Both South America and Asia had their hottest years on record while sea levels, measured by tide gauges and satellites, were also the "highest ever recorded."
"The future is happening now," Petteri Taalas, WMO Secretary-General, said.
"The alarming rate of change we are now witnessing in our climate as a result of greenhouse gas emissions is unprecedented in modern records," Taalas added.
These extremes show no sign of abating, with the first two months of 2016 setting new monthly temperature records, the WMO added.
"The startlingly high temperatures so far in 2016 have sent shockwaves around the climate science community," David Carlson, director of the World Climate Research Programme (WCRP), said. The WCRP is co-sponsored by WMO.
The WMO's report comes in the wake of last year's historic global agreement at the COP21 summit in Paris. There, world leaders from 195 countries agreed to limit global warming to "well below" two degrees centigrade.
"Our planet is sending a powerful message to world leaders to sign and implement the Paris Agreement on climate change and cut greenhouse gases now before we pass the point of no return," Taalas said.
"Today the Earth is already 1°C hotter than at the start of the twentieth century. We are halfway to the critical 2°C threshold."
While the adoption of national climate change plans might not be enough to avoid a rise of 3 degrees Celsius, Taalas stated that worst case scenarios could be avoided with "urgent and far-reaching measures to cut carbon dioxide emissions."