Thursday, October 3, 2013

Helping the IPCC with decadal trend graphs

The IPCC AR5 has a new "decadal average" graph designed to hide the statistically insignificant global warming over the past 20 years. Since nobody wants to be accused of cherry-picking starting dates and using a decadal average instead of a decadal trend line, let's graph the decadal linear trends for each starting year since 1988. This paints a quite different picture than the IPCC decadal average graph, showing a clear halt in "decadal average" and "decadal trend" global warming starting at the beginning of the 21st century.

The decadal mean temperature graph 

October 1, 2013 Reblogged from The IPCC Report

Perhaps the most ridiculous graph in the IPCC AR5 SPM is this one showing “decadal mean” temperature.

A few points about this graph: 

As far as I know, such a graph has not been used in any peer reviewed publication
The graph was not in the draft version of the SPM subjected to expert review
No such graph has been used in any of the previous IPCC reports.
I’m not aware of any such graph being used in any other field of science – any examples?

So why is the graph so bad? It’s hard to see why it is necessary to point this out. Firstly, it takes a graph with about 160 data points on it, and reduces this to just 16, effectively throwing away most of the data. Secondly, the appearance of the graph depends very much on how you choose to do the 10-year cuts. They seem to have chosen either 0-9 or 1-10 bins (it’s not clear which) so that the last two or three years aren’t included at all. But if we chose 5-4 bins, the picture would probably look quite different (has anybody done this?). The introduction of this graph into AR5, with no such graph in the previous reports, leaves the IPCC open to accusations of trying to “hide the decline” in warming this decade, though of course the levelling off is clear in the graph above, so the graph seems quite pointless.

In the draft version of the SPM reviewed by scientists, this graph was not there, perhaps because the authors were aware that it might be criticised. This illustrates the point about the authors having carte blanche to insert whatever they like into the final version after the review. The decadally averaged graph was there in the main section of the report, in chapter 2, Fig 2.20 (In the final draft version, it is Fig 2.19). In my review comments, I was very critical of this graph (“Fig 2.20 – I am surprised to see this absurd figure still in the SOD. No such figure appears in the cited paper Morice et al, or in any other published paper I am aware of , or in previous IPCC reports. Such a figure would be widely and rightly ridiculed as an attempt disguise the recent slow-down of warming.”)

The IPCC responded to my criticism by putting the graph in the SPM.

I have not seen much comment on this graph. But Reiner Grundmann tweeted “Summary for policymakers dodges issue of ‘pause’ in global warming. New fig.1 makes problem invisible” and “So SPM replaced the ‘dodgy sandwich’ graph with an ‘elevator’ graph of decadal temp rise. Good PR, but is it sustainable?” on the day the SPM was published.

This type of graph seems to have originated in a Met Office press release from 2009, although the IPCC version seems to be based on this one from 2012 from the EEA.


  1. In regard to climate change scientists and governments, the problem is, those with expertise have no power, and those with power have no expertise.

    Greed will always blind, and governments are easily swayed by blind power.

    Governments are voted in by the people to govern “for” the people, not “for” big business.

    This cartoon refers;