5 ms·

Bear in mind that (a) you're just pulling it from the atmosphere and burying it, not splitting the C from O2 so you can use it as fuel again, and (b) there are

Bear in mind that (a) you're just pulling it from the atmosphere and burying it, not splitting the C from O2 so you can use it as fuel again, and (b) there are applications like long-haul jets and cement production where eliminating emissions isn't that easy. To put some numbers on (a), David MacKay's book has some numbers[1]: > The laws of physics say that the energy required must be at least 0.2 kWh per kg of CO2.... > Lackner told me in June 2008 that, in a dry climate, the concentration cost has been reduced to about 0.18–0.37 kWh of low-grade heat per kg CO2. The compression cost is 0.11 kWh per kg. Thus Lackner’s total cost is 0.48 kWh or less per kg. Burning a kilogram of coal generates 8 kWh[2] and 2.42 kg CO2[3]. So that's 8 kWh generated, requiring 1.16 kWh to pull 2.42 kg CO2 back out out of the atmosphere. So about 15% of the energy obtained by putting carbon in the atmosphere is needed to remove it. [1] https://www.withouthotair.com/c31/page_244.shtml https://www.withouthotair.com/c31/page_244.shtml) [2] https://www.euronuclear.org/glossary/coal-equivalent/ https://www.euronuclear.org/glossary/coal-equivalent/ [3] https://360energy.net/how-does-using-energy-create-carbon-emissions/ https://360energy.net/how-does-using-energy-create-carbon-em...

guiriduro 5y ago
> there are applications like long-haul jets and cement production where eliminating emissions isn't that easy. I disagree, there's an easy solution to eliminating those emissions: have zero long-haul jets and zero cement production. Before this gets (inevitably) downvoted, the more interesting question is why do we need either, what alternatives are there, how fundamentally we're willing to question our biases and expectations over what counts as a necessity. If saving our environment is an overriding priority, then the extent of the compromises we have to make can be made clearer.
- HPsquared 5y ago
  It's not actually easy to ban long-haul travel. It's technologically simple, which is probably the angle you are looking from, but politically very difficult.
  - ashtonkem 5y ago
    We can drastically reduce our usage of jets though. There is no reason why people should be flying between SF and LA, or NYC and Boston. Those are well within comfortable range of high speed rail, which is electric. Once we’ve shifted all the excess air travel over to rail, that will leave a much smaller set of jet travel to offset.
    - spfzero 5y ago
      If you look at a map of all airline flights there are many thousands of short-range flights. Replacing them all with trains would be interesting. Just the right-of-way property transactions would be daunting. Look at California as a lesson in how this can't be easily done. The other thing is, people move around. Airlines can change flights easily to map to demographic changes; that's a major strength of air travel. Not as easy to rip up tracks and start over.
      - Robotbeat 5y ago
        It's much easier, IMHO, to switch over these short haul flights to electric aircraft than to High Speed Rail in the US. By the time even one major new HSR route will be finished, we'll have certified and be flying electric passenger aircraft with just as much speed and just as long of a route (500 miles) BUT with ability to go anywhere in the country by hopping.
        GekkePrutser 5y ago
        I kinda doubt it will go that quickly. See how many problems Boeing had with their lithium batteries in the 787. And those were just auxiliary power. This will take a hundred times that many batteries with the scale bringing many engineering challenges. And then the totally different engines.. I think it'll take a long time to have a battery powered airliner built, in mass production and as reliable and safe as current airliners. There's a lot of stuff to be built from scratch without half a century of trial and error to learn from. I think biofuels might be a better option for aviation until the tech has time to catch up.
- deleted 5y ago
  [deleted]
- jjk166 5y ago
  This would be a lot more insightful if we hadn't already spent decades and billions of dollars looking for greener alternatives only to find that they don't exist.
- karaterobot 5y ago
