IPCC report spurs climate advocates onward
By Rick Knight
On August 6, the Intergovernmental Panel on Climate Change (IPCC) issued the first chapter of its latest comprehensive climate report, the Sixth Assessment Report (AR6). For background, the IPCC issues these ARs at intervals of five to seven years, with other special reports, like the Special Report on 1.5°C issued in 2018, sandwiched in between as circumstances dictate.
The just-released AR6 volume is The Physical Science Basis of Climate Change, with three more volumes (impacts, solutions, and a synthesis) yet to come. When this one hit the street, environmental writers got busy with their interpretations. But it’s important for CCL volunteers to understand this work in the context of CCL’s mission, and that understanding is not always well-served by even the most thoughtful media commentary. So, here is the view from your Research Department.
Retrospective from prior reports
In terms of where the climate now stands, the AR6 science report follows the same general arc as earlier reports. It confirms that the planet is warming more than any natural cycle can explain, and it’s been ramping up regularly since about 1970. Climate scientists’ best estimate is that global warming over the past 150 years is caused entirely by the buildup of greenhouse gases, predominantly from extracting and burning fossil fuels for energy. If there were any vestiges of doubt with respect to human responsibility, they have now been erased.
As for what’s happened since AR5 was released in 2014, there are no big surprises. Emissions have continued going up, and the climate has responded more or less as expected. AR6 explored the consequences, both global and regional, of historical warming: sea-level rise, heat waves, precipitation extremes, stronger tropical cyclones, drought, and even “compound” extreme weather events in which some of these climate impacts exacerbate others (like extreme heat and drought fueling worse wildfires). Links between global warming and extreme weather have come more clearly into focus, and the authors take pains to help policymakers understand how their particular nation or region is likely to be affected.
The latter two-thirds of AR6 concern what the future holds. The IPCC treats this question via five modeled climate scenarios based on what are called ‘Shared Socioeconomic Pathways’ [SSPs], explained here by CCL’s new Research Coordinator Dana Nuccitelli, ranging from the most optimistic (SSP1-1.9) to the least (SSP5-8.5). Fully understanding the implications of these scenarios requires an understanding of climate risk.
Here’s a video where Dana summarizes key take-home points regarding human-caused global warming and increasingly extreme weather:
Yogi Berra once said, “It’s tough to make predictions, especially about the future.” This is true, especially when trying to get 234 scientists from 66 countries to agree on them. But climate science predictions are not about certainties; they are about risk. Various terms used in the report, like “limited agreement,” “high confidence,” “more likely than not,” etc., are intended to convey this.
The climate change number that has been seared into the public’s consciousness is 1.5 degrees Celsius, which puts climate risk into a numerical context. Unfortunately, its connotations have been distorted in several ways. To many, it’s come to represent a cliff’s edge that, once crossed, sends us tumbling into a bottomless chasm. Predictably, that is leading many people, especially young people, to despair for their future. On the other hand, a large swath of the public who are still unconvinced of the reality or seriousness of climate change may perceive 1.5 degrees as a trivially small number, compared to the temperature swings we observe in our daily lives. These are two bookends of misunderstanding.
In reality, 1.5°C has no special scientific significance in terms of what will or will not happen at that precise point. The AR6 report even states (in Section D.6) that it might take as long as 20 years to even know with certainty whether we’ve exceeded it.
We suggest paying closer attention to a number in the IPCC report that’s easier to nail down and also more intimately connected to the root cause of climate change: the carbon budget. This is the amount of fossil carbon (expressed in GtCO2, or gigatons of CO2) that, when burned, would create an unacceptable risk of surpassing certain temperature thresholds and the associated climate change consequences. It doesn’t mean those bad things will happen if we exceed that budget, but that the probabilities that they will happen become unacceptably high. This is best expressed in Table SPM.2 (p. SPM-38), reproduced in simplified form below.
This shows that if we burn less than 300 GtCO2 this century, we have an 83% chance to keep warming below 1.5°C; if we burn 900 Gt, we only have a 17% chance. If you wanted to place your bet on a 50:50 chance, you could pick 500 Gt. While this is still not an easy concept to wrap our heads around, it does give us discrete numerical targets that link directly with our behavior. Right now, the world is emitting about 36 Gt per year, of which the U.S. contributes around 5.3 Gt. Both 2020 and 2021 are essentially over, so that 300 Gt budget is down to about 230 Gt, or about 6 years’ worth of global carbon emissions at current rates.
Translating risk into action
How quickly must we cut these emissions to minimize these risks? To answer that, the IPCC presents the five scenarios mentioned above. The left-hand chart below shows the CO2 emission curves that give us a better-than-50:50 chance of following global temperature curves shown in the right-hand chart.
As scientists, the IPCC must consider whatever scenarios are plausible given the geopolitical landscape, but as climate advocates, our perspective is entirely different. Our task is to influence policy and drive it toward the best possible outcome. Our goal should be to aim for SSP1-1.9 — the 1.5°C scenario — and turn it into reality. As the first chart shows, that is achievable, but requires emissions to be cut rapidly. It also shows that carbon-negative technologies (bringing emissions into the gray area below zero) will be necessary, but the immediate, urgent task is to get current emissions to zero as quickly as we can.
Working in the right direction
The IPCC’s first release in their AR6 suite of reports reinforces the urgency of action, but also presents a very important subtext: the risk of dire consequences from global warming continues to increase, but no matter where we find ourselves, we can always make the future better than it would be without our participation.
This is exactly why we continue to advocate for a rising carbon price: it’s the fastest way to cut emissions and keep total carbon consumption as low as possible. And with the U.S. still possessing the world’s strongest, most diverse, and most influential economy, as well as having emitted far more total carbon emissions than any other country, it’s imperative that we take the lead in making this happen. Everything in the first IPCC AR6 report underscores this fact.
Above all: don’t freak out but don’t let up!
Rick Knight is a Research Coordinator for CCL