Sacred Headwaters #5: Carbon Sequestration
Carbon sequestration -- or "negative emissions" -- is a tool for climate change mitigation. What is it, how important is it, and to what degree can we rely on it?
Sacred Headwaters is a bi-weekly newsletter that aims to guide a co-learning process about the existential issues and planetary limitations facing humanity and about how we can reorient civilization in a way that will enable us to thrive for centuries to come. If you’re just joining us, consider checking out the first issue for some context and read through the other issues when you can. The newsletters are not strictly sequential, but this exploration is meant to build on knowledge and understanding over time. Subscribe below if you haven’t already:
Sacred Headwaters #5: Carbon Sequestration
Last month at the World Economic Forum in Davos, carbon sequestration was the talk of the town, mainly through the “one trillion tree initiative.” Even President Trump signed on. The term carbon sequestration is often used to refer to technical approaches — “scrubbing” CO2 directly from the air or from industrial flues with chemical substrates. That’s one type, but sequestration occurs naturally through many processes, and we can enhance (or destroy) these processes with human action (see issue #3 on soil and regenerative agriculture). It’s also referred to as “negative emissions” and it’s generally considered a critical part of any successful climate action plan. Every IPCC-modeled pathway to 1.5C (a target that is increasingly unrealistic) requires emissions to go net negative in the coming decades. Other studies have argued that even 2C is impossible without negative emissions. The important caveat here is that these negative emissions aren’t needed to reduce (or offset) current emissions — they’re critical for actually shrinking the concentration of GHGs in the atmosphere after we’ve brought emissions as low as possible. The projected scale of negative emissions technologies (NETs) is quite small in comparison to the actual emissions reductions we can — and must — achieve.
In this newsletter, we’ll learn about the different approaches to negative emissions and where they fit into a broader plan for climate change mitigation, and, for some of them, how they mesh with holistic approaches to ecological restoration and sustainability.
Glossary
There’s a lot of jargon in this issue, so I’ll define a few terms here for clarity:
NETs - negative emissions technologies. This is basically an all-encompassing term for carbon sequestration strategies.
CCS - carbon capture and storage
BECCS - bio-energy with carbon capture and storage
CDR - carbon dioxide removal
AFOLU - agriculture, forestry, and other land use
I also realize I’ve been using the word “sustainability” a lot, and that it’s meaning is both a bit fuzzy and politically charged. It became common in 1987 when the UN Brundtland Commission defined “sustainable development” as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” This definition bound sustainability to development (and economic growth) in the modern dialogue, something we’ve been struggling to overcome ever since. In my view, sustainability in the human context is the ability of our civilization to thrive — or maybe even just to exist — indefinitely. In the broader earth system context — of which we are inherently a part — it means maintaining a degree of relative stability along the lines of what we’ve seen over the last 10-12,000 years of the Holocene. Both of these contexts impact and are impacted by social (human) and biophysical processes. At a basic level, a civilization that relies on consuming (and not replacing) a finite resource is by definition unsustainable. The only resource that’s regularly added to the earth system from outside is solar energy.
Our actions now are determining whether or not human civilization as we know it can be “sustainable.”
(“Indefinite” in human terms is obviously not indefinite. The sun will heat up over the next couple billion years, engulfing our planet before eventually dying a fiery death — although other uncontrollable factors will likely end our great experiment before that happens).
“The ultimate guide to negative-emission technologies” (10 minutes)
This short piece introduces the main players in negative emission technologies: reforestation / afforestation, BECCS, direct air capture, soil carbon, biochar, and enhanced weathering. A couple notes about the article. First, the timeline graph included is out of date and targets 2C — you’ll notice it has an inflection point at 2015 in total emissions. We haven’t yet seen that inflection and it’s now 2020. The IPCC says that to limit warming to 1.5C, we need to reach “net zero” by 2050; this graph shows net zero at 2075 (a timeline more plausible for a 2C scenario). Second, the author numbers the approaches, but those numbers don’t seem to reflect anything. Third, this list isn’t exhaustive — other approaches such as ocean fertilization (enhancing the growth of natural carbon-consuming organisms like plankton) are being researched as well. Many of these techniques are listed as solutions by Project Drawdown. Feel free to read more about them there.
