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Recent trends in CO2 emissions

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Guest commentary by Corinne Le Quéré, Michael R. Raupach, and Joseph G. Canadell

There is a letter in Nature Geoscience this month by Manning et al (sub. reqd.) “Misrepresentation of the IPCC CO2 emission scenarios” discussing some recent statements about the growth rates of CO2 emissions compared to the IPCC scenarios that informed the climate modeling in the last IPCC report. In it they refer to results published by us and colleagues in a couple of recent papers (Raupach et al. 2007; Le Quéré et al. 2009), and to statements made by others on the basis of our results (Ganguly et al. 2009; Anderson et al. 2008; Reichstein 2010). Specifically, Manning et al object to the claim that “current CO2 emissions from fossil fuel burning were higher than the values used in climate projections by the IPCC”.

We agree with the Manning et al’s main point, and appreciate the chance to provide some clarification on the graph in question and subsequent use of our result. To be specific, recent emissions were not higher than each and every one of the climate projections by the IPCC, as has been claimed by some other studies citing our work, although they were near the top end of the range.

So what is the claim of ‘misrepresentation’ based on?
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On attribution

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How do we know what caused climate to change – or even if anything did?

This is a central question with respect to recent temperature trends, but of course it is much more general and applies to a whole range of climate changes over all time scales. Judging from comments we receive here and discussions elsewhere on the web, there is a fair amount of confusion about how this process works and what can (and cannot) be said with confidence. For instance, many people appear to (incorrectly) think that attribution is just based on a naive correlation of the global mean temperature, or that it is impossible to do unless a change is ‘unprecedented’ or that the answers are based on our lack of imagination about other causes.

In fact the process is more sophisticated than these misconceptions imply and I’ll go over the main issues below. But the executive summary is this:

  • You can’t do attribution based only on statistics
  • Attribution has nothing to do with something being “unprecedented”
  • You always need a model of some sort
  • The more distinct the fingerprint of a particular cause is, the easier it is to detect

Note that it helps enormously to think about attribution in contexts that don’t have anything to do with anthropogenic causes. For some reason that allows people to think a little bit more clearly about the problem.
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Claude Allègre: The Climate Imposter

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Guest Commentary by Georg Hoffmann

In mathematical proofs, it’s a well-known fact that if at some point you divide by zero accidentally or on purpose, then you end up being able to prove absolutely anything you want – for instance, that 2+2=5 or that 1+1=0. The same phenomena appears to govern any number of publications that conclude that climate science is all a fraud – at some point, an impossible calculation is performed and from then on, anything (and everything) can be proven. Critical thinking appears to vanish.

The latest example is that of Claude Allègre – whose recent book “The climate imposture” would have you believe at least six impossible things before breakfast and a great many more before dinner. This is notable because Allègre is one of the most eminent figures in science communication in France, Academie de Sciences member, Crafoord prize winner, former minister of education and research and a fixture on the late night talk shows in France (including a topical satirical version of the ‘muppets’). One might expect a certain degree of rigour from an author with such a pedigree, but on the contrary, nearly every explanation, graphic, or citation in this book is misleading or just plain wrong. If Allègre was not such a high profile figure in France, this nonsense would have been dismissed and ignored, instead, it is regular fodder for the late night talk shows. In my entire career I have never seen so many factual errors in a single publication. It is truly a remarkable work!
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