Radiative Forcing of Climate Change Expanding the Concept and Addressing Uncertainties (2005) / Chapter Skim
Currently Skimming:
6 Research Approaches to Furthering Understanding
6 Research Approaches to Furthering Understanding
Pages 117-143
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From page 117... ...
Current observational approaches include in situ and surface-based monitoring of greenhouse gases and aerosols; satellite-based observations of atmospheric composition, land cover, and solar variability; and intensive campaigns that utilize aircraft-based observations with in situ and satellite measurements to study processes in detail. Observations of climate response, such as surface temperature or ocean heat content, also provide important information about climate 117
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From page 118... ...
TransCom activity (http://transcom.colostate.edu/) has provided a forum for standardizing and comparing these inverse model analyses, but model transport errors ultimately limit their ability to exploit the relatively sparse surface air observations in terms of regionally resolved source and sink constraints (Gurney et al., 2002)
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From page 119... ...
. A number of inverse model studies have been conducted to constrain sources of methane using long-term observations from the NOAA CMDL network (Hein et al., 1997; Houweling et al., 1999; Wang et al., 2004)
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From page 120... ...
A global climatology of total ozone columns extending back to 1979 is available from the Total Ozone Mapping Spectrometer (TOMS; see Figure 6-1) and other sensors, and has been used extensively and successfully for trend analyses (WMO, 2003)
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From page 121... ...
Despite these limitations, for this short-lived forcing, unlike for other such species, chemical transport models are not needed to evaluate the forcing because of the presence of a reliable, continuous global monitoring network. The inadequacy of current tropospheric ozone observations for constraining global distributions and trends has spurred the concept of an Integrated Global Atmospheric Chemistry Observation System (IGACO)
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From page 122... ...
-2 6 m (W 8 10 forcing 12 TOA 14 16 18 20 0 0.1 0.2 0.3 0.4 0.5 0.6 Aerosol optical depth FIGURE 6-2 Direct observations of clear-sky forcing efficiency. The top panel shows the reduction at the surface due to aerosols as a function of the aerosol optical depth, while the bottom panel shows the same at the top of the atmosphere.
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From page 123... ...
. Closure experiments were conducted using a collection of vertically resolved measurements of aerosol size and composition with simultaneous vertical profiles of spectrally resolved optical depth.
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From page 124... ...
. The success of these studies clearly illustrates the need for accurate observations of radiation budget, aerosol optical depth, and cloud fraction and cloud type at the surface (in selected regions)
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From page 125... ...
Ground-based experiments have studied the role of cloudparticle interactions through fog events and showed that chemical composition is a key factor in determining cloud droplet activation properties (Noone et al., 1992)
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From page 126... ...
Field campaigns provide a complementary method to advance understanding of land surface processes. Campaigns such as BOREAS (for the boreal forest region of Manitoba and Saskatchewan)
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From page 127... ...
RESEARCH APPROACHES TO FURTHER UNDERSTANDING 127 FIGURE 6-3 Observations of the land cover in the Great Lakes region of the United States and Canada, obtained by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Terra satellite.
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From page 128... ...
Observations over only 2.5 cycles are insufficient to characterize the extremes of solar cycle irradiance variability or to detect speculated longer-term irradiance changes. The extant record of total solar irradiance is compiled from observations made by half a dozen individual radiometers, cross-calibrated to account for individual absolute uncertainties and instabilities.
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From page 129... ...
. The Argo network of ocean floats and satellite observations of ocean altimetry have been used to estimate trends in ocean heat content (Levitus et al., 2000, 2001; Willis et al., 2003)
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From page 130... ...
. In order to infer ocean heat content changes from sea level estimates, however, one must make potentially restrictive assumptions regarding the thermal contributions to ocean heat content changes versus contributions from changes in continental runoff and glacial melting.
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From page 131... ...
. Key parameters for which benchmark measurements are crucial include among others sea level altimetry, solar irradiance, global positioning system (GPS)
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From page 132... ...
Finally, surface tension and wettability of organic particles must be measured in order to predict cloud droplet activation properties. The thermodynamic properties of organic and some mineral components are not well understood.
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From page 133... ...
This information would be valuable in relating to observed temporal and spatial changes in ocean heat content. For example, can the atmospheric reanalyses help explain the observed focusing of ocean warming in the midlatitudes of the Southern Hemisphere, and will this continue into the future?
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From page 134... ...
and inverse models-have been developed to assist scientists in relating sources to atmospheric concentrations. Chemical Transport Model Analyses Aerosols and ozone have short atmospheric lifetimes and hence inhomogeneous atmospheric distributions.
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From page 135... ...
The generally higher carbon monoxide levels in September are attributed to South American fire emissions and the transport of carbon monoxide across the Atlantic Ocean from Southern Africa fires. SOURCE: NASA Goddard Space Flight Center.
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From page 136... ...
. Indeed, the warming resulting from this eruption, the radiative flux comparisons with satellite observations, the cooling of the troposphere, the change in precipitable water, and the winter warming in northern high latitudes are all at least qualitatively well simulated, attesting to a degree of confidence in the working of climate models (Ramachandran et al., 2000; Ramaswamy et al., 2004; Soden et al., 2002; Stenchikov et al., 2002)
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From page 137... ...
Almost all global CTM studies of aerosols so far have been mass-only simulations that do not resolve the aerosol size distribution, mixing across components, or phase. This is evidently problematic for radiative forcing calculations and, in particular, prevents simulations of the indirect effect except through loose empirical relationships between cloud droplet number concentrations and preexisting aerosol mass concentrations (Boucher and Lohmann, 1995)
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From page 138... ...
. Future inverse model studies should make use of available observations of aerosol surface concentrations and optical depths, as well as the information contained in the observed correlations between species concentrations, for example, between CO2 and CO (Suntharalingam et al., 2004)
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From page 139... ...
is also needed. There is a broadly consistent view between different climate models and empirical proxy-based reconstructions of hemispheric mean surface temperature changes in past centuries.
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From page 140... ...
. CLIMATE MODELS Applications of climate models include developing better understanding of processes and predicting future conditions.
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From page 141... ...
At present, the relationship can only be derived between cloud droplet number and sulfate aerosols, sea salt, and organic carbon; no concurrent data for dust or black carbon and
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From page 142... ...
. Because the aerosol indirect effect is based on the change in cloud droplet number concentration, some models predict cloud droplet number concentrations using one of the abovedescribed physically based aerosol activation schemes as a source term for cloud droplets (Ghan et al., 1997; Lohmann et al., 1999)
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From page 143... ...
The argument against the robustness of the long-range connectivity involves possible oversensitivity of the climate models that have been used in the studies and the statistical significance of the results. To address these comments, climate models with appropriate sensitivity and resolution should be used to perform experiments with observed regional anomalies of diabatic forcing, as well as with realistic perturbation simulations (such as between natural and current landscapes)
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