Let me hark back to GCM for a minute. The models all are tuned to 20th century temps - that is they all reproduce temps pretty well and would generally be considered a failure if they couldn't be validated in this way. The projections to 2100 however have temperature increasing from 1 to 10 degrees (or more in some very extreme cases). This is because the models all rely more or less on judgement and approximation. That is they are heuristic tools - rules of thumb - rather than having a unique solution. The solution is assumed to fall somewhere in the range of estimates.
The method is unexceptional but a 'reality check' is commonly applied to heuristic solutions. In this case we have a simple check already alluded to. For an increase of 80 ppmv of CO2 since the mid 1940's there is an associated 0.6 degree temperature rise. We are at about 386 ppmv and expected (BAU) to increase to 590 ppmv by 2100. So an additional 200 ppmv giving a 1.5 degrees rise? Within the solution space. Assuming there is a little more heating of 0.5 degrees 'in the pipeline' (according to Jim Hanson) - say a maximum of 3 degrees by 2100. I am not hugely relaxed about that - and we risk (as climate is a nonlinear oscillator) either snowball or hothouse earth. But take ten deep breaths and start figuring how to get off the BAU trajectory without dismantling global economic systems. On Dec 28, 3:24 pm, James Annan <[email protected]> wrote: > Robbo wrote: > > Even such a seemingly simple question as to the rate of recent warming > > is subject to wide interpretation. Climate fluctuates strongly > > principally in line with ENSO. Large interannual and decadal changes > > in surface temperature makes the interpretation of trend sensitive to > > both the end points and to the length of the record. > > > Period Trend (degrees C/decade) > > > 1900 - 2008 0.07 > > 1945 2008 0.11 > > 1958 2008 0.13 > > 1979 1997 0.11 > > 1976 2008 0.17 > > > Table 1: A quick comparison of periods and temperature trends > > One interesting thing about that IMO is that despite the apparently wide > range of warming trends depending on endpoints, climate models manage to > match them all pretty well. > > James -- You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/globalchange
