The report also pointed out that Arctic ice was at a record low, rainfall increased causing floods around the world and a number of countries experienced drought.
Extreme weather events, such as Superstorm Sandy in the US and Typhoon Bopha in the Philippines, were linked to climate change and the damage and death toll could be exacerbated by rising sea levels.
Michel Jarraud, the secretary-general of the WMO, said the extreme events in 2012 were "a sign of things to come".
"Although the rate of warming varies from year to year ... the sustained warming of the lower atmosphere is a worrisome sign," he said.
Jarraud said the warming climate has made extreme weather events more likely.
"Natural climate variability has always resulted in such extremes, but the physical characteristics of extreme weather and climate events are being increasingly shaped by climate change.
"For example, because global sea levels are now about 20cm higher than they were in 1880, storms such as Hurricane Sandy are bringing more coastal flooding than they would have otherwise."