Re: Global warming in the pipeline | Oxford Open Climate Change | Oxford Academic

[Robert Chris]

Hansen et al’s long awaited paper Warming in the Pipeline was finally published on 2 November after several revisions following its prepublication appearance towards the end of last year.  This allowed Professor Michael Mann to get his rebuttal in a day early.  With Hansen challenging the ‘orthodox mainstream’ view that rapid cuts in carbon emissions are no longer a sufficient policy response, with Mann claiming they are, the stage is now set for a mighty battle between these two titans of the science of climate change.  I am a mere spectator in this.  I’m not qualified to be in the ring, but I am qualified to judge the fight.

Mann’s rebuttal wins him few points in this opening round.  Rather than critique Hansen et al’s work, he sets out his own opinions and supports them with many references (of varying quality) to what he refers to as the orthodox and mainstream position and several straw man arguments.  This amounts to little more than a claim that his facts are bigger and better than Hansen’s.  Much like an old fashioned pissing contest. This is a level of argumentation that does no justice to the gravity of the issues at stake.  Until their differences are resolved, policymakers will understandably sit on their hands genuinely not knowing what to do in the best interests of humanity and the rest of life with whom we share this planet.  It is critical that that resolution be achieved without undue delay because if Hansen is right, it will be vital to lose as little time as possible in coming to terms with the policy implications. 

Hansen et al’s paper, like most such academic works, consists of an argument in the form of a series of premises linked together by logical reasoning to reach a set of conclusions.  To rebut the argument and demonstrate that the conclusions are unsound, it is necessary to show either (or both) that one or more of the premises is untrue, or the reasoning is invalid.  Mann does neither. 

Restating his own argument, however well referenced, is not a rebuttal of Hansen’s because it does not allow for the possibility that there are problems with the premises and reasoning of his own case.  He ignores the possibility of systemic bias and groupthink that often characterises such orthodox and mainstream positions before they crumble in the wake of paradigm shifts.  The history of knowledge is replete with such instances.  Indeed, were that not so, we’d still be living in caves.

Two critical factors that will need addressing are risk and uncertainty both of which contribute to our sense of urgency.  Both Mann and Hansen agree that rapid deep cuts in emissions are essential and not yet happening at anything like the necessary pace.  But what Mann does not make clear is the nature and extent of the risk of that continuing not to happen at sufficient pace, and how that impacts urgency.  If the risks of under-reacting are not too great, then we have the luxury of waiting to see how things unfold.  However, if the risks of under-reacting are severe, even existential, there is considerable urgency, and prudence dictates that we should overreact.  A proper risk analysis of our situation and options is essential if policymakers are to act in our best interests.

It is to be hoped that either directly or through their champions and proxies, Mann and Hansen will sort this out in the very near future so that the rest of us know what best to do.

In the following paragraphs I give a brief review of Mann’s rebuttal in terms of the quality of his argumentation.  This is not about which of Hansen and Mann has a better grasp of the climate science, but solely whether Mann’s rebuttal of Hansen’s position is presented in a convincing manner.  I hope that Prof Mann will read this and take the opportunity to produce a more robust critique of Warming in the Pipeline that in turn will provoke a resolution of these two currently conflicting positions.  It is vital that these issues are resolved at the earliest opportunity.

Mann gives seven ways in which he considers Hansen et al to have failed by ‘a longshot’ to have met the necessary standards to challenge ‘the prevailing scientific understanding’.  Let’s have a quick look at Mann’s arguments.

1.       No warming is in the pipeline – Mann argues that the zero emissions commitment (ZEC) clearly shows that on achieving net zero emissions, surface temperatures stop rising.  He therefore claims that there would be no warming in the pipeline once we get to net zero.  Whatever one’s view of ZEC being at or close to 0^oC, Hansen et al do not discuss it other than briefly to dismiss net zero as likely to be achieved any time soon.  It seems perverse to criticise their paper on these grounds since they are clear that their case is built on constant atmospheric GHG concentrations.  As Mann acknowledges, in that scenario there would be considerable warming in the pipeline.  A more coherent criticism might have been to argue for the unsoundness of the premises that net zero emissions would not be achieved sufficiently soon or that atmospheric concentrations would not remain at their current level.  Mann doesn’t do that.  This is a straw man argument.

