"At that price we’d be better off just planting a bunch more trees instead."
Ugh. No, we wouldn't. Planting trees doesn't solve anything. If water is flowing into a bathtub faster than it is draining out, you do not solve the problem by making the bathtub slightly bigger. If you don't change the inflow or outflow, a one-time increase in the amount of storage doesn't do anything except very slightly delay the crisis.
Trees are NOT "the lungs of the world." A mature forest is carbon neutral. For trees to work as a carbon sink, you'd have to cut them down as soon as they mature and then preserve the wood in some way so it can't burn or rot. This is simply not a scalable way to reduce carbon flows. It's too slow, it's too expensive, and what do you do with all the leaves, wood, and other debris?
If you want to do bio-extraction, at least do it in a way that makes sense. Grow something cheaper, faster growing, and much easier to sequester. For example, we could grow Azolla on vast shallow ponds adjacent to the Arctic Ocean every summer. Azolla floats and grows insanely fast in 20+hours of sun, with no fertilizer. When the ponds are covered, open the gates and let the whole mass flow out to sea, where it will die in the saltwater and sink to the bottom.
This is how nature did it. It's very probably how we got from "hothouse earth" to the current climate. There's a thick layer of mud at the bottom of the Arctic that is basically a solid mass of preserved Azolla, containing teratonnes of carbon that used to be in the atmosphere.
Once you have shaped the ponds, it pretty much works for free anywhere you have north-flowing rivers and streams. And, unlike adding to the fixed *stock* of carbon in trees, it would increase the annual *flow* of carbon out of the atmosphere.
The international economic effects of such a system would be interesting too. Most of the first world would need to charge a carbon tax or otherwise find a way to pay Russia and Canada to extract and sequester carbon for them, although the U.S. might be able to do much or all of its own carbon extraction and sequestration along the north and northwestern edge of Alaska. Over time, as the West passes carbon neutrality and into negative net carbon flows, it will become politically unacceptable to ask the West to carry the whole burden. At that point, developing nations will need to get to carbon neutrality either through renewable energy or by charging a carbon tax and contributing to the extraction and sequestration process.
Joanne Chory at Salk is engineering plants to store their carbon as suberin, a cork-like substance that lasts for decades. And also to produce a ton of hummus... I don't know what that does for the climate, but my default position is that more hummus can only be good thing.
There's a lot of potential forest restoration, with co-benefits, that would buy some time for renewables expansion. It's a good way to hand money to developing countries, too. But Azolla is really interesting.
This is really cool stuff. Do you know if anyone has done some sort of analysis on cost/scale that you can achieve with this method? And why does it need to be so far north. wouldn't any freshwater basin close to a salt-water basin work?
BTW, I really agree on the tree thing. Trees die, and the degree of forestation needed to make a real dent is huge and probably untenable. But people just focus on the initial reduction, not how much land will be needed over time.
The basics for scaling are in the capture ratio: 6 tonnes per acre of carbon drawdown (1.5 kg/m2/yr). Call it roughly 1500 tonnes/square kilometer or 4,000 tonnes/square mile per year. So we're talking huge areas. But the ponds themselves can be very shallow, just a few inches, so you can terrace vast areas of otherwise frozen land along any river and it still won't take much water. (Bonus: the ponds freeze and make shiny mirrors that increase albedo most of the year.)
This would be a huge undertaking, requiring arctic-proofed graders and such to terraform a frozen landscape. But every other biomass extraction project would be similarly huge. The advantages here are that i) it's doable, ii) the land is largely empty, iii) once the ponds are built they keep on working, iv) it requires almost no supplemental fertilizer or energy, and v) unlike reforestation, it actually keeps on removing carbon every year and dumping it in a true sink, altering the all-important flows in a meaningful way.
One reason Azolla is so attractive is that it can fix its own atmospheric nitrogen. The main limit on growth is usually phosphorus and a pinch of sulphur, both of which are generally available in shallow ponds in areas with organic material (e.g., runoff from permafrost). Another reason is growth rate. With 20 hrs of light near the Arctic, Azolla doubles in biomass every 3-5 days (~2-3 days if it's warmer), so it grows explosively during the season.
> "why does it need to be so far north?"
