David Whitehouse: ‘Pause’ For Thought

  • Date: 23/09/13
  • Dr David Whitehouse

The media’s handling of the ‘pause’ in global surface temperature has been a failure for science communication and science journalism.

 

This week’s IPCC AR5 report will state that the ‘pause’ in the global land and sea surface temperature observed since 1997 is a real and unexplained phenomenon, despite the IPCC’s head Rajendra Pachauri’s puzzling denial on the BBC Today programme (no link available yet) that it even exists.

The fact is nobody predicted it, and it’s inclusion in the IPCC report is central to any assessment of the climate, where it has been and where it is going. At a stroke this takes away one of the major lines of argument against anyone who had questioned the previous orthodoxy that the global surface temperature showed a steady and predictable rise.

It has been said many times that computer models can explain the global temperature for the last 30 years – the period of the recent global warming spell. Even if that was true some years ago it is no longer. The fact that the ‘pause’ is unexplained means that the last 30 years are not reproducible in a way that is satisfactory.

Some disagree. Professor Myles Allen of Oxford University says that the forecasts made by climate scientists “have been absolutely spot on” in terms of predicting subsequent levels of global warming. The paper in question is a letter published in the journal Nature Geoscience entitled “Test of a decadal climate forecast.” The Climate Brief website said that this “new paper shows a forecast the Met Office made more than 15 years ago has been ‘remarkably accurate’ in predicting global temperature rise.” The letter compares a Met Office climate forecast made in 1999 (published in 2000) against actual temperature data up to 2012. It shows they match to within a few hundredths of a degree. Sounds very good but reserve judgment a while, because the devil is in the detail.

In 1999, scientists from the Met Office and the University of Oxford used the HadCM2 climate model to predict the global temperature increase up to 2012. They predicted that December 2002 – December 2012 would be 0.25 degrees C warmer than August 1986 – August 1996. And it is. A quick look at the Hadcrut4 data (rounded to the years end for a quick look) shows the difference is 0.27 degrees C.

But an important point that slightly takes the edge off this achievement is that the proposed increase in global temperature had already been reached before the original paper was even published! In the Hadcrut4 global annual average temperature database there has been no statistically significant increase since 1997, a fact apparent in earlier global temperature datasets. One way of looking at it is that the authors of the paper predicted an increase in global temperatures after the paper was published in 2000. There hasn’t been any increase. I suppose if they had been really confident in their figures they could have compared their prediction with the temperature at the time they wrote the paper, and predicted a lack of warming in the next decade.

In addition their starting period August 1986 – August 1996 includes the Mt Pinatubo eruption that caused global temperatures to dip. This means that their initial period is artificially low and that part (roughly 20%) of their predicted increase is actually a recovery from the Pinatubo eruption.

Even the impression that there has been a steady underlying increase in global temperatures throughout the 80s, the 90s and the 00s is falsified if you look at the data in another way, as we did last year.

Such subtleties were lost in Carbon Brief’s (“We fact-check stories about climate science”) analysis of the paper. As Dr Peter Stott, co-author of the new research, told Carbon Brief, this suggests the forecast is pretty accurate. He says: “The results show that previous projections showing substantial warming over the course of the 21st century have been borne out by observations so far this century.”

No it hasn’t, and that’s the point and significance of the ‘pause’ that the IPCC will highlight.

In addition, the ‘pause’ of the past 16 years and the rise in global surface temperature go together. Uncertainty about the cause of one is also uncertainty about the cause of the other. If the ‘pause’ is due to natural climatic variability obscuring an estimated 0.3 deg C rise in global surface temperature over the past 16 years, then the same natural climatic variability would have played a prominent role in the warming of the previous 15 years. This is what makes the IPCC’s statement that mankind is responsible for 95% of the recent climatic variability so untenable. Mankind is certainly not responsible for the ‘pause.’

Communication Breakdown

The ‘pause’ is also important because of the lessons it provides about climate communication.

Until just over a year ago, many of the more vocal climate scientists and many in the media were adamant that mentioning the warming ‘pause’ was akin to being a denier that climate change is happening, for whatever reason. This is despite the fact that the ‘pause’ was being well discussed in the peer-reviewed scientific literature. Media outlets were in the main unwilling to have anyone speak about it because it would provide ‘false balance.’

The ‘false balance’ problem maintains that in situations where an overwhelming majority of scientists believe one thing, and only a small minority are against it, then to have one representative from each camp implies a 50:50 balance which can give the wrong impression to the casual reader or listener.

I’ve always thought that the ‘false balance’ problem was a non-issue. Any good reporter can inform the audience of the background of the ‘debate’ and put the sides into context before they are heard. ‘False balance’ is also an anathema to science journalism which should be about debate and argument as well as imparting information.

Now that the ‘pause’ has made the transition from sceptical to mainstream the exclusion of it from previous debates because of the ‘false balance’ argument can be seen for what it was. It actually kept the truth from the audience. It was censorship. It’s no good saying that in the past it looked like a wrong idea. It turned out to be the right idea, and journalism – the testing of viewpoints in the cauldron of debate – misled the audience. In addition it showed that many environment reporters and commentators did not truly understand science, basic data analysis or were even familiar with what was being said in the peer-reviewed literature as opposed to press releases. For example some maintained that “the period since 1997 is not particularly special,” something that the IPCC will now disagree with.

The handling of the ‘pause’ in global surface temperature has been a failure for science communication and science journalism.

Feedback: david.whitehouse@thegwpf.org