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The problem with plants is that they do not sequester CO2 permanently; plants grow, die, and decompose, releasing carbon back into the atmosphere. Trees certain

The problem with plants is that they do not sequester CO2 permanently; plants grow, die, and decompose, releasing carbon back into the atmosphere. Trees certainly work as a buffer in the sense that carbon in plants is carbon not in the atmosphere, but the amount you could hold is tiny in comparison to the amount that must be sequestered back in order to make a meaningful change in atmospheric and oceanic CO2 composition. Nonetheless, plants have important benefits, since they alter the local climate by changing the albedo and perspirating. Perspiration of plants in jungles helps to create clouds and regulate humidity, and would help to counteract some of the negative effects of climate change.

TheAdamAndChe 10y ago
Biochar is a possible method to permanently store the CO2 captured from plant matter. Playing devil's advocate here, water vapor is an incredibly powerful greenhouse gas, even more so than CO2.
- m_coder 10y ago
  I was hoping that someone would mention biochar. Heating your house using the leftover heat from the process of creating biochar could be carbon negative.
  - TheAdamAndChe 10y ago
    I agree there's potential in its use, but what I'm afraid of is 1) the high nutrient requirements needed to grow the biochar at a scale useful to offset global warming, and 2) Biochar is basically coal, which could be burned and converted into CO2 again.
    - nine_k 10y ago
      Bury it back. We seem to have huge cavities from used-up coal mines. We could refill them.
      - luck_fenovo 10y ago
        I have a new answer for the Fermi paradox. Any sufficiently advanced civilization will develop an extreme "leave no trace" view for ecological reasons. They refill coal mines, plant trees where there were once cities, and silence radio emissions so that everything appears to be in its "natural" state.
        schiffern 10y ago
        "Any sufficiently advanced civilization is indistinguishable from nature."
        jacobush 10y ago
        Love it!
    - schiffern 10y ago
      >the high nutrient requirements needed to grow the biochar We seem to have forgotten that natural forests are incredibly productive, and don't need artificial fertilizer. So we have a proof-of-concept. How do they do it, and how can we emulate those processes? Spoiler alert: soil (along with the root action of plants) is essentially a flat biological nanomachine that breaks down solid rock and fixes nitrogen, manufacturing fertilizer in-situ. https://www.youtube.com/watch?v=x2H60ritjag https://www.youtube.com/watch?v=x2H60ritjag Of course the logical way to do this is not to create some vast new land use category ("carbon forests" or similar), but to transition our largest current land use category -- agriculture -- from a carbon-releasing to a carbon-sequestering mode. It also helps to increase biomass per hectare in suburbs, by transitioning our current low-carbon-density lawns over to a biome that buffers substantial amounts of carbon. This is the fundamental insight behind Permaculture btw, which has been working on figuring out exactly what this looks like. It's a hard problem yes, but one with existential importance for humanity. >Biochar is basically coal, which could be burned and converted into CO2 again. ...so don't do that. :) It's it obvious that burning coal also needs to stop for effective climate mitigation? In this application, density matters. Biochar is extremely low density, and high in surface area, which makes it an ideal soil amendment which buffers rainwater and provides microbial habitat (not to mention raw carbon for building into soil biomass). By contrast actual coal is nearly worthless in this application.
ced 10y ago
Isn't soil basically just decomposed organic matter, i.e. a big carbon store? What fraction of a plant's carbon goes into the soil vs. into the air?
- masklinn 10y ago
  In most soils the carbon is eventually released by the decay process (through decompositor organisms), though some generally stays sequestered (witness terra preta for instance). Some soils like peats and taiga are strong sinks as they prevent complete decay of organic material, and thus release of the carbon (until they're burned away).
- ph0rque 10y ago
  By burying a plant, you could consciously make that fraction very close to 1. This is a way to fertilize the soil for future plants, and is called hugelkultur.
  - bunderbunder 10y ago
    Hugelkulture doesn't involve burying the plants very deeply though - I suspect that it's shallow enough that CO2 that's released during decomposition can easily make it back to the surface. Most the CO2 from fossil fuels comes from ancient bogs, where plants were prevented from decomposing for long enough that they could eventually turn into materials like coal and petroleum. In essence, they were a result of taking plant matter _out_ of the biosphere, which is sort of the opposite of hugelkultur's goal.
    - ph0rque 10y ago
      Hugelkultur is intended primarily to act as a long-term (5-20 year) fertilization and water absorption mechanism, so that other plants planted on top of the mound grow better. In that context, you will have a net-positive CO2 absorption (or, a net-negative CO2 release into the atmosphere).
FooBarWidget 10y ago
Yes plants die. But don't they also multiply automatically? Doesn't that address the issue?
- Daishiman 10y ago
  Sure, but space is the limited resource over which they compete. Smaller plants that can't draw enough resources die or succumb to pests. It's much like animals that have a large number of offspring given their high mortality rate.
BurningFrog 10y ago
Wood can be preserved for centuries, and be very useful as a construction material during that time. Or you can sink it in the Baltic, where nothing consumes it.
schiffern 10y ago
>Trees certainly work as a buffer in the sense that carbon in plants is carbon not in the atmosphere, but the amount you could hold is tiny in comparison to the amount that must be sequestered Is it? Let's do the math. Absorbing the 350 teratonnes of human emitted carbon[1] over the 8.4 billion hectares of Earth's non-tundra / non-desert land surface area[2] works out to... 42 tonnes per hectare. If we can green deserts[3] that drops to 30 tonnes. That's 30-40 trees per hectare, at 1 tonne per tree.[4] Or 3 kg per square meter of soil carbon, the equivalent of 25-35 cm of topsoil. More likely some combination of the two. Soil carbon is stored up to 40 meters down by deep rooted plants.[5] Most of our land management is via agriculture, so agriculture seems to be the only lever long enough to make a dent. Practically this implies transitioning from soil destroying tillage to soil building cover crops, long-distance imported fertilizer to in-situ fertility produced by soil organisms, and ecologically unstable monocultures to resiliant polyculture, agroforestry, and rotational grazing systems. The "gotcha" question is not whether we can replace our existing agriculture with these systems. The question is whether we can replace our existing agriculture with itself. Any unsustainable system is, by definition, not a viable replacement for itself. [1] http://petrolog.typepad.com/climate_change/2010/01/cumulativ.. http://petrolog.typepad.com/climate_change/2010/01/cumulativ.... [2] http://cnx.org/contents/TWFXbERo@1/The-main-biomes http://cnx.org/contents/TWFXbERo@1/The-main-biomes [3] https://www.youtube.com/watch?v=2xcZS7arcgk https://www.youtube.com/watch?v=2xcZS7arcgk [4] http://cabiblog.typepad.com/hand_picked/2011/06/ever-wondere.. http://cabiblog.typepad.com/hand_picked/2011/06/ever-wondere.... [5] http://www.soilquality.org.au/factsheets/organic-carbon http://www.soilquality.org.au/factsheets/organic-carbon
- bluGill 10y ago
  Note that big farmers have already replaced "soil destroying tillage" with "soil building cover crops". Farm news is full of stories about early adopters 10 years ago bragging about how they are now building soil organic matter with a corresponding reduced need for fertilizer. The big farmers recognize the impact this has on the bottom line. Your mid sized farmers see that extra $10/acre in fertilizer as a cost of business and don't realize they could reduce it. Unfortunately "long-distance imported fertilizer to in-situ fertility produced by soil organisms" cannot work if food is exported off of the farm. Every gram of food taken off the farm includes some micro-nutrients - various minerals that are required for life that have been removed from the soil and taken elsewhere.

