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.
…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.