7 ms·

There really is very, very little carbon in the atmosphere, famously ~410 ppm. (Yes, that little bit is enough to absorb significantly more heat from the sun).

There really is very, very little carbon in the atmosphere, famously ~410 ppm. (Yes, that little bit is enough to absorb significantly more heat from the sun). So, whatever capture system you use, you'd need to move a lot of air through in order to produce a small amount of something like liquid hydrocarbon fuel. It will require thousands of times more air, by mass. Since the output fuel product is hundreds of times more dense, it would require a crazy large volume of air to extract the carbon necessary to fill a fuel tank. A corn field combined with a methanol fermentation and distillation facility is an example of a machine that does that. Very large.

PaulHoule 4y ago
The advantage of attempting it mechanically is that you might use less water and less fixed nitrogen. Water consumption is directly linked to how plants absorb CO₂ from the atmosphere, see https://ripe.illinois.edu/blog/difference-between-c3-and-c4-plants https://ripe.illinois.edu/blog/difference-between-c3-and-c4-...
photochemsyn 4y ago
Plants pull 100 gigatons of carbon out of the atmosphere every year and convert it to biomass (essentially, oxy-ammonia-hydrocarbons like sugars, proteins, fats, etc.). Humans pull about 6 gigatons of carbon out of the ground each year and pump it into the atmosphere. The reason this cycle doesn't exhaust the atmospheric pool, of course, is that animals and fungi (more the latter) break down biomass into CO2 and release it back into the atmosphere. That's not what I'd call 'very very little carbon'.
- lazide 4y ago
  On a planetary atmosphere level? It’s still tiny. Literally .0441% Getting anything at that concentration out is… generally not easy. Doable! But not easy. That it’s chemically low reactivity makes it even harder. Plants have spent billions of years evolving to do it, and from an energy perspective aren’t very efficient at it. Unless we want to burn even more oil trying to power the process or just make a tiny dent in it, we’ll need to not only figure out a somewhat efficient way to do it, but also figure out how to generate a massive amount of power without burning oil to power it.
  - ravenstine 4y ago
    For even more perspective, human breath can be easily composed of somewhere between 20,000 ppm and 40,000 ppm, and tens of thousands greater than that with enough energy expenditure. (I know this because I've actually measured this myself with research grade NDIR CO2 sensors) 441 ppm can be "a lot" depending on the gas and the expected effect. You don't want to breathe in 441 ppm of chlorine gas. But CO2 being fairly non-reactive makes 441 ppm of it relatively minuscule in contrast to the other predominant atmospheric gases. It's also nowhere near enough to cause outright catastrophe.
    - pencilguin 4y ago
      441 ppm CO2 turns out to be quite close to enough to cause global catastrophe.
      - lazide 4y ago
        Eventually. But no one is going to keel over dead due to suffocation today because of global CO2 concentration, which is ‘outright’. Pretty sure global minimum temperatures above 100F would also count as ‘outright’.
        pencilguin 4y ago
        There are already places where being without a cooling method other than sweating would be fatal, at least one day of the year. In many more places, crops are failing. People necessarily leaving these places will need to go where other people already are.
        deleted 4y ago
        [deleted]
        lazide 4y ago
        That happened before too, and has been (at lower frequency) for all of recorded history, near as we can tell. As noted, not an outright catastrophe right now. The discussion is about avoiding it becoming one, and relative impacts. Humanity isn’t going to be dead tomorrow because of this, but may be in more pain in a decade or two, and longer term even more so.
ravenstine 4y ago
You mean ethanol, right? I don't think it's produced by fermentation, at least not without a secondary process that removes the other hydrocarbon. That aside, yes, plant biomass to alcohol is a carbon-neutral tech that has already existed for a really long time. Let plants take carbon out of the atmosphere, ferment the starches and sugars into fuel alcohol, feed the remaining cellulose to animals, burn the fuel, eat the animals, and return most (but not all!) of the carbon back to where it came from. It's really an incredible process, but obviously its existence is a threat to the oil industry. If you've ever noticed the propaganda that ethanol is bad for engines and worse for the environment, well, just follow the money.
- marshray 4y ago
  D'oh! Yes, ethanol. Thanks for the correction!
- pencilguin 4y ago
  It takes a very great deal of hydrocarbon fuel to produce the ethanol going into our engines. When EVs displace gasohol-burning cars, the ag production, 30% of the maize crop, can go back to feeding people (or, more likely, feeding chickens); and we may hope the fuel used will be synthetics from atmospheric feedstocks. Brazil's sugar cane operations seem to produce more fuel than the process consumes.
nine_k 4y ago
But there are CO₂-rich exhausts in chemical plants and power plants, with concentrations well above 50%. This is where the capture could work efficiently. These likely produce a sizable portion of the carbon dioxide surplus. Capturing carbon from a jet engine will remain problematic, or slow. Maybe we should just grow more trees, extract solid carbon from them (by burning or otherwise), and bury it in old coal mines.
- lazide 4y ago
  Even more efficient than carbon capture from power plant exhaust? not pulling the carbon out of the ground and burning it to begin with It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place.
  - nine_k 4y ago
    You have to do something to the existing power plants, before you build out enough solar, wind, batteries, and nuclear. It capture is cheaper then rebuilding the plant, it may make sense to run it until the end of its planned service life. Certain things produce CO₂ as a part of non-power-generating chemical processes, like steelmaking, or producing cement for concrete. If the CO₂ can be captured economically, it would be a great win; there are few known remotely viable alternatives.
    - Schroedingersat 4y ago
      You're forgetting all the lifecycle emissions and the whole 'if capture is cheaper' part given that running a coal plant without CCS is more expensive than replacing it with new solar panels in many areas already.
  - rbanffy 4y ago
    > It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place. It kind of makes sense, if energy is cheap enough. If we have surplus energy, we can remove enough CO2 from the atmosphere to stop or even revert climate change. If we can desalinate water with that surplus energy, we can even use that extracted carbon to increase the amount of biomass on the surface. Both climate change and fresh water supply are solvable with abundant cheap energy.
machina_ex_deus 4y ago
This comment is inaccurate, the way CO2 traps heat isn't from the sun, but the thermal black body radiation from the surface.
- marshray 4y ago
  Do you have a link to something where I can read more about this?
__MatrixMan__ 4y ago
Home furnaces burn a lot of natural gas and put the water in the sewer and the CO2 in the air. I wonder how much tweaking the sewer system would need to start acting as a CO2 return system also. If it were a closed loop system you could at least be carbon neutral, and stockpiling methane for the winter is easier than stockpiling electricity.
- stephen_g 4y ago
  I think the upgrade to far, far more efficient heat pumps would be small compared to the cost of that...
deleted 4y ago
[deleted]
_hypx 4y ago
Direct carbon capture makes sense whenever you have a high concentration of CO₂ emissions. The most obvious are cases where you can get pure carbon, not CO₂. Other times, it might be also worth capturing the CO₂ from something burning. Direct carbon capture from the air will probably be the most expensive solution, but it is still doable. You figure that eventually it will be subsidized.
puffoflogic 4y ago
The other problem with carbon capture (if you could overcome the low concentration issue somehow) is that the result of the tragedy of the commons isn't just "oops the temperature went up by 2°", it's "oops we killed off all plant life on Earth simultaneously and now nearly every living thing on Earth will be dead within a few years".
- marshray 4y ago
  It took centuries to increase atmospheric CO2 to problematic level. If we are so lucky as to have to worry about overcorrection, I'm confident we'll be able to find the 'off' switch to whatever solution in time.