TheAdamAndChe 10y ago

Biochar is a possible method to permanently store the CO2 captured from plant matter. Playing devil's advocate here, water vapor is an incredibly powerful greenhouse gas, even more so than CO2.

m_coder 10y ago
I was hoping that someone would mention biochar. Heating your house using the leftover heat from the process of creating biochar could be carbon negative.
- TheAdamAndChe 10y ago
  I agree there's potential in its use, but what I'm afraid of is 1) the high nutrient requirements needed to grow the biochar at a scale useful to offset global warming, and 2) Biochar is basically coal, which could be burned and converted into CO2 again.
  - nine_k 10y ago
    Bury it back. We seem to have huge cavities from used-up coal mines. We could refill them.
    - luck_fenovo 10y ago
      I have a new answer for the Fermi paradox. Any sufficiently advanced civilization will develop an extreme "leave no trace" view for ecological reasons. They refill coal mines, plant trees where there were once cities, and silence radio emissions so that everything appears to be in its "natural" state.
      - schiffern 10y ago
        "Any sufficiently advanced civilization is indistinguishable from nature."
        jacobush 10y ago
        Love it!
  - schiffern 10y ago
    >the high nutrient requirements needed to grow the biochar We seem to have forgotten that natural forests are incredibly productive, and don't need artificial fertilizer. So we have a proof-of-concept. How do they do it, and how can we emulate those processes? Spoiler alert: soil (along with the root action of plants) is essentially a flat biological nanomachine that breaks down solid rock and fixes nitrogen, manufacturing fertilizer in-situ. https://www.youtube.com/watch?v=x2H60ritjag https://www.youtube.com/watch?v=x2H60ritjag Of course the logical way to do this is not to create some vast new land use category ("carbon forests" or similar), but to transition our largest current land use category -- agriculture -- from a carbon-releasing to a carbon-sequestering mode. It also helps to increase biomass per hectare in suburbs, by transitioning our current low-carbon-density lawns over to a biome that buffers substantial amounts of carbon. This is the fundamental insight behind Permaculture btw, which has been working on figuring out exactly what this looks like. It's a hard problem yes, but one with existential importance for humanity. >Biochar is basically coal, which could be burned and converted into CO2 again. ...so don't do that. :) It's it obvious that burning coal also needs to stop for effective climate mitigation? In this application, density matters. Biochar is extremely low density, and high in surface area, which makes it an ideal soil amendment which buffers rainwater and provides microbial habitat (not to mention raw carbon for building into soil biomass). By contrast actual coal is nearly worthless in this application.

