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What CO2 Emissions Level Would Stabilize Atmospheric CO2 Level?

  1. Aug 14, 2009 #1
    I was reading a new paper titled "Impacts of Climate Change on Marine Organisms and Ecosystems" when I came across this statement:

    It has been suggested that a CO2[atm] of 450 ppm is a critical threshold beyond which catastrophic and irreversible change might occur [7] this would bring a global mean temperature rise of 2C above pre-industrial values. At present rates, this threshold will be passed by 2040, but climate-related systems are notoriously non-linear [14]. By 2040, some particularly sensitive marine ecosystems such as coral reefs and ice-covered polar seas could already have been lost, and other unexpected consequences may arise [15].​


    This caused me to wonder what level of annual CO2 emissions would we have to reach in order to stabilize at a level under 450PPM as opposed to reaching the 450PPM level in 2050 or 2060 or 2100?

    Even if we reached a 80% reduction in CO2 emissions, would it cause the CO2 levels to stabilize or only increase more slowly? We have good measurements on CO2 going back to 1959 and it has been increasing during the entire period. Unless there is some evidence to suggest that the capacity of the BioSphere to absorb CO2 has increased during that period, then it isn't obvious what level of emissions other than zero would cause it to stabilize.
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Aug 16, 2009 #2


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    Roughly speaking, CO2 emissions would have to be cut in half in order to stabilize the atmosphere at 450 ppm. In addition, with continual population growth, this means that per capita emissions would have to be cut even more. Furthermore, as oil and natural gas reserves run out, it's obvious that we will be burning more and more coal, which emits more CO2 per unit of energy.

    The capacity of the biosphere to absorb CO2 does vary. Over the long haul, it is limited by the amount of precipitation on silicate and carbonate rocks/soils. Since global warming also leads to increased precip, eventually (no matter what humans do) CO2 levels will stabilize. However, it will be a much wetter world if we leave it to Mother Nature.

    On the other hand, there is a chance that we humans may wish to fix the problem and the easiest way to do that would be to fertilize the oceans with iron.
  4. Aug 17, 2009 #3
    I finally found some documentation in this report "Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations" "Figure 4.7. Fossil Fuel and Industrial CO2 Emissions Across Scenarios (GtC/yr).". It can be downloaded here:

    http://www.globalchange.gov/publications/reports/scientific-assessments/saps/294" [Broken]

    The graphs are in gigatons of Carbon, so you have to multiply by 3.67 to translate to CO2. There are 3 different scenarios: IGSM, Merge and MiniCAM. They have different assumptions about how much CO2 the ocean will take up, but they tend to agree with Xnn said that we would need to reduce emissions to 4 billion tons of carbon by 2050.

    I tend to agree with Xnn, that iron fertilization might be the best solution for Carbon sequestration. It is actually mentioned in the original paper that I cited that I cited, but they seemed to consider it too risky. If the alternative is catastrophic, then I'm not exactly sure what they mean by risky.
    Last edited by a moderator: May 4, 2017
  5. Aug 17, 2009 #4


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    With a realistic potential of being even more catastrophic.

    Seriously. Deliberately trying to manipulate a large complex system that we imperfectly understand with processes where we don't know all the consequences is risky, in precisely this sense.

    This doesn't mean that the balance of potential risks and possible benefits falls always means you don't try such manipulations. But the risk is there.

    Cheers -- sylas
  6. Aug 17, 2009 #5
    Frankly carbon sequestration seems to me to be safest type of geoengineering. All we are doing is keeping the CO2 from increasing, which seems to me far more benign than other approaches I've seen.

    I would think using a relatively dead part of the ocean for the experiments, to minimize the collateral effects, would be prudent. I also think bioengineering an algae to maximize the sequestration effect would be a good idea.

    If we can't get buy in from China and India for restricting CO2 emissions, I'm not sure what alternatives we have. Getting down to 4 Gigatons of Carbon per year is a difficult goal even with universal buy in.
  7. Aug 17, 2009 #6
    The danger with iron fertilization is that as the phytoplankton blooms die and sink, they also decay. The bacteria that feed on the dead biomass use up available oxygen, creating large http://toxics.usgs.gov/hypoxia/hypoxic_zone.html" [Broken] in the worlds oceans.

    The best form of carbon sequestration is to http://www.eprida.com/" [Broken]
    Last edited by a moderator: May 4, 2017
  8. Aug 17, 2009 #7
    As far as I know, dead zones are associated with a different kind of phytoplankton, not the kind that is useful for sequestering carbon. One of the reasons we need to do more experiments is to figure out how to stimulate the kinds of algae we need.

    I think that converting carbon into topsoil is a good idea also.
    Last edited by a moderator: May 4, 2017
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