Quantifying uncertainty in AGW
My friends, I need your help.
I have written a paper on quantifying the uncertainty of effects due to global warming, but the subject is too big for one person. Nevertheless, I have tried to—in one location—list all of the major areas of uncertainty, and I have attempted to quantify them as well. I would like your help in assessing my guesses. I am not at all certain that I have done an adequate or even a good job with this.
At this link is the HTML version of the paper I am giving in Spain (I used latex2html to encode this; it is not beautiful, but it is mostly functional).
At this link is the PDF version of the paper, which is far superior to the HTML. This paper, complete with typos, is about draft 0.8, so forgive the minor errors. Call me on the big ones, though.
I would like those interested to download the paper, read it, and help supply numbers for the uncertainty bounds found within. I would ask that you not do this facetiously or glibly, or that you not purposely underestimate the relevant probabilities. I want an open, honest, intellectual intelligent discussion of the kinds and ranges of uncertainties in the claims of effects due to global warming. For example, the words “Al Gore” should never appear in any comment. If you have no solid information to offer in a given area, please feel free to not comment on it.
The abstract for the paper is
A month does not go by without some new study appearing in a peer-reviewed journal which purports to demonstrate some ill effect that will be caused by global warming. The effects are conditional on global warming being true, which is itself not certain, and which must be categorized and bounded. Evidence for global warming is in two parts: observations and explanations of those observations, both of which must be faithful, accurate, and useful in predicting new observations. To be such, the observations have to be of the right kind, the locations and timing where and when they were taken should be ideal, and the measurement error should be negligible. The physics of our explanations, both of motion and e.g. heat, must be accurate, the algorithms used to solve and approximate the physics inside software must be good, chaos on the time scale of predictions must be unimportant, and there must be no experimenter effect. None of these categories is certain. As an exercise, bounds are estimated for their certainty and for the unconditional certainty in ill effects. Doing so shows that we are more certain than we should be.
My conclusions (which will make more sense, obviously, after you have read the paper) are
Attempting to quantify, to the level of precision given, the uncertainties in effects caused by global warming, particularly through the use of mathematical equations that imply a level of certainty which is not felt, can lead to charges that I have done nothing more than build an AGW version of the infamous Drake equation (Drake and Sobel 1992). I would not dispute that argument. I will claim that the estimates I arrived at are at least within an order of magnitude of the actual uncertainties. For example, the probability that AGW is true might not be 0.8, but it is certainly higher than 0.08.
The equations given, then, are not meant to be authoritative or complete. Their purpose is to concentrate attention of what exactly is being asked. It is too easy to conflate questions of what will happen if AGW is true with questions of is AGW true. And it is just as simple to confuse questions of the veracity and accuracy of observations and with the accuracy of the models or their components. People who work on a particular component are often aware of its boundaries and restrictions, and so are more willing to reduce the probability that this component is an adequate description of the physical world, but they are usually likely to assume that the areas on which they do not have daily familiarity are more certain than they are. Ideally, experts in each of the areas I have listed should supply a measure of uncertainty for that area alone. I would welcome a debate and discussion on this topic.
I also would not make the claim that I have accurately listed all the avenues where uncertainty arises (for example, I did not even touch on the uncertainty inherent in classical statistical models). But the ones I did list are relevant, though not necessarily of equal importance. We do have uncertainty in the observations we make and we do have uncertainty in the models of these observations. At the very least, we know empirically that we cannot predict the future perfectly. Further, the claims made about global warming’s effects are also uncertain. Taken together, then, it is indisputable that we are less certain that both global warming and its claimed effects are true than in either AGW or its effects alone.
Thanks everybody.
9 comments March 28th, 2008
