Niwa denies ACT Party leader Rodney Hide's claim that it has misled cabinet ministers over temperature measurements showing global warming in New Zealand.
National Institute of Water and Atmospheric Research (Niwa) communications manager Michelle Hollis said the state science company rejected the claim.
The crown research institute also bluntly rebutted the attack Mr Hide mounted today on the integrity of its climate science.
"Niwa stands by the professionalism and integrity of its scientists," the organisation's chief climate scientist David Wratt said.
There were many lines of evidence which pointed to climate warming in this country, he said.
These included ship-based measurements and shrinking glaciers as well as land-based temperature measurements, such as those in Niwa's longterm 7-station series (of adjusted data) and an 11-station series (of unadjusted data).
Niwa has previously said the temperatures compiled from the seven locations - Auckland, Masterton, Wellington, Hokitika, Nelson, Lincoln and Dunedin - show "striking agreement" on temperature fluctuations between years and also on long-term trends.
They use data adjusted to made to allow for changes over the decades, such as when the position, type or location of thermometers was altered: Dunedin has the longest history, but its climate readings have been taken at six different sites.
The 7-station series indicated a rise of 1.1degC per century, and the 11-station temperature record showed a rise of 1.3degC per century.
Dr Wratt rejected Mr Hide's allegation to a Federated Farmers meeting at Hamilton that warming periods shown by two key sets of measurements did not coincide.
"When the 7 and 11 series data are overlaid, the differences are more pronounced than the similarities," Mr Hide claimed.
But Dr Wratt released a graph of the two sets of measurements overlaid to show they had very similar trends.
"The warmer and cooler periods clearly do coincide," he said. This was despite the fact the graph was based on separate sets of data, only one of which had been adjusted.
Dr Wratt rejected Mr Hide's statement that he and a lobby of climate sceptics, the NZ Climate Science Coalition, had not been able to document details of the adjustments to raw data because there was no "schedule of adjustments".
Niwa had posted its 7-station temperature series online, and Dr Wratt said that a schedule of adjustments required to create the series was also available from the web page.
"Niwa makes all its original climate data freely available over the web for anyone to analyse," he said. This had been the case since July 2007, and the adjusted 7-station series was made available to members of the Climate Science Coalition a year earlier than that.
Last year Niwa researchers provided an open briefing to MPs, "which was attended by Rodney Hide", Dr Wratt said.
Mr Hide's speech to farmers today re-opened a drawn-out row over the scientific integrity of the nation's temperature record - largely driven by the Climate Science Coalition.
Raw data from a group of seven long-running stations showed no rising or falling temperature trend, except when the data was adjusted by researchers, said Mr Hide, whose party is opposed to the Emissions Trading Scheme scheduled to take effect on July 1.
But Dr Wratt said international climatologists accept the need to make adjustments in data - which was not the same as fiddling or manipulation - and Niwa kept all the original, unadjusted data secure in the national climate database, which anyone could access free over the internet.
Niwa was further documenting the 7-station series, and would post those details on its website.
NZPA