Jaws of the Snake

Making Sense of the Politics of Extreme Climate Projections

DALL-E, Show me RCP8.5 as a snake

Policy making involves choosing among alternative possible courses of action in order to achieve desired outcomes. Policy analysis maps the consequences of decision alternatives and where they might take us. Both policy making and policy analysis have politics because people don’t always agree on where we should be headed, the means to achieve desired ends, and our maps of the terrain that we use to get from here to there.

At the highest levels of debate over climate policies, climate modeling may have seemed to have made such discussions unnecessary. Climate models are often invoked to tell us that if we continue as we have been, then we risk near-certain catastrophe. They also are used to tell us that if we implement climate mitigation policies, then we eliminate that risk of catastrophe.

That makes decision making simple and obvious, right?

It is this apparent simplicity that has led to climate scientists, and modelers in particular, to be viewed as the go-to experts for advice on climate policy. This approach to climate policy analysis has also placed scientific authority at the center of political debates — climate scientists vs. skeptics and deniers.

Of course, climate policy is much more complex than this, but for better or worse, public and political discourse has been reduced to a debate centered on scientific predictions of our collective long-term futures. Climate modelers have the unique expertise and authority to give us a window into those futures, so of course— the argument goes — they should have authority in politics.

I noticed this dynamic for the first time almost 30 years ago when working on my PhD dissertation on the roles of climate science in climate policy. Back then it was possible to read every U.S. congressional hearing on climate that had ever been held.

These hearings invariably followed the same script: A distinguished panel of climate scientists would offer prepared testimony on their research and what their research said about the climate future. Invariably, members of Congress would then focus their questions to these scientists on what policies should be implemented.

Research shows that these dynamics persist — legacy media and social media emphasize the IPCC Working Group 1 and 2 reports, which provide projections of climate futures and their impacts, and de-emphasize Working Group 3 which has expertise in energy systems and technologies of mitigation. Anyone paying attention to climate policy and politics will be familiar with these dynamics.

Prophesy rules the discourse and prophets are our priests.

Climate prognosticators have assumed such a prominent role in climate policy discussions no doubt because of the longstanding biases in favor of the physical sciences in and out of the sciences. Another reason however is more specific — climate projections have for many decades shown a huge gap between where we thought we were headed versus where would would wind up if we changed course, making the policy calculus seem simple and obvious.

You can see this huge gap in the figure below showing projected global average surface temperature change to 2100, from the IPCC Fifth Assessment Report in 2013, for its baseline (high) and low mitigation scenarios.¹ The gap between the scenarios is large enough that it still exists even when uncertainties are included, represented by the shaded areas. This gap — when applied to impacts and outcomes — is often cited as showing the benefits of climate mitigation, such as in the current draft of the U.S. National Climate Assessment.

IPCC AR5 SPM

I’m going to call that gap the “jaws of the snake,” as illustrated in the figure below.

Open wide!

Once you are aware of the jaws of the snake, you will see it everywhere in the projections in climate research and assessment.

Last week Glen Peters, of CICERO in Oslo and one of my favorite climate experts,² posted on X/Twitter a jaws of the snake figure illustrating the implications of different types of uncertainty when comparing low and high emissions scenarios. You can see Glen’s post and figure below.

I noticed that Glen was using SSP4-6.0 as the high scenario and SSP1-1.9 as the low scenario. These two scenarios are arguably on the upper end, implausible as a baseline, and on the lower end, infeasible as mitigation. So I asked Glen if he could produce a similar figure with more plausible/feasible scenarios — specifically SSP2-4.5 on the upper end and SSP1-2.6 on the lower.

Glen graciously agreed and shared the figure below.

What do we see? The jaws of the snake are closed! As Peters explained, “They overlap quite a lot. Which is why I picked the two I did (19 and 60).”

As our view of the long-term climate future becomes less catastrophic, due initially to moving beyond misleading, implausible scenarios and then continuing into the future as decarbonization accelerates, the jaws of the snake will close even tighter. A narrowing of plausible futures is an inevitable consequence of climate policy progress, which by definition means a convergence between where we are headed and where we choose to go.

Of course, closing jaws of the snake does not mean that climate change goes away or is not important to address. It does mean that we will need to be more thoughtful and scientifically grounded in our assessment of the implications of different paths into the future.³

Closing jaws of the snake have profound implications for climate science, policy and politics. Here are a few:

• Advocates for climate action will have much more difficulty pointing to climate model results to assert unequivocal near-term benefits of climate policy on the behavior of the climate. More technically, the “timescale of emergence” of detectible influences of climate policy on the behavior of the climate system will likely extend much further into the future, and for many phenomena, well into the next century or beyond.⁴

• There will thus be strong political pressures (from both outside and inside the science community) to hold on to extreme scenarios — a la RCP8.5 — or conjure up new approaches to producing extreme outcomes, such as by boosting assumed climate sensitivity. Keeping such extremes in play would keep the jaws of the snake open. Meantime, those opposed to climate action will push to present the jaws of the snake as being closed. Thus, it will be important to have institutions that can play things straight in the face of the political push and pull.⁵

• Here is where things get a bit complicated: Closing jaws of the snake presents a political risk for climate scientists who have long been used to being viewed as climate policy experts despite (typically) having little expertise in policy, economics or energy. As a result, the politics of expertise and perceived authority no doubt will create pressures to present those jaws as being wide open for as long as possible.

• Climate mitigation policies that cannot be justified based on the jaws of the snake will benefit from a broader base of justifications — such as economics, security, access and non-climate environmental benefits. A broader base would improve the political robustness of arguments for mitigation and if done effectively, expand political support for decarbonization.⁶ But at the same time — such a change in perspective would diminish the primacy of prognosticative climate modeling.

The future is not what it used to be. Science and policy need to keep up, regardless whose expertise wins and loses.

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1. Here is a “jaws of the snake” figure from the more recent IPCC AR6. Note that SSP2-4.5, which current policies are currently undershooting, is displayed with no associated uncertainty. If uncertainty were shown for SSP2-4.5, the jaws of the snake would be closed.

2. If you do not follow Peters on Twitter, I highly recommend it — @Peters_Glen — smart, honest, prolific.

3. Where “scientifically grounded” means the social, policy and economic sciences as well as the humanities and other expert knowledge.

4. Global average surface temperatures likely offer one of the best variables for identifying the jaws of the snake. When it comes to precipitation or, especially, extremes those jaws will be tightly closed.

5. I doubt the US NCA can play things straight. The IPCC has an opportunity to do so.

6. We don’t need the jaws of the snake to know that such a broader base of justification and support makes good sense.