CLIMATOLOGY

Warmer Weathering

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Science  04 May 2001:
Vol. 292, Issue 5518, pp. 813
DOI: 10.1126/science.292.5518.813b

Atmospheric CO2 traps heat through its role as a potent greenhouse gas. Eventually, however, atmospheric CO2 combines with water to form corrosive carbonic acid, which weathers silicate minerals. These combined effects should help to stabilize climate: As temperature rises, so does the rate of weathering, which should consume CO2 at a higher rate and decrease its concentration in the atmosphere, thus helping to lower global temperature. This hypothesis is simple to understand but difficult to prove.

Recently Ravizza et al. measured the isotopic composition of osmium in bulk marine sediments from around the time of the Late Paleocene Thermal Maximum (LPTM), an episode of unusual warmth 55 million years ago. They found a 220,000-year osmium isotopic excursion coincident with the LPTM that is consistent with an increased rate of weathering of young mantle-derived rocks. This finding suggests that a drawdown of CO2 caused by more rapid chemical weathering could have helped to arrest the LPTM warming and appears to support the idea that a temperature-dependent weathering-based mechanism can help to regulate climate on time scales of 104 to 105 years. — HJS

Paleoceanography16, 155 (2001).

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