Good statistic for climate science lecture: Atmospheric levels of carbon dioxide are currently increasing at an annual rate of 0.5%, “200 times faster than any changes that occurred during the last eight glacial cycles.” Albright, et al., Ocean Acidification Compromises Recritment Success of the Threatened Caribbean Coral Acropora Palmata, PNAS Early Edition, 10.1073/pnas.1007273107 (2010).
For instructors who include a geoengineering module, an interesting reading on the potential role of methane air capture is available in the journal Atmospheric Environment (Boucher & Folbert, Atmospheric Methane Removal as a Way to Mitigate Climate Change?, 33 Atmospheric Environment 3343-3345 (2010)).
Among the take-aways from the piece:
- Atmospheric concentrations of methane have increased from 715 ppbv in the pre-industrial era to 1774 ppbv currently;
- A reduction of methane levels to pre-industrial levels would alleviate a radiative forcing of 0.48 Wm-2, or even more methane concentrations were reduced below pre-industrial levels;
- Methane has a global warming potential of 25x more than carbon dioxide, and perhaps as much as one third if one takes into account indirect effects on sulphate particles;
- Most of the climate benefits from methane uptake would occur in the first 60 years of deployment of such approaches, though there would also be net climate benefits for 500 years;
- Methane capture would yield co-benefits, including reduce tropospheric ozone production, decreased stratospheric forcing from methane-derived water vapor a possible additional reduction of carbon dioxide through carbon dioxide capture and storage in the methane oxidation process;
- Existing technologies for methane air capture include cryogenic separation, molecular sieves or gates, and adsorption filters based on zeolite minerals, although none of these options are economically or energetically suitable at the current time.
Beyond providing a good jump off point of geoengineering issues, the piece helps remind students that reduction of GHGs beyond carbon dioxide can yield tremendous benefits. It also could stimulate a good discussion of how to prioritize scarce funding and the contrast of solar radiation management and carbon dioxide removal schemes in terms of potential impacts.