Climate Science

Historical Airs

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Science  14 Mar 2003:
Vol. 299, Issue 5613, pp. 1627
DOI: 10.1126/science.299.5613.1627b

Records of terrestrial paleotemperatures are difficult to assemble. Unlike marine environments, there is a lack of reliable proxies for temperature, and inferences must often be made based on modeling and inexact indices rather than accurately quantifiable parameters. This problem is acute in arid regions, making the reconstruction of past climate in Africa particularly challenging.

One of the promising approaches to determining terrestrial paleotemperatures is to measure the concentrations of dissolved noble gases in groundwaters. Because these gases display a range of temperature-dependent solubilities in water that varies with their masses, water temperature can be calculated by determining their concentrations. Beyerle et al. adopt a sophisticated version of this approach—by also measuring the stable isotope compositions of hydrogen and oxygen as well as 14C—to compile a record of temperature and humidity for the Sahel in southwest Niger since the late Pleistocene. Soil temperatures more than 6000 years ago were 2° to 5°C lower than they are today, which is cooler than has been assumed. They attribute this partly to atmospheric cooling, but also to recharge during more humid climate phases that had increased vegetation and a reduced difference between soil and air temperatures. — HJS

Geophys. Res. Lett.30, 1173 (2003).

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