PerspectiveOcean Science

A Faster Water Cycle

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Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 430-431
DOI: 10.1126/science.1205253

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Most of us treat water as a commodity, a consumable if vital substance that we access with a turn of a faucet. But water is also an integral part of the climate system, contributing to the delicate balance of energy and mass that regulates the temperature of our planet. This relationship is at the heart of the scientific community's concern that dramatic changes may be in store for the water cycle in the future (1). Moreover, given water vapor's role as the most powerful greenhouse gas in Earth's climate system, uncertainty about future water cycle change underlies much of the uncertainty in future climate projections (2). Fortunately, for geochemists, water is not an undifferentiated commodity, but rather exhibits subtle but measurable variations in its stable oxygen isotopic compositions. These differences allow researchers to trace past and present fluxes within the water cycle. On page 455 of this issue, Clementz and Sewall (3) use isotopic data from fossil teeth to reconstruct past global patterns of variation in water isotopic composition. They fill a major data gap in the geological record of the water cycle and provide evidence that fluxes of water through the tropical atmosphere were more vigorous during past periods of extreme global warmth.