2.       EEI is not increasing – Mann refutes Hansen et al’s claim by citing a competing source of which he was a co-author.  He does not explain what is wrong with the sources on which Hansen et al base their claim that EEI has doubled since 2000, one of which is titled ‘Satellite and ocean data reveal marked increase in Earth’s heating rate’.  There is no examination of why his source is better than Hansen’s.

3.       Surface warming is not accelerating – Mann goes to great lengths to show that there is no evidence of surface warming accelerating due to the recent changes in aerosol emissions.  This rebuttal was unnecessary because Hansen et al did not claim that there had been.  They explicitly refer to ‘predicted’ warming as being an inevitable consequence of these aerosol changes.  Another straw man argument from Mann.

4.       IPCC models not under-predicting human caused warming – here Mann’s refutation implies that Hansen et al wrongly claim that that models have under-predicted the warming.  Again, they make no such claim about past warming.  Their claim in this regard concerns future warming, which self-evidently is not yet evident.  Another straw man argument from Mann.

5.       No evidence that recent reductions in ship aerosol emissions ‘have played any substantial role at all in recent warming trends’ – Mann cites two sources to support his rebuttal of Hansen et al’s predictions in this regard.  Mann’s first authority is a paper published in 2009, before the recent changes in shipping emissions.  His second authority is a 2023 Tweet from Hausfather that just refers back to the same 2009 paper.  It is difficult to see how research undertaken before the aerosol emissions were reduced could show evidence of what had not yet happened.  Mann needs to provide a more convincing rebuttal than this.

6.        Paleoclimate records have climate sensitivity about right – Mann supports his rebuttal of Hansen et al’s interpretation of paleoclimate evidence in assessing equilibrium climate sensitivity (ECS) by citing his own non-peer reviewed article in New Scientist.  He then asserts that ‘there is no reason, based on the collective evidence from the paleoclimate record, to expect a climate trajectory substantially different from what current generation (i.e. IPCC) models predict’.  If there is one thing that Hansen et al do do, it is to explore in considerable detail the implications of new evidence from the paleo record.  Mann makes no attempt to engage with this material, seemingly summarily dismissing it as valueless.  This is not a worthy response from someone of Mann’s standing..

7.       Solar radiation management is potentially dangerous and a need for it is ‘motivated by what [Mann] consider[s] to be a fallacy, advanced by the article, that large-scale warming will be substantially greater than current-generation models project’.  Mann’s views here reflect the difference at the heart of this debate, namely, how much risk is associated with the predictions of those models.  Risk is generally understood to be the product of the probability of a peril occurring and the costs (monetary and otherwise) arising from that peril.  For Mann’s critique to have any purchase, he needs to flesh out the detail in this regard.  This will require a broadly based investigation of the various possible perils from different plausible climate change scenarios and their cost.  Mann has to do more than just assert his own opinion on these questions.

I close with a comment on Peter Eisenberger’s contribution below in which he says:

We certainly are facing a great threat but there is no science basis for arguing that [emissions reductions and removals alone (ERA)] are not adequate.

We all need to ponder the full implications of this statement.  First we must note that there being no science basis to argue that emissions reductions and removals alone are not adequate is the complement of there being no science basis that they are.  If you don’t know it’s inadequate, you can’t know that it's adequate .  Conversely, if you know it’s adequate, then you also know it’s not inadequate.  The sum of the probabilities of it being one or the other will always be 1 – it is logically certain that ERA will be either adequate or not.  Peter’s statement can thus be rewritten as:

We certainly are facing a great threat but there is no science basis for arguing that [emissions reductions and removals alone] are adequate.

