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Research objectives |
Effects on the Environment |
How measurements are made |
Measurement-based Assessments
Measurement-based Assessment of Aerosol Direct Radiative Effect and Forcing
Aerosols participate in the Earth's energy budget
directly by scattering and absorbing solar radiation and, to a lesser extent,
by absorption and emission of thermal infrared radiation. Moreover, the direct
absorption of radiant energy by aerosols can influence the atmospheric temperature
structure and, thereby, cloud formation - a phenomenon that has been labeled the
semi-direct effect. Aerosols also influence radiation indirectly
by acting as cloud condensation nuclei and, thereby, affecting cloud properties.
Aerosol radiative effect (by natural plus anthropogenic aerosols) or
aerosol radiative forcing (by anthropogenic aerosols) can play a
significant role not only in climate change but in a variety of environmental
issues like visibility degradation, the formation of photochemical smog,
and the photosynthesis and crop yields.
To learn more about aerosol radiative effects, go to the theory section.
If you want to see the numbers, go to the Cloud/Aerosol Database.
Recent IPCC report based largely on model simulations summarize
that the overall radiative forcing by anthropogenic aerosols is likely to be
negative and may be comparable in magnitude to the positive forcing of about
2.4Wm-2 by anthropogenic greenhouse gases. Large uncertainties exist in current
estimates of aerosol forcing because of incomplete knowledge concerning the
physical and chemical properties of aerosols as well as aerosol-cloud interactions.
The uncertainty for the aerosol direct radiative forcing is about a factor of 2 to 3
and that for the indirect forcing is much larger and difficult to quantify.
These uncertainties raise questions about the interpretation of the 20th
century temperature record and complicate the assessment of climate and
environmental impacts of aerosols. Accordingly, the US Climate Change Research
Initiative has specifically identified research on atmospheric concentrations
and effects of aerosols as a top priority.
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Reduction of these uncertainties requires a coordinated research strategy
that will successfully integrate data from multiple platforms
(e.g., ground-based networks, satellite, ship, and aircraft) and techniques
(e.g., in-situ measurement, remote sensing, numerical modeling, and data assimilation).
Model simulation is an indispensable tool of projecting future climate due to changes
of atmospheric aerosols. AEROCOM, an international initiative of scientists interested
in aerosols and climate, is documenting and intercomparing more than a dozen models and
a large number of observations to identify and reduce the uncertainty in current
global aerosol assessments.
In recent years, a great deal of effort has gone into improving measurements
and data sets, including the establishment of ground-based networks, the development and
implementation of new and enhanced satellite sensors, and the execution of intensive field
experiments in major aerosol regimes around the globe. As a result of these efforts it is
now feasible to shift the estimates of aerosol radiative effect and forcing from largely
model-based to increasingly measurement-based. In this new approach, satellite measurements
provide the basis for the regional- to global-scale assessments and chemical transport
models are used to interpolate and supplement the data in regions/conditions where
observational data are not available. Measurements from ground-based networks and
intensive field experiments are required for evaluating both the satellite retrievals
and the model simulations.
The Climate Change Science Program (CCSP) is developing and extending its
research activities to support policymaking and adaptive management, including
a generation of a set of synthesis and assessment products of aerosols. Under
the auspices of NASA HQ and the framework of CCSP, we in collaboration with
aerosol scientists from international community are reviewing measurement-based
understanding of aerosol direct radiative effect and forcing.
Research objectives |
Effects on the Environment |
How measurements are made |
Measurement-based Assessments
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