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| Titel |
The declining uptake rate of atmospheric CO2 by land and ocean sinks |
| VerfasserIn |
M. R. Raupach, M. Gloor, J. L. Sarmiento, J. G. Canadell, T. L. Frölicher, T. Gasser, R. A. Houghton, C. Le Quere, C. M. Trudinger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 13 ; Nr. 11, no. 13 (2014-07-02), S.3453-3475 |
| Datensatznummer |
250117498
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| Publikation (Nr.) |
 copernicus.org/bg-11-3453-2014.pdf |
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| Zusammenfassung |
| Through 1959–2012, an airborne fraction (AF) of 0.44 of total
anthropogenic CO2 emissions remained in the atmosphere, with
the rest being taken up by land and ocean CO2
sinks. Understanding of this uptake is critical because it greatly
alleviates the emissions reductions required for climate mitigation,
and also reduces the risks and damages that adaptation has to embrace.
An observable quantity that reflects sink properties more
directly than the AF is the CO2 sink rate (kS),
the combined land–ocean CO2 sink flux per unit excess
atmospheric CO2 above preindustrial levels. Here we show from
observations that kS declined over 1959–2012 by a factor
of about 1 / 3, implying that CO2 sinks increased more slowly
than excess CO2. Using a carbon–climate model,
we attribute the decline in kS
to four mechanisms: slower-than-exponential CO2 emissions
growth (~ 35% of the trend), volcanic eruptions (~ 25%),
sink responses to climate change (~ 20%), and
nonlinear responses to increasing CO2, mainly oceanic (~ 20%).
The first of these mechanisms is associated purely with
the trajectory of extrinsic forcing, and the last two with intrinsic, feedback
responses of sink processes to changes in climate and atmospheric
CO2. Our results suggest that the effects of these intrinsic,
nonlinear responses are already detectable in the global carbon
cycle. Although continuing future decreases in kS will
occur under all plausible CO2 emission scenarios, the rate of
decline varies between scenarios in non-intuitive ways because
extrinsic and intrinsic mechanisms respond in opposite ways to changes
in emissions: extrinsic mechanisms cause kS to decline
more strongly with increasing mitigation, while intrinsic mechanisms
cause kS to decline more strongly under high-emission,
low-mitigation scenarios as the carbon–climate system is perturbed
further from a near-linear regime. |
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