Given Peter’s claim that we don’t have a science basis for arguing that ERA is adequate, should we not be looking for something else to create a portfolio of responses that in aggregate would have a science basis to support their adequacy?

There are many good reasons, from basic physics to the analogue of volcanic eruptions, to know with certainty that there are ways to directly cool the climate to  reduce the risk of excessive global warming.  The issue is whether this can be done in ways that reduce that risk while not creating unacceptable risks elsewhere.  The question that Prof Mann and Peter might want to reflect on is, given that we don’t know whether ERA is sufficient, and moreover, that there are some good reasons to believe that it might be insufficient, albeit that these reasons might not be conclusive, why would we not want to begin the process in earnest of developing and deploying direct climate cooling in a controlled and responsible manner such that it can be terminated if it emerges that its beneficial potential cannot be realised without overwhelming offsetting negative effects?  How does that make scientific sense?

Regards

Robert Chris

On 03/11/2023 07:12, Peter Eisenberger wrote:

Most importantly we are in fact all on the same team and we all agree time is running out. 

Mann and Hansen are each acting in the best tradition of scientific disagreement. 

From my perspective they both seem to fail to take CDR into account into their scenarios 

even though the majority of the scientific community including the IPCC has acknowledged it needs to 

be part of the solution. Net emissions -amount removed from the atmosphere minus the amount emitted 

is the critical variable and this is critical  because the poor on this planet need to have their basic needs met. Zero emissions means to them a reduced rate of eliminating poverty . One is left to speculate whether the people focussed on eliminating fossil fuels is a result of their long and important battle with the energy industry in the past. The energy industry has recognized climate change and they are acting to address it which was not the case even five years ago. They still remain critical to economic prosperity in the global south.  In my opinion it is time to move on beyond demonizing the energy industry. To be clear I greatly respect the efforts of Mann and Hansen both scientifically and because being a whistle blower  is never easy - in fact it is always hard and gets personal. 

My concern about the response of the SAI community is that it does  seem  to depend on arguing we are facing a doomsday future 

and the inadequacy of alternative paths. We certainly are facing a great threat but there is no science basis for arguing that the alternative paths are not adequate. At its core it depends on creating fear about the future. We know the fight or flight response to fear and that  fear has caused many conflicts. I am certainly not suggesting that advocates for SAI do not believe what they are saying.  

My view for what it is worth is that we all have to come together in the spirit of Manns response to JIm and together 

determine the best path forward based on the knowledge we have. We need to  make the hard choices about the best path forward. We need to agree  to focus our talents and energy on the path selected. In this sense the real limitation is not what distortions the external world has that prevents acting but it us for our failure to make the hard choices and provide them to the decision makers. 

Let me end as I b egan -Most importantly we are in fact all on the same team and we all agree time is running out. .

Peter 

        

On Thu, Nov 2, 2023 at 2:33 PM Ye Tao <t...@rowland.harvard.edu> wrote:

This post by Mann demonstrates that he lacks an understanding of time-dependent dynamics: things like impulse and step response function. Or maybe he does, but is playing into the general ignorance of the public regarding such things.

Not sure which one is worse and what that says about how we choose academic leaders.

Ye

On 11/2/2023 11:46 AM, H simmens wrote:

The only direct interaction between Mann and Hansen I’ve been able to find is this brief exchange in July (Mann’s tweet is at the top)

Herb Simmens
Author of A Climate Vocabulary of the Future

“A SciencePoem and an Inspiration.” Kim Stanley Robinson
@herbsimmens
HerbSimmens.com

On Nov 2, 2023, at 11:34 AM, robert...@gmail.com wrote:



Game on!  It'll be interesting to see how Hansen responds, if indeed he does.  For us lesser mortals, it seems quite important that these titans sort this out because such critical differences at this level can only undermine policy progress in whatever direction it should be taken.

