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| Titel |
What can be learned about carbon cycle climate feedbacks from the CO2 airborne fraction? |
| VerfasserIn |
M. Gloor, J. L. Sarmiento, N. Gruber |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 16 ; Nr. 10, no. 16 (2010-08-20), S.7739-7751 |
| Datensatznummer |
250008717
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| Publikation (Nr.) |
 copernicus.org/acp-10-7739-2010.pdf |
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| Zusammenfassung |
| 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. |
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