No sooner had I digested the Target Atmospheric CO2 paper than another one (pdf) arrived, courtesy of James Hansen’s mailing list.
The paper “Implications of ‘peak oil’ for atmospheric CO2 and climate”, Pushker A. Kharecha and James E. Hansen (pdf) makes a similar argument to that in “Target Atmospheric CO2″, though there are some differences.
I’ll try to keep the translation brief this time.
Summary
The paper seeks to show that we can keep CO2 below 450ppm [Hansen argued for less in “Target Atmospheric CO2″] by avoiding burning coal to the atmosphere, and using a high price of CO2 to deter the use of unconventional (e.g. tar sand) and other expensive sources of oil. Various Peak Oil scenarios imply that we can keep below 450ppm CO2, based on the Bern carbon cycle model, with both a static pulse response function (PRF) and a dynamic PRF. That is, even if some carbon cycle feedbacks are allowed for, CO2 can be kept below 450ppm if we burn all the existing conventional oil and natural gas reserves.
Points of note
1. The authors acknowledge that the concept of “reserves” of fossil fuels is flawed – if the price of oil (say) goes up, “reserves” magically grow, simply because more of the resources become economically exploitable.
2. The authors acknowledge that they have provided only “an approximate lower bound for the proportion of fossil fuel CO2 emissions that remain airborne.” i.e. they are being optimistic. But they don’t consider that climate feedbacks will kick in below 450ppm, so as long as we stay below that we’ll be OK.
3. We have to keep “cumulative global emissions from coal between the present and 2050… to ~100GtC or less (note that the IPCC considers proven global coal reserves to be >1200GtC).