A couple things to think about as you learn about these technologies. Which ones are reductive in both their approach and their effect? What are the possible problems with reductive approaches? And which ones are potentially important beyond their direct impacts on GHGs?
“What genuine, no-bullshit ambition on climate change would look like” (15 minutes)
The IPCC Special Report on Global Warming of 1.5C referenced above came out in October 2018 and made a bit of a splash with its reliance on NETs, which is why most of the articles I’m including in this newsletter came out shortly afterwards. In this piece, David Roberts (an excellent climate reporter at Vox) looks at a handful of studies that attempted to draw scenarios for 1.5C while minimizing the need for negative emissions technologies. The results? There’s a path forward, but the only option that completely eliminates the need for BECCS is to set ambitious and transformative goals — and then meet all of them. Roberts ultimately reaches what is really the only sane conclusion: “go as hard and fast as possible, forever and ever, amen.” We will likely need NETs to reduce warming in the latter half of the century, but we cannot plan on solving carbon budget overshoot with negative emissions later — we need to try as hard as we can to meet our goals through traditional emissions reductions.
“Negative emission technologies: What role in meeting Paris Agreement targets?” (15 minutes)
Please read the summary and section 4 — “Policy Implications” — of this report from the European Academies’ Science Advisory Council.
This report looks at the current state, projected potential, and possible side effects of the available NETs, ultimately concluding that the IPCC overstates the plausibility of CO2 removal. The authors emphasize that while we need every tool in the box — and that research into NETs should continue — our primary focus must be on emissions reduction and other more traditional mitigation strategies. In section 4 (and in the annexes if you’d like to learn more), they look at each approach, comparing the scientifically estimated potential (in gigatonnes carbon per year) and other possible impacts. Importantly, they contextualize NETs within the earth system, pointing out that BECCS — and afforestation and ocean fertilization — have the potential to actually cause reverse effects on climate through secondary effects, worsening climate change instead of bettering it. They conclude that supporting certain NETs and continuing to research CCS is important, but that these technologies cannot broadly be relied upon.
“Soil as Carbon Storehouse: New Weapon in Climate Fight?” (10 minutes)
Soil carbon is, of course, not a new weapon — humans have been sequestering carbon in soil for at least 3000 years. But it is a powerful one, and it’s one that offers a holistic approach to managing our position in the earth system rather than just reducing atmospheric CO2. If you missed issue #3, we read about how soil degradation due to industrial agricultural practices is threatening our food supply. Turns out, solving that also enhances soil carbon. The moniker “soil carbon” extends beyond agricultural land as well. Restoring wetlands, coastal deltas, and other sensitive ecosystems has the potential to sequester large amounts of carbon…and to provide flood control, protection against rising sea levels, and more. Win win. In what is basically a footnote, the IPCC calls these “co-benefits” of AFOLU-related CDR, but when many other sequestration approaches are both expensive and potentially harmful for important human systems (land use for BECCS, etc.), soil carbon and ecosystem restoration start to look very appealing.
Book Recommendation: Carbon Capture, Howard Herzog
Howard Herzog is a researcher at MIT who has spent decades working on carbon capture and storage technologies. This book is an overview of that work, explaining the steps involved in the process, discussing ongoing (as of 2018) efforts to deploy CCS technologies, and assessing the political landscape surrounding implementation. He believes that negative emissions has a critical role to play in our efforts to combat climate change. But he also believes that role is fundamentally limited and that we cannot depend on it to compensate for short-term overshoot in the latter half of the century, a message that is likely beginning to sound familiar at this point.