Energy and Changes in the Environment - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 39

Table 2-1b. Motor Vehicle Distance Traveled
Average miles per vehicle (1,000)
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Total Cars Buses Vans Trucks

pickups
SUVs
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1970 10.0 10.0 12.0 8.7 13.6
1980 9.5 8.8 11.5 10.4 18.7
1985 10.0 9.4 7.5 10.5 20.6
1990 11.1 10.3 9.1 11.9 23.6
1991 11.3 10.3 9.1 12.2 24.2
1995 11.8 11.2 9.4 12.0 26.5
2003 12.2 11.2 10.3 11.5 27.3
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of a greenhouse where the heat is let in through the glass but most of it is
prevented from escaping. If the earth did not act like a giant greenhouse,
temperatures at the earth's surface would be about 35°C (60°F) colder than
they are, and life on earth would be much different.
These greenhouse gases might be affected by human actions. A rise
in temperature of about 5°C (9°F) in the next fifty years would be equal to
a rate of climate change almost ten times faster than the average observed
rate of change. Temperature changes of this magnitude could transform
patterns of rainfall, drought, growing seasons and sea level.
The greenhouse effect is a well known theory. Fourier's concept
of planetary energy balance began the current understanding of the
greenhouse effect, which depends on the principle of an energy balance
of the asymmetric influence of the atmosphere on incoming light versus
outgoing infrared.
The sun is the main source of the earth's climate has surface
temperatures of about 6,000°C (10,800°F) which produce radiant energy
at very short wavelengths. Almost half this energy reaches the earth's
surface.
Particles and gases in the earth's atmosphere absorb about 25% of
this energy and 25% is reflected back to space by the atmosphere, mostly
from clouds. About 5% of the incoming solar radiation is reflected back
to space from the surface of the earth, mostly from bright regions such as
deserts and ice fields. A 1-square-meter surface (39 inches by 39 inches),
placed above the atmosphere will collect about 1,370 watts of radiant