Tuesday, January 09, 2007

Baer on Stern

Paul Baer posted his Comment on the Stern Review on Post-NormalTimes some time ago. I tried commenting but it seemed to vanish in the spam-trap, so I'll comment a little more substantively here instead.

Like many, Paul rejects the Stern Review. However, in his case, it's because he thinks Stern doesn't go far enough. It's a lengthy article which I recommend you to read and make up your own minds over, but I think I've got the essence of it here:
  1. Melting the Greenland Ice Sheet would be a "catastrophe"
  2. Catastrophes are things that we must do everything possible to avoid
  3. 550ppm CO2 leaves open a significant probability that the GIS would melt
  4. Therefore, we must reject 550ppm as a target
In a break from tradition, I'm not even going to complain about his climate sensitivity estimates, as although he does take some of the high climate sensitivity estimates rather more seriously than they deserve, that probably doesn't qualitatively refute his argument. Even with a sensible sensitivity of 2.5C, 550ppm CO2 could result in a large-scale melting of the GIS (based on my understanding of what people think). Of course this is likely to be a glacially slow process. but I don't deny it could happen in the long term.

My complaint is rather that he doesn't define "catastrophe" anywhere (except implicitly as "something we must avoid at all cost"), and therefore doesn't actually go to the trouble of justifying including GIS melt in this category. Nor does he attempt the difficult but necessary step from the idealistic but unrealistic "avoid at all costs" to any analysis of how feasible it is, and what the costs and benefits actually might be. As a result, the whole essay seems to be lengthy illustration of the logical fallacy known as "begging the question".

On a related issue, I was looking through the BBC news pages on Stern, and found these clangers in their summary:
  • If no action is taken on emissions, there is more than a 75% chance of global temperatures rising between two and three degrees Celsius over the next 50 years
  • There is a 50% chance that average global temperatures could rise by five degrees Celsius
I don't have any idea where they might have got this nonsense from, I'm sure it is not in Stern's summary of climate science, exaggerated as that is. I don't believe there is a single active climate scientist who would defend either of these statements, even if the second is interpreted as meaning by 2100 rather than the implied 2050.

From the same page, I also don't believe:
  • Crop yields will decline, particularly in Africa
and would be willing to bet against it. That is, I expect crop yields to increase for decades into the future, as they have done in the past (eg random google).

And more subtly, the alert reader will note in the following:
  • Extreme weather could reduce global gross domestic product (GDP) by up to 1%
  • A two to three degrees Celsius rise in temperatures could reduce global economic output by 3%
  • If temperatures rise by five degrees Celsius, up to 10% of global output could be lost. The poorest countries would lose more than 10% of their output
  • In the worst case scenario global consumption per head would fall 20%
  • To stabilise at manageable levels, emissions would need to stabilise in the next 20 years and fall between 1% and 3% after that. This would cost 1% of GDP
that all of the climate-related "losses" and "costs" are presented as the upper end of their uncertainty ranges, whereas the cost of mitigation is a wonderfully confident and precise "this would cost 1%" even though Stern's estimate of the cost of stabilisation is right at the bottom end of all published estimate (even John Quiggin struggles to defend it here: "a range of costs for a 60 per cent reduction in emissions of between 1.8 and 4.2 per cent, with a midpoint of 3 per cent, which is in the upper part of the Stern range").

Uncertainty is a wonderfully versatile thing in the right hands :-)

Well JQ thinks my quotation of him is "tendentious, to put it mildly". So you'd better go and read his whole post and see for yourselves how much of a ringing endorsement he provides. It's not really central to the point I was making on the selective treatment of uncertainty though.


Ronin Geographer said...

I'm sorting out technical glitches on the PNT - as soon as these are resolved, your comment should show up. In the meantime, I think Paul's main point is not that we should adopt the "idealistic but unrealistic" goal of avoiding the melting of the GIS at whatever the cost, but that we have not even begun to consider the actual implications and what it would actually cost so that we can debate trade-offs among realistic choices. That was also the main point of the classic paper he referenced, on "The Worth of a Songbird."

Ronin Geographer said...

