Edward Greisch: See the chart on page 274 of “Six Degrees” by Mark Lynas. Mark Lynas says we have until 2015 to BEGIN REDUCING our total CO2 output and we have until 2050 to actually reduce our CO2 output by 90%. Mark Lynas says if we don’t follow the schedule in Six Degrees, we will encounter positive feedbacks which will take the control of the climate out of our hands. Civilization may fall anyway well before 2050, but we can avoid going extinct by 2100. Mark Lynas says we have to hold the CO2 level to 400 parts per million to have a 75% chance of avoiding the positive feedbacks. Is Mark Lynas correct? 8 years is a very tough timetable to stop the building of coal fired power plants and replace some coal fired power plants with nuclear. I doubt that anything else other than a plague that kills a few billion people could make a dent within 8 years.No matter what the circumstance, unless we are finally extinct, there is always a best we can do. We should strive in our imperfect way to stay close to that.
[Response: From other estimates I’ve seen, Lynas’ timetable seems about right if the goal is to avoid 450 ppm. To avoid 400ppm, even his timetable is a bit of a stretch. However, with regard to the impacts of exceeding 400ppm (or even 450ppm), if you are quoting Lynas correctly I would differ with his assessment. There is no magic threshold crossed at 450 that commits us suddenly to the kind of catastrophic changes you mention, and certainly not to extinction of humanity by 2100. If we can’t hold the line at 450, there are still harms to be avoided by stopping short of doubling. If we can’t stop doubling, there are still harms to be avoided by preventing tripling, and so forth. But his general sentiment that we can’t drag our feet on this is correct. –raypierre]
Thursday, December 20, 2007
Ray on a response on RealClimate says nicely something I have been trying to say to the doomsayers:
Posted by Michael Tobis at 4:40 PM