If the Azolla decays or gets eaten, the carbon is just going to get recycled. The bottom of the Arctic is the perfect cold storage facility, as close as we can get to an infinite carbon sink. You COULD do it with really deep ocean in any area where there's no upwelling, but the problem would be getting the Azolla far enough out to sea and sinking it without just feeding and fertilizing the existing biosphere.
In the Arctic, that's basically taken care of for you if you just let existing rivers sweep it out to sea. Plus, the ponds would not compete with any existing forests, swamps, or agricultural land.
Would it work in other places with a fairly steep dropoff to cold water,maybe like some parts of Chile or Korea? I'd guess so, but then you would get into competition for land and fresh water. In that case, it would probably be better to just collect, bale, and transport crop residue from farms, and barge it out to sea.
This article discusses the practical challenges and the costs :
Thanks, that was a very good explanation. In my mental model of this sort of process I always thought the difficulty would be in digging some sort of hole or other place to put all the stabilized carbon. Never thought you could just sink it in the ocean, and it's such a great and obvious solution in retrospect
This is the optimistic take (which is what I’d expect from you, Noah).
Kevin Drum, seeing absolutely zippo collective progress in decreasing CO2 emissions despite the science showing that climate catastrophe was looming even as far back as the ‘90’s, is far more pessimistic:
1. You can't hold people _morally responsible_ for actions commited before those actions were generally recognised as a moral wrong.
Climate Change wasn't on the agenda before, say, 1980. It's obtuse to ascribe emmisions before that.
2. You can't hold people _morally responsible_ for things their ancestors did.
3. If you're going to do this CO2 legacy stuff, you need to discount early emissions by planetary sink capacity.
4.... and why start at industrialisation? Why not count breathing and log burning from the year 0?
5. I look forward to an article which considers what the economic state of the rest of the world would be if the west hadn't industrialised, and properly ascribes the West a credit for it's innovation and capital accumulation.
One thing I like to add is that you as a citizen of rich country hugely benefits from what your ancestors did so it isn't just "pay for one's ancestors’ irresponsible lifestyles"
Here's something I've wondered. Could DAC infrastructure be dual-purposed to pull other pollutants out of the air? Given the massive public health benefits of reducing regular old smog (and such), that could seemingly create a huge additional benefit to weigh against the cost, help curb intra-US climate injustice (if the big dual filtration plants were smartly located), and maybe even get China on board, since they seem quite concerned with old fashioned pollution. I have no idea how this would work technically. But it seems like, if you're already building the massive fans, why not filter the air as, or just before, you pull the carbon out of it...
The most important thing rich countries can do is spend as much money as possible in clean technology. Where it exists we need it to be as cheap as possible. Where it doesn’t we need to find a way.
Does anyone know of an article or post that explains the science of carbon capture? I'd like to understand the thermodynamics of it. Why exactly is it so hard? Is it entirely a function of the sparsity of CO2 molecules per unit air, or are there chemistry reasons too? Is the CO2 spread smoothly through the atmosphere or is there more of it at certain layers? What is the lower bound on how much energy is required to sort air into CO2 / non-CO2 components? Etc. I've never managed to find a good resource on this.
Most techniques use a two step process: first, the CO2 is adsorbed onto a solid material, and second, the material is heated to remove either the CO2 or, more frequently, to catalyze the reaction that allows you to just remove the C. That process is very energy intensive, which makes the whole process very expensive, and, unless the energy source is clean, actually pretty dirty. Better catalysis would probably help, as would figuring out some way to monetize the C byproduct. I've seen proposals to use it as a basis for building materials, but they remain highly speculative at this point.
Thanks - I’ve seen articles about the techniques. What I’m looking for is something explaining the basic science - the limits to solutions from physics or chemistry.
The enthalpy of formation for CO2 is -393.5 kJ/mol (negative meaning that forming it releases heat). So converting a mole of CO2 back into C and O2 costs at least that much energy. A mole of CO2 is 44 kg, so it costs 8.9kJ per kg of CO2 chemically processed. (If you prefer watts as a measure, it's 8.9 kW to process a kg of CO2 every second.)
Current global CO2 output is 37 gigatons per year, or about 33.5 teragrams. 33.5 Tg/year * 8.9 kJ/kg = 9.4 megawatts, at a constant rate, to zero out global CO2 emissions by chemical means. That's... actually not too bad. My math could be off by a lot since this is all just based on quick googling, but anywhere in that ballpark is not too bad.
