What can be learned about carbon cycle climate feedbacks from the CO2 airborne fraction?

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Author(s) Gloor, M., Sarmiento, J.L., Gruber, N.
Publication Type Journal Items, Publication Status: Published
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Title What can be learned about carbon cycle climate feedbacks from the CO2 airborne fraction?
Author(s) Gloor, M.
Sarmiento, J.L.
Gruber, N.
Journal or Series Title Atmospheric chemistry and physics
Volume Number 10
Issue Number 16
Start Page 7739
End Page 7751
ISSN 1680-7316
Publisher European Geophysical Society
Publication Place Katlenburg, Lindau
Publication Date 2010
Abstract The ratio of CO2 accumulating in the atmosphere to the CO2 flux into the atmosphere due to human activity, the airborne fraction AF, is central to predict changes in earth's surface temperature due to greenhouse gas induced warming. This ratio has remained remarkably constant in the past five decades, but recent studies have reported an apparent increasing trend and interpreted it as an indication for a decrease in the efficiency of the combined sinks by the ocean and terrestrial biosphere. We investigate here whether this interpretation is correct by analyzing the processes that control long-term trends and decadal-scale variations in the AF. To this end, we use simplified linear models for describing the time evolution of an atmospheric CO2 perturbation. We find firstly that the spin-up time of the system for the AF to converge to a constant value is on the order of 200-300 years and differs depending on whether exponentially increasing fossil fuel emissions only or the sum of fossil fuel and land use emissions are used. We find secondly that the primary control on the decadal time-scale variations of the AF is variations in the relative growth rate of the total anthropogenic CO2 emissions. Changes in sink efficiencies tend to leave a smaller imprint. Therefore, before interpreting trends in the AF as an indication of weakening carbon sink efficiency, it is necessary to account for trends and variations in AF stemming from anthropogenic emissions and other extrinsic forcing events, such as volcanic eruptions. Using atmospheric CO2 data and emission estimates for the period 1959 through 2006, and our simple predictive models for the AF, we find that likely omissions in the reported emissions from land use change and extrinsic forcing events are sufficient to explain the observed long-term trend in AF. Therefore, claims for a decreasing long-term trend in the carbon sink efficiency over the last few decades are currently not supported by atmospheric CO2 data and anthropogenic emissions estimates.
DOI 10.5194/acp-10-7739-2010
Additional Notes Received 22 March 2010, Revised 18 June 2010, Accepted 21 July 2010, Published 20 August 2010
Document Type Article
Publication Status Published
Language English
Assigned Organisational Unit(s) 03731
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NEBIS System Number 004294181
Source Database ID WOS-000281432800015
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  author = "Gloor, M. and Sarmiento, J.L. and Gruber, N.",
  title = "{W}hat can be learned about carbon cycle climate feedbacks from the {C}{O}2 airborne fraction?",
  journal = "Atmospheric chemistry and physics",
  year = 2010,
  volume = "10",
  number = "16",
  pages = "7739--7751",

E-Citations record created: Mon, 20 Sep 2010, 06:19:29 CET