Niwa’s temperature data raises questions

Christchurch has one of New Zealand’s longest temperature records, with weather readings in the Botanic Gardens dating back to 1863.

Which makes the claim that Christchurch is heating up more quickly than other parts of the country, based largely on an urban record that only goes back to 2002, seem pretty dubious.

How did Niwa – the National Institute of Water and Atmospheric Research – calculate that Christchurch’s temperatures are now 0.7 degrees Celsius higher than they were at the end of 2004, a very short period on which to build any kind of convincing case?

Blue Skies Weather forecaster Tony Trewinnard has called Niwa on its use of the Kyle St, Riccarton site – surrounded by concrete, traffic and industry – to determine the figure, when less than two kilometres away is the Botanic Gardens’ weather enclosure, largely unaffected by recent human activity.

Trewinnard says Niwa’s 0.7C calculation and claims about what the figure means are ‘‘bad science’’. It certainly seems to be selective sci- ence, particularly when you consider the Botanic Gardens has only experienced a non-storymaking 0.1C rise in temperatures since 2004, according to Niwa.

He says over the past 11 years Kyle St temperatures have averaged 0.2C higher than the Gardens but since the start of 2015 it has been 0.8C warmer. Clearly something has changed in the Kyle St environment to increase temperatures there.

Asked why Niwa focused on the 0.7C Kyle St rise rather than the Gardens’ 0.1C, Niwa meteorologist Ben Noll said part of the comparison included use of 1981-2010 temperature figures from the Gardens and Lincoln.

Temperatures have certainly been higher than normal so far this year, thanks to El Nino and warmer seas around New Zealand. But that does not necessarily mean the 0.7C figure is more likely to be correct.

Bickering about temperature data may seem a classic first-world problem. But it is vital the most robust weather data is collected and the best science is done as our climate changes. The Government will determine future policy and spend billions of dollars on remediation based on the authenticity of such figures.