A Note
from the IGAC Chair:
Guy Brasseur
Atmospheric Chemistry
and Climate
At the end of the 19th century,
the Swedish Nobel laureate Svante Arrhenius suggested that a
doubling in atmospheric carbon dioxide (from coal burning) would
increase the Earth's mean temperature by 5-6 degrees Celsius.
Numerous climate models have been developed in recent decades
to study in more detail the atmosphere's response to such human-induced
perturbations. Though early models focused entirely on CO2, in the last 10-15 years climate researchers
have recognized the importance of such chemically and radiatively
active gases as methane, nitrous oxide, halocarbons and ozone.
Some of these are produced by the biosphere, but their concentrations
are all perturbed on the global scale by human activities. These
greenhouse gases contribute to global warming.
Now a variety of aerosols are
being recognized for their impact on climate. Sulfate aerosol
particles, produced through coal burning, scatter back to space
a significant fraction of incoming solar radiation, leading to
potential regional cooling in industrialized/urbanized areas.
In this issue of IGACtivities, Barry Huebert and Don Lenschow
discuss several field campaigns designed to investigate the chemical
and microphysical processes involved in the formation and fate
of these aerosols. Because aerosol particles are believed to
serve as condensation nuclei for the formation of clouds, aerosols
of anthropogenic origin are expected to produce an indirect climate
forcing through changes in the optical properties of the clouds.
This difficult scientific issue is discussed in the following
pages by John Seinfeld and Richard Flagan.
Other types of aerosols are also
significant. Black carbon (soot) tends to absorb a fraction of
the solar and terrestrial radiation, thus warming the atmosphere.
Irina Sokolik describes in this issue how mineral dust affects
the atmosphere's radiative balance and hence the climate system.
Sea salt and organic aerosols are additional particles that need
to be considered in comprehensive climate studies.
One of IGAC's foci is atmospheric
aerosols. The importance of this issue for global change is becoming
increasingly evident. Aerosols not only affect climate, they
play an important role in the chemistry of the stratosphere and
troposphere through a number of heterogeneous reactions, and
have a significant impact on the intensity of photolytic radiation.
They affect visibility, damage plants, and can be detrimental
to health. But, while fouling the air, aerosols also create beautiful
sunsets!
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