6 ms·

I did some calculations on this a while back, using the energy requirements of direct air capture (DAC) CO2 removal that we currently know how to produce and de

by tzs 3y ago

I did some calculations on this a while back, using the energy requirements of direct air capture (DAC) CO2 removal that we currently know how to produce and deploy. The results I got where that if we built a very large solar farm (500 000 km^2) operating at the efficiency of current commercial solar farms and used all its output to power DAC CO2 removal, that would be enough to remove about half as much CO2 as we currently emit each year. In effect it would be as if we had cut emissions back to 1970 levels. Note that since the solar farm would just be used to power DAC, it would not need electrical infrastructure outside the farm itself. We just need a place where we can put in 500 000 km^2 of solar panels and a bunch of DAC facilities. The atmosphere does a good job of distributing CO2 so the solar/DAC facility doesn't need to be near any heavy CO2 emitters either. BTW, the output of a 500 000 km^2 solar farm per year is about equal to the total yearly energy use of humanity, which shows just how insane the amount of solar energy available is. Let's call this one Human Energy Unit (HEU). Build two HEU's worth of solar/DAC and we are effectively carbon neutral. Of course you wouldn't have to build these as 500 000 km^2 facilities. 500 facilities of 1000 km^2 would do, or any other combination that gives us 1 HEU total of energy that is all used for DAC. How far could we take this? The 5 largest subtropical deserts in the world have enough room to hold 30 HEUs worth of solar farms. If we built all those and turned them all on at once it would take one year to remove enough CO2 to get us down to 320 ppm, which is around the levels we had in 1960. Two years would take us back to levels last seen around 1800. 6 years would get us down to pre-industrial levels. That was all using technology that we have today. It would be a huge project, but it does not require any new science or new engineering. Just a lot of money, politics, manufacturing, and construction.

