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Hide The Decline

September 29, 2013
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By Paul Homewood

 

In an attempt to downplay the recent halt in global warming, the IPCC have claimed in their Summary for Policymakers that:

 

As one example, the rate of warming over the past 15 years (1998–2012; 0.05  °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 °C per  decade.)

  

Simply translated, this means that warming has slowed down to just under half what it was before. This message has been quickly picked up by the media, which, of course, was the main intention.

The dreadful Geoffrey Lean comments in the Telegraph:

 

The IPCC did, however, address a much more substantial sceptical point, that the temperature increase at the Earth’s surface has slowed down since 1998 to about 40 per cent of its average rate since 1951 – something it accepts it didn’t predict. One reason is that 1998, the year invariably chosen by sceptics, was one of the warmest ever.

   

So, at a stroke, the “pause” has become a “slowdown, but still significant” in the public’s eyes. But look deeper, and you will see this is a piece of devious trickery.

 

Is 1998 the best place to start?

First, let’s get rid of the 1998 red herring. The implication is that you can only get this “slowdown” by picking 1998 as the start year. The reality is that temperatures have been flat since 2001, which was a neutral ENSO year, and therefore comparable to this year. The Wood For Trees graph below shows this well.

Figure 1

http://www.woodfortrees.org/plot/hadcrut4gl/from:2001/to:2013/trend/plot/hadcrut4gl/from:2001/to:2013

 

They could also have mentioned that RSS satellite data actually shows a drop in temperature since 1998, not the small (and statistically insignificant) amount shown by HADCRUT4.

 

 

Figure 2

http://www.woodfortrees.org/plot/rss/from:1998/to:2013/trend/plot/rss/from:1998/to:2013

 

Longer term trends

But much more important than this attempt to deflect attention form the pause, is the way the IPCC have totally misrepresented the longer term trends. Figure 3 shows HADCRUT4 numbers going back to 1941.

 

Figure 3

http://www.woodfortrees.org/plot/hadcrut4gl/from:1941/to:1979/trend/plot/hadcrut4gl/from:1941/to:2013/plot/hadcrut4gl/from:1979/to:2001/trend/plot/hadcrut4gl/from:2001/to:2013/trend

 

Spot what they have done? Their base period of 1951-2013, against which they have measured post 1998 trends, includes:-

  1. 28 years of cooling – 1951-79
  2. 22 years of warming – 1979-2001
  3. 12 years of cooling again – 2001-2013

So, in total, during 40 out of the 62 years there has been a cooling trend. They are comparing a statistically insignificant amount of warming since 1998, with three decades of cooling. The result is to make this small trend sound much more significant than it is.

It would surely have been more honest to have compared the post 1998 trend with the 1979-98 period. If they had have done this, of course, most people would realised that the much trumpeted global warming really had stopped for the time being. And, in the IPCC’s eyes, that was not the message they wanted people to hear.

By this dodgy use of statistics and the 1998 red herring, they have also tried to distract attention from the clear fact that temperatures really have flatlined since 2001.

 

How temporary is the “temporary pause”?

It is commonly argued that a short pause in warming, of a decade or so, is not unexpected, amidst all the natural variability.. Back in 2010, the UK Met Office commented:

 

Recent Met Office research investigated how often decades with a stable or even negative warming trend appeared in computer-modelled climate change simulations.

Jeff Knight, lead author on the research, says: “We found one in every eight decades has near-zero or negative global temperature trends in simulations. Given that we have seen fairly consistent warming since the 1970s, the odds of one in eight suggest the observed slowdown was due to happen.”

 

But, if you go back to 1941, you have actually got 50 years of near zero or negative trends, and only 22 years of warming.

So which is the norm, and which is the rarity?

 

Footnote

It appears that the IPCC’s Thomas Stocker now claims that climatic trends should not be considered in periods of less than 30 years.

I don’t remember the IPCC suggesting that after just a decade of warming, when they wrote their first report.

