Monday, May 12, 2008

Margins of error

Interesting post here from Roger Pielke Jr. He has been asking, if both cooling and warming are "consistent" with the theory of AGW, how that theory could ever be falsified. At the AGW advocacy blog Real Climate a relevant post was put online, and so Pielke analyses the argument therein.

Here's the nub of it. Graphs of predicted temperatures, or anomalies, (should) have error bars showing, say, what range of values fall within a 95% confidence level. The bigger the bars the less precise the model. But also, the bigger the bars the greater the range of values that could be said to be "consistent" with that model. If the bars are big enough, even a stable or cooling trend would fall within the 95% confidence ranges of a model that forecasts warming. As Pielke puts it:

... it means that the greater the uncertainty in modeling -- that is, the greater the spread in outcomes across model realizations -- the more likely that observations will be “consistent with” the models. More models, more outcomes, greater consistency – but less certainty. It is in this way that pretty much any observation becomes "consistent with" the models.

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