bwestergard 3y ago
I'm curious, did you try to calculate the mass of ores that would need to be mined?
- tzs 3y ago
  No, I just wanted to know if we covered some large deserts with solar panels could that power enough DAC to make a difference. A quick Googling to find current worldwide solar panel production suggests that it would take about 90 years of current production for the panels for a 500 000 km^2 solar farm, so to build enough to just cancel out current emissions would need about 180 times the resources that currently go annually into solar panel production. So we'd probably need to increase mining (and several other things) by about 20x if we wanted to use this approach to get enough DAC to bring emissions to net zero. I think that's about as far as I can go. I don't know enough about the availability of various resources to figure out if the various things needed are abundant enough and accessible enough that we could increase production by 20x.
  - hedora 3y ago
    Prices of panels keep halving, so that suggests potential production keeps doubling.
tiffanyg 3y ago
Fortuitous timing from my perspective. I was just thinking in the past day or two about fiddling with numbers in the more mundane 'replace current energy use' w/ 'renewables' realm. The impetus being simply having an extra moment for my mind to regale me w/ impending potential horrors in light of Exxon's release only days ago of their "ha ha, we're definitely sailing right past CO2 etc. required to stay under 2C of global average temp increase by 2050, M'Fers!" report ... I thought, of course, of the always attractive "breakthrough" possibility, but ... in particular, fusion isn't it.* So, deployment of renewables is the obvious solution ... and, solar, in particular, has made massive strides in the past decade+. What you're talking about is actually much more attractive, though. Sounds like a potentially great implementation / execution. And, all of this - much more rapid deployment for (electric) power generation, or, even better, as you propose, I think - seems like exactly the context in which a new "TVA" (Tennessee Valley Authority) or similar (maybe even "Apollo Project") would be the way to actually get it done with the urgency that seems warranted. Of course, the US coffers have been so raided, it may take the kinds of "national pain" experienced around a century ago to generate the political "housecleaning" required to, well really, "right the "USS USA". As usual, it's not clear the will is there in the electorate. But, I'd say this much for sure: as old as I am now, the behavior of people older than me has disgusted me in many ways for years, and anyone younger than me should be thoroughly pissed off, I think. I don't want to veer into more of a rant - suffice it to say ... if you look at the benefits a certain generation enjoyed, then consider their voting for policies / tax breaks likely to deny such benefits to future generations (already happening, of course - take a look at college tuitions in the US, for just one example), it's a travesty. In any case, I think another commenter raised a good point regarding the materials requirement. I'd imagine that would be "paid back" many times over very easily by the scheme overall, but don't know for sure ... I know there have been issues with having enough of the right type of sand to make high (enough) purity silicon wafers for chip manufacture ... but, my knowledge is very limited in these areas in general. If anyone has a real handle on what the materials side of this type of scheme looks like, I'd be interested... * It was always such an attractive idea ... sounds so perfect ... until you know about neutron generation / flux and realize that something like a "tokamok", in particular, is just not likely to be economical AT ALL (the problem being that without some method to contain neutrons or method for preventing generation, you bombard your materials and end up having to replace / "decontaminate" / etc. far too quickly ... at least, based on my sense of best methods available around 10 years ago ... last time I was involved in any work even marginally related to anything in that field). In any case, even if we have or can determine ways of further reducing neutron generation or ... doing something w/ Higgs or something to deal better w/ the neutron problem, seems like it'd take more like a "miracle" than a breakthrough at this point for it to have any bearing on the climate problem on the timescale relevant. Edit: realized couple oversights / clarifications (not that it's likely to matter, but, prefer to put in anyway): I have nothing against fission apart from its merits. It's been expensive and track record hasn't been good - plus waste, proliferation, etc. concerns. Practically, it's the cost issue (generally related to the other issues I mentioned, of course). I keep waiting for the advanced / modular / "standard design" reactors we've been promised for years... the track record vis-a-vis AP-1000 (already rather old, but, at least deploying) is not confidence inspiring. Regarding "certain generation", I've known too many from that generation who sat in taxpayer funded jobs essentially not fulfilling THEIR responsibilities as they RAILED against taxes and the POOR. I have a dim view based on personal experience - too many I knew were spoiled and hypocritical to an unbelievable degree. Of course, that doesn't mean there aren't plenty who were decent etc. So, obviously, I don't mean to blanket condemn any generation ... usual qualifications etc. apply.
gpm 3y ago
What happens to the CO2 in the extraction model you used? Collected into tanks that we then have to deal with?