I'm sorting out technical glitches on the PNT - as soon as these are resolved, your comment should show up. In the meantime, I think Paul's main point is not that we should adopt the "idealistic but unrealistic" goal of avoiding the melting of the GIS at whatever the cost, but that we have not even begun to consider the actual implications and what it would actually cost so that we can debate trade-offs among realistic choices. That was also the main point of the classic paper he referenced, on "The Worth of a Songbird."

William M. Connolley said...

Bad news for Stern: "Under a BAU scenario, the stock of greenhouse gases could more than treble by the end of the century, giving at least a 50% risk of exceeding 5°C global average temperature change during the following decades."

Thats from the exec summary. You were too kind... I'm not sure where this comes from, though. Stern is very poor at sourcing stuff.

James Annan said...


Well the tripling is what you get with A2 (770ppm CO2, probably more as CO2e) plus 100ppm of carbon cycle feedback, and then 3C sensitivity gets you to about 5C (at equilibrium, not at 2100!). So not entirely crazy, but a bit of fantasy. 550ppm CO2e by 2035, which he also mentions, is more far-fetched - that is 4.5ppm CO2e per year from here on, and there is (as you have illustrated) precious little sign of any acceleration at all in CO2, let alone that level (and methane isn't going up at all)!

Of course the journalists all take this "at equilibrium" stuff back to the date at which the CO2 level hits the mark. But it seems he did explicitly claim that "On current trends, average global temperatures will rise by 2 - 3°C within the next fifty years or so" which is definitely wrong.

William M. Connolley said...

Why is 550 Co2e by 2035 so hard? We're at 450 now (aren't we?) so thats only 3.3 CO2e per year, which is perhaps possible

James Annan said...

Stern uses a present-day value of 430ppm CO2e, so 550ppm in 2035 requires just over 4ppm per year (average) over the next 29 years (I think I used 27 by mistake to get 4.5ppm above). Currently the increase is barely over 2ppm CO2, with methane if anything dropping. With methane already being so far behind A2, It would require an astonishing acceleration to catch up the lost ground so quickly.

Anonymous said...

Hi James - thanks for linking to my essay on the Stern Review. I think, however, that you misunderstood what I was trying to do. Your attempt to summarize my argument is not far from what I actually believe, but it was not the main argument in this essay; rather I was attempting the much more limited task of showing why Stern’s argument that economic analysis rules out stabilization targets of 450 ppm or lower is not robust. As I stated in my conclusion, “An analysis of Stern's approach can show that its conclusions aren't compelling, but the positive case for a truly precautionary policy must stand on other grounds.”

I do think that there is a more than prima facie case that three meters or more of sea-level rise, even over centuries, would reasonably count as a “catastrophe.” More importantly in this context, however, the Stern Review (or more precisely, the PAGE2002 model it uses) has a category of monetized “catastrophic impacts,” and there is little doubt that the melting of the GIS is among the impacts which are intended by Stern to be included in this category. For example, on p. 151, he writes “Further, Chapter 1 detailed emerging evidence of risks that higher temperatures will trigger massive system ‘surprises’, such as the melting and collapse of ice sheets and sudden shifts in regional weather patterns like the monsoons. Thus there is a danger that feedbacks could generate abrupt and large-scale changes in the climate and still further losses. Existing IAMs largely omit these system-change effects; including them is likely to increase cost estimates significantly.”

Given this assumption, the rest of my argument really boils down to this:
1) To argue that cost benefit analysis shows that any specific stabilization target is not economically justified requires establishing the plausible upper bound on damages associated with stabilization at that level (technically we’re concerned with marginal damages, but the basic argument is the same).
2) Given “significant” probability that triggering of the melting of the GIS may begin as low as 2ºC (a reasonable interpretation of the “flaming arrow” and the research on which it is based), it is not credible that there is effectively zero probability of measurable “catastrophic” impacts up to 3ºC.
3) Since the monetization of catastrophic impacts is demonstrably not robust, the upper bound on the costs of climate change has not been established, and therefore the claim that stabilization at or below 450 ppm is not economically warranted has not been adequately supported.

