WMO secretary-general Michel Jarraud said it would almost certainly be one of the three hottest years recorded. ''The decade from 2001 to 2010 has set a new record - it will be the warmest decade ever since we have records,'' he said.
The 2010 heatwave has hit some of the world's poorest and most vulnerable areas, with swathes of northern Africa and southern Asia sweltering through record average temperatures. New benchmarks were also set at the Greenland ice sheet and the Canadian Arctic, with average temperatures more than three degrees above normal.
But in a snowed-in northern Europe, Britain, Germany, France and Norway were likely to have their coolest year since 1996. Temperatures are also below average in parts of Siberia, South America and the south-eastern United States.
Australia fell between the highs and lows - about 0.2 degrees above average, but significantly cooler than last year.
Globally, the temperature is an estimated 0.55 degrees warmer than the average across sea and land between 1961 and 1990. Scientists say this is in line with warming predicted due to increased greenhouse gas emissions trapping heat in the lower atmosphere.
The head of climate analysis at the Bureau of Meteorology, David Jones, said the dip in Australian temperatures was largely due to the strongest La Nina event in at least three decades. It had brought drenching rains, cooling the continent by between a quarter and half a degree. ''We continue to get variations year to year but the background pattern is one of the planet warming and Australia continuing to warm,'' Dr Jones said.
Extreme weather in line with scientific predictions included Pakistan's worst flooding, costing more than 1500 lives. In Moscow, the average temperature in July was 7.6 degrees above average. About 11,000 deaths were attributed to the extreme heat.