A couple of weeks ago I blogged about NIWA’s climate summary for 2008, but inexplicably missed a most excellent response to the figures from the NZ Climate “Science” Coalition’s energy expert Bryan Leyland. He must have been digging through some dusty tomes in the library, because he arrived at the astonishing conclusion that New Zealand was warmer 141 years ago:
New Zealandâ€™s national average temperature of 12.9 degrees C during 2008, described by NIWA as â€˜milder than normalâ€ was in fact cooler than it was 141 years ago, this, and worldwide drop in temperatures since 1998, demonstrate that claims of man-made global warming have lost touch with reality.
Mr Leyland said it is important that all New Zealanders, but especially politicians, understand the significance of the two sets of temperature readings.
Quite so, Bryan, quite so. Let’s see if I can help out a littleâ€¦
This chart shows the full data series for NZ annual average temperature, stretching back to 1853. But what’s this? It looks like 1867 was cooler than 2008. What’s going on? Surely Bryan would have taken care to ensure that he was choosing comparable figures, but it appears he didn’t:
The 1867 temperature readings are contained in the Transactions and Proceedings of the Royal Society of New Zealand 1868-1961, which contain tables, described as forming â€œthe most reliable data for judging of the climate of New Zealand, extracted from the reports of the Inspector of Meteorological Stations, for 1867.â€
I wonder when this list was compiled? At least 48 years ago, it appears. And it would have been based on a different methodology to the NIWA data. In other words, Bryan is comparing apples to oranges, and ending up with a fruit salad. If we look at the NIWA data, 1867 was certainly a bit warmer than the years either side, but the period from the 1860s to 1920s was markedly cooler on average than today, and 2008 was significantly warmer than 1867.
Look again at the NIWA data, and we can see that Bryan missed a really big cherry. 1861 was a very warm year — warmer than 2008. If you want to compare two years out of 150, he would have done better to pick those two Pacific Roses. It wouldn’t have proved anything about global warming, of course, because NZ’s average temperature is not a proxy for global temperature, and you can’t determine a trend just by drawing a line between the start and end points on a graph. In this instance, a quick eyeball of the data shows the obvious — lots of cold years in Victorian times, lots of warm years recently.
There’s another problem with using 1861, however. The NZ temperature record is generally said to begin in 1867 because that was the year that met stations around the country standardised on using Stevenson screens around their thermometers. Earlier temperature records are therefore subject to more potential error. But I don’t suppose that would have worried Bryan, who continues his analysis with an explanation of why we need to compare the two years:
â€œFirstly, they are 141 years apart which is a more accurate period for changes in climate with its natural cycles of warming and cooling. To put this difference of 0.2 degrees C into perspective it should be compared to the fourth assessment report by IPCC in 2007 that the world warmed by 0.6 degrees C in the previous 100 years. Temperature variations of this tiny extent are meaningless and certainly do not justify the extreme mitigation measures currently being discussed.
As we’ve seen, the difference is greater than Bryan’s cherry-picked data suggests, and if you look back over the last 100 years, NZ has actually warmed by 0.7ÂºC — more than the globe as a whole. Now there’s an inconvenient truth for Leyland to chew on. However, undaunted by reason, he continues:
â€œSecondly, this gives the lie to the myth about carbon dioxide as a cause of so-called global warming. We know from Siple ice cores that the level of CO2 in the atmosphere was 290 ppm, and we know from the American readings at Mauna Loa that the level today is almost a third higher at 385 ppm. CO2 increased but warming didn’t,â€ Mr Leyland concluded.
The world and NZ did warm, so we have prima facie evidence that carbon dioxide might have played a role. Correlation does not prove causation, but we have clinching evidence — the radiation physics of the atmosphere, which tells us that greenhouse gases warm the planet. So more gas, more warming.
That’s something I hope our politicians will remember. Bryan might think he can fool some of the people some of the time, but if this is the best he can do he might as well give up now.
(Original chart supplied by Jim Renwick, additional comments by Jim Salinger, arrows etc by me. My thanks to the Jims for their prompt assistance.)