stavros 3y ago
I find it funny that we're carbon neutral if we build two HEUs. Surely, we can just build the one, shut down all other energy production, and call it a day?
- rayiner 3y ago
  No, because people in Bangladeshi villages don’t have induction stoves.
  - AnthonyMouse 3y ago
    Wouldn't it cost less to replace their stoves than to double energy costs?
    - rsaesha 3y ago
      It would. By simple thermodynamics we can be 100%, not 99%, 100% sure, that the energetic cost of removing CO2 from the freaking atmosphere is higher than the benefit of putting it there in the first place.
      - staunton 3y ago
        Maybe there is a way to be sure of that but "benefit" isn't even a concept in "simple thermodynamics". That's not an argument for anything.
        AnthonyMouse 3y ago
        If you want the process to be sustainable then it has to be reversible. Burning 1000W worth of fuel only to spend >1000W of electricity to remove it from the atmosphere and turn it back into fuel is clearly a net cost compared to just using 1000W of electricity to cook your food. Or less than that with non-inductive methods, since electric heat pumps can produce more than 1000W of heat from 1000W of electricity by removing some of it from the environment. A non-sustainable process that converts fuel to CO2 and then into a solid or liquid that isn't fuel could theoretically have positive efficiency, but it is by no means guaranteed to (especially when the competition is heat pumps), even if it did by a small margin it could still cost significantly more, and it implies that you're eventually going to both run out of fuel and convert it all into an enormous amount of industrial waste.
mortureb 3y ago
So it’s completely unreasonable. We’re not going to be building 100km2 solar plants let alone a 1000km2 one. Even if we do, something like that is enough for the energy requirement of a few countries so the CO2 problem would probably fix itself
- foota 3y ago
  The largest solar plant seems to be ~100 square km: https://en.m.wikipedia.org/wiki/Bhadla_Solar_Park https://en.m.wikipedia.org/wiki/Bhadla_Solar_Park
  - nvm0n2 3y ago
    It says it covers an area of 56 square kilometers. But, it's not laid out as a square, large amounts of that area are empty. Also: "The Bhadla Solar Park has faced some challenges due to its location and scale. One of the main challenges has been dust accumulation on the solar panels, which reduces their efficiency and output. The park is also located in an arid region that experiences frequent dust storms and sandstorms."
- Aerroon 3y ago
  Whether it's unreasonable or not, I don't think we have much of a choice. Obviously the goal is to move as much stuff off of GHG emissions, but we've done a lot of damage to the atmosphere. If you look at a CO2 graph in the atmosphere over 40,000 years our GHG emissions are basically a vertical line: https://en.wikipedia.org/wiki/File:CO2_40k.png https://en.wikipedia.org/wiki/File:CO2_40k.png
  - mortureb 3y ago
    I would think that if we stop putting it out there and let the trees take care of the rest we might make it. But this is an uninformed opinion.
    - Aerroon 3y ago
      Nature would eventually take care of it, but that would take centuries. On top of that, it's unlikely that we will be able to cut all GHG emissions. Having some amount of carbon capture seems important.
sublinear 3y ago
> the output of a 500 000 km^2 solar farm per year is about equal to the total yearly energy use of humanity And discovering this factoid didn't lead you to realize how insane the whole idea is? > Just a lot of money, politics, manufacturing, and construction. Oh yes. Surely just a matter of that. I understand you're more interested in getting ballpark numbers than actually solving this problem though, so thanks for sharing.
hedora 3y ago
This is a fantastic analysis. I think a lot of sibling comments are missing an important point: Say we build enough solar to produce enough energy for peak demand. That’s going to end up wasting multiple HEU’s of electricity during the day (unless we build an insane number of batteries). For reference, cities currently cover 3 500 000 km^2 of the earth. Also, solar density is still improving, and other sources of energy exist.
falcolas 3y ago
> The 5 largest subtropical deserts in the world have enough room to hold 30 HEUs worth of solar farms. If we built all those and turned them all on at once Funny enough, this was done in the SF novel “The Hail Mary Project”, and derided by the scientists in the book for furthering climate problems dramatically by turning a normally heat reflective surface into a heat absorbent surface. Worth investigating before committing our deserts to power collection.
- lozenge 3y ago
  It's not a real concern. Might make for a good science Fiction story though. https://yaleclimateconnections.org/2009/11/superfreakonomics-climate-contrarianism/ https://yaleclimateconnections.org/2009/11/superfreakonomics...
WalterBright 3y ago
Irrigate the desert and plant 500 000 km^2 of trees seems a lot more practical. And we get lots of building materials as a side effect.
- tsimionescu 3y ago
  We need to store about 10B tons of C per year if we were to be carbon neutral. We're going to need to build a lot of megastructures out of wood to even keep pace.
  - blkhawk 3y ago
    Plus wood for building is NOT a permanent carbon storage mechanism. You would need to entomb that wood deep underground where it cannot decay.
    - WalterBright 3y ago
