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Vehicle efficiency,
less driving
C
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Building efficiency,
insulation
Power plant
efficiency,
fuel switching,
carbon capture
em
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Hi
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7
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Alternative energy
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Billions of tons of carbon emitted per year
14
0
1950
2000
Year
Protect forests, soils
2050
Figure 9.2 We could stabilize or even reduce carbon emissions now if we
focus on multiple modest strategies.
manageable parts, this 7 GT can be subdivided into seven wedges, each
representing 1 GT of carbon we need to cut.
Cutting one of those gigatons could be accomplished by increasing fuel economy in our cars from 30 to 60 mpg. Another gigaton
could be eliminated if we reduced reliance on cars (with more public
transit or less suburban sprawl, for example) and cut driving from an
average 10,000 miles to 5,000 miles per year. Better insulation and
efficient appliances in our houses and office buildings would equal
9.1 What Is the Atmosphere?
Earth’s atmosphere consists of gas molecules, relatively densely
packed near the surface and thinning gradually to about 500 km
(300 mi) above the earth’s surface. In the lowest layer of the atmosphere, air moves ceaselessly, flowing, swirling, and continually redistributing heat and moisture from one part of the globe to
another. The daily temperatures, wind, and precipitation that we call
weather occur in the troposphere. Long-term temperatures and precipitation trends we refer to as climate.
The earliest atmosphere on earth probably consisted mainly of
hydrogen and helium. Over billions of years, most of that hydrogen and
helium diffused into space. Volcanic emissions added carbon, nitrogen,
oxygen, sulfur, and other elements to the atmosphere. Virtually all of
the molecular oxygen (O2) we breathe was probably produced by photosynthesis in blue-green bacteria, algae, and green plants.
Clean, dry air is 78 percent nitrogen and almost 21 percent
oxygen, with the remaining 1 percent composed of argon, carbon
dioxide (CO2), and a variety of other gases. Water vapor (H2O in gas
another wedge. Increased efficiency in our coal power plants
would equal another wedge.
These steps add up to 4/7 of the stabilization triangle, using currently available technologies. The remaining 3/7 can be accomplished
by capturing and storing carbon at power plants, by changing the
way power plants operate, and by reducing reliance on coal power.
Another set of seven wedges, including alternative energy, preventing deforestation, and reducing soil loss, could put us on a trajectory
to reduce our CO2 emissions and prevent disastrous rates of climate
change. Further details on the wedges are given later in this chapter.
The net effect of these strategies is likely to be economic
gain, which contradicts many traditional fears of economists and
politicians that we cannot afford climate mitigation. Many of
the needed changes involve efficiency, which means long-term
cost savings. Employment is likely to increase as new cars and
appliances replace old ones, and as we insulate more buildings.
There are other potential benefits, too. Efficient cars will save
household income. Cleaner power plants will reduce asthma
and other respiratory illnesses, saving health care costs as well as
improving quality of life. Less reliance on coal will reduce toxic
mercury in our food chain, because coal burning is the largest
single source of airborne mercury emissions.
In this chapter we’ll examine the evidence for climate change
and its consequences, as well as important issues in air pollution.
To begin, we’ll discuss what our climate is, and how it works.
For related resources, including Google Earth™ place marks
that show locations where these issues can be seen, visit
http://EnvironmentalScience-Cunningham.blogspot.com.
Further Reading
Pacala, S., and Socolow, R. 2004. Stabilization wedges: Solving the
climate problem for the next 50 years with current technologies.
Science, 305 (5686): 968–72.
form) varies from near 0 to 4 percent, depending on air temperature
and available moisture. Minute particles and liquid droplets—
collectively called aerosols—also are suspended in the air. Atmospheric aerosols and water vapor play important roles in the earth’s
energy budget and in rain production.
The atmosphere has four distinct zones of contrasting temperature, due to differences in absorption of solar energy (fig. 9.3). The
layer immediately adjacent to the earth’s surface is called the troposphere (tropein means to turn or change, in Greek). Within the
troposphere, air circulates in great vertical and horizontal convection currents, constantly redistributing heat and moisture around the
globe (fig. 9.4). The troposphere ranges in depth from about 18 km
(11 mi) over the equator to about 8 km (5 mi) over the poles, where
air is cold and dense. Because gravity holds most air molecules close
to the earth’s surface, the troposphere is much denser than the other
layers: it contains about 75 percent of the total mass of the atmosphere. Air temperature drops rapidly with increasing altitude in this
layer, reaching about –60°C (–76°F) at the top of the troposphere.
Chapter 9
Air: Climate and Pollution
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