  Upvoted, because I think it's a legitimate question. I don't think you're actually saying let's stop all long-haul flights and cement production. You're saying that if we actually believed something was an existential risk to civilization, we'd put almost any option on the table for mitigating it, even if only to rule it out. I assume there is a list of sacred things we wouldn't even consider doing without, no matter the cost in human lives. But is jet travel and cheap construction on that list or not? Maybe, maybe not.
  - Robotbeat 5y ago
    Concrete and jet travel are not existential. They're a few percent of the total. 3% for cement and 2% for aviation. Less than 1% for long haul aviation. If that was it the only thing left, we'd have no problem. That's at pre-industrial emissions level. https://ourworldindata.org/uploads/2020/09/Emissions-by-sector-%E2%80%93-pie-charts.png https://ourworldindata.org/uploads/2020/09/Emissions-by-sect... Long haul aviation makes immigration feasible without dangerous long ship trips, which are worse emissions than long haul aviation. So we should keep them around in some form, but we can improve the efficiency and even electrify them.
- Robotbeat 5y ago
  I would say it's pretty dang tough to not have cement. What do you use for a house foundation? Many apartments are made of cement and essentially every building uses a cement foundation. Luckily, cement is not a big part of the total emissions. Neither is long haul travel, particularly. Short haul flights are about half of all passenger-miles in air travel, can be made fully electric, and long-haul and medium haul flights can be split up into multiple legs for almost every route. EDIT:I will say there are ways to reduce CO2 emissions from cement. You can make clinker with electric heat just fine. But half the CO2 is from the clinker itself. Over time, cement will absorb the CO2 it emitted as it fully cures, but that can take a century. It’s possible to accelerate that process. It’s also possible to use alternatives, like sulfur cement.
  - loufe 5y ago
    > Luckily, cement is not a big part of the total emissions. This is patently false. A quick search shows a number of 8% of global CO2 going to cement production and use emissions.
    - Robotbeat 5y ago
      “Patently false?” No, I see 3% in direct emissions from the cement itself: https://ourworldindata.org/uploads/2020/09/Emissions-by-sector-%E2%80%93-pie-charts.png https://ourworldindata.org/uploads/2020/09/Emissions-by-sect... (As far as indirect emissions like transport, the heat to make the clinker, etc, then yeah, I can believe that it gets to 8% total.)
  - vbezhenar 5y ago
    > What do you use for a house foundation? Rocks. > Many apartments are made of cement Make them from wood.
  - Emma_Goldman 5y ago
    >Neither is long haul travel, particularly. Aviation and shipping make up 5-6% of GHG emissions, not a trivial amount. Aviation is projected to expand several-fold by 2050 which, in the context of decarbonisation, means it will take up a progressively larger fraction of global emissions over time. It will be one of the last and greatest challenges - which is exactly why it will require offsets, carbon capture or otherwise. The aviation's offset market, CORSIA, is already one of the most developed in the world. Your optimism about electrifying aviation is not shared by the industry.
- Dylan16807 5y ago
  But why make it so binary? We can make biofuel at some price. We can capture CO2 at some price. Build that into the product and there's no reason to reduce to zero.
q1w2 5y ago
I don't see how we're going to use CO2 as energy again. It's not like the original hydrocarbons we dug up.
- DennisP 5y ago
  Right, which is why mostly the idea is to just bury the CO2. However, if you do want to make fuel from it, say for airliners, then it's totally possible, you just have to add hydrogen, and more energy than you'll get from burning the fuel. E.g. the Sabatier process to make methane.
  - GekkePrutser 5y ago
    But if you already have loads of hydrogen to play with you might as well just burn that, right?
    - Baeocystin 5y ago
      Spend much time working with hydrogen as a fuel and you'll mostly be learning just how amazingly convenient sticking your hydrogens on to carbon chains is compared to the alternative.
    - pharke 5y ago
      Carbon is the ideal hydrogen storage system. It raises the critical point by 160K and increase the density achievable at normal temperatures and pressures drastically. Don't discount the energy that needs to go in to pressurizing and cooling hydrogen, it results in significant CO2 production. I'd be very interested in seeing a comparison of the energy requirements for methane production vs. hydrogen storage, I have a feeling that it would favour methane if you accounted for all of the variables.

