This article was produced by Earth | Food | Life, a project of the Independent Media Institute.
Human activity—mostly the burning of fossil fuels—has raised Earth’s atmospheric carbon content by 50 percent, from 280 parts per million (ppm) to 420 ppm. Since the start of the Industrial Revolution, we’ve released approximately 950 billion metric tons of carbon into the air. Every year, humans emit more than 40 billion metric tons of carbon dioxide (CO2) into the atmosphere, as of 2021 measurements. Even if we stop burning fossil fuels now, the amount of CO2 already in the atmosphere will cause Earth’s climate to continue warming for decades, triggering heat waves, droughts, rising sea levels, and extreme weather.
Climate scientists warn that if we want to avert catastrophe, a significant amount of excess atmospheric CO2 must be captured and sequestered. The process is called carbon dioxide removal (CDR), and it has been receiving more attention as nations, states, and industries strive to meet their climate goals. But how should we go about doing it?
There are two broad strategies: biological and mechanical. Nature already absorbs and emits about 100 billion metric tons of carbon dioxide every year through the natural processes in the biosphere—including plant growth—an amount 2.5 times humanity’s annual carbon output. So, according to advocates for biological carbon removal, our best bet is simply to help the planet do a little more of what it is already doing to absorb carbon. We could accomplish this through reforestation, soil-building agricultural practices, and encouraging kelp growth in oceans.
On the other hand, advocates for mechanical carbon removal point to technologies that successfully capture CO2 in the laboratory; if these machines were scaled up, those advocates tell us, we could create an enormous new industry with plenty of jobs while removing atmospheric carbon and reducing climate risk. Scientists are exploring several chemical pathways for direct air capture (DAC) of carbon and ways to sequester CO2 in porous rock formations. Revenue streams come from government subsidies or from the use of captured CO2 in enhanced oil recovery (EOR).
So, which pathway—nature or machines—holds more promise?
In its sixth assessment report, released in March 2023, the Intergovernmental Panel on Climate Change (IPCC), the United Nations body that regularly assesses the current state of climate science, points out that “biological CDR methods like reforestation, improved forest management, soil carbon sequestration, peatland restoration[,] and coastal blue carbon management can enhance biodiversity and ecosystem functions, employment[,] and local livelihoods.”
On the other hand, notes the IPCC, the implementation of mechanical DAC along with underground sequestration of CO2 “currently faces technological, economic, institutional, ecological-environmental and socio-cultural barriers.” Further, the current global rates of mechanical carbon capture and storage “are far below those in modeled pathways limiting global warming to 1.5°C to 2°C.”
In a study published in the journal PLOS Climate in February 2023, a team of American scientists analyzed the benefits and downsides of the two pathways in detail. They used three criteria: effectiveness (“[d]oes the process achieve a net removal of CO2 from the atmosphere” once all inputs and outputs are accounted for?), efficiency (“[a]t a climate-relevant scale… [of a billion metric tons of CO2 per year], how much energy and land are required?”), and impacts (“[w]hat are the significant co-benefits or adverse impacts [on nature and society]?”).
The team gathered data and crunched the numbers. The lead author, June Sekera, a carbon researcher and visiting scholar at the New School for Social Research in New York, concluded:
“[B]iological sequestration methods, including restoration of forests, grasslands, and wetlands and regenerative agriculture, are both more effective and more resource efficient in achieving a climate-relevant scale of CO2 removal than are techno-mechanical methods—which use machinery and chemicals to capture CO2. Additionally, the co-impacts of biological methods are largely positive, while those of technical/mechanical methods are negative. Biological methods are also far less expensive.”
In this comparative study, the scores for natural versus mechanical carbon removal methods were not close: Natural methods won in every category—and by a significant margin. The problem with machine-based carbon removal is not just that current technologies are immature (with the hope of getting better with more research and investment), but also that using machines is inherently inefficient, costly, and risky. On the other hand, removing carbon by restoring nature costs less, is more effective at reducing atmospheric carbon, and offers numerous side benefits.
The American study also noted that its findings “that biological methods exhibit superior effectiveness in comparison to DAC are consistent with data reported in the 2022 IPCC study.” It added in plain terms: “According to the IPCC, not only are biological methods of CDR more effective than DAC…, but their effectiveness is projected to increase significantly over time.”
As if to underscore that conclusion, a separate study published in March 2023 in the journal Nature Climate Change concluded that the protection and rewilding of even a small targeted group of wildlife species would help facilitate the capture and storage of enough carbon to keep the global temperature below the tipping point of warming 1.5 degrees Celsius above pre-industrial levels.
You might expect, therefore, that policymakers would currently be directing all of their support toward natural carbon removal methods. But you’d be wrong. Government policy support in the form of subsidies is being shoveled mostly into mechanical carbon removal.
