Energy and Changes in the Environment - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 44

merged into the International Alliance of Automobile Manufacturers
claims that today's automobiles are up to 96% less polluting than cars 35
years ago but automobiles still produce a quarter of the carbon dioxide
generated annually in the United States.
GLOBAL WARMING
Carbon dioxide, in combination with other greenhouse gases such
as methane and ozone, can trap the sun's heat. In the century from 1890 to
1990, the average surface temperature of the earth increased by 0.3 to 0.6
degrees Celsius. This temperature rise, which has lengthened the growing
season in parts of the northern hemisphere, may have occurred naturally,
although such a change would be notable.
The global warming issue has become a major concern. But, it was
not that long ago that global cooling was being promoted. During the
1970s, several extreme weather events, including freezing conditions in
Florida, produced fears over decreasing temperatures. In 1974, the CIA
even issued a report claiming that decreases in temperature could affect
America's geopolitical future.
In the 1980s, the focus shifted to global warming, as a result of the
unusual drought and heat wave of 1988. Climate scientist James Hansen
reported to Congress that he was 99% sure that the greenhouse effect was
contributing to global warming. This fueled a growing apprehension over
rising temperatures that had the attention of the media and the public.
Environmentalists obsessed over the role of modern life in global
warming used this attention to push goals such as improving air quality
and preserving forestland. Some studies indicate that human influence
accounts for 75% of the increase in average global temperature over the last
century, but others argue that up to nine other factors are more important
than human activity and Mars and Venus are also experiencing warming
trends.
Changes in global ocean currents or in the amount of energy emitted
by the sun could be a major part of the change. Most of industry including
the oil, gas, coal and auto companies see the problem as a theory in need of
more research, but many cry for serious action to reduce fossil fuel use.
Most scientists do not debate whether global warming has occurred,
they accept it, but the cause of the warming and future projections about
the results is questioned. The proposed National Energy Policy Act of 1988,