March 7, 2014, by Warren Pearce
What does climate sensitivity mean? Peace for our time…or the wrong battle?
Rose and Peace, Andreas Perhab
A very quick post on this week’s big news in the climate blogosphere: a new report on climate sensitivity, Oversensitive, written by Nicholas Lewis and Marcel Crok published by the Global Warming Policy Foundation (GWPF). The GWPF’s role is discussed in a new Klimazwiebel post by my colleague, Reiner Grundmann, while Ed Hawkins’s Climate Lab Book blog hosts an illuminating and vibrant discussion of the science, both in Piers Forster’s main post, and below the line where commenters from many perspectives debate the methods and data involved. Here, I will look at the idea that the Lewis and Crok report marks a watershed moment in
A convergence of views?
A report by Matt McGrath for the BBC captures the flavour of some social media chatter on the report, noting that while Crok and Lewis’s estimate for climate sensitivity is certainly towards the lower end of the IPCC range, it still predicts a total of 2.9C warming by 2100 compared to pre-industrial levels, if we stay on our current emissions trajectory (we have already experienced 0.8C of the 2.9C total). So, McGrath points out, maybe the views of some climate sceptics actually fall within the range of possible sensitivity values posited by the IPCC, albeit at the low end.
This should not be a surprise. As I wrote last July, high profile sceptics such as Anthony Watts and Andrew Montford:
agree with the mainstream view that the greenhouse effect brings about atmospheric warming as a result of carbon emissions, but dispute levels of climate sensitivity.
The report by Crok and Lewis helps to present this sceptic position in a more coherent form than the constant whirl of blogosphere debate. However, will it really help to take the ‘war out of global warming’, as Matt McGrath snappily proposes? McGrath’s report ends with a quote from Ed Hawkins:
If we broadly agree on this [that there will be significant future warming], the debate can crucially move on to what action is needed to deal with a warming planet
Sounds plausible, but I would argue it is unlikely. The quote pithily captures a persistent misnomer in the climate debate. It assumes that there is a linear model for deciding policy: first we agree the science, then we determine the policy. If one complains that the science has not been agreed up to now, how did the UK come to pass the Climate Change Act in 2008? The Act, for all its faults, did signify a basic acceptance of the fundamental physics behind the greenhouse effect, and the risks and uncertainties around its impacts. To assume that this still a live question, other than amongst a very limited number of authors, is a mistake.
So why the continuing debate, or ‘war’ as many portray it? Because in political terms, such a consensus about physics is akin to a ‘consensus without an object’. More precisely, the meaning of any agreement on climate sensitivity remains contested. If society is accustomed to the 0.8C we have already had, what will an extra 2.1C mean? Attempts to answer this question using socio-economic and ecological modelling are fraught with uncertainties. If, as is often argued, climate models are more testable and robust than economic models, this is not necessarily good news for supporters of stronger climate policies. It merely highlights how determining the meaning of future climate change, and the politics and policies which grow out of such meaning, is open to continuing debate. Indeed, while climate sensitivity remains uncertain one might reasonably assume that the uncertainties in projecting the impacts of warming are even greater. Not to mention the significant geographical disparities in impacts, which risk being sidelined by debates revolving around a single number for global temperature change.
So, where does this leave us? As is often the case in climate change…much in the same place as before, alas. A broad, if slightly ragged, agreement on a range of climate sensitivity which, while of interest within the physical sciences, does not significantly add understanding to the policy debate. We should not treat climate science as a computer game, where we complete levels by obtaining certainty in various facts, in order to reach the ‘boss level’ of good climate policy. Rather, accept that uncertainties will always exist – not just in various types of modelling, but in the meaning of those models – and continue to consider the best courses of action to chart in the light of persistent uncertainties and ambiguity.
As Daniel Sarewitz wrote ten years ago:
The technical debate – and the implicit promise that “more research” will tell us what to do – vitiates the will to act. Not only does the value dispute remain unresolved, but the underlying problem remains unaddressed… Yet one question remains: what, then, becomes of science? One part of the answer is: nothing, it is still there, in the background, along with all the other influences on people’s political interests and behavior. But the other part of the answer is that science is liberated to serve society and the environment…
It’s hard and frustrating, of course, to realise the limitations of scientific enquiry in supporting the hard business of political action. But it remains as necessary as ever. One should not expect the apparent solving of one scientific puzzle or another to make the political debate any more peaceful.
Simply put, the paper is yet another pseudo-scientific contribution to the political debate over what to do, intended only to retard progress. Been there, done that, got the T-shirt, why so much explication?
FYI TCR and ECS are quantities that can never exist in the real world, and are useful only as model benchmarks. Even using them to e.g. project GMST for 2100 isn’t valid given the necessity of assuming that fast feedbacks won’t have a major impact by then even though some of them have already been observed to be kicking in. Earth system sensitivity (ESS) is the only such quantity with any hope of being grounded in the real world, and even it isn’t directly relevant to the near future given that it still describes an equilibrium state requiring several centuries of level CO2 to come into being. Note that it’s not even possible to attempt to calculate the real-world transient earth system response (a term I think I just made up; hopefully the meaning is clear) using GCMs. Some work has been done using simpler models, and it’s scary stuff. (See Kevin Anderson and Jim Hansen on this general subject.) Note that the likes of Lewis and Crok do not go there, preferring instead to advance a debate that is in essence fake. Or, to sum up such distracting efforts in the form of a question, are you familiar with three-card monte?
[…] phrase which seems to indicate a shift in the climate change debate. Related to this, the issue of climate sensitivity was discussed in one of Warren’s posts. A paper in PLOS ONE by Warren, myself and two colleagues […]
Pure pessimistic speculation by Steve Bloom! The fact is that the warming of the Earth halted while CO2 emissions are at their supposed highest ever having increased from 300ppm to 400ppm. The scientists don’t know why the inescapable conclusion is that they underestimated natures contribution to the warming in the first place. Data always trumps models but people like Hansen and Bloom want to believe the opposite – apparently based on mere pessimistic gut feelings.
Progress may be Steve Blooms definition of climate policy but in reality it is regression because we are aiming to replace reliable, cheap energy with unreliable expensive and inadequate energy. For the population at large that will mean fuel poverty leading to excess deaths and economic ruin. We need less hypocritical, sanctimonious, name-calling and more realisation of reality; renewables are simply not ready to replace fossil fuels and that is why there is no progress, only regress. The cure is obviously far worse for humanity than the putative disease.