In the U.S., the primary subsidy for mechanical CDR is the federal 45Q tax credit, introduced in 2008, which offers $10 to $20 per metric ton of CO2 captured and stored. But there are also carbon offset credit programs (including the California Low Carbon Fuel Standard), subsidies for building CO2 pipelines, and subsidies for the production of alternative fuels (including ethanol and hydrogen) that rely on carbon capture technology to be considered “low-carbon.” The Inflation Reduction Act of 2022 significantly increased the number of credits in 45Q and broadened eligibility, and included federal subsidies for oil producers who pump CO2 underground to make it easier to extract trapped petroleum—which is by far the most common way of using captured CO2.
The Bipartisan Infrastructure Law, which President Biden signed in November 2021, included billions in federal funding for carbon capture projects. In the Midwest, as a result, there has been a rush to build thousands of miles of CO2 pipelines for carbon sequestration—a frenzy that has set off regulatory chaos and is pitting farmers and Native Americans against biofuel plant operators and venture capitalists. Researchers continue to spend time and money finding new chemical pathways to mechanical CO2 capture—resources that could instead be diverted to biological CO2 removal methods. Even AI is being enlisted in mechanical carbon capture efforts.
There are also subsidies that, in effect, promote nature-based CDR methods, including soil conservation and wetlands restoration programs, but these programs were not initially intended for carbon capture and sequestration, and they are not optimized for that purpose. In November 2022, at the global COP27 climate summit in Cairo, the Biden administration announced the “Nature-Based Solutions Roadmap,” an outline of strategic recommendations to put America on a path to “unlock the full potential of nature-based solutions” to address “climate change, nature loss, and inequity.” The roadmap calls for updating policies, providing funding, training a nature-based solutions workforce, and prioritizing research, innovation, knowledge, and adaptive learning to advance nature-based solutions. However, the roadmap remains, for the most part, in the realm of good intentions.
There’s only so much funding available for climate solutions, and the total amount is woefully inadequate. Only strategic investment will obtain significant results for the dollars spent, and it is now clear which path will get results.
Given the clear superiority of nature-based solutions, why is so much support still going toward mechanical carbon capture? Poor judgments in the past have created funding streams and projects with a momentum of their own. Most of the gold-rush fever surrounding mechanical carbon capture can be attributed simply to the lure of subsidies for building new DAC plants and pipelines.
In a 2018 article published by the Thomson Reuters Foundation, Justin Adams—who at the time was the managing director for global lands at the U.S.-based environmental nonprofit Nature Conservancy—urged the European Union to take the lead on using nature-based solutions in the climate crisis fight. “Many economists and policy advisors ignore the potential of natural climate solutions at our peril,” warned Adams’s article, calling a 2018 report by the European Academies’ Science Advisory Council (EASAC) “short-sighted” for downplaying the potential of nature-based climate solutions.
“Natural climate solutions are in fact the world’s oldest negative emissions technology,” Adams wrote. “By managing carbon dioxide-hungry forests and agricultural lands better, we can remove vast quantities of greenhouse gases from the atmosphere and store them in trees and soils.”
The science tells us that policymakers and investors have so far been wrong to advocate so strongly for mechanical CDR solutions to the detriment of biological ones. The fate of future generations is at stake, and we cannot afford to waste both time and money on techno-fixes that are ineffective at achieving our climate goals. The clear path forward to addressing the looming catastrophic effects of climate change is to restore nature.
Teaser photo credit; By NOAA’s National Ocean Service – Kelp Forest, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=46868953
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I always appreciate Richard’s organized clarity in his writing. A couple of questions I would raise:
-Is the New School study biased? They generally have a very specific political position, which shows up in their paper, for instance, in their rejection of offsets and trading schemes, some of which have been very effective, contrary to Sekera et al.’s claims in the paper. Their evidence that supports their very generalized claim that “offsets harm indigenous people” comes from the website of a biased advocacy organization.
-Is the science around biological carbon sequestration well developed, including accounting methods? I think that we are still learning about this, and it may take time to figure out how to measure and which methods result in viable long-term storage.
These results have been obvious to me for years. It is good to see more rigorous confirmation, but it won’t stop our slide to disaster. The only use for captured CO2 is to “sequester” it by using it to increase oil production. That is the real goal..
