Another Geoengineering Approach: Air Capture

For instructors including a module on climate geoengineering, an interesting reading choice would be an article by Klaus Lackner at The Earth Institute of Columbia University, K.S. Lackner, Capture of Carbon Dioxide from Ambient Air, 176 European Physical Journal Special Topics 93-106 (2009) (subscription required). Lackner’s piece focuses on a carbon dioxide removal (CDR) geoengineering scheme that hasn’t been discussed in this blog yet, air capture of carbon dioxide. Air capture schemes are viewed by proponents as one of the potentially most desirable forms of climate geoengineering because they might avoid some of the most serious possible side effects of other schemes, e.g. alteration of precipitation patterns or depletion of the ozone layer (potential side effects of stratospheric sulfur dioxide injection) or potentially serious ocean ecosystem impacts in the case of ocean iron fertilization. The article is pretty technical, however, so probably not appropriate for undergraduate students or law students.

Among the key take-aways of the piece:

  1. Sorbent-based air capture would use a sorbent, a material used to capture gas or liquids, to capture carbon dioxide from the air; given the dilution of carbon dioxide in air, this is the only practical air capture scheme. The system would consist of a large filter standing in an airflow covered with carbon dioxide-selective sorbents;
  2. The primary cost consideration in a carbon dioxide air capture system will be sorbent recycling;
  3. The study concluded that a successful sorbent candidate could be a resin material similar to Marathon A, produced by Dow Chemical. It’s anticipated that future research will improve the efficiency of such systems;
  4. Ten million units of the nature discussed in the study (most likely deployed in large “capture parks”) would collect 3.6 Gt/yr of CO2 if the unit size stays constant. With potential increased collection capacity, ten million units could remove 10 to 20Gt of CO2 on an annual basis. Annual carbon dioxide emissions are currently about 29 Gt annually;
    • An alternative to deploying so many units would be to scale up the size of the units;
    • Some air capture could also be effectuated by portable collector units that could be deployed in areas of high emissions. However, the optimal approach is effectuate air capture where the carbon dioxide might be used (e.g. for enhanced oil recovery, the author suggests) or stored;
  5. While the first generation air capture units might cost $200 per ton of carbon captured, this could drop to $30 per ton through further advances in technology, adding 7 cents to a liter of gasoline;
  6. Air capture could also foster the development of large-scale renewable energy.  H2O and CO2 can be used feedstock to produce synthetic hydrocarbon fuels like methanol, dimethyl-ether or long chained alkanes like gasoline or diesel

Many commentators believe that Lackner’s estimates for the cost of air capture are wildly optimistic, even assuming the effectiveness of the approach, so this could lead to an interesting discussion about the opportunity costs of pursuing research and deployment of this technology. Moreover, many of the questions associated with carbon capture and sequestration (potential danger of accidental releases of sequestered carbon dioxide, the need for a very large transportation network, and NIMBY issues associated with finding venues for storage) apply in this context also.

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