Following up on my previous post on the potential positive feedback mechanism of cloud cover, a new study in Nature (Dorrepaal, et al., Carbon Respiration from Subsurface Peat Accelerated By Climate Warming in the Subarctic, 460 Nature 616-620 (2009)) reveals another potentially massive positive feedback mechanism: accelerated carbon release as a consequence of enhanced peatland respiration induced by warming trends. The field study, conducted in a subarctic petland, indicated that a 1°C increase in temperature would accelerate respiration rates by 60% in spring and 52% in the summer on the site, a much greater rate than projected in previous studies. While the researchers express appropriate caution about projections from studies of this nature given their short duration and correlative nature, they conclude that a 1°C increase in temperature could result in a release of an additiona 38-100 megatons of carbon per year. Put in perspective, the EU Kyoto Protocol target for emissions reductions is approximately 92 megatons of carbon per year.
For those of you that include a science component in your courses, this is a very good case study of how warming may indeed beget substantially more warming, and again, the importance of operationalizing the precautionary principle.