guiriduro 5y ago

> there are applications like long-haul jets and cement production where eliminating emissions isn't that easy. I disagree, there's an easy solution to eliminating those emissions: have zero long-haul jets and zero cement production. Before this gets (inevitably) downvoted, the more interesting question is why do we need either, what alternatives are there, how fundamentally we're willing to question our biases and expectations over what counts as a necessity. If saving our environment is an overriding priority, then the extent of the compromises we have to make can be made clearer.

HPsquared 5y ago
It's not actually easy to ban long-haul travel. It's technologically simple, which is probably the angle you are looking from, but politically very difficult.
- ashtonkem 5y ago
  We can drastically reduce our usage of jets though. There is no reason why people should be flying between SF and LA, or NYC and Boston. Those are well within comfortable range of high speed rail, which is electric. Once we’ve shifted all the excess air travel over to rail, that will leave a much smaller set of jet travel to offset.
  - spfzero 5y ago
    If you look at a map of all airline flights there are many thousands of short-range flights. Replacing them all with trains would be interesting. Just the right-of-way property transactions would be daunting. Look at California as a lesson in how this can't be easily done. The other thing is, people move around. Airlines can change flights easily to map to demographic changes; that's a major strength of air travel. Not as easy to rip up tracks and start over.
    - Robotbeat 5y ago
      It's much easier, IMHO, to switch over these short haul flights to electric aircraft than to High Speed Rail in the US. By the time even one major new HSR route will be finished, we'll have certified and be flying electric passenger aircraft with just as much speed and just as long of a route (500 miles) BUT with ability to go anywhere in the country by hopping.
      - GekkePrutser 5y ago
        I kinda doubt it will go that quickly. See how many problems Boeing had with their lithium batteries in the 787. And those were just auxiliary power. This will take a hundred times that many batteries with the scale bringing many engineering challenges. And then the totally different engines.. I think it'll take a long time to have a battery powered airliner built, in mass production and as reliable and safe as current airliners. There's a lot of stuff to be built from scratch without half a century of trial and error to learn from. I think biofuels might be a better option for aviation until the tech has time to catch up.
deleted 5y ago
[deleted]
jjk166 5y ago
This would be a lot more insightful if we hadn't already spent decades and billions of dollars looking for greener alternatives only to find that they don't exist.
karaterobot 5y ago
Upvoted, because I think it's a legitimate question. I don't think you're actually saying let's stop all long-haul flights and cement production. You're saying that if we actually believed something was an existential risk to civilization, we'd put almost any option on the table for mitigating it, even if only to rule it out. I assume there is a list of sacred things we wouldn't even consider doing without, no matter the cost in human lives. But is jet travel and cheap construction on that list or not? Maybe, maybe not.
- Robotbeat 5y ago
  Concrete and jet travel are not existential. They're a few percent of the total. 3% for cement and 2% for aviation. Less than 1% for long haul aviation. If that was it the only thing left, we'd have no problem. That's at pre-industrial emissions level. https://ourworldindata.org/uploads/2020/09/Emissions-by-sector-%E2%80%93-pie-charts.png https://ourworldindata.org/uploads/2020/09/Emissions-by-sect... Long haul aviation makes immigration feasible without dangerous long ship trips, which are worse emissions than long haul aviation. So we should keep them around in some form, but we can improve the efficiency and even electrify them.
Robotbeat 5y ago
I would say it's pretty dang tough to not have cement. What do you use for a house foundation? Many apartments are made of cement and essentially every building uses a cement foundation. Luckily, cement is not a big part of the total emissions. Neither is long haul travel, particularly. Short haul flights are about half of all passenger-miles in air travel, can be made fully electric, and long-haul and medium haul flights can be split up into multiple legs for almost every route. EDIT:I will say there are ways to reduce CO2 emissions from cement. You can make clinker with electric heat just fine. But half the CO2 is from the clinker itself. Over time, cement will absorb the CO2 it emitted as it fully cures, but that can take a century. It’s possible to accelerate that process. It’s also possible to use alternatives, like sulfur cement.
- loufe 5y ago
  > Luckily, cement is not a big part of the total emissions. This is patently false. A quick search shows a number of 8% of global CO2 going to cement production and use emissions.
  - Robotbeat 5y ago
    “Patently false?” No, I see 3% in direct emissions from the cement itself: https://ourworldindata.org/uploads/2020/09/Emissions-by-sector-%E2%80%93-pie-charts.png https://ourworldindata.org/uploads/2020/09/Emissions-by-sect... (As far as indirect emissions like transport, the heat to make the clinker, etc, then yeah, I can believe that it gets to 8% total.)
- vbezhenar 5y ago
  > What do you use for a house foundation? Rocks. > Many apartments are made of cement Make them from wood.
- Emma_Goldman 5y ago
  >Neither is long haul travel, particularly. Aviation and shipping make up 5-6% of GHG emissions, not a trivial amount. Aviation is projected to expand several-fold by 2050 which, in the context of decarbonisation, means it will take up a progressively larger fraction of global emissions over time. It will be one of the last and greatest challenges - which is exactly why it will require offsets, carbon capture or otherwise. The aviation's offset market, CORSIA, is already one of the most developed in the world. Your optimism about electrifying aviation is not shared by the industry.
Dylan16807 5y ago
But why make it so binary? We can make biofuel at some price. We can capture CO2 at some price. Build that into the product and there's no reason to reduce to zero.

q1w2 5y ago

I don't see how we're going to use CO2 as energy again. It's not like the original hydrocarbons we dug up.

DennisP 5y ago
Right, which is why mostly the idea is to just bury the CO2. However, if you do want to make fuel from it, say for airliners, then it's totally possible, you just have to add hydrogen, and more energy than you'll get from burning the fuel. E.g. the Sabatier process to make methane.
- GekkePrutser 5y ago
  But if you already have loads of hydrogen to play with you might as well just burn that, right?
  - Baeocystin 5y ago
    Spend much time working with hydrogen as a fuel and you'll mostly be learning just how amazingly convenient sticking your hydrogens on to carbon chains is compared to the alternative.
  - pharke 5y ago
    Carbon is the ideal hydrogen storage system. It raises the critical point by 160K and increase the density achievable at normal temperatures and pressures drastically. Don't discount the energy that needs to go in to pressurizing and cooling hydrogen, it results in significant CO2 production. I'd be very interested in seeing a comparison of the energy requirements for methane production vs. hydrogen storage, I have a feeling that it would favour methane if you accounted for all of the variables.