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Ross McKitrick's avatar

The WWA group use the Generalized Extreme Value distribution to characterize annual maxima. They estimate a "nonstationarity" parameter (the coefficient tying the center of the distribution to global avg temp) using maximum likelihood. Use of GEV adds a layer of opacity to what they are doing but in the data I've worked with you get pretty much the same results (in terms of finding statistical significance) just using ordinary regression, which is more transparent and has a lot of tools available for specification testing and for correcting things like serial correlation, omitted variables bias and spatial dependence.

The WWA people also stack the deck by constructing their counterfactual climate using a model like FaIR in which CO2 is the only thing that changes the climate. So they use smoothed global mean temperature as the only explanatory variable to explain any change in the annual extreme value, and then they construct a counterfactual return period using a model in which only CO2 changes temperature. So it's a closed loop that can only ever tie extreme weather events to CO2. It's pretty pathetic but obviously impresses the heck out of the editors of Nature journals.

Sharon F.'s avatar

Whatever happened to the old "correlation is not causation" we learned in science school. Has that been formally overturned? But even Wikipedia has an entry on it.https://en.wikipedia.org/wiki/Correlation_does_not_imply_causation

So we are supposed to believe correlation does not imply causation except in the case of climate change?

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