      We still need building materials, and trees are cut down all the time for building materials and paper. Besides, wood decays very, very slowly. There's a couple trees nearby that were felled 25 years ago, and they are just starting to rot. Besides, they don't have to be buried that deep. People are still finding intact bodies in bogs in England from thousands of years ago. They're just a few feet down. In the desert things decay pretty slowly, too. See Sylvester, the cowboy mummy in a museum in Seattle that was found in a sand dune in Arizona with a bullet hole in him.
      - blkhawk 3y ago
        you think 25 years is enough to store CO2 in? even 1000 years is not enough since we will need to entomb all available wood. But that is all stupid anyway because of this: To start reversing the CO2 emission we would need as many trees it takes to take up the current CO2 emissions and then a bit more. From what I found you can estimate every m³ (a bit less than 1 American fridge) of Wood stores 1 ton of CO2. Say each hectare of Forest with fast growing trees produces ~ 10m³ per year (more when they are cut down but they need to grow over a decade+. So if they take 10 years that is 100m³ wood yield at the end). Humanity produced by some estimates 37 billion tons of CO2 in 2020. That means you need 3.7 billion hectare of forest. The USA has a land area of 157.7 million hectare. So you need an area of 23 times the LAND area of the United States of America just for trees just to HALT CO² at today's level. How well are fast growing trees growing in the Arizona desert btw?
tsimionescu 3y ago
You're ignoring a huge part that makes this (as well as virtually all other carbon capture plans) useless: where do you store all the carbon? We are currently emitting ~37B tons of CO2 per year. That's ~0.375 C, so assuming we only store the carbon, that's ~10B tons of C per year. For reference, the Empire State Building is ~365K tons - so you'd need to build ~30 thousand empire state buildings per year with the captured carbon.
- regularfry 3y ago
  In fairness, the Empire State Building is mostly empty space. If what you have is elemental carbon, the same mass is a cube with 6m sides. Which, yes, you then need 30,000 of so it doesn't make the whole thing that much easier.
- concordDance 3y ago
  10B tons of C is a mere 10 cubic kilometers. For context, we have individual open pit mines of over 2 cubic kilometers.
- tzs 3y ago
  If we had emitted 37 billion metric tons of CO2 a year each year for the last 400 years that would be a total of about 1.48 x 10^19 grams of CO2. That's more than we now have in the atmosphere so this gives us a convenient upper limit. 12/44th of the mass of CO2 is from carbon, so that is 4 x 10^18 g of carbon to deal with if we wanted to store all the carbon current in atmospheric CO2. The density of carbon depends on what form it is in--diamond is a lot denser than graphite, which is a lot denser than carbon powder. Let's store it as graphite, which has a density of 2.2 g/cm^3. We'd need 1.8 x 10^18 cm^3 for that much powdered carbon, or 1.8 x 10^12 m^3, or 1800 km^3. But remember that we are getting all this carbon we need to deal with using energy from massive solar farms. Put the solar panels a few meters off the ground, and dump the graphite under the solar panels. If the graphite was dumped into a pile 1 m tall it would need 1800 km^2 of area. That would be just a tiny fraction of the area available under the amount of panels we'd have to be using to capture that much carbon. Spread evenly under all the panels it would be less than a millimeter.
replygirl 3y ago
i would be beyond surprised if covering 10% of the planet's land in solar didn't require any new science or engineering. i doubt we even have the labor force or materials to pull it off, timeline notwithstanding
- tzs 3y ago
  It’s only 10% if we want something that can lower CO2 to preindustrial levels in under a decade. It’s under 0.7% if we just want to stop the increase.
  - deleted 3y ago
    [deleted]
bouncycastle 3y ago
Plants are basically self-replicating solar panels with efficient CO2 removal & storage.
- david-gpu 3y ago
  Plant matter is carbon neutral unless you cut it down and find a way to stop it from burning down or decomposing for thousands of years.
  - phh 3y ago
    It's carbon neutral on the order of magnitude of a century. If we were to plant a forest in the Sahara, it'll largely be net positive capture for at least 3 decades, and then we'll be able to replace coal with that wood, making a global net zero (but we'd already have reduced co2 in the atmosphere). Replacing oil with wood would probably require quite a lot of work though (as making the desalination plants to make a forest)
  - truculent 3y ago
    Or you can permanently increase the area given over to plant matter
    - Aerroon 3y ago
      That's a one-time thing though and plants have already naturally spread to basically everywhere that they can spread.
      - truculent 3y ago
        So, for example, we have cleared forests to make way for farmland. Reversing that would increase the total amount of carbon held. Perhaps I should have said increasing the amount of equilibrium biomass or something to more clearly include rewilding or ecosystem changes. It’s not just plants that are a carbon store, after all. I don’t think this is likely to represent a full solution, if that is the subtext to your comment.
lima 3y ago
500000 km^2 is a little less than the entire area of France, for anyone wondering.
thelastgallon 3y ago
500 000 km^2 = 708 km x 708 km A single 708 km x 708 km would have these corners (Paris, Berlin, Vienna, Milan):https://goo.gl/maps/DTxdVCcK3aYUEirw8 https://goo.gl/maps/DTxdVCcK3aYUEirw8 (Rough approximation!) 30 of these: 21,240 km x 21,240 km

