On the irrelevance of the "hockey stick" fight

This is for climate science and/or climate policy geeks only. Back on November 21st, 2005, Roger Pielke, Jr. wrote a post that (I think) nicely summarized the irrelevance of the tussle over Michael Mann’s hockey stick reconstruction of proxy temperature data. Roger began with this:

A few weeks ago we posed a challenge to both parties involved in the so-called “hockey stick” debate to explain why the rest of us ought to care about the debate. We asked, “so what?” We received responses from Steve McIntyre and Ross McKitrick while everyone on the other side declined to participate, though a few showed up in the comments. Here I’d like to offer a few assorted reflections on the responses and the subsequent discussion.

1. First, thanks to Steve McIntyre (SM) and Ross McKitrick (RM) for providing thoughtful responses. The responses motivated a healthy discussion and for me provided some greater insight into the dynamics of the ongoing debate within the climate community not just over the hockey stick, but broader issues as well.

2. Interestingly enough, the response from SM is completely in agreement with RealClimate contributors Stefan Rahmsdorf (SR) and William Connelley (WC) that the “hockey stick” debate is pretty much irrelevant to the scientific question of whether or not greenhouse gases will affect the future climate. Consider:

SR: “The discussions about the past millennium are not discussions about whether humans are changing climate; neither do they affect our projections for the future.”

WC: “Why is this fight important to the rest of us? the answer is: you shouldn’t. It isn’t..”

SM: “I’m inclined to agree that, for the most part, the Hockey Stick does not matter to the great issue of the impact of 2xCO2.”

This agreement is interesting because it means we can move beyond the often invoked assertion that the hockey stick is the keystone supporting the entire scientific basis of climate science. Others may assert that the hockey stick is a scientific keystone, but apparently not the principals involved in this debate.

There is much more detail, and exhausting nitpicking in the comments, so continue reading…

2 thoughts on “On the irrelevance of the "hockey stick" fight

  1. The hockey stick is irrelevant to climate science in the way that the phlogiston theory is irrelevant to thermodynamics. But it is relevant to the question “Is CAGW science?”

    In fact, the dumping of the Medieval Warm Period, of which the hockey stick is the most unsightly symptom, is what caused me to put an “X” in the last empty box in the “Is it a pseudoscience” chart. The “dumping established science for wholly inadequate reasons because it conflicts with the pseudoscience” box. (The type example is Velikovsky changing an archaeological date from 5000 BC to 500 BC by just saying, “There are one too many zeroes here.” What Mann did was not at that level, but saying that it would be silly to subject his results to the standard statistical test for significance was pretty good.)

  2. As a paleoclimate researcher myself I am a proponent of the idea that the past record of earth-system behavior has much to teach us about the system’s sensitivity to perturbations, and to the range of possible states the climate system is capable of attaining.

    But the question of whether there was or was not a Medieival Warm Period (the central point of contention in the “Hockey Stick” debates), while interesting on several levels, does not give us much insight into the future climate impact we might expect from our enhancement of the greenhouse effect. The reason is, while some proxy records indicate a Medieval period as warm or perhaps warmer than present climate, there is no indication what, if anything, forced the anomaly (though ice-core records of CO2 say no it was not GHGs). We know there are climate oscillations for which the external forcing if any (e.g. solar output) is unknown. The proxy records that do show a Medieval warm period (such as those published by Mann and co-authors last year in Science) suggest it was a regional rather than a global anomaly, suggesting regional rather than global drivers such as changes in atmospheric GHG concentrations.

    The problem is that now we are applying a global radiative forcing, and the question is, how will the system respond?

    Even past climate oscillations in which GHGs are implicated, like the glacial-interglacial cycles of the past ~ million years, only provide imperfect (though important and insightful) tests for climate sensitivity to greenhouse effect enhancement. That is because, first, there were other external perturbations forcing climate (namely orbital variations) and GHGs were likely acting as feedbacks (along with other feedbacks such as dust and albedo) to amplify the primary forcing (or at least pacing) mechanism. Secondly, we are changing the GHG radiative about 2 orders of magnitude faster than the G-IG cycles. Finally, we have driven GHG levels well beyond their ranges during those cycles, so if you think of the glacial-interglacial cycles as a “calibration” we are already outside the calibration range.

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