Another local climate change denial meme

By Ken Perrott 24/12/2010

I commented in Painted into a corner? that the release of NIWA’s report of the recalculation of New Zealand’s 7-station  long term  temperature series had called the local climate change deniers’ bluff. It was time for them to apologise, withdraw their slanderous attacks on NIWA and move on.

Yeah, right! That may have been the sensible thing to do, but of course they are in it for the politics, not the science. So the attacks continue.

Gareth at Hot Topic has an excellent summary of the action (see A Christmas cracker for the cranks). And of course the denier trolls have descended on his post with quite hilarious arguments. One is their claim “this new series shows no warming has occurred here since about 1960.”

Well, of course the series shows nothing of the sort. They appear to basing this incorrect claim on a paragraph in the report which says:

“The unusually steep warming in the 1940-1960 period is paralleled by an unusually large increase in northerly [air] flow during this same period. On a longer timeframe, there has been a trend towards less northerly flow (more southerly) since about 1960. However, New Zealand temperatures have continued to increase over this time, albeit at a reduced rate compared with earlier in the 20th century. This is consistent with a warming of the whole region of the southwest Pacific within which New Zealand is situated.”

Never the less these trolls and their public spokespersons, Richard Treadgold and Brian Leyland are working hardto push this meme. And they claim support from their “eyeball” analysis of the graph in NIWA’s report.

But all the data is available (Seven station data and 11 station data) and anyone can do their own analysis to check these claims.

So what does this data show?

The figure below shows that there is indeed a significant and relatively large increase in temperature in the 1940-1960 period (4.4°C/century compared to 0.9°C over the whole period). NIWA was perfectly justified in drawing attention to this and suggesting a reason for it.

But it also shows that the temperature trends after 1960 are similar to the overall trend (0.85 cf 0.91°C/century).  And the trend before 1960 is also similar (0.7°C/century). So much for that troll meme!

Mind you, we have to acknowledge that  the statistical significance of the smaller data sets are inevitably lower (although the 1940-1960 period has a range of 2.4 – 6.3°C/century at the 95% confidence level). The table provides an idea of the statistical significance.

Period Trend °C/century 95% confidence 90% confidence
1009-1959 0.69 -0.15 -1.54 -0.01 – 1.40
1960-2009 0.85 0.03 -1.67 0.17 -1.53
1909-2009 0.91 0.62 — 1.19 0.67 — 1.14

Remember this data is for only seven stations, so determining trends over shorter times inevitably faces problems of statistical significance.

However, we do have data for the 11 stations where no adjustments were required. I have plotted that below.

Remember, different stations so results will differ, but the statistical significance will be better because there are more stations. The trend here for 1960 – 2009 is 1.12°C/century. And the ranges:

0.39 – 1.86 at the 95% level; 0.51 – 1.74 at the 90% confidence level.

This means that if 20 different sets of measurements were made over that period at these stations only one trend would be outside the range 0.4 -1.9°C/century.

I know that Leyland, Treadgold and their organisations will keep pushing this meme of no warming after 1960. But they are completely wrong. The data shows otherwise.

Not that this has stopped them in the past.

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