ced 10y ago

Isn't soil basically just decomposed organic matter, i.e. a big carbon store? What fraction of a plant's carbon goes into the soil vs. into the air?

masklinn 10y ago
In most soils the carbon is eventually released by the decay process (through decompositor organisms), though some generally stays sequestered (witness terra preta for instance). Some soils like peats and taiga are strong sinks as they prevent complete decay of organic material, and thus release of the carbon (until they're burned away).
ph0rque 10y ago
By burying a plant, you could consciously make that fraction very close to 1. This is a way to fertilize the soil for future plants, and is called hugelkultur.
- bunderbunder 10y ago
  Hugelkulture doesn't involve burying the plants very deeply though - I suspect that it's shallow enough that CO2 that's released during decomposition can easily make it back to the surface. Most the CO2 from fossil fuels comes from ancient bogs, where plants were prevented from decomposing for long enough that they could eventually turn into materials like coal and petroleum. In essence, they were a result of taking plant matter _out_ of the biosphere, which is sort of the opposite of hugelkultur's goal.
  - ph0rque 10y ago
    Hugelkultur is intended primarily to act as a long-term (5-20 year) fertilization and water absorption mechanism, so that other plants planted on top of the mound grow better. In that context, you will have a net-positive CO2 absorption (or, a net-negative CO2 release into the atmosphere).

FooBarWidget 10y ago

Yes plants die. But don't they also multiply automatically? Doesn't that address the issue?

Daishiman 10y ago
Sure, but space is the limited resource over which they compete. Smaller plants that can't draw enough resources die or succumb to pests. It's much like animals that have a large number of offspring given their high mortality rate.

BurningFrog 10y ago

Wood can be preserved for centuries, and be very useful as a construction material during that time. Or you can sink it in the Baltic, where nothing consumes it.

schiffern 10y ago

>Trees certainly work as a buffer in the sense that carbon in plants is carbon not in the atmosphere, but the amount you could hold is tiny in comparison to the amount that must be sequestered Is it? Let's do the math. Absorbing the 350 teratonnes of human emitted carbon[1] over the 8.4 billion hectares of Earth's non-tundra / non-desert land surface area[2] works out to... 42 tonnes per hectare. If we can green deserts[3] that drops to 30 tonnes. That's 30-40 trees per hectare, at 1 tonne per tree.[4] Or 3 kg per square meter of soil carbon, the equivalent of 25-35 cm of topsoil. More likely some combination of the two. Soil carbon is stored up to 40 meters down by deep rooted plants.[5] Most of our land management is via agriculture, so agriculture seems to be the only lever long enough to make a dent. Practically this implies transitioning from soil destroying tillage to soil building cover crops, long-distance imported fertilizer to in-situ fertility produced by soil organisms, and ecologically unstable monocultures to resiliant polyculture, agroforestry, and rotational grazing systems. The "gotcha" question is not whether we can replace our existing agriculture with these systems. The question is whether we can replace our existing agriculture with itself. Any unsustainable system is, by definition, not a viable replacement for itself. [1] http://petrolog.typepad.com/climate_change/2010/01/cumulativ.. http://petrolog.typepad.com/climate_change/2010/01/cumulativ.... [2] http://cnx.org/contents/TWFXbERo@1/The-main-biomes http://cnx.org/contents/TWFXbERo@1/The-main-biomes [3] https://www.youtube.com/watch?v=2xcZS7arcgk https://www.youtube.com/watch?v=2xcZS7arcgk [4] http://cabiblog.typepad.com/hand_picked/2011/06/ever-wondere.. http://cabiblog.typepad.com/hand_picked/2011/06/ever-wondere.... [5] http://www.soilquality.org.au/factsheets/organic-carbon http://www.soilquality.org.au/factsheets/organic-carbon

bluGill 10y ago
Note that big farmers have already replaced "soil destroying tillage" with "soil building cover crops". Farm news is full of stories about early adopters 10 years ago bragging about how they are now building soil organic matter with a corresponding reduced need for fertilizer. The big farmers recognize the impact this has on the bottom line. Your mid sized farmers see that extra $10/acre in fertilizer as a cost of business and don't realize they could reduce it. Unfortunately "long-distance imported fertilizer to in-situ fertility produced by soil organisms" cannot work if food is exported off of the farm. Every gram of food taken off the farm includes some micro-nutrients - various minerals that are required for life that have been removed from the soil and taken elsewhere.