by Judith Curry

The climate change debate has entered what we might call the “Campfire Phase”, in which the goal is to tell the scariest story. – Oren Cass (twitter)

David Wallace-Wells has a recent cover story in NYMagazine: The Uninhabitable Earth. Subtitle: Famine, economic collapse, a sun that cooks us: What climate change could wreak — sooner than you think. The article has generated a firestorm of controversy and debate.

In terms of what is technically wrong with the NYMag article, Andy Revkin pretty much sums it up perfectly with this tweet:

Scariest stuff isn’t worst-case science; it’s bad fit of @ deepuncertainty & time scales with indiv. & collective human risk/response traits.

Apart from the predictable takedowns by the AGW ‘unconvinced,’ there has been substantial resistance to the NYMag article from elements of what is usually regarded as the ‘alarmed’ contingent:

If this reaction seems surprising to you, you are not the only ones surprised:

Ryan Maue (twitter): Privately more than one journalist told me they were afraid to push back against the NY Mag climate horrors piece.

IMO, the most interesting articles are those that defend development and discussion of worst case scenarios:

‏ : I for one think that worst case scenarios should be interrogated. Technically and morally.

I for one think that worst case scenarios should be interrogated. Technically and morally. Joe Romm in ThinkProgress: Thus, the question remains: what is a plausible worst-case scenario for climate change this century?

Dave Roberts in Vox: In defense of worst-case scenarios in journalism.

A few other articles with interesting points:

Fabius Maximus: After 30 years of failure to gain support of the US public for massive public policy measures to fight climate change, climate activists now double down on the tactics that have failed them for so long. This post explains why it will not work. Nor should it. Instead they should trust the IPCC and science, showing both the good and bad news.

SF Chronicle: If you honestly believe that climate change will end all life on Earth (it won’t) or lead to some dystopian hell, what policies wouldn’t you endorse to stop it?

Consensus enforcement in the Age of Trump

So, what is going with Mann et al. in trashing the alarming NYMag article?

I saw many such ‘alarmed’ articles (perhaps not as comprehensive) in the Age of Obama, spouting alarmist predictions and concerns. Further, the White House seemed to encourage this, as evidenced by the whitehouse.gov web site and the statements of Science Advisor John Holdren. I never saw any push-back on this from the consensus-enforcing scientific establishment.

In the Age of Trump, alarmism clearly doesn’t influence the policy makers; the best that consensus-enforcing scientific establishment can hope for is to enforce the not very scary IPCC consensus.

And why does this matter to them? Surely this consensus enforcement is antithetical to the scientific process and progress. It seems to be all about ‘action’ — presumably as defined by the Paris Agreement. According to Mann et al., too much alarm makes people give up on attempting ‘action.’ Never mind that the proposed actions will have a small impact on the climate (even if you believe the climate models) during the 21st century.

Others disagree, such as Weizmann and Wagner (e.g. Climate Shock), who push the alarming ‘fat tail’ argument as the rationale for ‘action’ (greater uncertainty increases the urgency for action).

Well, I suspect that neither approach will spur ‘action’ — what is needed are new technologies. Until then, people, corporations and nations will pursue their short-term economic well being.

Deep Uncertainty

In understanding climate change risk, and deciding on the ‘if’ and ‘what’ of ‘action’, we need to acknowledge that we don’t know how the climate of the 21st century will play out (Deep Uncertainty, folks). Four possibilities:

It is possible that human-caused climate change will be swamped by much larger natural climate variability. It is possible/plausible that the sensitivity of the climate is on the low end of the IPCC envelope (1.0-1.5C), with a slow creep of warming superimposed on much larger natural variability. It is possible/plausible that the IPCC projections are actually correct (right for the wrong reasons; too much wrong with the climate models for much credibility, IMO). It is possible that AGW and natural variability could conspire to cause catastrophic outcomes

We can’t put probabilities on these possible scenarios, the uncertainties are too deep. We can speculate as to the relative likelihoods of these scenarios, but we don’t know, and there will be widespread disagreement. The negotiated IPCC consensus notwithstanding, I don’t regard #3 as any more likely than #2. There are some that regard #1 as the most likely outcome. Apart from advocacy groups hyping alarm, there has not been much serious attention paid to #4.