Regards

Robert

On 02/11/2023 14:13, H simmens wrote:

 Here’s a response/rebuttal from Michael Mann to Hansen. The game is now on between the two most prominent US climate scientists. Let’s see if the mainstream media pick up on it  

https://michaelmann.net/content/comments-new-article-james-hansen

Let’s hope that Michael is correct with regard to the science and not Jim’s SRM advocacy which he labels a ‘gambit’.  

Herb

Herb Simmens
Author of A Climate Vocabulary of the Future

“A SciencePoem and an Inspiration.” Kim Stanley Robinson
@herbsimmens
HerbSimmens.com

On Nov 2, 2023, at 8:47 AM, H simmens <hsim...@gmail.com> wrote:



The key language on cooling in the paper:

Third, we must take action to reduce and reverse Earth’s energy imbalance. Highest priority is to phase down emissions, but it is no longer feasible to rapidly restore energy balance via only GHG emission reductions. Additional action is almost surely needed to prevent grievous escalation of climate impacts including lock-in of sea level rise that could destroy coastal cities world-wide. At least several years will be needed to define and gain acceptance of an approach for climate restoration. This effort should not deter action on mitigation of emissions; on the contrary, the concept of human intervention in climate is distasteful to many people, so support for GHG emission reductions will likely increase. Temporary solar radiation management (SRM) will probably be needed, e.g. via purposeful injection of atmospheric aerosols. Risks of such intervention must be defined, as well as risks of no intervention; thus, the U.S. National Academy of Sciences recommends research on SRM [212]. The Mt. Pinatubo eruption of 1991 is a natural experiment [213, 214] with a forcing that reached [30] –3 W/m2. Pinatubo deserves a coordinated study with current models. The most innocuous aerosols may be fine salty droplets extracted from the ocean and sprayed into the air by autonomous sailboats [215]. This approach has been discussed for potential use on a global scale [216], but it needs research into potential unintended effects [217]. 

This decade may be our last chance to develop the knowledge, technical capability, and political will for actions needed to save global coastal regions from long-term inundation. (My bolding) 

Herb Simmens
Author of A Climate Vocabulary of the Future

“A SciencePoem and an Inspiration.” Kim Stanley Robinson
@herbsimmens
HerbSimmens.com

On Nov 2, 2023, at 8:31 AM, H simmens <hsim...@gmail.com> wrote:





This appears to be the real thing. The long awaited paper by James Hansen and colleagues:

A description of the paper in Phys.org:

Herb Simmens
Author of A Climate Vocabulary of the Future

“A SciencePoem and an Inspiration.” Kim Stanley Robinson
@herbsimmens
HerbSimmens.com

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On 11/3/23 4:17 PM, Robert Chris wrote:

given that we don’t know whether ERA is sufficient, and moreover, that there are some good reasons to believe that it might be insufficient....

This precisely pinpoints the main flaw I found in the Mann rebuttal. He opened and closed by restating, without support (even from IPCC), that ERA will be sufficient and therefore no CDR or SRM should be necessary.

But see:

Randers, Jorgen, and Ulrich Goluke. "An earth system model shows self-sustained thawing of permafrost even if all man-made GHG emissions stop in 2020." Scientific Reports 10.1 (2020): 18456.

https://doi.org/10.1038/s41598-020-75481-z

(appended)

According to Randers and Goluke, we need at least 33 GtCO2e CDR per year. "In other words, building 33,000 big CCS plants and keep them running forever."

We should also be thinking about slowing permafrost melt.

See also:

Lenton, T. M., Rockström, J., Gaffney, O., Rahmstorf, S., Richardson, K., Steffen, W., & Schellnhuber, H. J. (2019). Climate tipping points—too risky to bet against. Nature, 575(7784), 592-595.

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[Dan Miller]

Hi Robert:

I’ll weigh in here. I agree with your analysis showing that Mann did not provide a cogent rebuttal to Hansen’s paper.

