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more than 11 billion in 2200. Other experts predict that numbers will continue to rise into the foreseeable fu-
ture, to as many as 19 billion people by the year 2200.
Although rates of population increase are now much slower in the developed world than in the developing
world, it would be a mistake to assume that population growth is primarily a problem of developing countries.
In fact, because larger amounts of resources per person are used in developed nations, each individual from the
developed world has a much greater environmental impact than does a person from a developing country. Con-
servation strategies that would not significantly alter lifestyles but that would greatly lessen environmental im-
pact are essential in the developed world.
In the developing world, meanwhile, the most important factors necessary to lower population growth rates
are democracy and social justice. Studies show that population growth rates have fallen in developing areas
where several social conditions exist. In these areas, literacy rates have increased and women receive economic
status equal to that of men, enabling women to hold jobs and own property. In addition, birth control informa-
tion in these areas is more widely available, and women are free to make their own reproductive decisions.
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 tem-
perature also has increased – by about 0.6 Celsius degrees (1 Fahrenheit degree) within the past century. At-
mospheric scientists have found that at least half of that temperature increase can be attributed to human activ-
ity. They predict that unless dramatic action is taken, global temperature will continue to rise by 1,4 to 5,8 Cel-
sius 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.
The ozone layer, a thin band in the stratosphere (layer of the upper atmosphere), serves to shield Earth from
the Sun’s harmful ultraviolet rays. In the 1970s, scientists discovered that chlorofluorocarbons (CFCs)-chemicals
used in refrigeration, air-conditioning systems, cleaning solvents, and aerosol sprays-destroy the ozone layer.
CFCs release chlorine into the atmosphere; chlorine, in turn, breaks down ozone molecules. Because chlorine is
not affected by its interaction with ozone, each chlorine molecule has the ability to destroy a large amount of
ozone for an extended period of time.
The consequences of continued depletion of the ozone layer would be dramatic. Increased ultraviolet radia-
tion would lead to a growing number of skin cancers and cataracts and also reduce the ability of immune sys-
tems to respond to infection. Additionally, growth of the world’s oceanic plankton, the base of most marine
food chains, would decline. Plankton contains photosynthetic organisms that break down carbon dioxide. If
plankton populations decline, it may lead to increased carbon dioxide levels in the atmosphere and thus to
global warming. Recent studies suggest that global warming, in turn, may increase the amount of ozone de-
stroyed. Even if the manufacture of CFCs is immediately banned, the chlorine already released into the atmos-
phere will continue to destroy the ozone layer for many decades.
In 1987, an international pact called the Montreal Protocol on Substances that Deplete the Ozone Layer set
specific targets for all nations to achieve in order to reduce emissions of chemicals responsible for the destruc-
tion of the ozone layer. Many people had hoped that this treaty would cause ozone loss to peak and begin to de-
cline by the year 2000. In fact, in the fall of 2000, the hole in the ozone layer over Antarctica was the largest
ever recorded. The hole the following year was slightly smaller, leading some to believe that the depletion of
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