PaulHoule 4y ago

The advantage of attempting it mechanically is that you might use less water and less fixed nitrogen. Water consumption is directly linked to how plants absorb CO₂ from the atmosphere, see https://ripe.illinois.edu/blog/difference-between-c3-and-c4-plants https://ripe.illinois.edu/blog/difference-between-c3-and-c4-...

photochemsyn 4y ago

Plants pull 100 gigatons of carbon out of the atmosphere every year and convert it to biomass (essentially, oxy-ammonia-hydrocarbons like sugars, proteins, fats, etc.). Humans pull about 6 gigatons of carbon out of the ground each year and pump it into the atmosphere. The reason this cycle doesn't exhaust the atmospheric pool, of course, is that animals and fungi (more the latter) break down biomass into CO2 and release it back into the atmosphere. That's not what I'd call 'very very little carbon'.

lazide 4y ago
On a planetary atmosphere level? It’s still tiny. Literally .0441% Getting anything at that concentration out is… generally not easy. Doable! But not easy. That it’s chemically low reactivity makes it even harder. Plants have spent billions of years evolving to do it, and from an energy perspective aren’t very efficient at it. Unless we want to burn even more oil trying to power the process or just make a tiny dent in it, we’ll need to not only figure out a somewhat efficient way to do it, but also figure out how to generate a massive amount of power without burning oil to power it.
- ravenstine 4y ago
  For even more perspective, human breath can be easily composed of somewhere between 20,000 ppm and 40,000 ppm, and tens of thousands greater than that with enough energy expenditure. (I know this because I've actually measured this myself with research grade NDIR CO2 sensors) 441 ppm can be "a lot" depending on the gas and the expected effect. You don't want to breathe in 441 ppm of chlorine gas. But CO2 being fairly non-reactive makes 441 ppm of it relatively minuscule in contrast to the other predominant atmospheric gases. It's also nowhere near enough to cause outright catastrophe.
  - pencilguin 4y ago
    441 ppm CO2 turns out to be quite close to enough to cause global catastrophe.
    - lazide 4y ago
      Eventually. But no one is going to keel over dead due to suffocation today because of global CO2 concentration, which is ‘outright’. Pretty sure global minimum temperatures above 100F would also count as ‘outright’.
      - pencilguin 4y ago
        There are already places where being without a cooling method other than sweating would be fatal, at least one day of the year. In many more places, crops are failing. People necessarily leaving these places will need to go where other people already are.
        deleted 4y ago
        [deleted]
        lazide 4y ago
        That happened before too, and has been (at lower frequency) for all of recorded history, near as we can tell. As noted, not an outright catastrophe right now. The discussion is about avoiding it becoming one, and relative impacts. Humanity isn’t going to be dead tomorrow because of this, but may be in more pain in a decade or two, and longer term even more so.

