Tuesday night was the annual Sigma Xi induction banquet on campus (I’m currently the president of the local chapter, and have been scrambling to organize the whole thing in between all my other responsibilities these past few weeks). Sigma Xi, for those not familiar with it, is the scientific research honor society– like Phi Beta Kappa for science nerds. We had thirty-odd students nominated for membership based on research they have done as undergraduates, and had a little banquet and induction ceremony to celebrate their accomplishments.

Tradition for this sort of thing calls for an after-dinner talk about something science-related. My fallback plan was to cop out and give a version of the talk I did at the Perimeter Institute last fall, but happily for everyone involved, my first choice came through. Professor Don Rodbell of the Geology department gave a talk about the work he’s done studying lakes in the Andes.

The basic message can be summarized as: tropical glaciers are weird. Don and a long series of students and collaborators have looked at the behavior of glaciers as recorded in high mountain lakes and moraines, going back a few tens of thousands of years, and what they find doesn’t really track with what people see in Northern Hemisphere glaciation.

Specifically, the core samples they have from a bunch of these lakes shows something kind of peculiar. The Andean glaciers appear to have expanded significantly a bit more than 20,000 years ago, but right around the point where the ice sheets in North America and Europe hit their maximum extent, the glaciers in the Andes practically disappeared. They rebounded sharply a few thousand years later, right around the time that the ice started to retreat in the Northern Hemisphere.

They see the same basic pattern in a bunch of different climate proxies, over a wide range of places in South America. This suggests that the climate in the tropics, or at least that part of the tropics, is driven by some different mechanisms than the things that drive climate in the polar regions.

This is emphatically not a denial of the evidence of modern warming, which is extremely solid, and not really open to debate. Rather, it’s a reminder that climate is a really complicated thing, and that the consequences of changes in climate can go off in unexpected directions. He pointed out that this may have particularly dire implications for the people who live on the high plains of Peru, who are almost entirely dependent on glacial melt water. If those glaciers disappear (as they are doing at a rapid rate), the whole region might become uninhabitable.

The work in question is apparently not without controversy– there’s apparently some argument about the dating of their samples, which would affect the timing of the glacial retreat. He makes a pretty solid case for it, though, at least to this non-geologist. Climate science and geology types with actual knowledge to bring to bear are more than welcome to expand on this in the comments.

Comments

  1. #1 R Simmon
    May 27, 2009

    Did Dr. Rodbell mention an climate proxies that measured precipitation? Glacier extent depends on both temperature and snowfall.

  2. #2 mikec
    May 27, 2009

    I’m kind of a climate geek so I read a lot of articles about various things that are related to climate. Is there some Chicago Manual of Climate Style that dictates a defensive penultimate paragraph denying the author’s denial of global warming?

    Here is a discovery that, if true, at least somewhat undermines the validity of the climate models that underpin global warming theory. I mean, a model that took this data into account might produce different projections, right? Otherwise it wouldn’t be unexpected. So why the defensive paragraph indicating that, in spite of the potential impact of the new discovery, the old theory remains entirely intact and “not really open to debate?”

    We’ve become such weenies! Imagine Galileo: “Jupiter has moons! But that shouldn’t be taken to dispute the theory of epicycles, which is not really open to debate.”

  3. #3 Eric Lund
    May 27, 2009

    Here is a discovery that, if true, at least somewhat undermines the validity of the climate models that underpin global warming theory.

    Not necessarily.

    Remember that here we are dealing with paleoclimate reconstructions. To first order we expect temperatures to rise or fall over the planet as a whole. But to second order the changes need not be uniform, and the first order term is small enough here that the second order effects can change the sign of the overall result. It’s hard to get a good global proxy for all of the climate forcings, since we (obviously) don’t have direct observational data for that period. Furthermore, as the first commenter pointed out, precipitation is also a major factor here–glaciers will grow in a period of warm (but still below freezing) and wet weather, and shrink even in a cold period if it’s also extremely dry. Consider that the glacier on top of Mt. Olympus in Washington state is larger than what you see at the much higher and colder elevations of the Rockies–that’s because Mt. Olympus gets so much more snow.

    As for why the disclaimer: We all know there are quote miners out there who are looking for any excuse to claim that global warming is a hoax. Your historical analogy also falls flat, because Galileo’s work predated Kepler’s discovery that orbits are elliptical rather than circular, to say nothing of the fact that epicycle theory has no relation to whether the planets have moons. You can produce a solar system model with epicycles that is consistent with what was known in Galileo’s day. There were philosophical problems in Ptolemy’s model with Jupiter having moons, but not mathematical or physical problems.

  4. #4 Mark P
    May 27, 2009

    “Here is a discovery that, if true, at least somewhat undermines the validity of the climate models that underpin global warming theory.”

    Are you sure about that?

