In 2009, only the United States and Canada experienced conditions that were cooler than average. ''Given the current figures, large parts of southern Asia and central Africa are likely to have their warmest year on record,'' the report said.
Published as world leaders gathered in Copenhagen to consider climate change, it highlights extreme weather conditions around the globe this year, including three ''exceptional heatwaves'' in Australia, China's worst drought in 50 years and the wettest October in the US in 115 years.
Andy Pitman, co-director of the Climate Change Research Centre at the University of NSW, said this year should have been a cool year because of low solar activity and a recent La Nina weather event. ''The fact it ranked in the top 5 since 1850 is actually frightening,'' he said.
This year's heatwaves in NSW, Victoria and South Australia also did not bode well for next year, Professor Pitman said.
The report is based on data from a network of weather stations on land, ships, buoys and satellites.
This information was fed to three analysis centres, including one maintained jointly with the British Met Office by the Climatic Research Unit at the University of East Anglia, which has been at the centre of the climate email affair, after its computers were hacked.
The other two analysis centres are the US National Oceanic and Atmospheric Administration and the Goddard Institute of Space Studies at NASA.
Not only did Australia have three heatwaves - in January and February, August and November - winter was also exceptionally mild, the report said.
''Maximum temperatures were well above normal across the entire continent, reaching 6 to 7 degrees above normal in some parts.'' Climate extremes, including devastating floods, severe droughts, snowstorms, heatwaves and cold waves, were recorded in many parts of the world.
''This year the extreme warm events were were more frequent and intense in southern South America, Australia and southern Asia, in particular.''
India had an extreme heatwave in May, which caused 150 deaths, and a heatwave that hit northern China in June broke summer records in some areas.
In East Africa, a drought led to ''massive food shortages'', and drought in central Argentina also caused severe damage to agriculture, livestock and water resources, the report said.
In the Arctic, sea ice during the summer melt was the third lowest since satellite measurements began in 1979, ranking behind 2008 and the record year, 2007.
Globally, the combined sea surface and land surface air temperature for January to October this year is estimated at 0.44 degrees above the 1961 to 1990 annual average of 14 degrees, making it likely 2009 will rank in the top 10 years on record.