Of Particular Significance

An Interesting Data Point on Climate

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 10/29/2013

Particles are just so cool, and so very useful.  Scientists can learn about the past — for example, past climate — using “carbon dating”, a combination of biology and nuclear physics.

In this article in Geophysics Letters, covered in this Colorado University press release (with a somewhat inaccurate title), the abstract contains the statements…

…the extent to which recent Arctic warming has been anomalous with respect to long-term natural climate variability remains uncertain. Here we use 145 radiocarbon dates on rooted tundra plants revealed by receding cold-based ice caps in the Eastern Canadian Arctic to show that 5000 years of regional summertime cooling has been reversed, with average summer temperatures of the last ~100 years now higher than during any century in more than 44,000 years,…

Now how does this work? When the plants were alive, before they were covered with ice, they were taking in carbon from the atmosphere (remember plants absorb carbon dioxide and emit oxygen.) This carbon included both stable carbon (whose nucleus has 6 protons and 6 neutrons) and a form of unstable carbon (whose nucleus has 6 protons and 8 neutrons.) This is the carbon isotope known as Carbon-14; its nucleus “decays” to a nitrogen nucleus (by emitting a high-energy electron and an anti-neutrino). If you make some carbon-14 nuclei, half of them will have decayed after about 5400 years; half of those that remain will be gone by the time the next 5400 years have passed; and so on. But the atmosphere always has both stable and unstable carbon, because even though the unstable carbon decays away, collisions of cosmic rays (high-energy particles from outer space) with nuclei of atoms in the atmosphere replenishes the supply of Carbon-14.

While it is alive, therefore, the plant is absorbing both stable and unstable carbon, in amounts determined by the amounts in the atmosphere. However, once the plant dies, it takes in no more carbon from the atmosphere, and so its unstable carbon gradually disappears. By measuring the ratio of unstable to stable carbon that remains in the plant, one can infer how long ago the plant died.

If I understand correctly, the above-mentioned paper claims that some plants recently uncovered by melting ice on Baffin Island show no measurable unstable carbon at all. This implies they are at least 45,000 years old, and therefore that this part of Baffin Island is now ice-free for the first time in at least 45,000 years. That’s much longer than the warm period (the “Holocene”, the last 11,000 years) that the earth has been in since the last ice age. In short, the warming that is happening in the Arctic now is not typical of the warm period we’ve been in.

Is this important? Well, first, the usual but essential caution: as far as I know, this has been done only by one set of researchers so far, so accurate results are not guaranteed. If other researchers, especially ones who look in other parts of the globe, find similar results, that will be much more convincing. Second, what does this really tells us about climate? By itself, not much… it’s one data point. But it’s an interesting one. It contributes to a larger story. What we know for sure is that the Arctic is melting faster than anyone expected, and this result adds to the growing body of evidence that this level of warmth hasn’t been seen up north for a long, long time.

By the way, note that the question of whether the warming is human-caused is not addressed by this type of research. That requires other methods.

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19 Responses

  1. Slogans make for bad science, and “climate change/global warming” are terms that often create more confusion than clarity. In a literal sense, climate has been changing continuously since its origin, and is therefore not a particularly noteworthy observation. Feeding the ambiguity beast is neither helpful nor justified.