by tzs 3y ago

bwestergard 3y ago

I'm curious, did you try to calculate the mass of ores that would need to be mined?

tzs 3y ago
No, I just wanted to know if we covered some large deserts with solar panels could that power enough DAC to make a difference. A quick Googling to find current worldwide solar panel production suggests that it would take about 90 years of current production for the panels for a 500 000 km^2 solar farm, so to build enough to just cancel out current emissions would need about 180 times the resources that currently go annually into solar panel production. So we'd probably need to increase mining (and several other things) by about 20x if we wanted to use this approach to get enough DAC to bring emissions to net zero. I think that's about as far as I can go. I don't know enough about the availability of various resources to figure out if the various things needed are abundant enough and accessible enough that we could increase production by 20x.
- hedora 3y ago
  Prices of panels keep halving, so that suggests potential production keeps doubling.

tiffanyg 3y ago

Fortuitous timing from my perspective. I was just thinking in the past day or two about fiddling with numbers in the more mundane 'replace current energy use' w/ 'renewables' realm. The impetus being simply having an extra moment for my mind to regale me w/ impending potential horrors in light of Exxon's release only days ago of their "ha ha, we're definitely sailing right past CO2 etc. required to stay under 2C of global average temp increase by 2050, M'Fers!" report ... I thought, of course, of the always attractive "breakthrough" possibility, but ... in particular, fusion isn't it.* So, deployment of renewables is the obvious solution ... and, solar, in particular, has made massive strides in the past decade+. What you're talking about is actually much more attractive, though. Sounds like a potentially great implementation / execution. And, all of this - much more rapid deployment for (electric) power generation, or, even better, as you propose, I think - seems like exactly the context in which a new "TVA" (Tennessee Valley Authority) or similar (maybe even "Apollo Project") would be the way to actually get it done with the urgency that seems warranted. Of course, the US coffers have been so raided, it may take the kinds of "national pain" experienced around a century ago to generate the political "housecleaning" required to, well really, "right the "USS USA". As usual, it's not clear the will is there in the electorate. But, I'd say this much for sure: as old as I am now, the behavior of people older than me has disgusted me in many ways for years, and anyone younger than me should be thoroughly pissed off, I think. I don't want to veer into more of a rant - suffice it to say ... if you look at the benefits a certain generation enjoyed, then consider their voting for policies / tax breaks likely to deny such benefits to future generations (already happening, of course - take a look at college tuitions in the US, for just one example), it's a travesty. In any case, I think another commenter raised a good point regarding the materials requirement. I'd imagine that would be "paid back" many times over very easily by the scheme overall, but don't know for sure ... I know there have been issues with having enough of the right type of sand to make high (enough) purity silicon wafers for chip manufacture ... but, my knowledge is very limited in these areas in general. If anyone has a real handle on what the materials side of this type of scheme looks like, I'd be interested... * It was always such an attractive idea ... sounds so perfect ... until you know about neutron generation / flux and realize that something like a "tokamok", in particular, is just not likely to be economical AT ALL (the problem being that without some method to contain neutrons or method for preventing generation, you bombard your materials and end up having to replace / "decontaminate" / etc. far too quickly ... at least, based on my sense of best methods available around 10 years ago ... last time I was involved in any work even marginally related to anything in that field). In any case, even if we have or can determine ways of further reducing neutron generation or ... doing something w/ Higgs or something to deal better w/ the neutron problem, seems like it'd take more like a "miracle" than a breakthrough at this point for it to have any bearing on the climate problem on the timescale relevant. Edit: realized couple oversights / clarifications (not that it's likely to matter, but, prefer to put in anyway): I have nothing against fission apart from its merits. It's been expensive and track record hasn't been good - plus waste, proliferation, etc. concerns. Practically, it's the cost issue (generally related to the other issues I mentioned, of course). I keep waiting for the advanced / modular / "standard design" reactors we've been promised for years... the track record vis-a-vis AP-1000 (already rather old, but, at least deploying) is not confidence inspiring. Regarding "certain generation", I've known too many from that generation who sat in taxpayer funded jobs essentially not fulfilling THEIR responsibilities as they RAILED against taxes and the POOR. I have a dim view based on personal experience - too many I knew were spoiled and hypocritical to an unbelievable degree. Of course, that doesn't mean there aren't plenty who were decent etc. So, obviously, I don't mean to blanket condemn any generation ... usual qualifications etc. apply.

