The Climate Overshoot Commission Releases its Report
A dozen global leaders weigh in on the chance of exceeding the Paris temperature targets and what it means for climate response.
The Climate Overshoot Commission recently accomplished its work, releasing its report on the United Nations last Thursday, September 14. This report comes at the side of the U.N. General Assembly and a set of high-level climate and environment events, including the Sustainable Development Goals Summit, 18-19 Sept, and the Climate Ambition Summit, 20 Sept.
The Climate Overshoot Commission is a senior independent international body, consisting of twelve distinguished individuals from world wide, including former heads of presidency, national ministers, and leaders of major environment, development, and civil society organizations. Chaired by Pascal Lamy, former Director-General of the World Trade Organization, it was convened by the Paris Peace Forum. The UCLA Emmett Institute contributed to the establishment and work of the Commission in several ways. Two former Emmett Institute law fellows served on the Secretariat. UCLA law students provided research and analytic support to the Secretariat within the International Climate Law and Policy Clinic. I served as a senior advisor to the Secretariat. On this and a couple of subsequent posts, I’ll present highlights of the Commission’s contributions, with some commentary — my very own views, after all, not those of the Commission, which has very cogently spoken for itself.
There have been dozens of international commissions. A few of it’s possible you’ll recall the 1986 World Commission on Environment and Development, or Brundtland Commission, which first popularized the thought of “sustainable development.” Commissions generally aim to advance international debate on hard issues, typically when other bodies are constrained of their ability to achieve this. Commissioners bring experience, stature, broad global representation—but crucially, aren’t presently in political office, in order that they aren’t required to advance national positions. They’ll speak and discuss freely. Like its predecessors, the job of the Overshoot Commission was to say things which can be true and vital, but that other more politically constrained bodies are unable to say: to speak loudly about elephants within the room and naked emperors.
This boiled all the way down to two jobs. The primary was to sound the alarm concerning the imminent likelihood of worldwide heating exceeding the Paris temperature targets. The second was to say what this high risk of exceeding the targets— “overshoot”— means for climate response.
For the primary, the Commission did its job pretty much, albeit with some reservations. Its forceful opening message is that the likelihood of global-average heating exceeding 1.5°C above pre-industrial levels—the more ambitious of the Paris targets—is “alarmingly high and continues to rise.” This can be a stronger statement of this risk than has been made by any similarly high-level climate body, although not nearly as strong as is justified. Exceeding 1.5°C is virtually certain: indeed, it’s quite more likely to occur inside the subsequent decade. More seriously, the Commission was silent on the chance of exceeding the upper Paris goal, 2.0°C—with way more severe impacts than 1.5°C— which can also be high and mounting. The Commission did report recent assessments from three bodies—the IPCC, UNEP, and IEA —which have synthesized projections of end-of-century heating. These are pretty alarming. Just maintaining present emissions-cutting actions—i.e., no further strengthening, but in addition no backsliding—give end-of-century heating of three.2°C (IPCC), 2.6°C (UNEP), and a couple of.5°C (IEA); adding commitments in NDCs on top of current actions gets these all the way down to 2.8°C (IPCC) or 2.4°C (UNEP); and adding conditional commitments and long-term net-zero targets reduces these to 1.7°C (UNEP and IEA). Recuperating, but not very comforting.
Deciding how you can speak effectively about such projections is surprisingly hard, for a few reasons. First, such statements aren’t just scientific but are also political—intended to report what is thought or knowable a few risk, in such a way as to elicit a certain sort of response. All public-facing bodies just like the Commission fret over how you can sound the alarm that bad things are coming, to convey an appropriate level of action-motivating alarm without inducing despair and passivity. Second, there may be real uncertainty in such statements, which gets larger and is more depending on human alternative the further ahead you look. While exceeding 1.5°C is just about locked in, there may be a lot range for human motion in longer-term projections like 2.0°C, that the majority bodies —just like the three the Commission quoted—speak not when it comes to likelihood, but when it comes to if-then, conditional statements. If control measures are this strong, then we project this degree of heating. The Commission selected to deal with the 1.5°C goal, to talk very forcefully concerning the likelihood of exceeding it, but to not suggest certainty or unavoidability.
To offer the Commission credit where due—and it’s due in lots of places—on one point closely related to those projections, they were uncommonly and admirably frank: Noting the risks and the stark tradeoffs posed by aerosol pollution within the lower atmosphere. This pollution, mostly from burning fossil fuels that contain sulfur, has severe current environmental and health effects, estimated to kill greater than 5 million people per 12 months attributable to respiratory illness. It is usually exerting an inadvertent cooling effect that masks a big fraction—perhaps a 3rd to a half—of the climate forcing from previously emitted greenhouse gases which can be already within the atmosphere. This pollution needs to be cleaned up—and is being cleaned up—notably via the recently enacted tightening of restrictions on the sulfur content of marine bunker fuels adopted by the IMO. But cleansing this up will remove its cooling effect, which the IPCC recently estimated as 0.7°C.
One other related contribution the Commission made to climate clarity and realism (although lower than it perhaps may need) concerns using the term for which it was named, “Climate Overshoot.”