However, this is the best-case scenario - the absolute minimum you'd be able to pay without breaking the laws of thermodynamics. It doesn't take into account activation energy or any sort of waste heat generated by the process, so it's probably got little connection to the actual cost. But on the other hand, it means there's plenty of theoretical room for improvement!
- The more we can do to reduce the chance of high temperatures, the better. So, in this sense, I'm all for carbon capture, as the IPCC report spells out just how beneficial incremental differences in temperature reduction can be - less chance of drought, wild fires, etc.
- Admittedly though, I'm concerned carbon capture may become an excuse to allow for more fossil fuel consumption than would be the case if all externalities were reflected in the price. Specifically, my concern is fuel prices will only reflect the price of greenhouse gases, which don't necessarily reflect the impact they have on public health. Additionally, I'm curious as to how these carbon capture projects get funded. Does the US government fund the projects? If so, are we socializing a cost which should have been proportionally been borne more by industry?
Carbon capture is silly when proposed as a way to make coal plants green, but it seems that for something like cement manufacture, it would make sense to capture the CO2 as it comes out of the kiln. Direct air capture from open-air atmosphere seems like it shouldn't be the first resort, although a lot of it will be necessary.
I think it would make sense for SpaceX (and the rest of the launch industry) to commit to using synthetic air-capture fuels since it would help grow the early market for air capture and likely barely budge the cost of the launches.
"At that price we’d be better off just planting a bunch more trees instead."
Ugh. No, we wouldn't. Planting trees doesn't solve anything. If water is flowing into a bathtub faster than it is draining out, you do not solve the problem by making the bathtub slightly bigger. If you don't change the inflow or outflow, a one-time increase in the amount of storage doesn't do anything except very slightly delay the crisis.
Trees are NOT "the lungs of the world." A mature forest is carbon neutral. For trees to work as a carbon sink, you'd have to cut them down as soon as they mature and then preserve the wood in some way so it can't burn or rot. This is simply not a scalable way to reduce carbon flows. It's too slow, it's too expensive, and what do you do with all the leaves, wood, and other debris?
If you want to do bio-extraction, at least do it in a way that makes sense. Grow something cheaper, faster growing, and much easier to sequester. For example, we could grow Azolla on vast shallow ponds adjacent to the Arctic Ocean every summer. Azolla floats and grows insanely fast in 20+hours of sun, with no fertilizer. When the ponds are covered, open the gates and let the whole mass flow out to sea, where it will die in the saltwater and sink to the bottom.
This is how nature did it. It's very probably how we got from "hothouse earth" to the current climate. There's a thick layer of mud at the bottom of the Arctic that is basically a solid mass of preserved Azolla, containing teratonnes of carbon that used to be in the atmosphere.
Once you have shaped the ponds, it pretty much works for free anywhere you have north-flowing rivers and streams. And, unlike adding to the fixed *stock* of carbon in trees, it would increase the annual *flow* of carbon out of the atmosphere.
The international economic effects of such a system would be interesting too. Most of the first world would need to charge a carbon tax or otherwise find a way to pay Russia and Canada to extract and sequester carbon for them, although the U.S. might be able to do much or all of its own carbon extraction and sequestration along the north and northwestern edge of Alaska. Over time, as the West passes carbon neutrality and into negative net carbon flows, it will become politically unacceptable to ask the West to carry the whole burden. At that point, developing nations will need to get to carbon neutrality either through renewable energy or by charging a carbon tax and contributing to the extraction and sequestration process.
Joanne Chory at Salk is engineering plants to store their carbon as suberin, a cork-like substance that lasts for decades. And also to produce a ton of hummus... I don't know what that does for the climate, but my default position is that more hummus can only be good thing.
https://www.salk.edu/scientist/joanne-chory/
Humus - organic matter found in soil - is very different from hummus - the delectable Middle Eastern spread!
This is true - but Chory’s plants (if the program works) will produce both!
There's a lot of potential forest restoration, with co-benefits, that would buy some time for renewables expansion. It's a good way to hand money to developing countries, too. But Azolla is really interesting.
