Climate scientists say temperatures in New Zealand rose 1C between 1931 and 2008.
National Institute of Water and Atmospheric Research scientists said yesterday that the analysis of long-term measurements from seven weather stations showing warming was backed up by other observations, including measurements from ships.
A 1995 study identified an upward trend of about 0.7C from 1900 to 1993 in night-time minimum air temperatures measured from ships over the ocean surrounding NZ.
"That trend is similar to the trend from the seven-station land network over the same period," a Niwa spokesman said.
A senior climate scientist formerly employed by Niwa, Jim Salinger, has identified from the Niwa climate archives a set of 11 stations with long records where there have been no significant changes.
Niwa said: "When the annual temperatures from all of these sites are averaged to form a temperature series for New Zealand, the best-fit linear trend is a warming of 1C from 1931 to 2008."
The institute was responding to a row - the so-called "climategate" controversy in which the private emails of climate scientists were hacked and leaked on the internet by climate-change sceptics.