Geoscience Reference
In-Depth Information
Chapter 12
The Greenhouse Effect
and Global Warming
The two major global-scale environmental threats of
international concern since the 1970s have been global
stratospheric ozone layer loss and global warming.
As discussed in Chapter 11, the global ozone layer
is expected to recover by the mid-twenty-first cen-
tury because national and international regulations have
required the chemical industry to use alternatives to
chloro- and bromocarbons, which are the chemicals
primarily responsible for stratospheric ozone loss. Reg-
ulations are similarly responsible for improvements in
air quality and acid deposition problems in many parts
of the world since the 1970s (e.g., the U.S. Clean
Air Act Amendments of 1970 motivated U.S. automo-
bile manufacturers to develop the catalytic converter
in 1975, which led to improvements in urban air qual-
ity; regulations through the 1979 Geneva Convention
on Long-Range Transboundary Air Pollution led to the
amelioration of some acid deposition problems in the
1980s and 1990s). However, progress toward solving
the second major issue of international concern, global
warming, has been slow. In this chapter, global warming
is described and distinguished from the natural green-
house effect. In addition, historical and recent temper-
ature trends, both in the lower and upper atmosphere,
are addressed, and climate responses to increased pollu-
tion are examined. The chapter also discusses potential
effects of global warming and international and national
efforts to curtail it.
12.1. Temperature on Earth in the Absence
of a Greenhouse Effect
The natural greenhouse effect is the warming of the
Earth's troposphere due to an increase in natural green-
house gases. Greenhouse gases are gases that are
largely transparent to the sun's visible radiation but
absorb and reemit the Earth's thermal-IR radiation at
selective wavelengths. They cause a net warming of the
Earth's atmosphere similar to the way in which a glass
house causes a net warming of its interior. Because most
incoming solar radiation can penetrate a glass house but
a portion of outgoing thermal-IR radiation cannot, air
inside a glass house warms during the day as long as
mass (e.g., plant mass) is present within the house to
absorb the solar radiation, to heat up the air, and to
reemit thermal-IR radiation. The surface of the Earth,
like plants, absorbs solar radiation and reemits thermal-
IR radiation. Greenhouse gases, like glass, are transpar-
ent to most solar radiation but absorb a portion of the
Earth's thermal-IR radiation at selective wavelengths.
Global warming is the increase in the Earth's
temperature above that from the natural greenhouse
effect due to the addition of anthropogenically emit-
ted greenhouse gases and aerosol particle components
that directly absorb solar radiation. Important absorb-
ing aerosol particle components include black car-
bon (BC) and certain organic carbon compounds,
 
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