Note that this does not prove - because I did not try to prove - either that stabilization at 450 is economically warranted, or that it is warranted on other grounds, and thus I don’t think I have “begged the question.” I simply meant to show that those who would choose to justify their policy preferences on the basis that “Stern has shown that 450 ppm is not economically efficient” are, to put it bluntly, wrong. He has not shown this.

I do gesture at, but do not explore in detail, what an argument in favor of the 2ºC target would look like, including but not limited to reducing the risk of melting the GIS. I would not ever argue that such a goal should be achieved “at all costs,” and the suggestion that I (or others) do so is a bit of a straw-man argument. To restate my broadest point, however, the “worth of an ice sheet” is something we choose, not something that can be measured or predicted. Economic theory incorporates this as the “willingness to pay” to prevent some undesired impact; my argument (which Sylvia noted) is that we can’t know what we might (or should) be willing to pay to prevent such impacts unless and until we’ve had a much broader-based discussion of the values that are at risk.


GMB said...


What you have done Paul, is reverse the precautionary princople. We have been for 39 million in an ice age. Things have been getting steadily cooler during that time but took a very severe downturn when North and South America fused about three and a half million years ago.

And you reckon the precautionary lies in trying to PREVENT ice being melted off?

I just cannot wait to see what you guys come up with next. I don't see how you can POSSIBLY top this gigantic campaign of Wrong-Way Corriganism though.

Getting people famously worried about catastrophic warming on a planet with a one-way bias towards catastrophic cooling.

This is just bizzare. One can imagine something like this happening in some isolated medieval village with all of these toothless yokels freaking out about something or other.

But to get billions of people losing their heads and charging in the wrong direction. Well you guys must be very proud of yourselves.

The alarmists powers of persuasion must be just uncanny. But it would be less harmful if this mass hypnosis were being used on farm animals and as a sort of party trick.

John Quiggin said...

I think your quotation from me is a bit tendentious. The very next para reads "One part of this discrepancy can be resolved easily. The Stern report estimates the fossil fuel component of GDP at 3-4 per cent. Using a value of 3 per cent would halve my estimated range to between 0.9 per cent and 2.1 per cent." and my conclusion is "Overall, my assessment is that Stern’s central estimate, a cost of 1 per cent of GDP, is in the right ballpark. Stern is probably a bit on the optimistic side, but not wildly so."

James Annan said...


Well I did put a link for people to read it themselves :-) While you may have explained the origin of (part of) the discrepancy, that's not the same thing as agreeing with Stern - and indeed the bit you've just quoted makes it seem like you explicitly agree with my point that not only is Stern's 1% on the low side, but also presented in unreasonably confident terms in that BBC piece.

James Annan said...


Thanks for the comment. I'm still a bit unsure of the logic. I mean, if the worth of an ice sheet is simply something you choose for personal reasons rather than due to economic impact, then of course you can get any answer you want just by choosing a different number. I also don't see how you can honestly talk about this being a "catastrophe" when the loss is essentially an aesthetic one.

GMB said...

Ocean ice is really no problem.

But if there is a large sheet of ice on land in far Northern Europe, or in North America...... then this large sheet of ice on the land represents a standing threat to subsequent generations of humans and of the natural world.

And the very best we can hope for is that industrial CO2 will melt more ice then might otherwise have been melted.

We want to be in with a head start when conditions are such that the wall of white death starts moving forward, smashing all before it.

Hank Roberts said...

Paul writes: "... three meters or more of sea-level rise, even over centuries, would reasonably count as a 'catastrophe.'"

James writes: "this loss is essentially an aesthetic one."

Do you agree it's technically a catastrophe, a one-way change that's not reversible by backing up?


-- Hank Roberts

James Annan said...


It's quite clear that Stern/Paul's use of the term is not related to the mathematical definition, but rather the common English one. And given that the time scale of the melting is rather slower than the time scale of the forcing change it's not clear that it is really a useful concept. It's not suddenly going to snap into a new state. Paul's argument (which I may have misunderstood) seems to be that the "cost" of this cannot be primarily measured in economic terms but is instead a personal judgement about how much we like ice sheets (and our current coastlines, presumably).

C W Magee said...

