2011 is currently tied for the 10th hottest since records began in 1850 and Arctic sea ice has shrunk to record-low volumes this year, the U.N. weather office said Tuesday.
The 13 hottest years on the books all have occurred in the last 15 years, IMO's deputy director R.D.J. Lengoasa told reporters on the sidelines of the U.N. climate conference under way in South Africa.
"The science is solid and proves unequivocally that the world is warming," Lengoasa said. Human activity was a significant contributor to this trend, he said.
"Climate change is real, and we are already observing its manifestations in weather and climate patterns around the world," he said.
The preliminary report by the International Meteorological Organization is based on the first 10 months of the year.
It was released in Geneva and at the U.N. climate talks in South Africa, provided a bleak backdrop to negotiators who are seeking ways to limit pollution blamed for global warming.
2011 has been a year of extreme weather, the weather service said. Parching drought in East Africa has left tens of thousands dead, and there have been deadly floods in Asia, and 14 separate weather catastrophes in the United States with damage topping $1 billion each.
High temperatures saturated the Earth despite a La Nina event, when low surface temperatures in the equatorial Pacific Ocean has a cooling effect on the entire globe, the IMO said.
In an exhaustive study of extreme weather, the authoritative Intergovernmental Panel on Climate Change reported this month that such events will increase in frequency and intensity as the Earth continues to warm.
The IMO said the extent of Arctic sea ice in 2011 was the second-lowest on record, and its volume was the lowest. Scientists see the Arctic as the planet's most sensitive region and a barometer of the future.
The largest departure from the norm occurred in northern Russia, where thermometers soared and average 7.2 degrees Fahrenheit (4 degrees Celsius) above average in some places, and some stations reporting spring weather 16 degrees Fahrenheit (9 degrees Celsius) above normal.
The Russian Arctic and most of Siberia hold massive amounts of methane locked into the permafrost, carbon-rich soil that never thaws. Warmer summer temperatures mean a deeper thaw of permafrost and greater release of methane, a gas with a global warming potential 23 times more powerful than carbon dioxide.
The report came on the second day of the two-week conference in this South African coastal city attended by 192 parties seeking agreement on future action to curb climate change.
The talks will determine whether industrial countries will renew and expand their commitments under the 1997 Kyoto Protocol to reduce their greenhouse emissions and whether developing countries will accept binding limits on their emissions in the future.
Negotiators also are discussing how to raise $100 billion a year to help poor countries move to low-carbon economies and cope with the effects of global warming.
Explore further: Lights out in Australia as Earth Hour kicks off