Geography Reference
In-Depth Information
atmosphere. Most reputable scientists believe that these substances are the cause of the current warm-
ing trend.
The global greenhouse
The commonly held scenario for why the atmosphere is heating up likens the atmosphere to a
greenhouse, whose glass panes allow sunshine to penetrate the structure, but then contain the
solar energy's heat and prevent it from escaping. Of course, no giant glass roof hovers over
planet Earth. But gases in the atmosphere do act in much the same way (Figure 18-6). When
these gases are scarce, a considerable amount of solar energy is able to radiate off Earth's sur-
face back into the coldness of space. When they are abundant, however, they produce an at-
mosphere that absorbs or “traps” this same heat, resulting in a warming atmosphere. The gases
that accomplish this are called
greenhouse gases
and the over-all process is referred to as the
greenhouse effect
.
Following are two of the primary contributors to global warming:
Effects of the Industrial Revolution:
Carbon dioxide (CO
2
) is the most prolific green-
house gas. Although it's a naturally occurring substance, substantial quantities of it are re-
leased to the atmosphere when fossil fuels, wood, and other organic matter are burned. In-
creased fuel con-sumption, especially as regards to fossil fuels, has been a hallmark of the In-
dustrial Revolution. Before it began, the carbon dioxide content of the atmosphere measured
about 274 parts per million (ppm). By the beginning of the present century, that number had
risen to more than 360 ppm. Because global consumption of fossil fuels continues to rise, one
can only expect increasing levels of greenhouse gases in the atmosphere, and with them the
likelihood of increasing temperatures.
Emissions vary geographically. Because economic development and fuel consumption go
hand-in-hand, understandably developed nations generate a much greater portion of annual
emissions than do developing ones. And because the United States is the world leader in fossil
fuel consumption (see Chapter 16), it makes sense that it also leads the world in greenhouse
gas emission. During the 20th Century, the U.S. was responsible for an estimated 30.3 percent
of global carbon dioxide emissions. Europe accounted for another 27.7 percent and the lands
of the former Soviet Union another 13.7 percent
Effects of deforestation:
This era of increased fuel consumption has been complemented
by a general process of deforestation — first in Eurasia, then in North America, and now in
the tropical rainforest areas. Trees take in carbon dioxide from the atmosphere and give off
oxygen. Thus, when trees are cut and consumed, they are no longer available to effect this ex-
