Monday, September 26, 2016

Unsettled science, and more wickedness

Gernot Wagner and Richard Zeckhauser have a new paper out. It's title is 'Confronting Deep and Persistent Climate Uncertainty' and the motto of the paper is 'Climate science is not settled.' To avoid misunderstanding, the authors are not contrarians of climate policy, quite the contrary. Their argument is supposed to boost policies aimed at decarbonization.



The paper presents the deep uncertainty that stems from the fact that climate science has not been able to give a precise number for climate sensitivity. Simply put, this is the amount of warming we would get through a doubling of CO2 concentrations in the atmosphere. This amount has been estimated to be around 3 degrees, ranging from 1.5 to 4.5 deg C.

That range has persisted almost all of the past 35 years. That consistently wide range is the first and one of the two most significant uncertainties linked to climate sensitivity. Charney et al. (1979) first established the ’likely’ range of climate sensitivity that remains in use today, despite dozens of efforts to refine it.

The problem with the wide range is the vastly different social and economic consequences. Wagner and Zeckhauser are economists and focus on economic aspects. I will have something to say from a sociological perspective later on.

First the economic argument.  Basically, the higher the temperature rise, the more costly the consequences: 'Marginal damages from rising temperatures increase rapidly.' However, to achieve a higher temperature rise will take longer, so during that  time society will grow richer. An additional problem are 'tipping points' which could occur but their timing and size which are uncertain. As the authors put it,

Perfectly constructed expected damages curves take account of tipping points. Thus, any jumps in damages get accounted for by the slope of the certainty equivalent curve. In practice, computing such a curve is exceedingly difficult to do.

The IPCC has always stuck to the 1.5-4.5 range, with one exception. Between Assessment Reports Four and Five the lower bound of the ‘likely’ range was lowered.

In particular, in 2013, the IPCC lowered the lower bound from 2°C in 2007 back down to 1.5°C, where it had been since 1979.  Superficially, this looks like unambiguous good news; part of the distribution had shifted downward. That indeed would be unambiguous good news if the distribution outside the likely range remained the same. However, this expansion of the likely region reflected greater uncertainty. 
And:

Had global warming turned out to be less severe than previously thought, say if the whole distribution or even some portion of the distribution shifted downward, what would be cause for celebration. But merely reducing the bottom value of the likely distribution in the IPCC report hardly represents such a shift. Rather, it also spreads the overall distribution. Thus, it tells us about the current capabilities of climate science—notably the current understanding of the climate sensitivity parameter—and indicates that the uncertainties are greater than we thought. That alone is disturbing, since greater variability indicates greater expected cost. The news is, thus, bittersweet, a probable reduction in the mean in exchange for greater variability. And the surprise on uncertainty is even more disturbing, since the relationship between carbon dioxide emissions and global temperatures is perhaps the most studied relationship in the climate debate. Uncertainties elsewhere may be even greater. 

The authors then refer to Knight's definition of risk and uncertainty and argue that in climate change we are dealing with uncertainty (where we do not know probabilities, unlike in risk), even with ignorance (we don't know the likely future system states): 'It is the realm of unknown unknowns. That is the realm where we are with climate sensitivity and, hence, long-run climate change projections in general.'

I find this paper remarkable for two reasons. First, it does not pretend that climate policy must be based on 'virtually certain' science. It explores the deep uncertainties that exist in our knowledge, despite the fact that climate science has established some basics about detection and attribution. Second, the deep uncertainties resemble problems in social policy that are familiar to social scientists, to policy makers, and to the public at large. The analogy I made in my Nature comment is thus worth re-examining.

Remember, my argument was that climate change resembles economic policy, health policy or education policy much more than it resembles ozone policy. Take unemployment as an example. This is seen as undesirable but there is deep uncertainty about what rates of unemployment  will have hugely undesirable consequences. Social scientists have studied historical examples (like: Hitler's rise to power was based on surging unemployment) and therefore we need to stay below a certain unemployment rate to avoid a re-run of history (a more nuanced version of this can be found in a recent paper that argued a link between financial crises and the rise of right wing parties). You could develop scenarios for other political surprises, like the outbreak of left-wing insurgency, or of a descent into chaotic anarchy.

Likewise, climate scientists use historical analogues to establish 'tipping points' (of the sort: 'the last time we saw CO2 concentrations at these levels the planet was in such and such a state...Therefore we must do something about it urgently'). These are all more or less plausible conjectures, resting on an array of assumptions (most prominently the ceteris paribus -- but has the Earth/Society not changed in important aspects since 'then'? Can we be sure it has not? Can we be sure it has?)

Wagner and Zeckhauser argue that more uncertainty calls for more prudence and I agree with them. But the problem is that many other issues than climate change compete for the attention of decision makers, and the wider public. Most burning problems of today have to do with political violence, war, poverty, ill health. Climate activists like to proclaim climate change as the greatest problem facing mankind. But how do we know, and how could we measure and compare this?

11 comments:

Marcel Crok said...

"Second, estimates of the fundamental relationships in climate change,
notably climate sensitivity, are unlikely to tighten markedly in the near-term future. Critical uncertainties will persist."

Reiner, Although I totally agree with your final conclusions, I find it depressing that (smart) scientists just totally ignore the observational estimates of climate sensitivity that have become available.
At least they could have referred to Lewis/Curry 2014, that base their estimate for 100% on the numbers of the IPCC and on the assumption that close to 100% of the warming since 1850 is due to GHGs. Still the observations indicate a best estimate of around 1.65 C and a likely range of 1.25-2.45, see https://judithcurry.com/2014/09/24/lewis-and-curry-climate-sensitivity-uncertainty/
CMIP5 models have an average climate sensitivity of 3.4 C, so double the empirical estimate.

