NIWA today rejected allegations by Hon Rodney Hide that it had misled Cabinet Ministers over its analysis of New Zealand temperatures.
May 06, 2010
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Two New Zealand temperature series compared. The warmer and cooler periods clearly do coincide, despite the fact they use separate data-sets and only one (the seven-station series) uses adjusted data.
“I stand by the integrity and professionalism of our scientists,” says NIWA’s Chief Executive John Morgan. “NIWA is an internationally respected and responsible science organisation and we do not get involved in political commentary or process. NIWA will continue to conduct its science in a highly professional and ethical way.”
“There are many lines of evidence which point to New Zealand’s climate warming,” says NIWA’s Chief Climate Scientist, Dr David Wratt. “This evidence includes land-based measurements, ship-based measurements, and shrinking glaciers.”
At the heart of Mr Hide’s criticism are two independent time-series using land-based temperature measurements. These are the long-running 7-station series which uses a composite record of measurements for seven places around New Zealand and goes back more than 100 years; and an independent, 11-station series which uses measurements from another 11 stations and stretches back almost 80 years. The 7-station series uses adjusted data to account for site changes, whereas the 11-station series uses unadjusted data. Both show a long-term warming trend for New Zealand.
In specific response to Mr Hide’s criticisms:
NIWA has already published a schedule of adjustments for its 7-station series on this website.
Information about the 11-station series (for which no adjustments were made) is already available on this website.
The two series show very similar trends. The warmer and cooler periods clearly do coincide, despite the fact they use separate data-sets and only one uses adjusted data. This is shown clearly in the graph at the top right of this web page.
We wish to make clear the following:
• NIWA makes its original climate data freely available over the web for anyone to analyse, and it can be accessed here. This has been the case since 1 July 2007.
• The adjusted 7-station series was made available to a member of the NZ Climate Science Coalition on 19 July 2006.
• The need to make adjustments is internationally accepted amongst climate scientists. In climate science, it is a necessary and well-established process to ensure you are comparing apples with apples, such as when a site moved to a higher or more exposed location. NIWA keeps all the original, unadjusted data secure in the national climate database, which anyone can access free over the web.
• The initial 7-station series was documented in Dr Jim Salinger’s PhD thesis for Victoria University. This was reviewed and passed by expert examiners, and is available from the university. Since then, several papers have been published in the scientific literature documenting the methods used and analysing the results from this series. References are available on our website.
• NIWA has a project underway to further document the 7-station series, and will post this information on our website.
• When this issue first arose last year, NIWA provided an open briefing to MPs, which was attended by Mr Hide.