Which Climate Change Consensus? (Part 3)
There are some interesting questions being posed at the Which Climate Change Consensus? (Part 2) thread. Following are two questions from Graham Young that interests me. They seems to have been lost amongst the more general policy and economic discussion about Kyoto.
Your quotation from the MIT piece illustrates the problem that you have with your models. You say “a projected 18 percent increase [in CO2] resulting from fossil fuel combustion to the year 2000 (320 ppm to 379 ppm) might increase the surface temperature of the earth 0.5C”. Now CO2 is at 380 ppm and you are claiming a rise in surface temperature of 0.5 degrees.
So far, so good, but as we know that temperature of the earth can and does vary independently of CO2 concentrations, how do you know that the rise was due to CO2 alone? And if it wasn’t, then in fact you may have overshot or undershot by more than the 0.5 degrees. If you overshot, your modelling was completely unsuccessful, and if you undershot, then things are a lot worse than you thought.
The IPCC graph at http://www.grida.no/climate/ipcc_tar/wg1/figspm-4.htm is interesting.
It shows general trends between model and observations reaching more or less the same end point, but with significant divergences along the way. You’d probably get a better feel for this by graphing a rolling average.
But you might well be getting this result by massaging the factors that are programmed in until you get a reasonably good fit, but without those factors necessarily being the right ones if you are missing some ingredients.
I’ve gleaned some of my information from the graphs that Jennifer put up on the site on the 28th November. While you’re explaining your models, could you please tell me what the mechanism is that makes temperature dive just after the peaks in CO2 shown in those graphs?