However, it is useful to back up a bit and remember an observation by physicist John Wheeler, “We make the world by the questions we ask”. What are the questions asked by the climate models, and what kind of world are they making, and what other questions might we ask that would make other worlds? Could we ask other questions that would make a more tractable world for policy?
The climate models ask whether CO2 emissions will lead to atmospheric concentrations of 450-500 parts per million, and will that raise temperatures by 2 or 3 degrees Celsius, by a certain date, and what will be the likely physical consequences in climate and geography, and in what sequence, and according to what probability distributions, and what will be the damages inflicted by such changes, as well as the costs of abating them, and what are the ratios of the present values of the damage costs compared to abatement expenditures at various discount rates, and which discount rate should we use, and how likely is it that new information learned while we are constructing the model, will invalidate the results? What kind of world is created by such questions? Perhaps a world of such enormous uncertainty and complexity as to paralyze policy. Scientists will disagree on the answers to every one of these empirical questions.
Could we ask a different question that creates a different world? Why not ask, Can we systematically continue to emit increasing amounts of CO2 and other greenhouse gasses into the atmosphere without eventually provoking unacceptable climate changes? Scientists will overwhelmingly agree that the answer is no.
To make the point more simply, if you jump out of an airplane you need a crude parachute more than an accurate altimeter.
Go. Read it. He's just getting warmed up.
Update: Thingsbreak points out that you can read the same text with less strain on your eyes and your mouse hand at Grist.