by David Spratt
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Updated 29 September 2022
A significant paper on climate tipping points was published on 9 September, Exceeding 1.5°C global warming could trigger multiple climate tipping points. Having co-written a non-specialist’s overview on tipping points earlier this year, entitled Climate Dominoes, I looked forward to the new paper’s conclusions.
But on the very first page, there was a sense of science and politics on a collision course: the conclusions about appropriate climate goals did not seem to match the evidence, as I will explain below.
Now this is not a new story, but it points to the need to disentangle political conclusions from physical evidence. Often scientific reports and papers pull their punches, especially when it comes to IPCC, as we documented in our Breakthrough report, What Lies Beneath: The understatement of existential climate risks. But such reticence is not restricted to the IPCC.
The reasons for scientific reticence in the climate field are many, and may include:
- Hyper-specialisation that ignores or underplays systemic, compounding and non-linear processes.
- Problems of knowledge in disciplines where the physical reality is changing rapidly and at a rate such that there are few historical analogues.
- The scientific method’s emphasis on reproducible data and analysis, which means that uncertainties may lead to absences (“What I think is happening is X, but I can’t prove it in a peer-review manner, so I won’t mention it”).
- Over-reliance on modelling at the expense of other forms of knowledge, such as paleoclimatology (climate history) and judgements from expert elicitations.
- The related issue of a quantification fetish of presenting detailed, quantified (numerical) modelling results, but then only briefly noting more severe possibilities in a descriptive, non-quantified form. Because policymakers and the media are often drawn to headline numbers, this approach results in less attention being given to the most devastating, high-end, non-linear and difficult-to-quantify outcomes.
- Inappropriate approaches to risks given the existential possibilities, particularly the issue of the lower-probability, high-impact fat-tail risks, in which the likelihood of very large impacts is actually greater than would be expected under typical statistical assumptions.
- The sociology of scientists having a commonly-shared worldview: “Experts tend to establish a peer world-view which becomes ever more rigid and focussed… yet the crucial insights regarding the issue in question may lurk at the fringes.”
- Following the money, where research funding prioritises framings consistent with the current climate policy-making paradigm.
- Endemic bias, that is, not wanting to see certain outcomes. Prof. Kevin Anderson describes "an endemic bias prevalent amongst many of those building emission scenarios to underplay the scale of the 2°C challenge… In several respects, the modelling community is actually self-censoring its research to conform to the dominant political and economic paradigm".
- Erring “on the side of least drama”whose causes may include “adherence to the scientific norms of restraint, objectivity, skepticism, rationality, dispassion, and moderation”. This may cause scientists “to underpredict or downplay future climate changes”.
- The Devil’s Advocate Reward: “If a researcher comes up with an entirely new thought, experts tend to reflexively dismiss it as ‘speculative’, which is effectively a death warrant in the academic world. Whereas those who criticize the idea will be applauded, rewarded and promoted! This phenomenon is evident in every seminar, colloquium or learned-society assembly.”
- More overt political management, such as exhibited in the IPCC processes, whose highest decision-making levels are populated by professional political representatives of national governments, and subject to the diplomatic processes of negotiation, trade-offs and deals, and whose decision-making is a lower-common-denominator consensus model.
- The murky intersection of science and politics, which may be termed “regulatory science” or “co-production” (Sheila Jasanoff), a process which “straddles the dividing line between science and policy” as scientists and regulators try to provide answers to policy-relevant questions, such that “science is seen neither as an objective truth, nor as only driven by social interests, but as being co-produced through the interaction of natural and social orders”.
Above all, that should involve critical thinking about the methods being used. Prof. Hans Joachim Schellnhuber, Director Emeritus of the Potsdam Institute has noted in a foreword to our What Lies Beneath report that: “When the issue is the survival of civilization is at stake, conventional means of (scientific) analysis may become useless.”
