Show Warming After it Has Stopped Part 2

Last week I posted how Miles Allen had pulled off a trick to show warming in the 21st century after that trend had stopped in 1998. According to David Middleton at Watts up with That, the BBC’s Richard Black is using a similar decadal comparison to show that warming has continued. There are two Richard Black’s claim that the GWPF are cherry-picking the data. First, that an employee of the UK state broadcaster should choose to use a foreign temperature record over the UK one. Second, why the switch to decadal comparisons, when the IPCC has long used the norm.

Let me break this down with two graphs. Like with the previous posting, I see no scientific reason to necessitate why the starting point for the earth’s orbit of the sun has to be on 1st January. I therefore include all 12 month moving averages. That is Jan-Dec, Feb-Jan, Mar-Feb etc. I have also included three lines on my analysis. First the NASA GISSTEMP; second the HADCRUT3 and third the difference between the two.

The first graph shows the decadal change in the NASA GISS figures that Richard Black is talking about. Sure enough the only period where the 12 month average temperature anomaly is lower than a decade before is in 2008. Using the HADCRUT3 data reveals a similar pattern, but the negative period is much longer. If The HADCRUT3 decadal change is subtracted from the GISSTEMP, there is shown to be a greater decadal warming trend in the NASA than in the UK figures. This might suggest the reason for Richard Black’s preference for foreign data over that paid for by the UK taxpayer’s.

The second graph shows the 12 month moving average data – and clearly shows the reasons for both using decadal temperature changes over annual, and foreign data over British. From 1988 to 1997, there was no real warming trend if the Pinatubo cooling is removed from 1995. However the NASA anomaly seems to be around twice as volatile is the Hadley. But in 1998 the position reverses. The natural 1998 El Nino effect is twice according to the British scientists, as it is to Dr Hansen and his team. Post 1998 the story diverges. According to NASA, the warming resumes on an upward trend. According to the Hadley scientists, the 1998 El Nino causes a step change in average temperatures and the warming stops. As a result the NASA GISS warming trend is mirrored by its divergence from the more established and sober British series.

Showing Warming after it has Stopped

Bishop Hill points to an article by Miles Allen that

“examines how predictions he made in 2000 compare to outturn. The match between prediction and outturn is striking…..”

Bishop Hill points out that this using HADCRUT decadal data. Maybe a quick examination of the figures will reveal something? Using the HADCRUT3 data here is are the data for the last five decade.

This shows that the decadal rate of warming has been rising at a pretty constant rate for the last three decades. So all those sceptics who claim that global warming has stopped must have got it wrong then?

Let us examine the data a bit more closely.

The blue line is the Hadcrut annual anomaly figures from 1965 to 2010. The smoother red line is the 10 year average anomaly, starting with the 1956-1965 average and finishing with the 2001-2010 average. The decadal averages are highlighted by the red triangles.

The blue would indicate to me that there was a warming trend from 1976 to 1998, since then it has stopped. This is borne out by the 10 year moving average, but (due to the averaging) the plateau arrives five years later. But the story from the decadal figures is different, simply due to timing.

So what scientific basis is there for using the decadal average? Annual data seems reasonable, at it is the time for the earth make one rotation around the sun. But the calendar is fixed where it is because 1500 years ago Dionysius Exiguus devised a calendar with a mistaken estimate of the birth (or conception) of Jesus Christ as Year 1, and we have number base 10 possibly to the number of fingers we have. Both are a human artefact. Further, the data is actually held in months, so it is only due to the Christian calendar that we go from January to December. This means of the 120 possible periods for decadal averages, Myles Allen shows a cultural prejudice, and in choosing decadal averages, he shows a very human bias, over real world selectivity.

How does this affect the analysis of the performance of the models? The global temperature averages showed a sharp uptick in 1998. Therefore, if the models simply predicted a continuation of the trend of the previous twenty years, they would have been quite accurate. The fact was the prediction was higher than the outturn, so the models overestimated. It is only by exploiting the arbitrary construct of decadal data that the difference appears insignificant. Drop to 5 years moving average, and you will get a bigger divergence. Wait a couple of years, and you will get a bigger divergence. Use annual figures and you will get a bigger divergence. The result is not robust.