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| Titel |
Quantifying immediate radiative forcing by black carbon and organic matter with the Specific Forcing Pulse |
| VerfasserIn |
T. C. Bond, C. Zarzycki, M. G. Flanner, D. M. Koch |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2011-02-16), S.1505-1525 |
| Datensatznummer |
250009361
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| Publikation (Nr.) |
 copernicus.org/acp-11-1505-2011.pdf |
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| Zusammenfassung |
Climatic effects of short-lived climate forcers (SLCFs) differ from those of
long-lived greenhouse gases, because they occur rapidly after emission and
because they depend upon the region of emission. The distinctive temporal
and spatial nature of these impacts is not captured by measures that rely on
global averages or long time integrations. Here, we propose a simple
measure, the Specific Forcing Pulse (SFP), to quantify climate warming or
cooling by these pollutants, where we define "immediate" as occurring
primarily within the first year after emission. SFP is the amount of energy
added to or removed from a receptor region in the Earth-atmosphere system by
a chemical species, per mass of emission in a source region. We limit the
application of SFP to species that remain in the atmosphere for less than
one year. Metrics used in policy discussions, such as total forcing or
global warming potential, are easily derived from SFP. However, SFP conveys
purely physical information without incurring the policy implications of
choosing a time horizon for the global warming potential.
Using one model (Community Atmosphere Model, or CAM), we calculate values of
SFP for black carbon (BC) and organic matter (OM) emitted from 23
source-region combinations. Global SFP for both atmosphere and cryosphere
impacts is divided among receptor latitudes. SFP is usually greater for
open-burning emissions than for energy-related (fossil-fuel and biofuel)
emissions because of the timing of emission. Global SFP for BC varies by
about 45% for energy-related emissions from different regions. This
variation would be larger except for compensating effects. When emitted
aerosol has larger cryosphere forcing, it often has lower atmosphere forcing
because of less deep convection and a shorter atmospheric lifetime.
A single model result is insufficient to capture uncertainty. We develop a
best estimate and uncertainties for SFP by combining forcing results from 12
additional models. We outline a framework for combining a large number of
simple models with a smaller number of enhanced models that have greater
complexity. Adjustments for black carbon internal mixing and for regional
variability are discussed. Emitting regions with more deep convection have
greater model diversity. Our best estimate of global-mean SFP is +1.03 ± 0.52 GJ g−1
for direct atmosphere forcing of black carbon, +1.15 ± 0.53 GJ g−1 for black carbon including direct and cryosphere forcing,
and −0.064 (−0.02, −0.13) GJ g−1 for organic matter. These values depend
on the region and timing of emission. The lowest OM:BC mass ratio required
to produce a neutral effect on top-of-atmosphere direct forcing is 15:1 for
any region. Any lower ratio results in positive direct forcing. However,
important processes, particularly cloud changes that tend toward cooling,
have not been included here.
Global-average SFP for energy-related emissions can be converted to a
100-year GWP of about 740 ± 370 for BC without snow forcing, and 830 ± 440
with snow forcing. 100-year GWP for OM is −46 (−18, −92). Best estimates
of atmospheric radiative impact (without snow forcing) by black and organic
matter are +0.47 ± 0.26 W m−2 and −0.17 (−0.07, −0.35) W m−2
for BC and OM, respectively, assuming total emission rates of 7.4 and
45 Tg yr−1. Anthropogenic forcing is +0.40 ± 0.18 W m−2 and −0.13
(−0.05, −0.25) W m−2 for BC and OM, respectively, assuming anthropogenic
emission rates of 6.3 and 32.6 Tg yr−1. Black carbon forcing is only
18% higher than that given by the Intergovernmental Panel on Climate
Change (IPCC), although the value presented here includes enhanced
absorption due to internal mixing. |
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