Following on June 20's "Norway Launches World’s First Full-Scale Carbon Capture and Storage Value Chain".
From Austin Vernon's substack, April 28:
How cheap can it pull CO2 from the air?
Thanks to Nina, Jenny, Fridrik, Nan, Dan, Judy, and Frauke for their help and teaching on this subject. Any mistakes are my own.
Prompt
Enhanced rock weathering is a method to remove carbon dioxide from the atmosphere and store it permanently. Some of its best features are simplicity, permanence, and scale. The mechanism is that carbon dioxide in the air reacts with rock particles to form stable carbonates. There are many times more rocks than we need to remove industrial-era emissions."Why aren't we grinding up mountains yet?" is a question I've been curious about. Folks from Stripe Frontier and Orca Sciences have taught me a lot about the topic.
The promise is still there, but the road is more challenging than at first glance. The difficulty increases after considering rock quality, reaction kinetics, logistics, ocean impacts, mining operations, and MRV (Measurement, Reporting, and Verification).
Intro
We have more carbon dioxide in the atmosphere than we'd like, and it is an acid gas. Acid gases form acidic solutions when they dissolve in water. The magic of enhanced rock weathering is finding basic rocks that can react with and neutralize CO2 into bicarbonate or precipitated carbonates. Below are the reactions for olivine, which is one of the most commonly proposed rock types:Mg2SiO4 + 4CO2 + 2H2O => 2Mg2+ + 4HCO3- + SiO2
Each ton of olivine removes 1.25 tons of CO2 in the aqueous reaction. This reaction is only relevant for dumping the rocks in the ocean because smaller reservoirs can't maintain that much bicarbonate.
There is also a route that forms carbonates:
Mg2SiO4 + 2CO2 => 2MgCO3 + SiO2
The reaction is two steps, with the first forming bicarbonate ions and the second reaction producing carbonates:
Mg2+ + 2(HCO3-) => MgCO3 + CO2 + H2O
The carbonate reaction does not store as much CO2 as the bicarbonate phase.
Overall, the CO2/bicarbonate/carbonate buffer system is integral to how rock weathering proceeds.
Evaluating Previous Cost Claims
Part of the hype around rock weathering is claims that it could be done for $10/ton of CO2 removed at scale. A cost like this would make a gallon of fuel carbon neutral for only ~$0.10.Diving further into the costs suggests that the conditions where this might be true are strict:
Tens of millions of tons per year scale.
Extremely large, contiguous, and high purity reserves with minimal overburden.
Inexpensive electricity (<$20/MWh).
Zero cost of capital.
No verification, testing, or pollution concerns.
Ocean disposal to get the bicarbonate bonus.
A mine located less than 5 kilometers from the ocean.
The ocean is the warm water variety to speed reaction rates.
Acceptance of long time horizons or new grinding technology.
It isn't clear whether these conditions are available in any location on Earth. High-quality reserves tend to be in smaller veins within larger deposits. Existing olivine mines are small and far from the ocean or in cold places. Pollution is a concern because deposits usually contain small amounts of metals like nickel that can cause localized issues in the ocean. The material might not fully react before settling on the bottom, and measuring this is challenging.
Quotes for high-purity olivine from existing mines are over $100/ton because of their sub-scale nature and the mining difficulty. One of the main mines in the US, Twin Sisters in Washington, isn't even accessible year-round.
$10/ton does not seem realistic.
Land-Based Weathering
Nan, Dan, and Judy at Frontier suggested that land-based weathering might be under-explored because transportation, pollution, land use, and MRV could be improved even if each ton of rock is less efficient. There are many more feasible locations and fewer regulatory and social barriers. Frontier's ultimate goal is to remove a trillion tons of CO2, which requires rock mass equivalent to Mount Everest."How cheap can weathering a giant pile of rocks be?" becomes the question.
