emissions, bringing unprecedented destruction as glaciers melt, sea levels rise and small island states are submerged.
(Additional reporting by Tom Miles in Geneva, reporting by Jon Herskovitz, Editing by Maria Golovnina and Janet Lawrence)