Sensitivity and consensus; theory and practice

by Gareth on May 22, 2013

97So Cook et al1 confirms that there really is a consensus in climate science: 97% of the peer-reviewed literature over the last 20 years supports the fact that humans are responsible for the warming. It’s a solid result, confirming the earlier work of Oreskes and others, but its importance lies in the fact that public perceptions of that consensus lag behind reality. As John puts it:

Quite possibly the most important thing to communicate about climate change is that there is a 97% consensus amongst the scientific experts and scientific research that humans are causing global warming. Let’s spread the word and close the consensus gap.

Indeed. Count this as my small contribution. Meanwhile, another recent paper very nicely demonstrates that the existence of a consensus on the basic facts of warming does not mean that scientists have to agree about everything.

A letter by Otto et al in Nature Geoscience discussing estimates of transient climate sensitivity2 has been hailed as suggesting that near-term warming might be slightly less than expected. Unsurprisingly, this has been seized upon by the usual suspects as evidence we don’t need to do anything, but the paper really contains little to gladden a sceptics heart. Here’s Myles Allen (one of the authors of the paper) in the Guardian:

…at face value, our new findings mean that the changes we had previously expected between now and 2050 might take until 2065 to materialise instead. Then again, they might not: 1.8C is within our range of uncertainty; and natural variability will affect what happens in the 2050s anyway.

There’s plenty of room for debate within the climate science community about the new paper’s findings and methodology3, at the same time as there’s an overwhelming consensus about the bigger picture. That’s science in action. But transient climate sensitivity is a highly technical metric, and as Allen points out, not really very relevant to working out what to do about climate change. We have a a very good idea about the planetary carbon budget, and we know we have to cut emissions — the sooner the better.

The bigger picture — one that’s missed in technical debate, and in the communication of a fairly conservative consensus — is that our experiment in planetary geoengineering is already running out of control. The rapid loss of Arctic sea ice shows no signs of slowing down, and is well ahead of even the most aggressive model predictions. We can already detect significant impacts on northern hemisphere weather patterns.

Long before we reach CO2 doubling, the Arctic will be ice free all summer and the northern hemisphere climate will have changed beyond anything experienced in the history of humanity. Now that really is policy relevant, and it needs to be communicated with considerable force…

  1. Yes, that Cook — the one from Skeptical Science and The Climate Show. Quantifying the consensus on anthropogenic global warming in the scientific literature, John Cook et al 2013 Environ. Res. Lett. 8 024024
    doi:10.1088/1748-9326/8/2/024024 []
  2. The response of the climate system to a doubling of atmospheric CO2 over pre-industrial levels, at the time of doubling — that is, before most of the climate system has a chance to catch up. []
  3. And to judge from my emails, there’s a lot of that going on at the moment. []

{ 6 comments… read them below or add one }

John Russell May 22, 2013 at 8:17 pm

So, we might be heading for the cliff slightly slower than we thought we might be? Big deal.

Does it actually matter to lay people and politicians what the climate sensitivity actually is, if all it refers to is the speed at which we’ll arrive at a future where the environment and therefore life as we know it is severely compromised? When a range of possible outcomes has ‘not-too-bad’ at one extreme and ‘catastrophe’ at the other, it’s best to concentrate the mind on the worse end of the possibilities, however small the chance.

Thomas May 22, 2013 at 8:54 pm

Well put. Unfortunately at the dark side they are busily distilling every bit of information for crumbs like a bunch of mad chickens that they can present out of context and upside down so to speak in their desperation to ‘prove’ to themselves that AGW is not happening. As if it is (AGW happening), their entire world view and action paradigm would be an utter misfit to cope with reality.
Indeed, papers like Otto et.al or Tung & Zhou, who theorize about the AGW trend being perhaps a bit slower than commonly accepted, would only be delaying the inevitable by a short time, very short indeed, on a geological time scale.

In fact, the Tung & Zhou paper had been briefly hailed by the likes of WUWT as proving that its all not so bad… only to be hushed down rather quickly again as they realized that this paper, perhaps more clearly than any other, distilled a straight and unmitigated AGW trend out of the data after deducting all known or calculated natural oscillations and variations with absolutely no hiatus whatsoever over the last 16 years in the underlying AGW trend, which they acknowledge, in sight.

The danger is, that policy makers will take any message they can get as an excuse to leave real action on emissions reductions in the way-to-hard-basket. And the arm-chair climatologists in the denier cave will eek them on. A sorry and sordid spectacle where people prefer to defend their bewildering delusions on climate change over saving the planet and a civil society for future generations. The price some people are willing to pay for their pride….

Dave Frame May 23, 2013 at 9:59 am

“The danger is, that policy makers will take any message they can get as an excuse to leave real action on emissions reductions in the way-to-hard-basket.”

Actually it doesn’t work like that. It’s not the case that worse problem=more action and easier problem=less action. It’s more complicated than that.

In any case, the Otto paper is doing exactly what scientists should – doing research and publishing the results, irrespective of what various political tribes might make of it. [I gather it’s been an odd few days for Alex, Myles and co, given the great variety of interpretations people have read in to the piece.]

Thomas May 23, 2013 at 4:06 pm

By all means, Otto et.al. and also Tung & Zhou do exactly what science is all about and are making interesting contributions well worth while considering carefully.
And if indeed we are given a decade or so delay in temp developments that would be excellent news as we need all the extra time we can get to implement a pathway through all this.

But I reiterate my fear that any new evidence that indicates a delay in the arrival of the more serious consequences of AGW will delay or even derail action and debate at a time when action now would be far more effective and less costly than “panic button” reactions later.

Rob Painting May 23, 2013 at 6:40 pm

“I gather it’s been an odd few days for Alex, Myles and co, given the great variety of interpretations people have read in to the piece”

That very few seem to have read the paper & supplementary seems to be the common denominator of the articles I’ve read thus far.

Thomas May 23, 2013 at 7:58 am

Tropical upper atmosphere shows fingerprint of GW and correlation to models: http://www.sciencedaily.com/releases/2013/05/130522131158.htm

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