More national temperature records were reported broken around the world than in any previous decades, the report said, and there was an increase in deaths from heatwaves, particularly pronounced during the extreme summers in Europe in 2003 and in the Russian Federation during 2010.
The WMO analyzed global and regional trends, as well as extreme events such as Hurricane Katrina, floods in Pakistan and droughts in the Amazon, Australia and East Africa.
While overall temperature rise has slowed since the 1990s, the WMO says long-term temperatures are still rising because of greenhouse gases from human activity.
Some climate change doubters have fastened on the lack of movement in temperatures throughout the decade, but Judah Cohen, director of seasonal forecasting at Atmospheric and Environmental Research, said the issue hinged on the time frame.
"For longer periods [two decades or longer] we found a robust and a statistically significant warming trend," he told BBC News.
Nearly 94 percent of reporting countries had their warmest decade in 2001-2010, the WMO survey found.