The last decade has been confirmed as the warmest on record for New Zealand.

Figures released by New Zealand's National Institute of Water and Atmospheric Research (Niwa) on Wednesday showed the years from2000 to 2009 were slightly warmer than the previous warmest decade in the 1980s.

NIWA Principal Scientist, James Renwick, said the finding is consistent with a World Meteorological Organization statement that the decade from 2000 to 2009 is likely to be the warmest on record globally.

The warmer climate was due to a combination of natural variability and a background warming trend, he said.

While the decade was warmer, last year was a chilly one for New Zealand, with the average temperature in 2009 slightly colder than the average from 1971 to 2000.