The IPCC range in early reports was solely based on the GCM's. However, in AR5 it was based on the low values of the empirical estimates and the high values of the models (ignoring the paleo estimates for simplicity here, these are highly uncertain). They admitted this in footnote 16 in the SPM, which was the reason Lewis and I wrote our report.

As Judith Curry has shown on her blog, US government is ignoring these empirical estimates as well for their calculations of the social cost of carbon.

Marcel



Werner Krauss said...

Reiner,

you ask: "Climate activists like to proclaim climate change as the greatest problem facing mankind. But how do we know, and how could we measure and compare this?"

This is a strange question. Not only climate activists, but 192 or so presidents of states agreed in Paris that climate change is a problem of high importance that should be dealt with globally. Is that not enough? Who else has should agree? God? The angels? Donald Trump?

Anonymous said...

Wagner and Zeckhauser argue that more uncertainty calls for more prudence and I agree with them. But the problem is that many other issues than climate change compete for the attention of decision makers, and the wider public. Most burning problems of today have to do with political violence, war, poverty, ill health. Climate activists like to proclaim climate change as the greatest problem facing mankind. But how do we know, and how could we measure and compare this?

Ist das nicht eine falsche Frage? Meiner Meinung nach sollten die gar nicht konkurrieren, sondern auf ähnlicher, wie auch immer, Ebene behandelt werden, vielleicht sogar im Zusammenhang.

Sie wollten wahrscheinlich fragen: sollten die Anliegen der Fossilindustrie auf der gleichen Aufmerksamskeitsebene liegen wie die Anliegen der Umweltaktivisten? Richtig? Sie konnten das bloß nicht so richtig ausdrücken, oder? Oder kamen sie gar nicht auf diese Idee?

Naja.

Gruß,
WAIIMHN

Anonymous said...

@ Marcel Crok

I think the discrepancy between model results (+ other observational methods!) and the results using a simple energy balance model (e.g. Otto et al, Lewis/Curry) has disappeared. In short: results for ECS based on energy balance concepts have a bias towards lower values.

Kyle Armour gave a nice summary in Nature:
http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3079.html

See also Victor Venema's blog post:
http://variable-variability.blogspot.de/2016/07/climate-sensitivity-energy-balance-models.html

Andreas

Anonymous said...

PS:

So I think the next IPCC report will raise the lower end of ECS to the old range of 2 - 4,5°C.

But this should not affect the conclusions of Wagner and Zeckhausen or Reiner's points. So let's return to the main topic.

Andreas

@ReinerGrundmann said...

Marcel

I think wagner and Zeckhauser deliberately wanted to stay away from controversies about ECS so decided to use only IPCC data. Their point still applies, though: uncertainty persists.

Werner

The UN has signed many resolutions and made many aspirational statements. As Richard Tol points out, the Paris agreement obliges nations to have a climate policy, nothing specific. In practical political terms there is a competition in the political issue space, and it remains to be seen how climate change figures in this.
On the UN level I have not seen a statement that says climate change is the top priority, nor have I seen it at the national levels.

Victor Venema said...

Reiner Grundmann: "Wagner and Zeckhauser argue that more uncertainty calls for more prudence and I agree with them."

I fully agree with you. The uncertainty monster is not our friend.

Anonymous said...

That paper seems to have a very reasonable view on the situation, now how do you apply this to the debate? Where arguing is really happening, deep trenches have been dug already and the conversation resembles an artillery duel. This is due to the heated way people treat each other, sometimes caused by very questionable actions.
Additionaly there is a real imbalance of power, where one side is building up political entities (IPCC, energy policies, treaties) to force the other side but the effort and their cost could all be for naught. This very possible outcome is denied by all means.
Even the real money people have to spend for it is belittled by the "argument" these policies would be better anyways. This is increasingly shown to be nonsense and might be impossible to keep up with countries multiplying their CO2 emissions (China, India).

This (to me) inexcusable behaviour has brought up opposition of all kind, from serious and thoughtful to shrill and unrelenting. The demonization by psychology, an adoption of soviet psychological denounciation policy (lets call the opposition fools) could be the final shot that ends all opportunity to a solution.
Can the fools be stopped?
Who will enter the middle ground and put up a prudent, reasonable and independent (that is no conquered by lobbyism) Position?

@ReinerGrundmann said...

Andreas

The paper by Armour you link to is interesting. They say:

"Although the third term, doubling of atmospheric CO2, is called for in the strict definition of climate sensitivity,
the observed warming has been driven by a variety of climate forcing agents — primarily CO2, but also other GHGs such as methane, sunlight-blocking particles called aerosols, changing land use (for example the shift
from forests to farms) and more. Recently in Nature Climate Change, Marvel et al. showed that these non-CO2 forcings have distinct effects on temperatures that are not directly equivalent to CO2. These findings call for what amounts to a downward adjustment to the effective forcing on climate, and thus for an upward revision
to observational estimates of climate sensitivity and TCR — another 30% (or so) that is multiplicative with the revision by Richardson et al."

I want to emphasize the phrase "these non-CO2 forcings have distinct effects on temperatures that are not directly equivalent to CO2" but have partly driven the observed warming.

spiegelbot said...

@Reiner Grundmann

You want to emphasize that phrase because it seems to indicate that non-CO2 forcings have to be considered when contemplating mitigation?

@ReinerGrundmann said...

Andreas

in case you have not seen it, Nic Lewis wrote a rebuttal of Richardson/ Armour, see here:
https://judithcurry.com/2016/07/12/are-energy-budget-climate-sensitivity-values-biased-low/