Tuesday, August 17, 2010

Enough ado about hockey sticks: the worst is yet to come

Global warming deniers are making another attempt at discrediting the famed "hockey stick" graph, based on a paper (McShane and Wyner 2010) that purports to show mistakes in its statistical methods. While I don't have the statistical chops to assess the validity of either party's math, I did want to make two observations.

First, as others have noted, even if you assume that the new paper is the "correct" version, it doesn't look much different from other hockey stick graphs - if anything, the hockey stick shape in the new study is more pronounced.

More importantly, the hockey stick graph ultimately matters very little for what we should do about CO2, since it only measures past temperatures up to around the year 2000. What we really care about isn't the past temperature increase we've already observed, but rather the much larger future increase that's still to come assuming we do nothing about CO2. And that isn't accounted for in any existing hockey stick graph. I've taken the liberty of (unscientifically) adding this onto the McShane and Wyner hockey stick graph, using a simple average of the IPCC's low-end (1.1 degrees C) and high-end estimates (6.4 degrees C) for 21st century temperature increase:


Looks more like a hockey skate! Despite deniers' strange obsession with the past and lack of concern for the future (perhaps by virtue of their conservatism), the bottom line is this: the reliability of past temperature reconstructions matter very little compared to what we have in store... and it's about to get a whole lot hotter.

If this looks familiar, here's why:


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10 comments:

  1. I've made the point on a number of occasions with deniers who love to pick on the Hockey stick that paleo-climate is to climate science as fossil records are to evolutionary biology. In both cases, much of the work has to be inferred rather than explored directly. They both add a fascinating look into deeper history, however, from both evolutionary biology and climate science (regarding observed data), either is not essential to conclusions drawn in evolution and climate. The weight of evidence to support both is more than heavy enough without deep history exploration.

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  2. Well-said. The distinction I'd make is that climate science is primarily concerned with the future. Paleoclimate gives us interesting inferences about what climate does based on what it did in the past, but if the hole of paleoclimate collapsed, it wouldn't make one dent in the reality that CO2 --> global warming.

    That's the right way to reframe arguments over the hockey stick - not to defend the hockey stick, but to just say, "so - even if old temperature records are unreliable, we don't need that evidence to prove that CO2-->warming."

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  3. I'd say paleoclimatology is to climate science
    as piltdown man is to paleontology

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  4. Transition from "hockey stick" to "boomerang".

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