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The IPCC reports are authoritative. Basically there are a number of pathways to reduce emissions sufficiently quickly (and then to suck out pollutants from the

by ximeng 8y ago

The IPCC reports are authoritative. Basically there are a number of pathways to reduce emissions sufficiently quickly (and then to suck out pollutants from the air) to limit climate change: https://www.ipcc.ch/2018/10/08/summary-for-policymakers-of-ipcc-special-report-on-global-warming-of-1-5c-approved-by-governments/ https://www.ipcc.ch/2018/10/08/summary-for-policymakers-of-i... "The report finds that limiting global warming to 1.5°C would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport, and cities. Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air." It's going to be tough. Some discussion here: https://news.ycombinator.com/item?id=18181503 https://news.ycombinator.com/item?id=18181503 https://news.ycombinator.com/item?id=18814813 https://news.ycombinator.com/item?id=18814813 https://news.ycombinator.com/item?id=18389324 https://news.ycombinator.com/item?id=18389324 https://news.ycombinator.com/item?id=17221239 https://news.ycombinator.com/item?id=17221239

vkou 8y ago
> This means that any remaining emissions would need to be balanced by removing CO2 from the air. This is the most important sentence in that paragraph. If we're going to sit on our hands, waiting until 2030 to halve our emissions, and 2050 to zero them (Nobody has a plan for doing either of those things, by the way), we're then going to have to perform planet-scale carbon sequestration. No affordable planet-scale carbon sequestration technology currently exists, nor are we close to developing one.
- Iwan-Zotow 8y ago
  > No affordable planet-scale carbon sequestration technology currently exists Huh?!? What about just growing trees?
  - sliken 8y ago
    Trees are carbon neutral, not carbon sinks. You grow it, and it's a carbon sink. But then it dies. If by fire it's releases the CO2 quickly, if not it rots slowly and reduces the CO2 slowly. Neither are a fix for our short term problems. Growing algae or plankton on the ocean, where most of them die and land on the (mostly inert) deep ocean floor would help. Not perfect, but at least the CO2 is likely be consumed on the ocean floor slower than it's produced on the surface thanks to the cold, dark, high pressure environment on the ocean floor. One research claims that the limit for growth in many places in the ocean is a lack of iron. So spreading iron would lead to a huge increase in life. Unfortunately the impact seems to last days.
    - CuriousSkeptic 8y ago
      The IPCC report estimates a possibility of 2GT/year from afforestation. (And expect us to need 100-1000GT extracted by 2100 depending on how quickly we get rid of emissions.)
      - sliken 8y ago
        Right, so if you manage to start a healthy forest it is a carbon sink... as long as the biomass is increasing. After some decades it flattens out consuming land forever, but being mostly carbon neutral. So to offset a non-zero amount of carbon emissions you have to steadily increase the number of acres of forest. Unfortunately this puts pressure on other things like farming, which causes them to be more energy intensive to get enough density. From what I can tell the answers are things like nuclear, solar, and wind. Covering every parking lot with solar would be a good start.
        CuriousSkeptic 8y ago
        On that topic, I found this ted talk on the feasibility of various renewable energy sources quite eye opening https://youtu.be/E0W1ZZYIV8o https://youtu.be/E0W1ZZYIV8o
        CuriousSkeptic 8y ago
        Should perhaps add that the 2GT/y thing was in the context of tolerating a peak of 1.7 degrees and still being able to reach 1.5 by 2100 (since no scenario can stay below 1.5). It was not a bout a sustainable compensation for current emissions, if that was the impression.
  - graeme 8y ago
    I expect that covering the whole earth in forest wouldn't be enough. Humanity has reduced forest cover and released fossil carbon. You're proposing to undo the one but it won't undo the other.
  - vkou 8y ago
    Trees take years, and a lot of labour to grow, cut, and bury. A tree takes out ~1 tonne of carbon out of the atmosphere, over a 40 year lifespan. Since the industrial revolution, we've emitted 400 billion tonnes of carbon into the atmosphere. By 2050, we'll emit another 150 billion tonnes. If we want to sequester half of that, we'll need to grow, log, and bury 275 billion trees. Who is going to pay for this? Bonus points: Digging up coal, so you can burn it, at the same time that you're growing trees, so you can bury them, has got to be one of the worst ideas in the energy-economy space.

by ximeng 8y ago

vkou 8y ago

> This means that any remaining emissions would need to be balanced by removing CO2 from the air. This is the most important sentence in that paragraph. If we're going to sit on our hands, waiting until 2030 to halve our emissions, and 2050 to zero them (Nobody has a plan for doing either of those things, by the way), we're then going to have to perform planet-scale carbon sequestration. No affordable planet-scale carbon sequestration technology currently exists, nor are we close to developing one.

Iwan-Zotow 8y ago
> No affordable planet-scale carbon sequestration technology currently exists Huh?!? What about just growing trees?
- sliken 8y ago
  Trees are carbon neutral, not carbon sinks. You grow it, and it's a carbon sink. But then it dies. If by fire it's releases the CO2 quickly, if not it rots slowly and reduces the CO2 slowly. Neither are a fix for our short term problems. Growing algae or plankton on the ocean, where most of them die and land on the (mostly inert) deep ocean floor would help. Not perfect, but at least the CO2 is likely be consumed on the ocean floor slower than it's produced on the surface thanks to the cold, dark, high pressure environment on the ocean floor. One research claims that the limit for growth in many places in the ocean is a lack of iron. So spreading iron would lead to a huge increase in life. Unfortunately the impact seems to last days.
  - CuriousSkeptic 8y ago
    The IPCC report estimates a possibility of 2GT/year from afforestation. (And expect us to need 100-1000GT extracted by 2100 depending on how quickly we get rid of emissions.)
    - sliken 8y ago
      Right, so if you manage to start a healthy forest it is a carbon sink... as long as the biomass is increasing. After some decades it flattens out consuming land forever, but being mostly carbon neutral. So to offset a non-zero amount of carbon emissions you have to steadily increase the number of acres of forest. Unfortunately this puts pressure on other things like farming, which causes them to be more energy intensive to get enough density. From what I can tell the answers are things like nuclear, solar, and wind. Covering every parking lot with solar would be a good start.
      - CuriousSkeptic 8y ago
        On that topic, I found this ted talk on the feasibility of various renewable energy sources quite eye opening https://youtu.be/E0W1ZZYIV8o https://youtu.be/E0W1ZZYIV8o
      - CuriousSkeptic 8y ago
        Should perhaps add that the 2GT/y thing was in the context of tolerating a peak of 1.7 degrees and still being able to reach 1.5 by 2100 (since no scenario can stay below 1.5). It was not a bout a sustainable compensation for current emissions, if that was the impression.
- graeme 8y ago
  I expect that covering the whole earth in forest wouldn't be enough. Humanity has reduced forest cover and released fossil carbon. You're proposing to undo the one but it won't undo the other.
- vkou 8y ago
  Trees take years, and a lot of labour to grow, cut, and bury. A tree takes out ~1 tonne of carbon out of the atmosphere, over a 40 year lifespan. Since the industrial revolution, we've emitted 400 billion tonnes of carbon into the atmosphere. By 2050, we'll emit another 150 billion tonnes. If we want to sequester half of that, we'll need to grow, log, and bury 275 billion trees. Who is going to pay for this? Bonus points: Digging up coal, so you can burn it, at the same time that you're growing trees, so you can bury them, has got to be one of the worst ideas in the energy-economy space.