A few other points:

1. First, I summarized Hansen’s paper “for the masses” in a tweet that some might find useful:

2. Mann implies we can stay at 1.5ºC by reaching net zero by 2050! This is absurd. We are 1.5ºC (or very close) *this year* and will likely be at 1.6/1.7ºC next year. As Hansen points out, if we do hit that next year and El Niño going away drops temps by 0.2~0.3ºC, then we are effectively at 1.5ºC trend “for all practical purposes” next year! To claim we can stay within 1.5ºC by reaching net zero in 2050 makes me believe, as others have said, that Mann is smoking “hopium”. I believe this alone disqualifies Mann’s rebuttal.

Mann: "It is the basis of the concept of a “carbon budget” (i.e. the notion that there is a specified amount of cumulative carbon emissions up to a given point in time that keeps warming below a specified level), including the widely-cited rule of thumb that we must reduce carbon emissions to zero by 2050 to avoid more than 1.5C warming."

3. Note that "Net Zero by 2050" is as much of a scenario as "holding GHG concentrations constant" is. 

4. Hansen et al is saying that aerosol cooling is more than the IPCC says and GHG warming is also more. That’s why the Hansen and IPCC model net temps are about the same. But if Hansen is right (and I think he is), then there will be more warming when we eliminate aerosols (as part of going to Net Zero) and there will be more warming from the remaining GHGs than is assumed in Mann's ZEC scenario. Therefore, ZEC won’t result in temps that stop rising, though they will stop rising at some level above the temp we are at when zero emissions are achieved (assuming tipping points haven’t kicked in by then!). Another factor that may play out at ZEC is that the EEI is high, Hansen says. So at ZEC, the EEI (warming in the pipeline) is supposed to be canceled out by lowering CO2 levels caused by the oceans continuing to take up CO2 after emission stop. But if EEI is higher than assumed when those ZEC studies were done, then they might not exactly cancel and temps will be higher.

5. Mann implies that we can stay below 2ºC and that would be OK. As Hansen has pointed out in his Young Peoples paper, 1.5 or 2ºC is dangerous if we stay above those levels too long:

Hansen: "These considerations raise the question of whether 2 ◦C, or even 1.5 ◦C, is an appropriate target to protect the well-being of young people and future generations. Indeed, Hansen et al. (2008) concluded that “if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, . . . CO2 will need to be re- duced . . . to at most 350 ppm, but likely less than that”, and further “if the present overshoot of the target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.

A danger of 1.5 or 2 ◦C targets is that they are far above the Holocene temperature range. If such temperature levels are allowed to long exist they will spur “slow” amplifying feed- backs (Hansen et al., 2013b; Rohling et al., 2013; Masson- Delmotte et al., 2013), which have potential to run out of hu- manity’s control. The most threatening slow feedback likely is ice sheet melt and consequent significant sea level rise, as occurred in the Eemian, but there are other risks in pushing the climate system far out of its Holocene range. Methane release from thawing permafrost and methane hydrates is an- other potential feedback, for example, but the magnitude and timescale of this is unclear (O’Connor et al., 2010; Quiquet et al., 2015)."

6. On top of other risks that Mann ignores, we now know from Hansen and Danish researchers, that an AMOC collapse is expected around mid-century. This is the mother of all near-term tipping points. Since it is caused by fresh water inflow into the North Atlantic from a melting Greenland, it is clear that ERA will not stop a collapse. If we are lucky, Sunlight Reflection Methods (SRM) may prevent it.

7. Regarding who we should believe:

Imagine you are about to put your children on an airplane. But Mechanic Hansen says there is a problem with the engines & Mechanic Mann says everything is fine. Do you allow your children to take the flight?

Why do we treat the Earth, with all our children on it, differently?

Dan







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[Clive Elsworth]

Nicely put, Dan.

 

All very good points.

 

Clive

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