Earth Science

Understanding Environmental Change

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Science  19 Oct 2001:
Vol. 294, Issue 5542, pp. 481
DOI: 10.1126/science.294.5542.481a

Carbon dioxide (CO2) is an important component in Earth's radiative energy budget and acts as a bridge between organic and inorganic biogeochemical domains. Knowing how the concentration of CO2 in the atmosphere has varied is thus essential for understanding environmental change. Atmospheric CO2 concentrations can be measured directly, from bubbles of air trapped in polar ice, for as far back as 400,000 years ago, the age of the oldest Antarctic ice cores. For periods older than this, geochemical models and proxies must be used to provide indirect estimates.

Royer et al. discuss the theory and use of geochemical modeling of the long-term carbon cycle, and four paleo-pCO2 proxies (the δ13C of pedogenic carbonates, the δ13C of marine sedimentary organic carbon, the stomatal density of land plants, and the δ11B of marine calcium carbonate) commonly employed in atmospheric reconstructions. Models, which can be applied across the entire Phanerozoic, have low temporal resolution and increasingly large uncertainties with increasing age. Proxies can provide better resolution and precision but are subject to a variety of limitations and systematic errors that are not always easy to estimate.—HJS

Earth Sci. Rev.54, 349 (2001).

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