  2. To find summer heat higher than in at least 44,000 years is, philosophically, highly significant. It urges to try to find a scientific pattern of systematic data points supporting that picture globally.
    The poles are expected to warm up enormously, with total disappearance of the ice. Indications are that Antarctica is not secularly stable above 440 ppm CO2. We are already above that in CO2 equivalent (that is, adding 400 ppm of CO2 to other man made greenhouse gases, as methane and those used in refrigeration).
    In the Jurassic, and generally the whole dinosaur era (200 million to 65 million years ago), probably because of a lot of shallow seas (?), the planet was warm. There were crocodiles in Greenland and dinosaurs in Alaska and Antarctica (one does not know how they went through the 6 month night). At the time of the disappearance of various species 65 million years ago, the planet cooled down a lot, and species able to maintain a warm metabolism continuously (avian dinosaurs and mammals), or a cold metabolism for a long time (crocodilians, turtles, snakes, etc.) were left to rule.
    We are injecting CO2 at such high rate that one can expect the added heat to warm up enormously the two cold places: the poles and the deep ocean.
    Much noise is made about Antarctica’s ice cover augmenting. This is not completely true, and where it’s true, it was expected.
    First what’s not true: West Antarctica and the Antarctic peninsula are melting, and fast. Grass has actually appeared in the later, and flowering plants brought on scientists’ shoes are a problem.
    Second what’s only superficially true: the enrgy of the winds around Antartcia, by a generalization of the Equipartition of energy theorem, have augmented in speed. So winter ice spread far and wide more than it did before. In truth, there is less of it in volume.
    Third what is true: warm air carries more moisture. Extremely cold air carries no moisture at all. That’s why elevated (up to 4,000 meters) East Antarctica is the driest place on Earth (hence one looks for meteorites there). East Antarctica is warming up, so the air carries more moisture, and since it’s still very cold, it snows more.
    The potential for catastrophe is greater there; much of east Antarctica, under the enormous weight of the ice, is up to 200 meters below sea level. The margins are much less so, but they are often located at high latitudes (above the polar circle). So the sea water could infiltrate and melt the continental ice from below (that’s how the Hudson Bay ice shield melted in a few decades; this phenomenon is already launched in West Antarctica, where the sea margin is advancing at one kilometer per year, at least).
    This is a large scale physics experiment. And there is just one data point, the Earth itself.

  3. V clear explanation. You’re right that it has little to do with cause, but it’d be great to see one sometime on the multiple reasons to suspect that a 40% increase in GHG conc. is a culprit. I think physicists often give the best summaries of climate science..

  4. Are they assuming that the C12/C14 ratio in the atmosphere is the same in the past as it is today ?

    1. I’m not the expert, but the answer is (I believe) something between yes and no. The ratio isn’t entirely constant, presumably because cosmic ray rates aren’t constant either. But this is something you can check. Many objects are measured for which the dates are known via other means. So the fact that this ratio can drift somewhat over 50,000 years can (in part) be corrected for.

      Maybe someone more expert than me can give a more precise answer. Anyway, it’s not a source of uncertainty which is likely to entirely change the conclusion.

  5. Kudos Matt, for such a clear (and scientifically relevant!) example of carbon-dating, half-life, etc. A truly excellent job.

  6. I am missing a step connecting the age of the fossil and the ice. Do the fossils need ice to be preserved? Is it impossible that there was a glacier that brought them there?

        1. The Arctic is mostly ocean; the Antarctic is mostly continent; the effect of climate change may be dramatically different in these two regions. That’s why “climate change” is a better term than “global warming”, which means average increase in temperature averaged around the world, but does not mean “local warming everywhere”. Climate models predict some places will cool dramatically… whether you believe them or not is not the point, the point is that no one expects every place to get warmer, at least not initially.

          So no, it’s not related.

    1. If you refer to the extent of sea ice (the thin layer of ice that forms on the top of polar oceans): The sea ice extent is essentially a measure of the area that is covered by sea ice. This does not say something about the (vertical) thickness of the sea ice. However, for calculating the total ice volume (i.e., the total “amount” of ice), both factors are important as the volume is, roughly speaking: area times (mean) ice thickness.
      If strong winds (or ocean currents) distribute a given amount of sea ice over a larger area, the satellites will sea an increase in sea ice extent, although the ice volume in this example remains the same. A larger sea ice extent would be accompanied by a reduction in the mean ice thickness.
      I am not saying that this scenario is necessarily the case what happens now in Antarctica; I am just pointing out that one has to investigate the effects of the winds and ocean currents, that may move the sea ice to other and larger areas, and that alter the mean ice thickness, as well.

      Note that stronger winds are an expected result of an increase in the mean global air temperature.

      In the northern hemisphere, the decrease in sea ice volume in recent years is so dramatic because both the sea ice extent (i.e., the ice covered area) and the mean thickness of the sea ice are decreasing at the same time.

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