This is really cool stuff. Do you know if anyone has done some sort of analysis on cost/scale that you can achieve with this method? And why does it need to be so far north. wouldn't any freshwater basin close to a salt-water basin work?
BTW, I really agree on the tree thing. Trees die, and the degree of forestation needed to make a real dent is huge and probably untenable. But people just focus on the initial reduction, not how much land will be needed over time.
The basics for scaling are in the capture ratio: 6 tonnes per acre of carbon drawdown (1.5 kg/m2/yr). Call it roughly 1500 tonnes/square kilometer or 4,000 tonnes/square mile per year. So we're talking huge areas. But the ponds themselves can be very shallow, just a few inches, so you can terrace vast areas of otherwise frozen land along any river and it still won't take much water. (Bonus: the ponds freeze and make shiny mirrors that increase albedo most of the year.)
This would be a huge undertaking, requiring arctic-proofed graders and such to terraform a frozen landscape. But every other biomass extraction project would be similarly huge. The advantages here are that i) it's doable, ii) the land is largely empty, iii) once the ponds are built they keep on working, iv) it requires almost no supplemental fertilizer or energy, and v) unlike reforestation, it actually keeps on removing carbon every year and dumping it in a true sink, altering the all-important flows in a meaningful way.
One reason Azolla is so attractive is that it can fix its own atmospheric nitrogen. The main limit on growth is usually phosphorus and a pinch of sulphur, both of which are generally available in shallow ponds in areas with organic material (e.g., runoff from permafrost). Another reason is growth rate. With 20 hrs of light near the Arctic, Azolla doubles in biomass every 3-5 days (~2-3 days if it's warmer), so it grows explosively during the season.
> "why does it need to be so far north?"
If the Azolla decays or gets eaten, the carbon is just going to get recycled. The bottom of the Arctic is the perfect cold storage facility, as close as we can get to an infinite carbon sink. You COULD do it with really deep ocean in any area where there's no upwelling, but the problem would be getting the Azolla far enough out to sea and sinking it without just feeding and fertilizing the existing biosphere.
In the Arctic, that's basically taken care of for you if you just let existing rivers sweep it out to sea. Plus, the ponds would not compete with any existing forests, swamps, or agricultural land.
Would it work in other places with a fairly steep dropoff to cold water,maybe like some parts of Chile or Korea? I'd guess so, but then you would get into competition for land and fresh water. In that case, it would probably be better to just collect, bale, and transport crop residue from farms, and barge it out to sea.
This article discusses the practical challenges and the costs :
• Ocean Sequestration of Crop Residue Carbon: Recycling Fossil Fuel Carbon Back to Deep Sediments (https://pubs.acs.org/doi/full/10.1021/es8015556)
The same analysis can be used for Azolla, except you don't have to collect, bale, and transport Azolla, or barge it out to sea.
Thanks, that was a very good explanation. In my mental model of this sort of process I always thought the difficulty would be in digging some sort of hole or other place to put all the stabilized carbon. Never thought you could just sink it in the ocean, and it's such a great and obvious solution in retrospect
This is the optimistic take (which is what I’d expect from you, Noah).
Kevin Drum, seeing absolutely zippo collective progress in decreasing CO2 emissions despite the science showing that climate catastrophe was looming even as far back as the ‘90’s, is far more pessimistic:
https://jabberwocking.com/in-2040-we-will-collectively-decide-to-flood-the-atmosphere-with-aerosols/
He thinks that we’ll have to seed sulfate aerosols to block the sun in coming decades in desperation despite unintended effects.
In general, he’s more optimistic about American democracy but less techno-optimist than you. Maybe because he’s an older guy who has cancer.
In this case, Drum may be more on the money.
1. You can't hold people _morally responsible_ for actions commited before those actions were generally recognised as a moral wrong.
Climate Change wasn't on the agenda before, say, 1980. It's obtuse to ascribe emmisions before that.
2. You can't hold people _morally responsible_ for things their ancestors did.
3. If you're going to do this CO2 legacy stuff, you need to discount early emissions by planetary sink capacity.
4.... and why start at industrialisation? Why not count breathing and log burning from the year 0?
5. I look forward to an article which considers what the economic state of the rest of the world would be if the west hadn't industrialised, and properly ascribes the West a credit for it's innovation and capital accumulation.
