Okay, I finally succumbed and actually waded through some of the new paper by Monckton, Soon, Legates & Briggs called Why models run hot: results from an irreducibly simple climate model. I did it, so you don’t have to (and believe me, it’s really not worth it). I’m not even sure I actually quite get it, since it is so chock full of stuff that doesn’t really make a great deal of sense.
I, however, think I’ve worked it out. According to their model, temperature at time after a change in forcing is given by
where is the fraction of the forcing due to CO2, is the fraction of the equilibrium response attained by time , is the no-feedback sensitivity, and is the feedback factor, or closed-loop gain.
The fundamental figure is the figure to the right, which illustrates how the feedback factor, or closed-loop gain, would influence climate sensitivity. Now, as is clear from the figure, the maximum value for the closed-loop gain – or feedback factor – allowed by process engineers designing electronic circuits intended not to oscillate under any operating conditions, is 0.1. Therefore, since no process engineer would possibly design our climate to have a feedback factor greater than this, feedbacks have to be small, and the equilibrium climate sensitivity has to be about 1K per doubling of CO2.
So, there you have it, we can’t warm much over the coming century because the designers wouldn’t have designed a system that would allow for this. Of course, I should be honest and admit that I may have misunderstood the paper, but that’s mostly because it’s gobbledygook.
P.S. : Just it case the tone of this post isn’t completely obvious, no, our climate was not designed by process engineers and, no, the feedback factor is not constrained to be small.