A technical quibble–early on, this piece refers to DAC as mechanical carbon capture.But DAC means Direct Air Capture, and I’m sure Richard meant CCS as well–that’s Carbon Capture and Sequestration, where big, expensive, energy- wasting equipment is built onto things that emit CO2 (like power plants) to capture the carbon dioxide, and then pipe it to…but here we need another acronym, EOR, for enhanced oil recovery. And THAT’S the answer to the question of why governments (notably the US) are choosing to subsidize the less effective mechanical approach–as Daniel Cooper says, fat 45Q subsidies are arranging for taxpayers to pay the costs to capture CO2 so oil companies can use it to squeeze more oil out of old wells. I think the IRA did more to extend the life of the oil industry than of the climate, even without Manchin’s permitting reform–which he and the Republicans are gunning for yet again, and they’ll probably get it. This choice is only mysterious if you think the objective is to mitigate climate change. I believe that’s not even secondary with the democrats, it’s tertiary–and with the Republicans it’s not an objective at all.
But I’m very glad to see this piece. The faster word gets around that DAC/CCS/EOR are BULL the less money will be wasted on them.
It’s been pretty clear to anyone who knows anything about thermodynamics that significant “machine” CCS is impossible (it’s along the lines of, “what’s easier to ignite with a match – gasoline or water?” That, combined with “how much agency does humanity have left?”). Anderson and others have criticized the IPCC WG-III for badly overstating what’s even possible with carbon drawdown schemes. Kicking-the-can down the road and political resistance are probably the main reasons it’s being supported, but maybe there’s “honest” (as in “well-meaning”) technooptimism in there, too.
I guess much also depends on how you define “climate catastrophe.”
“It’s been pretty clear to anyone who knows anything about thermodynamics that significant “machine” CCS is impossible”
That all depends on how you define “significant”. We already have a demo plant that exceeded 55% thermal efficiency in generating electricity with 100% carbon capture (including compression), and they think closer to 60% should be attainable with a full scale plant. The plant uses one small turbine so it could have the flexibility of an open-cycle plant at far higher efficiency, and is within the efficiency range for combined-cycle plants while being much more flexible. The problem isn’t thermodynamics. The problem is economics–so long as there is no penalty for emitting carbon, or no reward for capturing and sequestering it.
“Nature already absorbs and emits about 100 billion metric tons of carbon dioxide every year through the natural processes in the biosphere…”
Which describes a process in equilibrium–where the long-term sequestration rate is something close to zero.
“according to advocates for biological carbon removal, our best bet is simply to help the planet do a little more of what it is already doing to absorb carbon.”
What we would need to do is shift the natural system strongly out of equilibrium, so that the net long-term sequestration rate goes from something small to something huge.
“Scientists are exploring several chemical pathways for direct air capture (DAC) of carbon and ways to sequester CO2 in porous rock formations.”
DAC represents a long-term research project. For the near term, carbon capture will take place mostly where carbon concentrations are high–such as at power plants.
“Revenue streams come from government subsidies or from the use of captured CO2 in enhanced oil recovery (EOR).”
More likely it will be both. We have other developed and potential uses for captured CO2, but right now EOR is the largest user by far. In the U.S. EOR consumes around 70 million tons of CO2 per year—roughly double the rate from eight years ago, and the rate of growth is increasing. Before carbon capture, virtually all the CO2 for EOR came from underground reservoirs, and the process of exploration, drilling, extraction, conditioning, compressing, and transporting all that CO2 had a considerable CO2 footprint of its own. If we got that CO2 from carbon capture instead, we could have nearly carbon-free electricity that is reliable and flexible (and could help support wind and solar) while also eliminating the exploration, extraction, processing, and compression CO2 footprint that goes with using underground CO2 sources. And increasing the productive life of existing wells reduces the pressure for more exploration and drilling of new wells.
“So, which pathway—nature or machines—holds more promise?”
Does anyone ask whether wind power or solar pv holds more promise? Most people recognize that both have their uses in different situations and we need both of them.
“In a study published in the journal PLOS Climate in February 2023, a team of American scientists analyzed the benefits and downsides of the two pathways in detail. They used three criteria: effectiveness (“[d]oes the process achieve a net removal of CO2 from the atmosphere””
Which would essentially disqualify CCS–which would likely only achieve a net reduction in the amount of CO2 being put into the atmosphere. But we’re going to need that too.
“The problem with machine-based carbon removal is not just that current technologies are immature (with the hope of getting better with more research and investment), but also that using machines is inherently inefficient, costly, and risky.”
Efficiency factors into cost. Not sure what risks are being referred to here, but those probably factor into cost as well. So it boils down to cost vs. return. In the case of CCS for EOR, it could soon be competitive against the extraction option. So the higher cost isn’t necessarily a problem.
“According to the IPCC, not only are biological methods of CDR more effective than DAC…, but their effectiveness is projected to increase significantly over time.”
Which doesn’t rule out the possibility that DAC could also improve over time. In the meantime, there’s CCS.
“In the U.S., the primary subsidy for mechanical CDR is the federal 45Q tax credit, introduced in 2008, which offers $10 to $20 per metric ton of CO2 captured and stored.”