8 Comments
  1. September 29, 2013 8:19 pm

    A blast from the past 10 year predictive forecast by Met Office (useful for policymakers…)
    http://web.archive.org/web/20080708230357/http://www.metoffice.gov.uk/corporate/pressoffice/2007/pr20070810.html

    next year is supposed to be 0.3C hotter than 2004 — oops..

    Met Office – 10 August 2007
    The forecast for 2014…

    Climate scientists at the Met Office Hadley Centre will unveil the first decadal climate prediction model in a paper published on 10 August 2007 in the journal Science. The paper includes the Met Office’s prediction for annual global temperature to 2014.

    Over the 10-year period as a whole, climate continues to warm and 2014 is likely to be 0.3 °C warmer than 2004. At least half of the years after 2009 are predicted to exceed the warmest year currently on record

    These predictions are very relevant to businesses and policy-makers who will be able to respond to short-term climate change when making decisions today. The next decade is within many people’s understanding and brings home the reality of a changing climate.

    The new model incorporates the effects of sea surface temperatures as well as other factors such as man-made emissions of greenhouse gases, projected changes in the sun’s output and the effects of previous volcanic eruptions — the first time internal and external variability have both been predicted.

    Team leader, Dr Doug Smith said: “Occurrences of El Nino, for example, have a significant effect on shorter-term predictions. By including such internal variability, we have shown a substantial improvement in predictions of surface temperature.” Dr Smith continues: “Observed relative cooling in the Southern Ocean and tropical Pacific over the last couple of years was correctly predicted by the new system, giving us greater confidence in the model’s performance”.

    Notes
    ◾Total global warming, on a decadal average, is 0.8 °C since 1900 (IPCC 2007)
    ◾1998 is the current warmest year on record with a global mean temperature of 14.54 °C

  2. September 29, 2013 8:45 pm

    Reblogged this on CraigM350.

  3. Michael Pooley permalink
    September 30, 2013 5:40 pm

    Are they deleting their past forecasts? neither of those links work anymore.

    • September 30, 2013 9:36 pm

      Just scan down to the bottom of the page.

      I don’t know if the Met have deliberately hidden the link. I suspect it is still in their archive somewhere.

      They sent me details of their 2007 decadal forecast when I asked under FOI, but fortunately we still have Wayback!

  4. catweazle666 permalink
    September 30, 2013 10:02 pm

    Hi Paul, with regard to your Fig 3 WtF plot, here’s my take on the whole HadCRUT4 dataset back to 1850.

    http://www.woodfortrees.org/plot/hadcrut4gl/from:1850/trend/plot/hadcrut4gl/from:1910/to:1940/trend/plot/hadcrut4gl/from:2001/trend/offset:-0.1/plot/hadcrut4gl/from:1860/to:1880/trend/plot/hadcrut4gl/from:1970/to:2000/trend/plot/hadcrut4gl/from:1880/to:1910/trend/plot/hadcrut4gl/from:1940/to:1970/trend/plot/hadcrut4gl/from:1850/to:1860/trend/plot/hadcrut4gl/mean:120

    It appears to show evidence of a clear ~60 year cycle which correlates quite nicely with the AMO, with an increase between 1850 and 2013 of 0.763838°C and a steady background trend of 0.466941°C per decade.

    Particularly striking is the similarity of the trend lines 1910-1940 and 1970-2000.

    On the superceded pre- “homogenisation” HadCRUT3 dataset, the similarity is even more marked.

    http://www.woodfortrees.org/plot/hadcrut3vgl/from:1850/trend/plot/hadcrut3vgl/from:1910/to:1940/trend/plot/hadcrut3vgl/from:2001/trend/offset:-0.1/plot/hadcrut3vgl/from:1860/to:1880/trend/plot/hadcrut3vgl/from:1970/to:2000/trend/plot/hadcrut3vgl/from:1880/to:1910/trend/plot/hadcrut3vgl/from:1940/to:1970/trend/plot/hadcrut3vgl/from:1850/to:1860/trend/plot/hadcrut3vgl/mean:120

    • catweazle666 permalink
      September 30, 2013 10:04 pm

      Oops, that should be 0.0466941°C per decade for HadCRUT4 1850-2013!

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