Monday, October 4, 2010

Nothing Wrong with The Hockey Schtick Graph

I frequently get comments asking why The Hockey Schtick graph banner starts in 1998. This new post from the Global Warming Policy Foundation explains why. [their banner begins in 2001, but the points are essentially the same]  
David Whitehouse: Nothing Wrong With Our Graph
The GWPF’s graph showing that the global average annual temperature hasn’t changed this century, drawn against a nice blue backdrop, is making a few people see red. Why this is I don’t exactly know as their logic, in contrast to their anger, isn’t entirely clear. Perhaps it is because it neatly summarises the uncertainties in climate science as well as common misconceptions (as was the intention) that some commentators find too uncomfortable to address, instead becoming deniers of basic scientific data. It certainly seems a difficult fact for some, but inconvenience is one thing, facts are another.
Those who complain that the graph is wrong, if they are to be fair and consistent, should now target the Royal Society in their sights as it has admitted this in its recent brochure on the science of climate change that the recent spell of warming ended in 2000.
They are not alone.  The Journal Science has said the pause in global temperatures is real, as do many refereed scientific papers in numerous journals. Also in State of the Climate in 2008, a special supplement to the August Bulletin of the American Meteorological Society, the UK Met Office Hadley Centre, no less, confirmed that in the past ten years the HadCRUT3 temperature data (there are problems with this data set regarding its reliability and how it calculates averages but it is probably the best we’ve got) shows no increase whatsoever. Their analysis showed that the world warmed by 0.07 +/- 0.07 deg C from 1999 to 2008, not the 0.20 deg C expected by the IPCC. Corrected for the large 1998 El Nino event (that made 1998 the hottest year on record) and its sister La Nina, the last decade’s trend is perfectly flat. There were even comments in the so-called Climategate emails along the lines of the temperature not increasing and “it’s a travesty” that we can’t explain it.
Professor Phil Jones of the University of East Anglia Climatic Research Unit also holds this view, saying yes in a BBC interview in response to the question; Do you agree that from 1995 to the present there has been no statistically significant global warming.

We live in the warmest decade, no one doubts that (though possibly not as warm as it was 1000, 2000 and 3000 years ago), and this explains why the world’s warmest years are clustered during that period. Look at the order of the warmest years, however, and you will see they are jumbled up and sit well within each other’s errors of measurement. There is no upward trend, just a plateau.
The latest warm period began in 1980. This means we have had 30 years of it. It is clear from looking at the data that it is composed of two distinct periods and it is not cherry picking to identify these as they stand out in the data. There is the period 1980 – 1995 when the world warmed, and the period 1995 – 2010 when it didn’t increase its temperature. We are told, by some, that 30 years is about the minimum for statistically significant climatic data to emerge. However, at 15 years each these two periods are now of equal statistical significance. If the standstill continues then it will soon become the dominant climatic factor of the past 30 years.
It is interesting to also note that the warming between 1980 and 1990 was not in itself statistically significant. This means that it was only the 5-year warming period 1990 -1995 (before it ceased) that has made all the difference to the statistics and significance of Earth’s warming in the past 30 years!
No climate computer model predicted the recent standstill but they have been used with hindsight to explain it. It has been suggested that natural cycles, oceanic cooling and solar influences, are responsible. The Met Office Hadley Centre ran a series of computer climate predictions all of which had programmed into them the 0.20 deg C long-term IPCC trend. They found that in many of the computer runs there were decade-long standstills, but none of 15 years. If one took that 15-year figure at face value it would mean that the data already accumulated has falsified the IPCC’s basic assumptions about the rate of warming. However, bearing in mind that the proposed explanation for the hiatus was arrived at post-hoc and relies on the same computer models that failed to predict it, one should be cautious. Modelling is one thing, real-world data is another and we should never confuse the two.
So whilst a few might not like it, there is nothing wrong with the GWPF’s temperature graph. In fact, it would be scientifically justifiable to replace it with a constant straight line with data scattered around the mean (the scatter between 2009 and previous years is insignificant). The graph is a useful discussion point that illuminates some of the problems in climatic research today. It has achieved its purpose in encapsulating a basic scientific fact about climate change and in stimulating debate.

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