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Carbon cycle

Sources, sinks and seasons

Nature volume 451, pages 26–27 (2008)Cite this article

Changes in the phasing of seasonal cycles of carbon dioxide in the atmosphere mark the time when a region becomes a source or a sink of CO2. One study of such changes prompts thought-provoking conclusions.

We are currently getting a 50% discount on the climatic impact of our fossil-fuel emissions. Since 1957, and the beginning of the Mauna Loa record of atmospheric carbon dioxide, only about half of the CO2 emissions from fossil-fuel combustion have remained in the atmosphere, with the other half being taken up by the land and ocean. In the face of increasing fossil-fuel emissions, this remarkably stable 'airborne fraction' has meant that the rate of carbon absorption by the land and ocean has accelerated over time1. Unfortunately, we have no guarantee that the 50% discount will continue, and if it disappears we will feel the full climatic brunt of our unrelenting emission of CO2 from fossil fuels. Indeed, climate models that include descriptions of the carbon cycle predict that terrestrial uptake of carbon will decrease in the next century as climate warms2. As they describe elsewhere in this issue (page 49), Piao et al.3 have used observational data to show that rising temperatures may already be decreasing the efficiency of terrestrial carbon uptake in the Northern Hemisphere.

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Figure 1: Zero-crossing (ZC) dates.

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  1. John B. Miller is at the University of Colorado and the NOAA Earth System Research Laboratory, 325 Broadway, Boulder, Colorado 80305, USA. john.b.miller@noaa.gov ,

    John B. Miller

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Miller, J. Sources, sinks and seasons. Nature 451, 26–27 (2008). https://doi.org/10.1038/451026a

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