We reward the capture of CO2 because that has broad political support. A more sensible approach would be a carbon tax and dividend system, but that has broad political opposition.
“Researchers continue to spend time and money finding new chemical pathways to mechanical CO2 capture”
It is the people funding the researchers who are spending the money.
“—resources that could instead be diverted to biological CO2 removal methods.”
If people aren’t investing in it, it’s because they don’t see a good business case for it. That isn’t going to improve by shutting down DAC and CCS research and development.
“There’s only so much funding available for climate solutions, and the total amount is woefully inadequate.”
So the goal should be to increase the total amount. Pitting our clean options against each other in a Thunderdome death-match isn’t helpful. And guess what will happen to that total funding amount if you chop out all of the options that conservatives and neo-libs want.
“Given the clear superiority of nature-based solutions, why is so much support still going toward mechanical carbon capture?”
Because despite the higher costs, the business case for the tech solutions remains strong.
“The science tells us that policymakers and investors have so far been wrong to advocate so strongly for mechanical CDR solutions to the detriment of biological ones.”
Advocating for one is not automatically to the detriment of the other. Both approaches have their uses.
“The fate of future generations is at stake, and we cannot afford to waste both time and money on techno-fixes that are ineffective at achieving our climate goals.”
It would take about 2 years to build a gas power plant that has 100% carbon capture, at a cost that’s maybe 30% higher than a gas plant with similar fuel efficiency but no carbon capture at all. We should be penalizing the plant that freely emits CO2, but that’s a political non-starter at this point. However, if we reward carbon capture and help establish that as best-practices for the industry, that could make it politically feasible to start penalizing worst-practices in the future.
Surprised that you neglected to mention how much energy is required for DACCS. To pull 1 GtCO2 out of the atmosphere per year would require 40% of all electricity presently generated. This is the reason the pilot plants are in Iceland, using cheap geothermal energy and easy-to-access basalt storage. This is not a technology that can scale. Meanwhile, some un-funded natural solutions, such as biochar from waste, actually produce energy as a co-product.
”
as nations, states, and industries strive to meet their climate goals.”
I trust this was poetic license? No entity is striving to meet their climate goals. They are merely giving lip service to goals and actually doing very little. In fact most of their actions are designed to increase emissions (mainly due to striving to grow their economy or business, but also as more is done to expand fossil fuel reserves).
I own a soil manufacturing business, where I improve topsoil with the addition of mulch and compost. https://www.resilience.org/stories/2019-08-01/drawing-down-atmospheric-carbon/
I did some rough calculations to determine how much carbon I am sequestering when I make soil. The soil tests between 8 and 9% Organic Matter and OM contains 58% carbon (from this source https://www.agric.wa.gov.au/measuring-and-assessing-soils/what-soil-organic-carbon ). Each cubic yard of soil I make weighs about 2,000 lbs and so based on my calculations it contains between 90 and 100 lbs of carbon. I make about 1000 tons of soil each year, which means I am sequestering 90,000 to 100,000 lbs of carbon or 45 to 50 tons of carbon each year. I’ve been doing this for 25 years and in the early years we were making two to three times the amount of soil I make now. But I’ll just go with 50 tons of carbon each year multiplied by 25 equals 1,250 tons of carbon, which is the minimum amount of carbon I’ve sequestered over the past 25 years.
It would be entirely feasible for any municipality that collects yard trimmings to make compost and soil as I do. And the demand for high quality soil is going up not down. If we expanded municipal programs with farm composting programs there is even more organics and value in their use.
How much organics are we talking about? “EPA analyzed information from state composting programs to calculate the composting of yard trimmings. This analysis resulted in an estimate of 22.3 million tons of yard trimmings composted or wood waste mulched in 2018 with a 63 percent composting rate. State-reported composting tonnages may vary on a yearly basis with the amount of storm debris composted.”
Composting organics reduces the volume from 50 to 95% depending on the length of composting. This means 22 million tons reduces to between 2-11 million tons. A 95% reduction is when the OM has completely turned into humus. Assuming a median value, we could make 5 million tons of compost to amend soils from the yard waste currently collected in the US. That would sequester 3 million tons of carbon each year. To convert a quantity of carbon to the equivalent quantity of carbon dioxide, we multiply by 3.67 and arrive at 10.6 million tonnes of CO2.
It won’t solve climate change (the US generates about 6,300 million tons of carbon dioxide emissions each year) but it certainly isn’t a bad way to reduce atmospheric CO2 while significantly improving topsoil’s ability to grow food organically, absorb rainwater, and recharge aquifers. And it is sure better than the alternatives of burning yard trimmings or burying them in landfills where they form methane as they decompose.