Balancing the Costs and Challenges
Basic rocks available in the trillions of tons tend to have slow reaction rates with atmospheric CO2. It is a challenge to add reactants and remove products efficiently enough for reactions to proceed at their kinetic limits. Rates can slow by orders of magnitude if ion diffusion becomes the limiting factor because diffusion time increases by the square of the distance.These issues compound because rock is not soluble in air. The reaction happens in a water intermediary. But, neither CO2 nor most rocks are very soluble in water. And there is hardly any CO2 in the air at 400 parts per million, anyway. Inexpensive weathering becomes a mass transport problem as much as a kinetic one.
Reaction Rates and Rock Selection
There are three factors crucial to rock selection:
Weathering Rate
CO2 Sequestration Amount per Unit Rock
Rock Availability and Quality
Determining the weathering rate is quite challenging. The literature has rates for Olivine dissolution that vary from 10^-8 to 10^-13 mol/m2-s at ambient conditions, a 100,000x difference (here, here, here, here, and here). The fastest rates are when the rocks are in acidic solutions, which isn't practical for weathering rock in atmospheric conditions because acidic solutions are poor at absorbing CO2, and acid costs money. The dissolution rates for neutral to alkaline conditions range from 10^-10 to 10^-13 mol/m2-s. Higher pH, high dissolved silica, carbonate precipitation, poor mixing, lack of hydration, and colder temperatures can all lead to several orders of magnitude slower rates and push the rate towards the 10^-13 mol/m2-s type numbers. The reaction rate of many other silicates, like feldspars, tends to be within an order of magnitude of olivine. Rocks with more calcium or magnesium not in silicate structures tend to be faster....
....MUCH MORE
I wanted this on the blog as a personal bookmark, he goes deep.
Previously:
November 7, 2007 - Engineered weathering process could mitigate global warming
May 9, 2025 - "XPRIZE Makes History, Awards $100M Prize for Groundbreaking Carbon Removal Solutions"
It's not enough just to capture the carbon, to prevent re-release you have to sequester it.
And do so in an affordable way. The rock weathering approach addresses both of those goals.
The next step will be to speed things up.Some background from January 2021:
"Elon Musk to offer $100 million prize for 'best' carbon capture tech"
Carbon capture is an approach the Norwegians among others are exploring but it is not easy. Because the concentrations of CO2 in air are so low, ~415 parts per million, you have to move a lot of air through your systems to get meaningful amounts of CO2 to sequester.
The other reasons are ideological. A lot of folks in the authoritarian crowd don't like it because it means that things don't have to change as much as they would like things to change. Wealth transferers don't like carbon capture because it directly attacks their rationalization for "climate reparations", always set with a starting point far enough back in time so that only Northern Hemisphere and in particular, western, countries owe x-number of trillions of dollars to southern and eastern countries. And then there are the....
Yeah, I've been doing this a long time.
Putting all that aside, prizes are good, a very efficient way to mobilize talent and creativity in a focused pursuit. I may even see if I can recruit a team of folks smarter than I to claim Elon's money....
Oxford Uni.: "The outlook for CO2 removal"
It is still far too expensive to be more than just demonstration projects, now and for another decade minimum.
And
as with all such conversations the promoters never, ever, speak of
degrees of warming avoided. If interested see after the jump.
From Dialogue Earth, June 10:
More clarity needed on CO2 removal in national climate action plans, finds Oxford University report
A nascent industry removing carbon from the atmosphere and storing it in trees, rocks and the ocean will need to quadruple in size by 2050 if the world is to keep temperature rise to within the internationally agreed threshold of 1.5C, a new report has found.
“Carbon dioxide removal” is defined by the UN’s climate science body, the IPCC (Intergovernmental Panel on Climate Change), as human activity that captures CO2 from the atmosphere and stores it for decades to millennia in geological, land or ocean reservoirs, or in products.
Around two billion tonnes of carbon are currently removed in this way each year, mostly using conventional methods such as afforestation and reforestation, wetland restoration and soil improvement.
However, an industry in more novel techniques has seen rapid growth in recent years. Such methods include: storing carbon in products like construction materials or “biochar”, a carbon-rich material produced by heating biomass in an oxygen-limited environment; enhanced rock weathering, which involves spreading finely ground silicate rock onto surfaces to speed up chemical reactions between rocks, water, and air; and direct air carbon capture and storage (DACCS), where carbon is separated from the air using chemical processes and deposited underground.