gpm 3y ago

What happens to the CO2 in the extraction model you used? Collected into tanks that we then have to deal with?

stavros 3y ago

I find it funny that we're carbon neutral if we build two HEUs. Surely, we can just build the one, shut down all other energy production, and call it a day?

rayiner 3y ago
No, because people in Bangladeshi villages don’t have induction stoves.
- AnthonyMouse 3y ago
  Wouldn't it cost less to replace their stoves than to double energy costs?
  - rsaesha 3y ago
    It would. By simple thermodynamics we can be 100%, not 99%, 100% sure, that the energetic cost of removing CO2 from the freaking atmosphere is higher than the benefit of putting it there in the first place.
    - staunton 3y ago
      Maybe there is a way to be sure of that but "benefit" isn't even a concept in "simple thermodynamics". That's not an argument for anything.
      - AnthonyMouse 3y ago
        If you want the process to be sustainable then it has to be reversible. Burning 1000W worth of fuel only to spend >1000W of electricity to remove it from the atmosphere and turn it back into fuel is clearly a net cost compared to just using 1000W of electricity to cook your food. Or less than that with non-inductive methods, since electric heat pumps can produce more than 1000W of heat from 1000W of electricity by removing some of it from the environment. A non-sustainable process that converts fuel to CO2 and then into a solid or liquid that isn't fuel could theoretically have positive efficiency, but it is by no means guaranteed to (especially when the competition is heat pumps), even if it did by a small margin it could still cost significantly more, and it implies that you're eventually going to both run out of fuel and convert it all into an enormous amount of industrial waste.

mortureb 3y ago

So it’s completely unreasonable. We’re not going to be building 100km2 solar plants let alone a 1000km2 one. Even if we do, something like that is enough for the energy requirement of a few countries so the CO2 problem would probably fix itself