One thing I like to add is that you as a citizen of rich country hugely benefits from what your ancestors did so it isn't just "pay for one's ancestors’ irresponsible lifestyles"
You may find this paper interesting. It proposes a method of Antartica dry ice based CO2 capture that would be doable with current technology. https://journals.ametsoc.org/view/journals/apme/52/2/jamc-d-12-0110.1.xml
Here's something I've wondered. Could DAC infrastructure be dual-purposed to pull other pollutants out of the air? Given the massive public health benefits of reducing regular old smog (and such), that could seemingly create a huge additional benefit to weigh against the cost, help curb intra-US climate injustice (if the big dual filtration plants were smartly located), and maybe even get China on board, since they seem quite concerned with old fashioned pollution. I have no idea how this would work technically. But it seems like, if you're already building the massive fans, why not filter the air as, or just before, you pull the carbon out of it...
Where are you on Nuclear Power?
The most important thing rich countries can do is spend as much money as possible in clean technology. Where it exists we need it to be as cheap as possible. Where it doesn’t we need to find a way.
Does anyone know of an article or post that explains the science of carbon capture? I'd like to understand the thermodynamics of it. Why exactly is it so hard? Is it entirely a function of the sparsity of CO2 molecules per unit air, or are there chemistry reasons too? Is the CO2 spread smoothly through the atmosphere or is there more of it at certain layers? What is the lower bound on how much energy is required to sort air into CO2 / non-CO2 components? Etc. I've never managed to find a good resource on this.
Most techniques use a two step process: first, the CO2 is adsorbed onto a solid material, and second, the material is heated to remove either the CO2 or, more frequently, to catalyze the reaction that allows you to just remove the C. That process is very energy intensive, which makes the whole process very expensive, and, unless the energy source is clean, actually pretty dirty. Better catalysis would probably help, as would figuring out some way to monetize the C byproduct. I've seen proposals to use it as a basis for building materials, but they remain highly speculative at this point.
Thanks - I’ve seen articles about the techniques. What I’m looking for is something explaining the basic science - the limits to solutions from physics or chemistry.
The enthalpy of formation for CO2 is -393.5 kJ/mol (negative meaning that forming it releases heat). So converting a mole of CO2 back into C and O2 costs at least that much energy. A mole of CO2 is 44 kg, so it costs 8.9kJ per kg of CO2 chemically processed. (If you prefer watts as a measure, it's 8.9 kW to process a kg of CO2 every second.)
Current global CO2 output is 37 gigatons per year, or about 33.5 teragrams. 33.5 Tg/year * 8.9 kJ/kg = 9.4 megawatts, at a constant rate, to zero out global CO2 emissions by chemical means. That's... actually not too bad. My math could be off by a lot since this is all just based on quick googling, but anywhere in that ballpark is not too bad.
However, this is the best-case scenario - the absolute minimum you'd be able to pay without breaking the laws of thermodynamics. It doesn't take into account activation energy or any sort of waste heat generated by the process, so it's probably got little connection to the actual cost. But on the other hand, it means there's plenty of theoretical room for improvement!
Thank you!
Two things (that contradict):
- The more we can do to reduce the chance of high temperatures, the better. So, in this sense, I'm all for carbon capture, as the IPCC report spells out just how beneficial incremental differences in temperature reduction can be - less chance of drought, wild fires, etc.
- Admittedly though, I'm concerned carbon capture may become an excuse to allow for more fossil fuel consumption than would be the case if all externalities were reflected in the price. Specifically, my concern is fuel prices will only reflect the price of greenhouse gases, which don't necessarily reflect the impact they have on public health. Additionally, I'm curious as to how these carbon capture projects get funded. Does the US government fund the projects? If so, are we socializing a cost which should have been proportionally been borne more by industry?
Carbon capture is silly when proposed as a way to make coal plants green, but it seems that for something like cement manufacture, it would make sense to capture the CO2 as it comes out of the kiln. Direct air capture from open-air atmosphere seems like it shouldn't be the first resort, although a lot of it will be necessary.
I think it would make sense for SpaceX (and the rest of the launch industry) to commit to using synthetic air-capture fuels since it would help grow the early market for air capture and likely barely budge the cost of the launches.
Heh. These are cooling towers for a carbon removal facility, hence it's subtracting pollution! :D