Overshoot scenarios initially appeared in integrated assessment models (IAMs). They’re projections during which some measure of environmental disruption initially exceeds a goal, e.g., one in every of the Paris global temperature targets, but then stops growing, reverses, and eventually returns to the goal level after this temporary period of exceedance. Calling these “overshoot scenarios” is sensible in describing model results, but is somewhat misleading in the actual world, since it implies that after you exceed a goal you might be on an overshoot trajectory, which can sooner or later reverse and return to the goal. In other words, the term suggests that such reversal and return is by some means automatic or easy, maybe even built into the definition of “overshoot.” But what is definitely highly likely will not be the entire overshoot trajectory, however the initial exceedance of the goal. How large and long-lasting the exceedance is, indeed, whether temperature actually returns to the goal in any respect reasonably than simply staying higher, is dependent upon what happens to net emissions afterwards. Returning to or below the goal, let alone doing so after only a small and temporary exceedance, will take the identical extreme reductions in emissions which have been so difficult to realize so far, now with the extra requirement that any continuing emissions be greater than offset by extreme scale-up of stable atmospheric removals. Current and coming advances in carbon-free technology will help, after all. But given many years of shortfall in reducing global emissions, and continuing structural aspects hindering needed sharp reductions, there isn’t any justification to assume this vast transformation will by some means get easy, let alone automatic, by the mere fact of exceeding the targets and suffering the resultant worse climate impacts. Fossil interests will keep fighting, even it’s to stretch their demise out longer reasonably than to live without end. Perhaps increasingly severe climate change and impacts will make transformative socio-technical change easier, but this is dependent upon political assumptions – theories of social change – that aren’t clear.
An illustration of the deep difficulty pondering coherently about exceedance and overshoot could be found right within the recent IPCC AR6 report—some extent the Commission discovered in the middle of its work but didn’t include in its report. The overshoot scenarios reported within the IPCC all fall into two buckets: “low overshoot,” during which 1.5°C is exceeded by at most 0.1°C (this bucket also features a tiny variety of scenarios with no overshoot in any respect, but to be somewhat glib, no person believes those); and “medium to high” overshoot, during which 1.5°C exceeded by 0.1 to 0.3°C. An informal read might be forgiven for inferring that these numbers reflect a reasoned conclusion by the IPCC that these are the most important overshoots the world will likely need to cope with. But unfortunately that’s not what it means in any respect. These buckets with their low overshoot numbers are a definitional artifact, arising from the year-2100 endpoint of the analyses. For a scenario to be called “overshoot,” it needed to get back to its goal by the year-2100 end of the analytic time horizon. Scenarios that peaked above 1.8°C—i.e., that exceeded 1.5°C by greater than 0.3°C this century– didn’t have time to get back below 1.5°C by the tip of the century, so weren’t labeled or analyzed as overshoot. Much more so, no scenario that exceeded 2.0°C might be called overshoot, because there will not be enough time on any trajectory to exceed 2.0°C, reverse, and return to 2.0°C by the tip of the century. So, the overshoot scenarios identified and analyzed as such are in reality the perfect possible trajectories during which 1.5°C is exceeded, which manage to get back to 1.5°C by 2100. The IPCC by no means ruled out or judged unlikely future trajectories with higher and longer-lasting exceedances. These are there—in reality, they’re clustered into buckets by their end-of-century heating. These include, for instance, the scenarios I reported above, during which continuance of present policies or NDC commitments without increasing ambition (granted, a scenario which may be unlikely on the pessimistic, no-action side) give end-of-century heating of three.2°C and a couple of.8°C, respectively (with the lower figures subsequently estimated by UNEP and the IEA, as noted above).
Having sounded the alarm concerning the likelihood of overshoot—albeit pulling their punches somewhat in concession to the perceived need to provide a positive message—the Commission’s second job was to say what this high risk of overshoot means for climate response.
At first cut, this is a straightforward story: do more of all the pieces and do it faster. But given the widespread desire to not face the stark likelihood of doubtless severe exceedance, there actually is more to say—particularly, that the gravity of risks requires consideration of more extreme or radical approaches to limiting climate change than have gained serious attention so far. It is not any longer acceptable to deem plausible solutions that may help inadmissible a priori.
The Commission did this and did it pretty much—to various degrees across the 4 major response types, of which they addressed all – mitigation, adaptation, removals, and solar geoengineering or SRM. Indeed, given the present state of climate debate, merely including all 4 response types with similar levels of scrutiny and detail represents a major contribution. In addition they presented a useful and original conceptual framework for occupied with climate responses in presence of overshoot, dividing the 4 response types into two pairs in line with which of two large-scale goals they pursue: Reducing the magnitude and duration of overshoot; and reducing the harms that follow from any given magnitude and duration of overshoot. The 2 responses that limit the magnitude and duration of overshoot are mitigation and removal: deep cuts in present and future emissions; and removing past emissions from the atmosphere and putting them somewhere long-term secure. The 2 ways to limit the harms resultant from any specific magnitude and duration of overshoot are adaptation and solar geoengineering (Sort-of, on the last one: the Commission doesn’t recommend solar geoengineering—in reality, its immediate advice is to enact a moratorium on it—however it also recommends researching it and beginning to discuss how you can resolve the governance problems it might raise). In addition they individually addressed climate finance; a cross-cutting response relevant to all responses.
I’m going to handle how the Commission handled each response type in subsequent posts, which I’ll put up at intervals of 1 or two days. The following two will individually consider the 2 response types where the Commission’s recommendations are most radical, most original, and almost definitely to draw controversy: mitigation and solar geoengineering. I’ll then review their evaluation and suggestions on adaptation, removals, and climate finance, and shut with a review of reactions to the Commission (which should begin to be clear by that time) and speculation on its impact.