foota 3y ago
The largest solar plant seems to be ~100 square km: https://en.m.wikipedia.org/wiki/Bhadla_Solar_Park https://en.m.wikipedia.org/wiki/Bhadla_Solar_Park
- nvm0n2 3y ago
  It says it covers an area of 56 square kilometers. But, it's not laid out as a square, large amounts of that area are empty. Also: "The Bhadla Solar Park has faced some challenges due to its location and scale. One of the main challenges has been dust accumulation on the solar panels, which reduces their efficiency and output. The park is also located in an arid region that experiences frequent dust storms and sandstorms."
Aerroon 3y ago
Whether it's unreasonable or not, I don't think we have much of a choice. Obviously the goal is to move as much stuff off of GHG emissions, but we've done a lot of damage to the atmosphere. If you look at a CO2 graph in the atmosphere over 40,000 years our GHG emissions are basically a vertical line: https://en.wikipedia.org/wiki/File:CO2_40k.png https://en.wikipedia.org/wiki/File:CO2_40k.png
- mortureb 3y ago
  I would think that if we stop putting it out there and let the trees take care of the rest we might make it. But this is an uninformed opinion.
  - Aerroon 3y ago
    Nature would eventually take care of it, but that would take centuries. On top of that, it's unlikely that we will be able to cut all GHG emissions. Having some amount of carbon capture seems important.

sublinear 3y ago

> the output of a 500 000 km^2 solar farm per year is about equal to the total yearly energy use of humanity And discovering this factoid didn't lead you to realize how insane the whole idea is? > Just a lot of money, politics, manufacturing, and construction. Oh yes. Surely just a matter of that. I understand you're more interested in getting ballpark numbers than actually solving this problem though, so thanks for sharing.

hedora 3y ago

This is a fantastic analysis. I think a lot of sibling comments are missing an important point: Say we build enough solar to produce enough energy for peak demand. That’s going to end up wasting multiple HEU’s of electricity during the day (unless we build an insane number of batteries). For reference, cities currently cover 3 500 000 km^2 of the earth. Also, solar density is still improving, and other sources of energy exist.

falcolas 3y ago

> The 5 largest subtropical deserts in the world have enough room to hold 30 HEUs worth of solar farms. If we built all those and turned them all on at once Funny enough, this was done in the SF novel “The Hail Mary Project”, and derided by the scientists in the book for furthering climate problems dramatically by turning a normally heat reflective surface into a heat absorbent surface. Worth investigating before committing our deserts to power collection.

lozenge 3y ago
It's not a real concern. Might make for a good science Fiction story though. https://yaleclimateconnections.org/2009/11/superfreakonomics-climate-contrarianism/ https://yaleclimateconnections.org/2009/11/superfreakonomics...

WalterBright 3y ago

Irrigate the desert and plant 500 000 km^2 of trees seems a lot more practical. And we get lots of building materials as a side effect.

tsimionescu 3y ago
We need to store about 10B tons of C per year if we were to be carbon neutral. We're going to need to build a lot of megastructures out of wood to even keep pace.
- blkhawk 3y ago
  Plus wood for building is NOT a permanent carbon storage mechanism. You would need to entomb that wood deep underground where it cannot decay.
  - WalterBright 3y ago
    We still need building materials, and trees are cut down all the time for building materials and paper. Besides, wood decays very, very slowly. There's a couple trees nearby that were felled 25 years ago, and they are just starting to rot. Besides, they don't have to be buried that deep. People are still finding intact bodies in bogs in England from thousands of years ago. They're just a few feet down. In the desert things decay pretty slowly, too. See Sylvester, the cowboy mummy in a museum in Seattle that was found in a sand dune in Arizona with a bullet hole in him.
    - blkhawk 3y ago
      you think 25 years is enough to store CO2 in? even 1000 years is not enough since we will need to entomb all available wood. But that is all stupid anyway because of this: To start reversing the CO2 emission we would need as many trees it takes to take up the current CO2 emissions and then a bit more. From what I found you can estimate every m³ (a bit less than 1 American fridge) of Wood stores 1 ton of CO2. Say each hectare of Forest with fast growing trees produces ~ 10m³ per year (more when they are cut down but they need to grow over a decade+. So if they take 10 years that is 100m³ wood yield at the end). Humanity produced by some estimates 37 billion tons of CO2 in 2020. That means you need 3.7 billion hectare of forest. The USA has a land area of 157.7 million hectare. So you need an area of 23 times the LAND area of the United States of America just for trees just to HALT CO² at today's level. How well are fast growing trees growing in the Arizona desert btw?

