Confusionist Judith Curry goes ‘wicked’ and mangles the work of Martin Weitzman

Climate change can be categorized as a “wicked problem.”[Note] Wicked problems are difficult or impossible to solve, there is no opportunity to devise an overall solution by trial and error, and there is no real test of the efficacy of a solution to the wicked problem. Efforts to solve the wicked problem may reveal or create other problems….

Xu, Crittenden et al. [Note] argue that “gigaton problems require gigaton solutions.” The wickedness of the climate problem precludes a gigaton solution (either technological or political).

Judith Curry abandoned science this year. She asserted I was “directly involved in Climategate”; James Annan explained “(S)He who refuses to do arithmetic is doomed to talk nonsense”; William Connolley eviscerated a recent paper on Antarctic sea ice (here), which notes, “The main problem with the paper is the uncritical use of invalid data”; and Bart Verheggen explained, “Her unfounded allegations are insulting for the whole profession.”

Her House testimony quoted above is another confusing mess. It uses the word ‘wicked’ in various forms 11 times, glomming onto a 27-year-old paper by an architect and an urban designer, apparently to prove that the climate ‘problem’ may be ‘impossible’ to solve and indeed that even trying to solve it may only make things worse.


Like much of what she is saying today, it is pseudoscientific garbage. She has utterly abandoned any interest in the actual science itself.

Her testimony simply asserts, “Based upon the background knowledge that we have, the threat does not seem to be an existential one on the time scale of the 21st century, even in its most alarming incarnation.” Of course, she can hide behind the undefined word “existential,” but for those who actually follow the recent science, which Curry clearly doesn’t since she hardly ever either quotes it or blogs on it.

The literature from the last year alone makes clear that doing nothing is the only surefire way to make things worse — most likely unimaginably worse with a confluence of catastrophes any one of which would motivate action and combined is indeed an existential threat to the health and well-being of billions of people (see “A stunning year in climate science reveals that human civilization is on the precipice”).

It simply makes no sense to try to make sense of what she is saying anymore. What, for instance, does this mean:

Weitzmann [sic] characterizes the decision making surrounding climate change in the following way:

“Much more unsettling for an application of expected utility analysis is deep structural uncertainty in the science of global warming coupled with an economic inability to place a meaningful upper bound on catastrophic losses from disastrous temperature changes. The climate science seems to be saying that the probability of a system-wide disastrous collapse is non-negligible even while this tiny probability is not known precisely and necessarily involves subjective judgments.”

When a comprehensive decision analysis includes plausible catastrophes with unknown probabilities, the policy implications can be radically different from those suggested by optimal decision making strategies targeted at the most likely scenario. Weitzmann [sic] argues that it is plausible that climate change policy stands or falls to a large extent on the issue of how the high impact low probability catastrophes are conceptualized and modeled. Whereas “alarmism” focuses unduly on the possible (or even impossible) worst-case scenario, robust policies consider unlikely but not impossible scenarios without letting them completely dominate the decision.

Aside from repeatedly misspelling his name — Google anyone? — Weitzman’s point is almost exactly the opposite of Curry’s (see my 1/09 post Harvard economist: Climate cost-benefit analyses are “unusually misleading,” warns colleagues “we may be deluding ourselves and others”).


Weitzman argues that the economic damages from possible catastrophic impacts (what he believes are unlikely) render traditional cost-benefit analyses pointless and should completely dominate decision-making. This is doubly true because Wetizman has underestimated the probability of these impact.

For completeness’s sake, I’ll review what Weitzman has in fact said.

Weitzman believes that the damage posed by, say, 6°C is considerably worse than what traditional cost-benefit analyses calculate.

Weitzman says, that for any fat-tailed distribution, like the damage function for unrestricted greenhouse gas emissions, it is the possibility of extreme negative outcomes that overwhelm the traditional cost-benefit analysis.

The extreme or fat tail of the damage function (click on figure at right) represents what Weitzman calls “rare climate disasters,” although as I’ve shown above, they aren’t rare at all, they are highly likely with business-as-usual emissions. For Weitzman, disaster is a temperature change (delta T) of > 6°C (11°F) in a century, as he explains in an earlier paper on the Stern Review on the economics of climate change:

Societies and ecosystems whose average temperature has changed in the course of a century or so by delta T > 6C (for U.S. readers: 6C = 11F) are located in the terra incognita of what any honest economic modeler would have to admit is a planet Earth reconfi…gured as science …fiction, since such high temperatures have not existed for some tens of millions of years”¦.

With roughly 3% IPCC-4 probability, we will “consume” a terra incognita biosphere within a hundred years whose mass species extinctions, radical alterations of natural environments, and other extreme outdoor consequences of a different planet will have been triggered by a geologically-instantaneous temperature change that is signi…cantly larger than what separates us now from past ice ages.

Weitzman says the IPCC Fourth Assessment gives the probability of such an “extreme” temperature change as 3%, and that “to ignore or suppress the signi…ficance of rare tail disasters is to ignore or suppress what economic theory is telling us loudly and clearly is potentially the most important part of the analysis” “” more important than the discount rate.

Indeed, in his most recent paper Weitzman says again,

Six degrees of extra warming is about the upper limit of what the human mind can envision for how the state of the planet might change. It serves as a routine upper bound in attempts to communicate what the most severe global warming might signify, including the famous “burning embers” diagram of the IPCC [above] and several other popular expositions.

One recent study asked 52 experts for their subjective probability estimates of triggering a “tipping point of major changes” in each of fi…ve possible categories: (1) the Atlantic meridional overturning circulation; (2) the Greenland ice sheet; (3) the West Antarctic Ice Sheet; (4) the Amazon rainforest; (5) the El Ni±o/Southern Oscillation. For what it is worth, at an average temperature increase of T [approximately] 6C the expected (probability weighted) number of such expert-assessment tipping points was three (out of a possible …five).

It is 6C warming “” and the multiple catastrophic outcomes it probably brings “” Weitzman says you really, really want to avoid.

Curry simply doesn’t understand the first thing about Weitzman’s work and so utterly misrepresents it.

For me, what is especially important about Weitzman’s analysis is that the science is now crystal clear that there is far greater chance than 3% chance we will have a total warming of 6°C in a century or so if we don’t reverse emissions trends soon.


Again, you can go here: “Hadley Center: Catastrophic 5.5–7°C warming by 2100 on current emissions path.” For the Hadley folks, there is a 50% chance warming will exceed 5.5°C if we listen to the do-nothing confusionists like Curry and Lomborg.

Or look at MIT 2009 analysis:

As Andrew Freedman at explained:

For the no policy scenario, the researchers concluded that there is now a nine percent chance (about one in 11 odds) that the global average surface temperature would increase by more than 7°C (12.6°F) by the end of this century, compared with only a less than one percent chance (one in 100 odds) that warming would be limited to below 3°C (5.4°F).

To repeat, on our current emissions path, we have a 9% chance of an incomprehensibly catastrophic warming of 7°C by century’s end, but less than a 1% chance of under 3°C warming.

“The take home message from the new greenhouse gamble wheels is that if we do little or nothing about lowering greenhouse gas emissions that the dangers are much greater than we thought three or four years ago,” said Ronald G. Prinn, professor of atmospheric chemistry at MIT. “It is making the impetus for serious policy much more urgent than we previously thought.”


Judith Curry would realize this if she had not abandoned science and if she actually read the work of the people she cites.