New article: Geoengineering and the pursuit of 350ppm

There’s an interesting new article on geoengineering in the journal Solutions, Greene, C. Monger, B. Huntley, M. 2010. Geoengineering: The Inescapable Truth of Getting to 350. Solutions. Vol 1, No. 5. pp. 57-66, discussing the potential role of geoengineering solutions in achieving the goal of stabilizing atmospheric concentrations of carbon dioxide at 350ppm .

Among the piece’s takeways:

  1. Until the recession, GHG emissions were growing at a rate that exceeded the worst case scenarios of the IPCC, “hence, there is no clear indication that the fossil to alternative energy transition has begun yet;”
  2. Even if atmospheric concentrations of carbon dioxide were to stabilize at the current level of 390 pppm, we are probably now committed to a mean global temperature increase of 2.4C (4.2F) by the end of the century, exceeding critical thresholds for dangerous climate change. When slow feedback processes  are included (e.g. centennial- to millennial-scale changes in the heat budget, especially those associated with alterations of surface albedo linked to advances and retreats of the planet’s cryosphere and vegetation cover), projected warming over the next few centuries could increase by a factor of two. The outcome could be “catastrophic,”
  3. If we overshoot 350ppm, the long residence time of carbon dioxide ensures that concentrations will stabilize on a 1000-year time scale at a level of approximately 40% of its peak enhancement, and mean global temperature will not drop substantially over the next millennium even as carbon dioxide concentrations decline; at this point, stabilizing at 350 ppm seems highly unlikely;
  4. None of the proposed solar radiation management options remove carbon dioxide from the atmosphere and thus do little to help achieve the goal of getting to 350ppm; moreover they could have serious negative implications, including potentially damaging the ozone layer and enhancing drought in certain regions. Nonetheless, SRM isn’t an option we should ignore given the possibility that it could help us postpone irreversible commitments to dangerous or catastrophic climate change;
  5. Carbon dioxide remediation methods will take longer to develop and deploy, but they offer potential solutions to climate change problems that solar radiation management can only postpone;
  6. The most frequently advocated carbon dioxide remediation method is large-scale industrial air capture. While the technology is among the potentially “most environmentally friendly” of geoengineering technologies, it currently comes at a projected cost of greater than $250 per ton of carbon,  at least an order of magnitude higher than current prices on carbon on the European market;
  7. One approach to reduce the energy costs of air capture systems is to combine them with systems being developed for bioenergy production, which has been estimated to potentially reduce the market price of air capture to approximately $100 per ton; however the limited availability of biomass raises the same environmental and food security issues that arise in the context of biofuels. A desirable alternative option could be algal aquaculture systems. One study projects that algal biofuel production utilizing approximately 7% of surplus, non-arable land in 2050 could replace fossil-based carbon emissions equivalent to approximately 6.7 gigatons of carbon annually;
  8. If a combined air capture/bioenergy system could bring down the cost of air capture and storage to as low as $100 per ton of carbon, it would cost society less than 1% of global GDP for the remainder of the century, similar to IPCC estimates of mitigation costs to stabilize carbon dioxide concentrations at 450 ppm.  The overall cost of the program is estimated at $85.5 trillion.

Among the questions for class discussion include the following:

1. Given the large costs of an air capture/bioenergy program, would a commitment to this program detract from mitigation initiatives. What would be the long-term implications if this geoengineering option did not prove to be viable?;

2. How do we weigh the potential benefits of solar radiation management approaches against the potential adverse effects described above?

3. Does the article adequately address the issue of potential risks associated with sequestration of captured carbon?

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