tsimionescu 3y ago

You're ignoring a huge part that makes this (as well as virtually all other carbon capture plans) useless: where do you store all the carbon? We are currently emitting ~37B tons of CO2 per year. That's ~0.375 C, so assuming we only store the carbon, that's ~10B tons of C per year. For reference, the Empire State Building is ~365K tons - so you'd need to build ~30 thousand empire state buildings per year with the captured carbon.

regularfry 3y ago
In fairness, the Empire State Building is mostly empty space. If what you have is elemental carbon, the same mass is a cube with 6m sides. Which, yes, you then need 30,000 of so it doesn't make the whole thing that much easier.
concordDance 3y ago
10B tons of C is a mere 10 cubic kilometers. For context, we have individual open pit mines of over 2 cubic kilometers.
tzs 3y ago
If we had emitted 37 billion metric tons of CO2 a year each year for the last 400 years that would be a total of about 1.48 x 10^19 grams of CO2. That's more than we now have in the atmosphere so this gives us a convenient upper limit. 12/44th of the mass of CO2 is from carbon, so that is 4 x 10^18 g of carbon to deal with if we wanted to store all the carbon current in atmospheric CO2. The density of carbon depends on what form it is in--diamond is a lot denser than graphite, which is a lot denser than carbon powder. Let's store it as graphite, which has a density of 2.2 g/cm^3. We'd need 1.8 x 10^18 cm^3 for that much powdered carbon, or 1.8 x 10^12 m^3, or 1800 km^3. But remember that we are getting all this carbon we need to deal with using energy from massive solar farms. Put the solar panels a few meters off the ground, and dump the graphite under the solar panels. If the graphite was dumped into a pile 1 m tall it would need 1800 km^2 of area. That would be just a tiny fraction of the area available under the amount of panels we'd have to be using to capture that much carbon. Spread evenly under all the panels it would be less than a millimeter.

replygirl 3y ago

i would be beyond surprised if covering 10% of the planet's land in solar didn't require any new science or engineering. i doubt we even have the labor force or materials to pull it off, timeline notwithstanding

tzs 3y ago
It’s only 10% if we want something that can lower CO2 to preindustrial levels in under a decade. It’s under 0.7% if we just want to stop the increase.
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bouncycastle 3y ago

Plants are basically self-replicating solar panels with efficient CO2 removal & storage.

david-gpu 3y ago
Plant matter is carbon neutral unless you cut it down and find a way to stop it from burning down or decomposing for thousands of years.
- phh 3y ago
  It's carbon neutral on the order of magnitude of a century. If we were to plant a forest in the Sahara, it'll largely be net positive capture for at least 3 decades, and then we'll be able to replace coal with that wood, making a global net zero (but we'd already have reduced co2 in the atmosphere). Replacing oil with wood would probably require quite a lot of work though (as making the desalination plants to make a forest)
- truculent 3y ago
  Or you can permanently increase the area given over to plant matter
  - Aerroon 3y ago
    That's a one-time thing though and plants have already naturally spread to basically everywhere that they can spread.
    - truculent 3y ago
      So, for example, we have cleared forests to make way for farmland. Reversing that would increase the total amount of carbon held. Perhaps I should have said increasing the amount of equilibrium biomass or something to more clearly include rewilding or ecosystem changes. It’s not just plants that are a carbon store, after all. I don’t think this is likely to represent a full solution, if that is the subtext to your comment.

lima 3y ago

500000 km^2 is a little less than the entire area of France, for anyone wondering.

thelastgallon 3y ago

500 000 km^2 = 708 km x 708 km A single 708 km x 708 km would have these corners (Paris, Berlin, Vienna, Milan):https://goo.gl/maps/DTxdVCcK3aYUEirw8 https://goo.gl/maps/DTxdVCcK3aYUEirw8 (Rough approximation!) 30 of these: 21,240 km x 21,240 km