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| Titel |
Potential temperature induced carbon-cycle feedbacks from solar radiation management geoengineering |
| VerfasserIn |
Catherine Scott, Naomi Vaughan, Piers Forster |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045788
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| Zusammenfassung |
| Ideas to reduce the amount of shortwave radiation coming into the Earth system, to address
the radiative imbalance caused by increasing greenhouse gas concentrations, have gained
increasing attention over recent years. Here, we investigated the potential temperature
induced carbon-cycle feedbacks that may arise due to such solar radiation management
(SRM) geoengineering interventions.
In this work, geoengineering is simulated by reducing the level of solar radiative forcing
over the 21st century in a reduced complexity, global climate-carbon cycle model, MAGICC
6 [1]. This simple model features a hemispherically averaged, upwelling diffusion ocean
component and has been calibrated using 19 atmosphere-ocean global climate models. The
harmonised emissions of the Representative Concentration Pathways (RCPs) are used to
force the future climate and SRM geoengineering is applied to offset a portion, or all, of the
positive radiative forcing generated by anthropogenic emissions. As noted previously by
Matthews and Caldiera [2], the application of SRM can reduce simulated atmospheric carbon
dioxide concentration considerably. Examination of the resulting carbon pools reveals that
this atmospheric reduction occurs due to the temperature sensitivities of terrestrial respiratory
fluxes. Since SRM artificially reduces surface temperatures, heterotrophic respiration
decreases when compared to the non-SRM control run, and therefore less carbon
leaves the soil pool. The simulated temperature response to SRM geoengineering
therefore represents a combination of the response to a direct reduction in incoming
shortwave radiation (i.e. the geoengineering intervention), and a response to increased
outgoing longwave radiation from a reduction in atmospheric carbon dioxide (i.e.
the carbon-cycle response to geoengineering). However, feedbacks within the
carbon-cycle are not solely temperature dependent and may also be largely driven by
precipitation, as well as changes to direct incoming shortwave radiation. Geoengineering
that involves a reduction to the incoming solar flux would likely induce spatially
inhomogeneous alterations to precipitation patterns [3, 4], so a full assessment of
carbon-cycle feedback response to SRM would necessitate incorporation of precipitation
driven feedbacks.
Here, the magnitude and duration of SRM geoengineering are varied, along with
concurrent anthropogenic emissions. MAGICC 6 was calibrated to emulate the
response of nine of the C4MIP models, allowing a first order assessment of likely
variation in the carbon cycle response. A range of other climate model parameters,
including climate sensitivity, were also varied within their likely uncertainty ranges to
explore the effect of the uncertainty in temperature response on the carbon cycle
response.
References:
.1. Meinshausen, M., S.C.B. Raper, and T.M.L. Wigley, Emulating IPCC AR4
atmosphere-ocean and carbon cycle models for projecting global-mean, hemispheric and
land/ocean temperatures: MAGICC 6.0. Atmos. Chem. Phys. Discuss., 2008. 8(2): p.
6153-6272.
2. Matthews, H.D. and K. Caldiera, Transient climate-carbon simulations of planetary
geo-engineering. PNAS, 2007. 104(24): p. 9949-9954.
3. Irvine, P.J., A. Ridgwell,and D. J. Lunt, Assessing the regional disparities in
geoengineering impacts. Geophysical Research Letters, 2010. 37:L18702
4. Bala. G., P. B. Duffy, K. E. Taylor, Impact of geoengineering schemes on the global
hydrological cycle. PNAS, 2008. 105: p. 7664-7669. |
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