Tuesday, March 3, 2009

Carbon dating and global warming

The prodigious mobilization of science that produced nuclear weapons was so far-reaching that it revolutionized even the study of ancient climates. Nuclear laboratories, awash with funds and prestige, spun off the discovery of an amazing new technique — radiocarbon dating.

The discovery of carbon dating is an interesting story in its own right and is described in several places, for example here. It is also described here, at the American Institute of Physics, part of a rather nice collection of essays on the discovery of global warming. The ratio of C-14 to C-12 on earth has varied significantly during the Earth's history. This variation is due to changes in the intensity of the cosmic radiation bombardment of the Earth, and changes in the effectiveness of the atmosphere in deflecting that bombardment. To compensate for this variation, dates obtained from radiocarbon laboratories are now corrected using standard calibration tables.

It was particularly interesting that, as Stuiver had suspected, the carbon-14 wiggles correlated with long-term changes in the number of sunspots. Turning it around, Suess remarked that "the variations open up a fascinating opportunity to perceive changes in the solar activity during the past several thousand years." The anomalies were evidence for something that many scientists found difficult to believe — the surface activity of the Sun had varied substantially in past millennia. Carbon-14 might not only provide dates for long-term climate changes, but point to one of their causes.

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