Can't we just melt West Antarctica under instrumentation, to determine the kinematics and refine the models for a possible greenland melt?

Anonymous said...

I agree that slow a climate change is not a catastrophe and we can and should adapt to it. but, ...

> Crop yields will decline, particularly in Africa

I think that THIS is likely -- a very unfortunate thing.

There are two very distinct issues are there.

One is my outlook of climate change. It is difficult to predict future distribution of aridity. But it is almost certain that local, short-term precipitation can increase in proportional to saturation specific humidity that is exponential in temperature, and that global mean precipitation does not increase so much because it must almost match global mean evaporation which is limited by energy balance at the surface where the input will increase more or less like log(CO2 conc.). Thus it is almost sure that precipitation tend to concentrate spatially and temporally. In some places there will be excess of precipitation which may lead to floods. Elsewhere precipitation does not increase to match evaporation locally and the land would be more arid.

The other thing is the capacity of agriculture. The increase of crop yield in the 20th century owe much to fossil fuel: chemical fertilizers, pesticides, machines (e.g. tractors), large-scale irrigation, etc. They do not logically depend on fossil fuel -- just on low-entropy energy resources. But practically we cannot immediately substitute them with renewable resources only (or even with nuclear power, for that matter). We cannot assume either that the future generations will magically find some novel low-entropy resources that we cannot access now.

After all, we cannot simply assume that future generations are richer, or more adaptable. The world will be outside the realm of experience of the age of fossil fuel. (I think this discussion should move to "globalchange" forum.)

James Annan said...

(I think this discussion should move to "globalchange" forum.)


Paul Baer said...

Hi James - I’ve been puzzling a bit about how to respond to your line of questions. A few points come to mind:

First, I want to be clear that in the context of the argument that I was making in my essay, all I needed to establish is that it is implausible that the economic impact of melting the Greenland ice sheet is effectively zero at a three degree global temperature increase. The possibility for substantial loss of both life and property seems to me to be significant. Again, whether you choose to call this catastrophic or not, it is clearly among the types of impacts Stern intended to include in that category; for the whole category to have zero economic risk past a 3ºC increase is even more implausible. Thus, to repeat my point, Stern hasn’t put an upper bound on the absolute or marginal costs of impacts, and thus his lower bound on stabilization targets is unsupported.

Secondly, I believe that the value associated with (for exmaple) preserving our coastlines is ethical and not merely aesthetic. I believe the same about species. I believe that it would be a moral catastrophe for 25% of species to go extinct even if there were no impact whatever on GNP from its happening. Whether one uses the word “catastrophe” is irrelevant; what matters, as you well note, is what you are prepared to give up in order to prevent it. I think that people who are already rich should be willing to pay quite a lot to reduce the multiple risks of impacts that grow as temperature rises towards and past 2ºC. (Frankly I believe that they should be required to do so; my own opinion is that it follows fairly straightforwardly from a reasonable, quasi-Rawlsian perspective on risk aversion.)

You may actually disagree that melting the greenland ice-sheet has any economic consequence. However, within the economic theory Stern embraces, our willingness to pay to preserve our coastlines or our species– whether for aesthetic, ethical or other reasons – is an economic quantity that is precisely commensurable with (for example) the dollar values of GNP; thus those “personal reasons” are in fact “economic impact.”

It’s a bit much to get into here, but I think that what this really shows is that the category “economic impact” is a bit of a metaphysical bugaboo. It is a point of pride of economics that the thing that’s measured in economic analysis is something that exists in the world, in the same metaphysical class as temperature or pressure, which gives economics its pretension of scientific objectivity. Yet (and this was one of Marx’s key insights) what appears as the economic value of an object is actually an emergent property of a complex set of social relationships, in which ideas about rights and justice are inextricably intertwined.

The example is simple and general: the economic value of an “externality” like the impacts from climate change is inextricable from our assumptions about whether one has a moral right to be protected from antropogenic climate change, and the institutions that exist or are created to protect and enforce any such rights. This is just to stress the point that we decide what the economic value is of all possible climate impacts; again, choice is prior to measurement. And it isn’t a narrowly personal decision; such decisions are made by individuals in the context of (to return to my theme) a very complex social environment. Even to think that the relevant consideration is the additive aggregation of peoples’ willingness to pay is a result of a choice; the simplistic utilitarianism of economics is most certainly not a “natural” phenomenon.