Last month, the world’s largest commercial DACCS plant, dubbed Mammoth, began operating in Iceland. It will draw down 36,000 tonnes of CO2 from the air every year and store it permanently underground, says the company behind it, Climeworks. The company is planning to build “multiple megaton hubs” in the US, meaning several facilities that can remove a million or more tonnes of CO2 per year.
Today such novel methods remove just 1.3 million tonnes of carbon a year, less than 0.1% of total carbon removals, with conventional methods responsible for the remaining 99.9%, the analysis found. But the researchers behind the report are optimistic that both novel and conventional methods can be scaled up to reach the estimated required level of 7-9 billion tonnes of CO2 per year by 2050.
Taken together, the carbon removal capacity proposed by companies globally would be sufficient to reach this, the authors found. However, they did not assess the likelihood of individual plans or announcements coming to fruition.
Diverse methodsThe report, which was led by academics at the University of Oxford’s Smith School of Enterprise and the Environment, but also involved more than 50 international experts, stresses that politicians, policymakers and business leaders should still be focussing on reducing emissions as the primary way to achieve net zero.But they argue that carbon dioxide removal (CDR) will also be needed to address climate change. CDR is advocated by the IPCC, which cites its potential to reduce emissions in the near term, to counterbalance unavoidable emissions in the medium term, and to achieve net-negative emissions in the longer term....
....MUCH MORE
From the outro of "Reminder of A Reminder of What Net Zero Means":
As always, the correct question to ask of each and every policy is how many degrees C will this proposal reduce the temperature. You don't want the airy-fairy answer in tons of CO₂ or number of automobile-equivalents, you want degrees.
The reason for this is: you have to do comparisons to judge the effectiveness of policy proposals and to do that you have to use the the tools of science (maths).
As we've said over the years - this version is from 2019 but there are many others:
In the last years of the last century there was an international agreement on global warming policy called the Kyoto Protocol. It was a pretty big deal.
It was going to be expensive for the developed economies but worth it.
You heard of it right? It was in all the papers.
And do you recall how much the Kyoto Protocol would cool the planet?
Of course not.
The U.N. and the NGO's and Enron* and the consultants and everybody involved elided right past that number.
The answer was (no, not 42), the answer to the question of how much would the Kyoto Protocol cool the earth was 0.07 degrees. But that's 0.07°C, which is more cooling than if it had been 0.07°F.
The answer was not from me, it's the analysis of the U.S. National Center for Atmospheric Research....****
*The first step is to get honest.
Like this guy, Enron's top lobbyist, John Palmisano, senior director for environmental policy and compliance who emailed from Kyoto:
If implemented [the Kyoto Protocol] will do more to promote Enron’s business than will almost any other regulatory initiative outside of restructuring of the [electricity] and natural gas industries in Europe and the United States…. The endorsement of emissions trading was another victory for us…. This agreement will be good for Enron stock!!It was time to turn deeds into dollars, he added:
Enron now has excellent credentials with many ‘green’ interests including Greenpeace, WWF [World Wildlife Fund], NRDC [Natural Resources Defense Council], GermanWatch, The US Climate Action Network, the European Climate Action Network, Ozone Action, WRI [World Resources Institute], and Worldwatch [Institute],” reported Palmisano. “This position should be increasingly cultivated and capitalized on (monetized).As gentle reader has surmised, we've been following this stuff for a long, long time.
....This has helped form my personal belief that carbon trading is not going to lower world temperature by even a half-a-degree.Tom Wigley of the National Center for Atmospheric Research estimated that Kyoto would result in a reduction from baseline of 0.06°C to 0.21°C . (under one Kyoto scenario 0.06 to 0.11°C, under another 0.11 to 0.21)....Here's the U.S. NCAR 2006 estimate of Kyoto's effects.
For example, in an October 1998 article in Nature, Martin Parry (Co-chair of the IPCC's Working Group II) said the effect of the Kyoto Protocol (and it's associated carbon trading, CDM etc. [articles 6,12 and 17 of the protocol]) would be a reduction of –0.05°C by the year 2050.