projected a 1.8° to 4.0°C (3.2° to 7.2°F) increase in
global temperature by the year 2100. The IPCC predicts
that we will observe higher maximum temperatures and
more hot days over nearly all land areas, higher mini-
mum temperatures, fewer frost days, fewer cold days,
and an increase in the heat index. We may also experi-
ence more intense precipitation events over many areas,
an increased risk of drought in the continental interiors
in the mid-latitudes, and stronger hurricanes in some
coastal areas.
Causes of Global Climate Change
Carbon dioxide (CO 2 ) and certain trace gases, including
methane (CH 4 ), nitrous oxide (N 2 O), chlorofluorocar-
bons (CFCs), and tropospheric ozone (O 3 ), accumulate
in the atmosphere as a result of human activities. The
concentration of atmospheric carbon dioxide has in-
creased from about 288 parts per million (ppm) approxi-
mately 200 years ago (before the Industrial Revolution
began) to 394 ppm in 2011 (}ÕÀiÊ°È). According to
the U.N. Food and Agriculture Organization, burning
carbon-containing fossil fuels accounts for about 70 to
75 percent of human-generated CO 2 increase. The re-
maining 25 to 30 percent is released through deforesta-
tion, particularly when people fell or burn tropical rain
forests. By 2050 the concentration of atmospheric CO 2
may be double what it was in the 1700s.
The combustion of gasoline in your car’s engine
releases not only CO 2 but also N 2 O, which triggers the
production of tropospheric ozone. Various industrial
processes, land-use conversion, and the use of fertiliz-
ers also produce nitrous oxide. CFCs (discussed later
in the chapter as they relate to depletion of the strato-
spheric ozone layer) are chemicals released into the
atmosphere from old, leaking refrigerators and air con-
ditioners. Methane is produced by the decomposition
of carbon-containing organic material by anaerobic
bacteria in moist places as varied as rice paddies, sani-
tary landfills, and the intestinal tracts of large animals.
Tundra that is thawing due to warmer global tempera-
tures also contributes methane—an example of an un-
fortunate feedback.
Global climate change occurs because these gases
ab sorb infrared radiation—that is, heat—given off by
Earth’s surface. This absorption slows the natural flux of
heat into space, warming the lower atmosphere.
Carbon dioxide (COÓ) in the atmosphere,
£xnÊÌÊ«ÀiÃiÌÊUÊ}ÕÀiÊ°ÈÊ
Note the steady increase in the concentration of atmospheric
CO 2 since 1958, when measurements began at the Mauna Loa
Observatory in Hawaii. This location was selected because it is
far from urban areas where factories, power plants, and motor
vehicles emit CO 2. The seasonal fluctuations correspond to
winter (a high level of CO 2 ), when plants are not actively growing
and absorbing CO 2 , and summer (a low level of CO 2 ), when plants
are growing and absorbing CO 2.1958 62 66 70 74 78 82 86 90 94 98 2002 06 1014
YearCarbon dioxide concentration (parts per million)320312328336344352360368376384392400Winter (high)Summer (low)Annual averageBased on data from the National Oceanic and Atmospheric Administration (NOAA).Photo from Jonathan Kingston/National Geographic Creative/Getty ImagesBecause CO 2 and other gases
trap the sun’s infrared radiation
somewhat like glass does in a
greenhouse, they are called green-
house gases. Greenhouse gases
accumulating in the atmosphere
as a result of human activitiesgreenhouse gases
Gases—including
water vapor, carbon
dioxide, methane, and
certain other gases—
that absorb infrared
radiation.Interpreting Data
If this rate of CO 2 increase continues, in
what year will the concentration exceed
450 ppm? Explain your answer.Global Climate Change 223