Like the glass panes in a greenhouse,
certain gases in the Earth’s atmosphere permit the Sun’s radiation to
heat Earth. At the same time, these gases retard the escape into space
of the infrared energy radiated back out by Earth. This process is
referred to as the greenhouse effect. These gases, primarily carbon
dioxide, methane, nitrous oxide, and water vapor, insulate Earth’s
surface, helping to maintain warm temperatures. Without these gases,
Earth would be a frozen planet with an average temperature of about
-18°C (about 0°F) instead of a comfortable 15°C (59°F). If the
concentration of these gases rises, they trap more heat within the
atmosphere, causing worldwide temperatures to rise.
Within
the last century, the amount of carbon dioxide in the atmosphere has
increased dramatically, largely because people burn vast amounts of
fossil fuels—coal and petroleum and its derivatives. Average global
temperature also has increased—by about 0.6 Celsius degree (1 Fahrenheit
degree) within the past century. Atmospheric scientists have found that
at least half of that temperature increase can be attributed to human
activity. They predict that unless dramatic action is taken, global
temperature will continue to rise by 1.4 to 5.8 Celsius degrees (2.5 to
10.4 Fahrenheit degrees) over the next century. Although such an
increase may not seem like a great difference, during the last ice age
the global temperature was only 2.2 Celsius degrees (4 Fahrenheit
degrees) cooler than it is presently.
Within
the last century, the amount of carbon dioxide in the atmosphere has
increased dramatically, largely because people burn vast amounts of
fossil fuels—coal and petroleum and its derivatives. Average global
temperature also has increased—by about 0.6 Celsius degree (1 Fahrenheit
degree) within the past century. Atmospheric scientists have found that
at least half of that temperature increase can be attributed to human
activity. They predict that unless dramatic action is taken, global
temperature will continue to rise by 1.4 to 5.8 Celsius degrees (2.5 to
10.4 Fahrenheit degrees) over the next century. Although such an
increase may not seem like a great difference, during the last ice age
the global temperature was only 2.2 Celsius degrees (4 Fahrenheit
degrees) cooler than it is presently.
The
consequences of such a modest increase in temperature may be
devastating. Already scientists have detected a 40 percent reduction in
the average thickness of Arctic ice. Other problems that may develop
include a rise in sea levels that will completely inundate a number of
low-lying island nations and flood many coastal cities, such as New York
and Miami. Many plant and animal species will probably be driven into
extinction, agriculture will be severely disrupted in many regions, and
the frequency of severe hurricanes and droughts will likely increase.,
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