Lawyers for the National Institute of Water and Atmospheric Research (NIWA) have hit back at claims by a group sceptical of global warming that the Institute’s temperature data is invalid.

The New Zealand Climate Science Education Trust, a branch of the NZ Climate Coalition, has brought a case before the High Court in Auckland against the country’s state-owned weather and atmospheric research body.

National Institute of Water and Atmospheric Research (Niwa) records show a national warming trend of almost one degree Celsius in the last century, a figure which the Trust says is unreliable and almost 50 per cent above the global average for the period.

Niwa’s lawyer Justin Smith told the court this morning that the plaintiff appeared to be manufacturing rules that suited its case.

“They do not come from anywhere but its counsel’s inventiveness. They change at the last minute and without notice when a plausible objection is raised.”

Mr Smith is currently outlining the defence’s response to six submissions made by the Trust, including whether Niwa had an obligation to adhere to “recognised scientific opinion”, and whether Niwa used contaminated data.

The dispute relates to readings from the “Seven-station Series” (7SS) – stations in Auckland, Masterton, Wellington, Nelson, Hokitika, Lincoln and Dunedin – used by Niwa for national temperature records.

The Trust says unscientific methods were used to reach the results, creating an unrealistic indication of climate warming.

“We’re not saying climate change doesn’t exist. We’re saying let’s at least make sure that evidence of this for New Zealanders is accurate,” Trust lawyer Terry Sissons previously told the court.

He challenged the way Niwa had adjusted temperatures recorded at stations, which he said were moved half a degree downwards on average in early readings.

The results had significantly affected the overall upwards rise in temperature, said Mr Sissons.

“Is that valid that you can expose a trend, simply by pushing down the readings in the early part to make them colder? Then when you compare them to the modern ones you get a steep increase.”

Instead of using the accepted international method to estimate how site changes had affected temperature and rainfall, Niwa instead used the untested techniques of former employee James Salinger, said Mr Sissons.

The disputed climate data had been used for a number of projects, had a “profound effect” on policy making, and was also used to predict future trends, he said.

The Trust is asking the High Court to invalidate the temperature record to stop Niwa from using the record to advise the Government and the public, and for Niwa to provide “full and accurate” temperature record.

– APNZ