(Replying to my own comment) I'm copy-pasting the Criticism section on Wikipedia:

Criticism

Members of the panel including Thomas Schelling and one of the two perspective paper writers Robert O. Mendelsohn (both opponents of the Kyoto protocol) criticised Cline, mainly on the issue of discount rates. (See "The opponent notes to the paper on Climate Change" [27]) Mendelsohn, in particular, characterizing Cline's position, said that "[i]f we use a large discount rate, they will be judged to be small effects" and called it "circular reasoning, not a justification". Cline responded to this by arguing that there is no obvious reason to use a large discount rate just because this is what is usually done in economic analysis. In other words, climate change ought to be treated differently from other, more imminent problems. The Economist quoted Mendelsohn as worrying that "climate change was set up to fail".[28]

Moreover, Mendelsohn argued that Cline's damage estimates were excessive. Citing various recent articles, including some of his own, he stated that "[a] series of studies on the impacts of climate change have systematically shown that the older literature overestimated climate damages by failing to allow for adaptation and for climate benefits."

Members of the panel, including Schelling, criticised the way this issue was handled in the Consensus project.[citation needed]

The 2004 Copenhagen Consensus attracted various criticisms:

Approach and alleged bias

The 2004 report, especially its conclusion regarding climate change was subsequently criticised from a variety of perspectives. The general approach adopted to set priorities was criticised by Jeffrey Sachs, an American economist and advocate of both the Kyoto protocol [29] and increased development aid, who argued that the analytical framework was inappropriate and biased and that the project "failed to mobilize an expert group that could credibly identify and communicate a true consensus of expert knowledge on the range of issues under consideration.".[30]

Tom Burke, a former director of Friends of the Earth, repudiated the entire approach of the project, arguing that applying cost–benefit analysis in the way the Copenhagen panel did was "junk economics".[31]

John Quiggin, an Australian economics professor, commented that the project is a mix of "a substantial contribution to our understanding of important issues facing the world" and an "exercises in political propaganda" and argued that the selection of the panel members was slanted towards the conclusions previously supported by Lomborg.[32] Quiggin observed that Lomborg had argued in his controversial book The Skeptical Environmentalist that resources allocated to mitigating global warming would be better spent on improving water quality and sanitation, and was therefore seen as having prejudged the issues.

Under the heading "Wrong Question", Sachs further argued that: "The panel that drew up the Copenhagen Consensus was asked to allocate an additional US$50 billion in spending by wealthy countries, distributed over five years, to address the world’s biggest problems. This was a poor basis for decision-making and for informing the public. By choosing such a low sum — a tiny fraction of global income — the project inherently favoured specific low-cost schemes over bolder, larger projects. It is therefore no surprise that the huge and complex challenge of long-term climate change was ranked last, and that scaling up health services in poor countries was ranked lower than interventions against specific diseases, despite warnings in the background papers that such interventions require broader improvements in health services."

In response Lomborg argued that $50 billion was "an optimistic but realistic example of actual spending." "Experience shows that pledges and actual spending are two different things. In 1970 the UN set itself the task of doubling development assistance. Since then the percentage has actually been dropping". "But even if Sachs or others could gather much more than $50 billion over the next 4 years, the Copenhagen Consensus priority list would still show us where it should be invested first." [33]

One of the Copenhagen Consensus panel experts later distanced himself from the way in which the Consensus results have been interpreted in the wider debate. Thomas Schelling now thinks that it was misleading to put climate change at the bottom of the priority list. The Consensus panel members were presented with a dramatic proposal for handling climate change. If given the opportunity, Schelling would have put a more modest proposal higher on the list. The Yale economist Robert O. Mendelsohn was the official critic of the proposal for climate change during the Consensus. He thought the proposal was way out of the mainstream and could only be rejected. Mendelsohn worries that climate change was set up to fail. [34]

Michael Grubb, an economist and lead author for several IPCC reports, commented on the Copenhagen Consensus, writing:[35]

To try and define climate policy as a trade-off against foreign aid is thus a forced choice that bears no relationship to reality. No government is proposing that the marginal costs associated with, for example, an emissions trading system, should be deducted from its foreign aid budget. This way of posing the question is both morally inappropriate and irrelevant to the determination of real climate mitigation policy.

Panel membership

Quiggin argued that the members of the 2004 panel, selected by Lomborg, were, "generally towards the right and, to the extent that they had stated views, to be opponents of Kyoto.".[32] Sachs also noted that the panel members had not previously been much involved in issues of development economics, and were unlikely to reach useful conclusions in the time available to them.[30] Commenting on the 2004 Copenhagen Consensus, climatologist and IPCC author Stephen Schneider criticised Lomborg for only inviting economists to participate:[36]

In order to achieve a true consensus, I think Lomborg would've had to invite ecologists, social scientists concerned with justice and how climate change impacts and policies are often inequitably distributed, philosophers who could challenge the economic paradigm of "one dollar, one vote" implicit in cost–benefit analyses promoted by economists, and climate scientists who could easily show that Lomborg's claim that climate change will have only minimal effects is not sound science.

Lomborg countered criticism of the panel membership by stating that "Sachs disparaged the Consensus ‘dream team’ because it only consisted of economists. But that was the very point of the project. Economists have expertise in economic prioritization. It is they and not climatologists or malaria experts who can prioritize between battling global warming or communicable disease," [33]

Thanks! My understanding of CC being controversial: Lomborg once was a member of Greenpeace, then became disillusioned with popular environmentalism and wrote the extremely controversial The Skeptical Environmentalist arguing against most popular environmental causes. The Economist and Wall Street Journal celebrated it as a fresh new look, while the Scientific American lambasted Lomborg as wrong and even scientifically dishonest. One Danish government commission accused Lomborg of fabricating data and plagiarism, while another criticized the previous commission's investigations.

I've read the book and tried to form my own view, but the rabbit hole is too deep. If anyone's interested in the object level question, try Slate Star Codex.

In any case, Lomborg is highly controversial in some circles and has had extremely high reputational stakes in the environmentalism debate for over a decade. So on second thought, I significantly agree with Jan: EA should be wary of close association with controversial figures (not to mention possibly unethical).

Separately, I think this gets to a more central question of EA's nature: Will we always demand truth at all costs, or is good enough really good enough? Will we work with pragmatic allies that don't share all of our underlying motivations? EA evolved in very high fidelity, academic-style circles, where truth-seeking and intelligence are paramount. But if doing good is the single objective, while truth is clearly extremely important, so is influence. GiveWell claims to have moved ~$500m or so at this point; CC is working in an arena with tens of billions at stake. Should we accept lower intellectual rigor if it means we can increase our scale 100x over?

I default to a commitment to truth, if only because lowering your standards is always possible at a later date, while regaining intellectual rigor is likely not. But it's certainly a question worth discussing.