Temperatures in NZ warmed 1degc since 1931 - Niwa

NZPA December 3, 2009, 9:00 PM

Climate scientists say temperatures in New Zealand have risen 1degC between 1931 and 2008.

National Institute of Water and Atmospheric Research (Niwa) scientists said today 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 0.7degC from 1900 to 1993 in night time minimum air temperatures measured from ships over the ocean surrounding New Zealand.

"That trend is similar to the trend from the seven-station land network over the same period," a Niwa spokesman said today.

"Also, sea surface temperatures measured from the same ships warmed by 0.6degC in that period".

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 at the site where measurements were taken.

"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 1degC from 1931 to 2008," Niwa said.

It was responding to a continuing 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 who accused them of manipulating data to show the world's climate is warming.

Dr Salinger -- who with colleague Jill Gunn reported in a scientific journal, Nature, 34 years ago, on southern hemisphere warming at a time when people were worrying about the next ice age -- and Kevin Trenberth, a scientist leading climate analysis at the US National Centre for Atmospheric Research were among the victims of the email leak.

In NZ, some sceptics used the controversy to argue the emails from the University of East Anglia's climate research unit suggested selective science and even collusion in preparing reports for the Intergovernmental Panel on Climate Change.

And the Climate Conversation Group and the Climate Science Coalition released their own analysis claiming that unadjusted temperature readings from seven weather stations with 100-year-plus records -- Auckland, Masterton, Wellington, Hokitika, Nelson, Lincoln and Dunedin -- were stable and did not show a warming trend.

But Niwa scientists said there were several reasons for adjusting the temperature record from specific site, including introducing new thermometers or sensors to a weather site, and changes to its exposure caused by growing vegetation or urban sprawl.

Wellington figures had to be adjusted down when the official weather site moved up 120m in altitude in 1928 from the Thorndon waterfront to Kelburn, which is about 0.8deg cooler, on average.

Ignoring major changes in site location would produce wrong results, the state-owned science company said.

"For the longer `seven station' time series, adjustments to account for significant site changes are necessary in order to provide a meaningful estimate of New Zealand temperature trends," it said.