The case in point, mentioned above, is a recent paper by McKay et al., Exceeding 1.5°C global warming could trigger multiple climate tipping points, which received a good deal of media coverage. Now this is a big picture, systems-level paper that certainly is not hyper-specialised or narrowly focussed.
What is highly unusual is the way the paper is presented on the Science website (see illustration above). Above the paper and the structured abstract is one paragraph immediately under the publication details, entitled “Getting tipsy” (itself an unusually non-scientific heading!), attributed to “HJS” which is apparently the Science senior editor, H. Jesse Smith, which says:
Climate tipping points are conditions beyond which changes in a part of the climate system become self-perpetuating. These changes may lead to abrupt, irreversible, and dangerous impacts with serious implications for humanity. Armstrong McKay et al. present an updated assessment of the most important climate tipping elements and their potential tipping points, including their temperature thresholds, time scales, and impacts. Their analysis indicates that even global warming of 1°C, a threshold that we already have passed, puts us at risk by triggering some tipping points. This finding provides a compelling reason to limit additional warming as much as possible (emphasis added).
By contrast, the paper’s abstract says that:
Current global warming of ~1.1°C above preindustrial temperatures already lies within the lower end of some tipping point uncertainty ranges. Several tipping points may be triggered in the Paris Agreement range of 1.5 to <2°C global warming, with many more likely at the 2 to 3°C of warming expected on current policy trajectories(emphasis added).
And the conclusion in the “Research article summary” is that:
“We show that even the Paris Agreement goal of limiting warming to well below 2°C and preferably 1.5°C is not safe as 1.5°C and above risks crossing multiple tipping points” (emphasis added).
The contrast is clear. HJS emphasises that even 1°C, which the world has already passed, is a threshold for some tipping points, whereas the papers authors choose to emphasise that “1.5°C and above risks crossing multiple tipping points” and that “several tipping points may be triggered in the Paris Agreement range of 1.5 to <2°C global warming”.
When risks are existential, emphasis must be given to understanding the feasible worst-case outcomes and working out how to prevent them. Clearly in the case of tipping points there is an unacceptable (and in reality a high probability) that some tipping points have already been crossed. This was the conclusion reached in the Breakthrough report, Climate Dominoes:
“At just 1.2°C of global average warming, tipping points have been passed for several large Earth systems. These include Arctic sea ice, the Greenland Ice Sheet, The Amundsen Sea glaciers in West Antarctica, the eastern Amazonian rainforest, and the world’s coral systems. The world will warm to 1.5°C by around 2030, with additional warming well beyond 1.5°C in the system after that. Yet even at the current level of warming, these systems will continue to move to qualitatively different states. In most cases, strong positive feedbacks are driving abrupt change. At higher levels of warming, the rate of change will quicken. The meme that “we have eight years to avoid 1.5°C and tipping points” should be deleted from the climate advocacy vocabulary. It is simply wrong.”
Certainly, in the case of West Antarctica, the evidence continues to pile in that the Thwaites glacier is primed to trigger a much wide loss of ice mass across the Amunsden sea glacial system, for example “Thwaites 'doomsday' glacier could begin rapid melt with 'just a small kick', researchers say”, reporting on new research consistent with the “doomsday” research released in late 2021.
Similarly, scientists now report that Greenland ice sheet has passed a point of system stability and is now “irreversibly committed” to a significant sea-level rise regardless of twenty-first-century climate pathways”.
So how can the authors of the Exceeding 1.5°C global warming could trigger multiple climate tipping points paper justify their emphasis on bad things happening after 1.5°C? They have done this by using language which in my opinion downplays the risks as the current level of warming of 1.1-1.2°C. Whilst accepting that “observations have revealed that parts of the West Antarctic ice sheet may have already passed a tipping point”, this gets summarised into language such as this: “1.1°C above pre-industrial already lies within the lower end of five climate tipping point uncertainty ranges” (emphasis added).
What does this communicate? “Uncertainty” to the average person means something like “we don’t really know”. If, instead, one said “there is an unacceptable risk that X has already occurred”, a different meaning would be transmitted.
