"Climate change is taking place before our eyes and will continue to do so as a result of the concentrations of greenhouse gases in the atmosphere, which have risen constantly and again reached new records," WMO Secretary-General Michel Jarraud said.
Delegates from nearly 200 countries are meeting in the Qatari capital of Doha to discuss ways of slowing climate change, including by cutting emissions of greenhouse gases that scientists say are warming the planet, melting ice caps, raising sea levels, and changing rainfall patterns with impacts on floods and droughts.
Discord between rich and poor countries on who should do what has kept the two-decade-old U.N. talks from delivering on that goal, and global emissions are still going up.
The WMO said global temperatures rose after initial cooling caused by the La Nina weather oscillation, with major heat waves in the U.S. and Europe. Average temperatures in January-October were the highest on record in the continental U.S., and the ninth highest worldwide.
Before that, a cold spell had much of the Eurasian continent in an icy grip between late January and mid-February, when temperatures in eastern Russia plunged to -50 degrees C (-58 F).
Cyclone activity was normal globally, but above average in the Atlantic, where 10 storms reached hurricane strength, including Sandy, which wreaked havoc across the Caribbean and the U.S. east coast.
Sandy wasn't the strongest cyclone, though. That was typhoon Sanba, which struck the Philippines, Japan, and the Korean Peninsula, "dumping torrential rain and triggering floods and landslides that affected thousands of people and caused millions in U.S. dollars in damage," the WMO said.
Droughts impacted the U.S., Russia, parts of China and northern Brazil. Nigeria saw exceptional floods, while southern China saw its heaviest rainfall in three decades.
But of all the weather events in 2012, the most ominous to climate scientists was the loss of ice cover on the North Pole. In September, scientists at the National Snow and Ice Data Center in Colorado said Arctic Sea ice measured 1.32 million square miles (3.41 million sq. kilometers) — which is 18 percent less than the previous record low, set in 2007. Records go back to 1979 based on satellite tracking.
The scientists said their computer models predict the Arctic could become essentially free of ice in the summer by 2050, but added that current trends show ice melting faster than the computers are predicting.