Climate Science

Untangling the Threads

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Science  23 Jul 2010:
Vol. 329, Issue 5990, pp. 371
DOI: 10.1126/science.329.5990.371-b

During the last deglaciation, between approximately 18,000 and 10,000 years ago, the atmospheric concentration of CO2 rose from around 180 to more than 260 parts per million. Although several plausible explanations for this increase have been proposed, it has not yet been possible to assign one over the others definitively. Lourantou et al. provide an additional constraint for the competing scenarios: a record of the isotopic composition of the carbon in atmospheric CO2 over the time interval in question. Because different sources of atmospheric CO2 have distinct carbon isotopic compositions, the authors could determine where in the carbon system the CO2 was coming from by comparing their data with proxy records related to carbon cycle processes, and also by conducting simulations using carbon cycle box models. They conclude that most of the increase in atmospheric CO2 was caused by Southern Ocean ventilation and upwelling, with additional contributions at various times from a decline in marine productivity and a buildup of terrestrial carbon. More sophisticated Earth system models that incorporate carbon cycle–climate feedbacks could help to disentangle the contributions of the processes involved in the rise.

Global Biogeochem. Cycles 24, GB2015 (2010).

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