A Plan for a Research Program on Aerosol Radiative Forcing and Climate Change (1996) / Chapter Skim
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3 SENSITIVITY/UNCERTAINTY ANALYSIS AND THE SETTING OF PRIORITIES
3 SENSITIVITY/UNCERTAINTY ANALYSIS AND THE SETTING OF PRIORITIES
Pages 89-106
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From page 89... ...
. The goal of the USGCRP is "to gain a predictive understanding of the interactive physical, geological, chemical, biological, economic, and social processes that regulate the total Earth system, and, hence, establish a scientific basis for national and international policy formulation and decisions relating to natural and human-induced changes in the global environment and their regional impacts." The ICARUS program should be incorporated and administered as a part of the USGCRP.
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From page 90... ...
Therefore, central to the ICARUS program is development of the understanding of aerosol forcing, as embodied in climate models: to describe, realistically, existing concentrations and properties of aerosol particles throughout the global atmosphere, thereby · to provide climate models with needed predictions of current and future anthropogenic aerosol radiative forcings, thereby · to meet the prime goals of the ICARUS program and the USGCRP, plus . to establish and continuously update rational choices of ICARUS ~.
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From page 91... ...
For example, an increase in the asymmetry parameter g leads to more solar radiation scattered toward the Earth and hence less back to space, which reduces the anthropogenic aerosol effect. According to Table 3.1, for a sulfate aerosol located below clouds, the most important aerosol property affecting the forcing is the asymmetry parameter.
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- ~cO _ _ ~O ~cn ~ o o Q > a) Atmospheric Property FIGURE 3.1 Sensitivity of aerosol forcing for an aerosol layer below cloud.
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From page 93... ...
Ct en O ~ O Ct5 ~Q O CO _ ~ - a) O Atmospheric Property FIGURE 3.2 Sensitivity of aerosol forcing for an aerosol layer above lowest cloud layer.
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to improve the quantitative base of these analyses, an immediate ICARUS thrust must be to improve quantitative understanding of indirect effects; (4) in the meantime, until understanding of indirect effects increases substantially, priorities can be defined only on a heuristic basis.
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Because sulfur emissions especially are expected to change rapidly during the next decade (with substantially greater increases from some rapidly developing economies, such as China's, and substantially smaller releases associated with acid rain regulations in other countries) , it might be supposed that, during the next decade, changes in direct radiative effects from inorganic particles (both increases and decreases)
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From page 96... ...
, caused mainly by nights warming more than days (Karl et al., 19951; because the magnitude of this DTR decrease is inconsistent with climate models that account only for increases in "greenhouse gases"; and because there are suggestions (Hansen et al., 1995) that this DTR decrease is caused by increases in low-level cloud cover (an expected indirect consequence of increasing anthropogenic aerosols)
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.o 0 c can O .~. ~1 ~_ ~1 .o o Indirect Direct ICARUS Phase 1 Goal FIGURE 3.5 Qualitative indication of relative funding priorities (resource allocations)
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From page 98... ...
AN EXAMPLE OF SENSITIVITY AND UNCERTAINTY ANALYSES In this section, we illustrate the sensitivity/uncertainty analysis method further by presenting both sensitivity and uncertainty analyses for direct radiative effects of sulfate particles. The goal here is to examine the framework more closely and, to this end, consider how only the rightmost bar in Figure 3.5 (i.e., costs to reduce uncertainties about direct effects of inorganic aerosols)
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From page 99... ...
, is the fractional cloud cover, is the albedo of the underlying surface, is the upward fraction of the radiation scattered by the aerosol, OCso4- iS the scattering efficiency of fine-particle sulfate at a reference low relative humidity (square meters per gram', f(RH' accounts for increase in scattering with increasing relative humid ~ty, is the source strength of SON (crams ner second)
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From page 100... ...
100 Cal Cal Cal Ct o ._ Cal C)
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101 o o o ~ ~ ~ t- ~ oo _ u~ O O ~ O0 0 cr~ t- ~ ~- ~ ~ ~ C~ ~ ~ .
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Component Uncertainties, Direct Effects, Sulfate Aerosols FIGURE 3.6 Plot of the uncertainties listed in Table 3.3A for sulfate aerosols, with a qualitative indication of the level to which the uncertainty could be set as a goal for the first phase of ICARUS research. From Figure 3.6 (showing uncertainties)
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From page 103... ...
C/) II Component Uncertainties, Direct Effects, Sulfate Aerosols FIGURE 3.S Qualitative indication of the relative costs to reduce the uncertainties shown in Figure 3.6, consistent with the research priorities shown in Figure 3.7, accounting for the cost of performing the research (e.g., a prorated portion of satellite costs to measure backscattered radiation)
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From page 104... ...
G ' ~i ~== ~ c' > c: > ~ ~ ~6 ~> 11111111. Component Uncertainties, Sulfate Aerosol Lifetime ICARUS Phase Goal FIGURE 3.9 Qualitative indication of the relative contributions from different processes to current uncertainty in the atmospheric lifetime of aerosol sulfate, with a qualitative indication of the level to which the uncertainty could be set as a goal for the first phase of ICARUS research.
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From page 105... ...
~ ~ - 1 1.1 ... Component Uncertainties, Sulfate Aerosol Lifetime FIGURE 3.10 Qualitative indication of funding priorities to reduce the uncertainties shown in Figure 3.9.
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