My guess is that little I can say here is likely to be persuasive to you. It might nonetheless be useful to both of us to be particularly clear about the points at which we disagree, so that we don’t talk past each other unnecessarily. If it’s simply that you find no moral or aesthetic value to the preservation of the aspects of the biosphere endangered by climate change, or not enough to justify the costs it would take to preserve them, well, I could certainly try to make the moral arguments; I’ve been working on them in various contexts, although I tend to think that the prevention of physical harm to humans is the dominant reason to reduce GHG emissions drastically. If you think that I overestimate the risks to such an extent that my precautionary objectives are unreasonably high, that’s something else again; I actually think that deciding what are “reasonable” worst case probabilities for policy planning is an essential task. Our debates (for example) about climate sensitivity PDFs are based on other kinds of arguments where I’m certainly less confident in my hypotheses, and more willing to consider the reasons for believing I’m wrong.

Anyway, I obviously enjoy these kinds of discussions in any case and you are presumably not the only one reading here. But I should get back to submitting my work for peer review :^)


Hank Roberts said...

I very much appreciate you all having these conversations in public, toward as Dr. Baer wrote

"deciding what are “reasonable” worst case probabilities for policy planning

From the BBC last September, the word "dangerous" might be useful to clarify for this thread:

"The East Antarctic core is the longest, deepest ice column yet extracted.

"Project scientists say its contents indicate humans could be bringing about dangerous climate changes.

"'My point would be that there's nothing in the ice core that gives us any cause for comfort,' said Dr Eric Wolff from the British Antarctic Survey (BAS).

"'There's nothing that suggests that the Earth will take care of the increase in carbon dioxide. The ice core suggests that the increase in carbon dioxide will definitely give us a climate change that will be dangerous,' he told BBC News.

"The Antarctic researcher was speaking here at the British Association's (BA) Science Festival. ..."

-- Hank Roberts

James Annan said...

Hank first cos it's the easier comment :-)

I'm sure that Eric is using "dangerous" as a shorthand for "2C warmer than pre-industrial" as this is the standard definition from the UNFCCC (which RPJr has strongly criticised, but that's another matter). I'm also sure that Eric is not making his own analysis of "danger" per se - he is an expert on ice sheets not impacts.

Based on current temperature trends (and a steady but not extraordinary rise in emissions), we'll get to +2C from pre-industrial in about 70 years or so - that is from the recent 0.7C warming, with another 1.3C at a rate of 0.18C per decade. Depending on emissions, it could be a bit sooner or later than that.

So based on the UNFCCC definition, there is no question IMO that we have the potential to cause "dangerous" climate change. I'm confident that the likes of Pat Michaels would broadly agree with that analysis, although he might try to push the expected date a little further towards 2100. But the interesting and important questions are what are the consequences of this "danger", how likely are they to occur, and what should we do to try to avoid it. That requires some quantitative analysis, not just bandying around emotive words like "danger" and "catastrophe" and "cannot be ruled out".

James Annan said...


There is, I think, a risk that you try to (or at least appear to try to) have your cake and eat it. By all means talk about your willingness to pay to preserve ice sheets for moral and aesthetic reasons, but don't be surprised if others don't share your judgements. AIUI Stern was trying to put numbers to the direct economic costs, not our emotions. OK, so you argue that ultimately all economic value is a social construct, but there is still a big difference between losing your home (or 25% of your crop) next year, and suffering the anguish of knowing that the world will look increasingly different in the centuries to come. You muddy the waters by claiming that "physical harm to humans is the dominant reason to reduce GHG emissions drastically", while simultaneously asserting that the (glacially slow) loss of an ice sheet is by itself such a large factor that it is by itself sufficient to completely overturn Stern's conclusions. It seems to me that they only thing that actually suffers in this process is your feelings. Or are you actually arguing that there will be direct economic costs (in Stern's terms, using his parameters) from this?