The IPCC consensus enforcers focus on #3. #2 is the lukewarm position. Michael Mann seems to regard consideration of #1, #2, #4 as ‘pernicious.’

I regard consideration of #1, #2, #4 as absolutely essential for both furthering scientific understanding and for understanding the risks from climate change. #2 gets a fair amount of play from the lukewarmer community (see especially Pat Michael’s book).

#1 and #4 are arguably the most interesting from the perspective of science, and also in terms of understanding the risks. Elements of natural climate variability are active areas of research; what is missing is a synthesis and assessment (something I’ve proposed for red team).

That leaves #4 as not having any serious scientific focus, beyond dystopian articles by journalists and cli-fi novels (and fat tail speculations by economists). #4 deserves some serious scientific attention.

A few additional tweets from Joseph Makjut:

This isnt about scaring people into action or not but thinking hard about what climate change might look like and who it might hurt.

Likewise, we should interrogate the scenarios where climate change is rather benign. What-up lukewarmers!?!

Keeping multiple versions of the future world in your head is hard, but wisdom comes from considering them all.

Back to ‘action.’ The Weitzmann fat tail argument says greater uncertainty increases the urgency of ‘action’ (Taleb is a fan of this argument). I’ve discussed the problems with this argument previously:

The point is this. Climate variability and change (whatever the direction or cause) has socioeconomic impacts, and it is useful to ponder the possibilities, independently of ‘action’ on CO2 emissions.

The plausible worst case scenario

Joe Romm states the issue perfectly:

Thus, the question remains: what is a plausible worst-case scenario for climate change this century?

Back in the day when Joe Romm and I were buddies(!), we discussed extensively the plausible worst cast scenarios. In fact, these were the subject of his book Hell and High Water.

I discussed the creation of worst case scenarios in these posts:

Based on everything that I’ve seen, it is very difficult to conclude that human-caused climate change is potentially a ‘ruin’ problem on the timescale of the 21st century. But climate change is interesting and important, independently of whether AGW is the dominant factor or not.

To make progress on this, we need to better understand climate shifts and abrupt climate change. Even though we can’t predict solar variability and volcanic eruptions, we need to consider a range of scenarios of these, not just a replica of the 20th century. We need to much better understand multi-decadal to millennial oscillations in the ocean.

My understanding of the climate system is that external forcing projects onto the modes of internal variability. How might these conspire to cause abrupt climate change in the 21st century?

With regards to plausible worst case scenarios, I’ve proposed the idea of a modal falsification test of specific worst case scenarios, that may be generated by climate models, inferred from historical data, or created as what-if scenarios. The modal falsification challenge is to attempt to falsify these extreme scenarios based on background knowledge (e.g historical climate change, physical limitations). If a scenario survives the falsification test, then it remains as a possible scenario. ‘Plausibility’ requires another layer of assessment and judgement. (It would be interesting to go back through Romm’s book to assess the plausibility 10 years post publication).

Note, this strategy is very different from the manufacture of mythical fat tails from pdfs (much loved by economists and statisticians) that simply do not exist given the level and types of uncertainties. However the fat tail approach and generation of plausible worst case scenarios that I propose share a common concern to understand the risk from the ‘worst case.’

One interesting case of plausible worst case scenario generation is provided by Jim Hansen, see this lengthy recent interview with Hansen in the NYMag.

So, assume that we generate a range of worst case future scenarios for the 21st century, ranging from #1 (including the potential for abrupt climate change purely from natural variability), through a range of sensitivities to human caused climate change, to #4 a conspiracy of human caused climate change and natural variability to cause very large climate change. And then reject the scenarios that can be falsified based on our background knowledge. Then what?

Well, then we are still faced with assessing the issue of whether the changed climate is ‘good’ or ‘bad’, and for whom and where. Not to mention the complexity of a political debate on how we might respond to any of this.

The bottom line is that the simple story pushed by the consensus enforcers of a simple climate problem and a simple energy solution is a goldilocks fairy tale. Given that their careers have been invested in this fairy tale, its little wonder that they regard anything other than their enforced consensus as ‘pernicious.’