ravenstine 4y ago

You mean ethanol, right? I don't think it's produced by fermentation, at least not without a secondary process that removes the other hydrocarbon. That aside, yes, plant biomass to alcohol is a carbon-neutral tech that has already existed for a really long time. Let plants take carbon out of the atmosphere, ferment the starches and sugars into fuel alcohol, feed the remaining cellulose to animals, burn the fuel, eat the animals, and return most (but not all!) of the carbon back to where it came from. It's really an incredible process, but obviously its existence is a threat to the oil industry. If you've ever noticed the propaganda that ethanol is bad for engines and worse for the environment, well, just follow the money.

marshray 4y ago
D'oh! Yes, ethanol. Thanks for the correction!
pencilguin 4y ago
It takes a very great deal of hydrocarbon fuel to produce the ethanol going into our engines. When EVs displace gasohol-burning cars, the ag production, 30% of the maize crop, can go back to feeding people (or, more likely, feeding chickens); and we may hope the fuel used will be synthetics from atmospheric feedstocks. Brazil's sugar cane operations seem to produce more fuel than the process consumes.

nine_k 4y ago

But there are CO₂-rich exhausts in chemical plants and power plants, with concentrations well above 50%. This is where the capture could work efficiently. These likely produce a sizable portion of the carbon dioxide surplus. Capturing carbon from a jet engine will remain problematic, or slow. Maybe we should just grow more trees, extract solid carbon from them (by burning or otherwise), and bury it in old coal mines.

lazide 4y ago
Even more efficient than carbon capture from power plant exhaust? not pulling the carbon out of the ground and burning it to begin with It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place.
- nine_k 4y ago
  You have to do something to the existing power plants, before you build out enough solar, wind, batteries, and nuclear. It capture is cheaper then rebuilding the plant, it may make sense to run it until the end of its planned service life. Certain things produce CO₂ as a part of non-power-generating chemical processes, like steelmaking, or producing cement for concrete. If the CO₂ can be captured economically, it would be a great win; there are few known remotely viable alternatives.
  - Schroedingersat 4y ago
    You're forgetting all the lifecycle emissions and the whole 'if capture is cheaper' part given that running a coal plant without CCS is more expensive than replacing it with new solar panels in many areas already.
- rbanffy 4y ago
  > It makes zero sense economically to expend a huge amount of energy to pull the carbon out of power plant exhaust and do something with it, when we can generate the energy without releasing the co2 in the first place. It kind of makes sense, if energy is cheap enough. If we have surplus energy, we can remove enough CO2 from the atmosphere to stop or even revert climate change. If we can desalinate water with that surplus energy, we can even use that extracted carbon to increase the amount of biomass on the surface. Both climate change and fresh water supply are solvable with abundant cheap energy.

machina_ex_deus 4y ago

This comment is inaccurate, the way CO2 traps heat isn't from the sun, but the thermal black body radiation from the surface.

marshray 4y ago
Do you have a link to something where I can read more about this?

__MatrixMan__ 4y ago

Home furnaces burn a lot of natural gas and put the water in the sewer and the CO2 in the air. I wonder how much tweaking the sewer system would need to start acting as a CO2 return system also. If it were a closed loop system you could at least be carbon neutral, and stockpiling methane for the winter is easier than stockpiling electricity.

stephen_g 4y ago
I think the upgrade to far, far more efficient heat pumps would be small compared to the cost of that...

deleted 4y ago

[deleted]

_hypx 4y ago

Direct carbon capture makes sense whenever you have a high concentration of CO₂ emissions. The most obvious are cases where you can get pure carbon, not CO₂. Other times, it might be also worth capturing the CO₂ from something burning. Direct carbon capture from the air will probably be the most expensive solution, but it is still doable. You figure that eventually it will be subsidized.

puffoflogic 4y ago

The other problem with carbon capture (if you could overcome the low concentration issue somehow) is that the result of the tragedy of the commons isn't just "oops the temperature went up by 2°", it's "oops we killed off all plant life on Earth simultaneously and now nearly every living thing on Earth will be dead within a few years".

marshray 4y ago
It took centuries to increase atmospheric CO2 to problematic level. If we are so lucky as to have to worry about overcorrection, I'm confident we'll be able to find the 'off' switch to whatever solution in time.