  5. #5 Chad Orzel
    May 27, 2009

    I’m kind of a climate geek so I read a lot of articles about various things that are related to climate. Is there some Chicago Manual of Climate Style that dictates a defensive penultimate paragraph denying the author’s denial of global warming?

    I’m going to guess that they do it to head off this sort of thing:

    Here is a discovery that, if true, at least somewhat undermines the validity of the climate models that underpin global warming theory.

    Because, well, no.
    There’s nothing in these findings that calls into question the general link between CO2 and temperature, or anything else. What it says is that the details of how changing climate affects different reasons are rich and complex.

    To go back to an earlier comment: Did Dr. Rodbell mention an climate proxies that measured precipitation? Glacier extent depends on both temperature and snowfall.

    Yes. One of the proxies showed that precipitation dropped off dramatically around the same time. I believe that the explanation of what’s going on is that at some point in the overall cooling trend, the amount of moisture reaching the high peaks of the Andes dropped off dramatically, and they stopped getting any precipitation, which in turn stopped the growth of the glaciers, even though the ice sheets were running wild in North America and Europe.

    I am not a geologist, though, and I’m basing that on a recollection of a couple of comments in a general-audience talk, so add salt to taste.

  6. #6 mikec
    May 27, 2009

    1. I said “undermined”, not “disproved.” As in, “created a cavity under”, not “collapsed.”
    2. Sure maybe the results can be explained away, but why be so timid about announcing new discoveries — assuring readers that the discovery really isn’t very important?
    3. Why does my historical analogy fall flat? Epicycles considerably predated Galileo, and the idea behind them was to explain how the apparent motion of the planets was consistent with an earth-centered universe. Moons around other planets was seen, correctly, as making that fairly problematic.
    4. Finally, I’m not sure that this is an important discovery. I’m just tired of people feeling they’re obliged to caveat every result with a disclaimer that it couldn’t possibly affect the current consensus. “To timidly go where everyone has gone before.”

  7. #7 cisko
    May 27, 2009

    Mike, no comment on the rest, but you’re just wrong about epicycles. The whole reason for epicycles was a Ptolemaic conviction that the heavens had to be geometrically perfect, thus all planets must move in circular paths. If you want to approximate ellipses with several circles, you’re going to run into problems.

    The problems arose with observational differences between epicyclic predictions of planet’s positions and actual observations. These became more and more obvious as measurements got better.

    The geocentric model had no connection to the need for epicycles, and in fact the heliocentric Copernican model still used epicycles. Astronomers could have happily created epicyclical models for the observed orbits of the Jovian moons. In fact, Kepler published a year before Galileo, so I don’t think anyone went to the trouble, or if they did it was quickly discounted.

    I think I owe a big debt to Dr. Heilbron that I actually remember this stuff. And I wasn’t even a history major…

  8. #8 cisko
    May 27, 2009

    Mike, no comment on the rest, but you’re just wrong about epicycles. The whole reason for epicycles was a Ptolemaic conviction that the heavens had to be geometrically perfect, thus all planets must move in circular paths. If you want to approximate ellipses with several circles, you’re going to run into problems.

    The problems arose with observational differences between epicyclic predictions of planet’s positions and actual observations. These became more and more obvious as measurements got better.

    The geocentric model had no connection to the need for epicycles, and in fact the heliocentric Copernican model still used epicycles. Astronomers could have happily created epicyclical models for the observed orbits of the Jovian moons. In fact, Kepler published a year before Galileo, so I don’t think anyone went to the trouble, or if they did it was quickly discounted.

    I think I owe a big debt to Dr. Heilbron that I actually remember this stuff. And I wasn’t even a history major…

  9. #9 cisko
    May 27, 2009

    Eep, sorry for the double post.

  10. #10 milkshake
    May 27, 2009

    …”the evidence of modern warming, which is extremely solid, and not really open to debate.”

    What is opened to debate are the mechanisms behind the modern warming and its actual extent – and, if the problem is serious, what ought to be done about it.

    It should be opened to debate if things were not so politicized by the self-righteous and pompous demagogues. The problem with the global activism lobby is that their arguments congealed into orthodoxy. When one starts questioning the sensibility of some of the proposed policies they jump up and call you a denialist – a repulsive vermin produced by crossing a holocaust denier with a creationist

  11. #11 Lab Lemming
    May 29, 2009

    The second paragraph is necessary for the following reason.

    In climate science, there are lots of scientifically interesting, genuine mysteries and questions which people are trying to answer.

    In public discussion of climate science, there is a huge disinformation campaign that tries to steer discussion of the discipline away from the actual science and into a manufactured controversy for which no scientific evidence exists.

    Proponents of the latter are so widespread and obnoxious that it is necessary to specifically state that one is actually talking about real science when discussing it.

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