And this is the problem. HJS’s short summary emphasises that 1°C has an unacceptable risk of being a threshold for triggering some tipping points, and we have already passed that point. That is very different from using language about uncertainty and emphasising that “1.5°C and above risks crossing multiple tipping points”.
It’s hard not to conclude that McKay et al have drawn conclusions that fit within the current Paris Agreement policy-making paradigm, even though much of the evidence the paper canvasses should lead to a different big-picture story about what is safe. Talking about 1.5-2°C buys into the delusion, still prevalent amongst policy-makers and aided and abetted by too many scientists, that there is some “carbon budget” left for this goal.
Instead, an emphasis on 1°C leads can help us understand how the risks have been underestimated and the reasons why decarbonisation is far from enough. These were two of the conclusions drawn in the Climate Dominoes paper:
Risks have been underestimated. The risks are systemic, but “quantifying the probability and severity of systemic risks is not possible due to their complex nature”. Because abrupt system change is happening faster than forecast, we are ill-prepared for what may happen. Ice-sheet loss and rising sea levels are a delayed response to warming. Australian scientists from the University of New South Wales report that: “An equilibrium climate under current temperatures would have a sea level several metres higher than what we have today (likely 5–10 metres higher). We also know that an equilibrium climate under current carbon dioxide (CO2) concentrations would have a sea level 5–25 metres higher” (emphasis added). Is this widely understood? Due to model limitations, we will not know exactly how the climate crisis will unfold until it’s too late. Is there a risk that the Hothouse scenario has already been initiated? Scientists have answered “yes”, thus: “We might already have lost control of whether tipping happens”. What actions would be required to mitigate this outcome, or the risk it may soon be triggered, depending on human actions over the next decade? These questions are barely being asked, let alone answered, yet the consequences of not having a sound response may be existential for human civilisation.
Decarbonisation is not enough. Even sharp reductions in emissions will not be enough to avoid crossing the 1.5°C threshold, and very likely the 2°C threshold, given record-breaking use of fossil fuels in 2021 and the forecasts for 2022-24. It is a big mistake to think we can “park” the Earth System at any given temperature rise – say 2°C – and expect it to stay there. 2°C may not be a point of system stability. Reducing the level of atmospheric CO2 by carbon drawdown is vital, but the drawdown impact is relatively slow. The more damaging impacts, and risk of triggering non-linear events — associated with a higher level of warming for several decades in overshoot scenarios — are understated or ignored. The need to cool the planet in order to avoid cascade/collapse/”Hothouse” scenarios needs to be taken seriously. There are proposals for more direct cooling of threatened systems — as advocated, for example, by the Climate Crisis Advisory Group and the Cambridge Centre for Climate Repair for the Arctic with marine cloud brightening — or of the planet as a whole, whether by mirrors or sulfates. Whilst not yet proven to be of net benefit, and/or cost effective, such proposals seem vital if Earth is to be kept below a level of warming where more system tipping points are activated and cascade into an avalanche of warming and system feedbacks that human actions will no longer have the capacity to rein in.
Former UK chief scientist, Sir David King, working as an adviser to the UK government, collaborated with the small-island states in the lead-up to the 2015 Paris climate conference, arguing successfully that global temperature should not go above a 1.5°C rise for safety. But in 2021, The Independent journalist Donnachadh McCarthy reported that King, the UK’s former chief scientist, “astounded me by saying he now realised this was wrong, and believes the passing of the Arctic tipping point has been reached... He said the 1.1°C rise that we already have is too dangerous —- and candidly admitted he believed US climate professor James Hansen had been right after all in 1988, when he warned the US Congress that we should not pass 350 ppm. We have now breached 415 ppm and are heading fast towards 500 ppm, Sir David said” (emphasis added).
It is not surprising that King, who acknowledges that the Greenland Ice Sheet has passed a point of system stability, is spearheading research efforts to find practical ways to cool and refreeze the Arctic as a matter of priority.
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