222 CHAPTER 9 Global Atmospheric Changes
- List the five main greenhouse gases and
describe the enhanced greenhouse effect. - Discuss some of the potential effects of global
climate change. - Give examples of strategies to mitigate or
adapt to global climate change.
E
arth’s average temperature is based on
daily measurements taken at several thou-
sand land-based meteorological stations
around the world, as well as data from
weather balloons, orbiting satellites, transoceanic ships,
and hundred of sea-surface buoys with temperature
sensors. These data show that the years 1998 and 2001
through 2010 were the hottest since records began in
the 1880s, and 2010 tied with 2005 as the hottest years
on record. According to the National Oceanic and At-
mospheric Administration (NOAA), global tempera-
tures in those years may have been the highest in the
last millennium. (Although widespread thermometer
records have been assembled only since the mid-19th
century, scientists reconstruct earlier temperatures us-
ing indirect climate evidence in tree rings, lake and
ocean sediments, small air bubbles in ancient ice, and
coral reefs.) The last two decades of the 20th century
were its warmest (}ÕÀiÊ°x).
Global Climate Change
LEARNING OBJECTIVES
Other evidence also suggests an increase in global
temperature. Several studies indicate that spring in the
Northern Hemisphere now comes about six days ear-
lier than it did in 1959, and autumn comes five days
later. Since 1949, the United States has experienced
an increased frequency of heat waves, resulting in in-
creased heat-related deaths among elderly and other
vulnerable people. In the past few decades, the sea
level has risen, glaciers worldwide have retreated, and
while hurricanes may not have become more frequent,
higher ocean surface temperatures have made them
increasingly severe.
Scientists around the world have been research-
ing global climate change for the past 50 years. As the
evidence has accumulated, those most qualified to ad-
dress the issue have reached a strong consensus that
the 21st century will experience significant climate
change. Almost all of that change will be attributed to
anthropogenic (caused by humans) release of green-
house gases into the atmosphere.
In response to this growing consensus, govern-
ments around the world organized the United Nations
Intergovernmental Panel on Climate Change (IPCC).
With input from hundreds of climate experts, the IPCC
provides a definitive scientific assessment of global cli-
mate change. In its most recent (2007) report, the IPCC1960 1970 1980 1990 2000 2010
YearMean annual global temperature (°C)14.013.814.214.414.614.8Based on data from the Global Land-Ocean TemperatureIndex, Goddard Institute of Space Studies (NASA).Photo from Scientific Visualization Studio, NASA GoddardSpace Flight Center.i>Ê>Õ>Ê}L>ÊÌi«iÀ>ÌÕÀi]Ê£ÈäÊÌÊ«ÀiÃiÌÊUÊ}ÕÀiÊ°xÊ
Data are presented as surface temperatures
(°C) for each year since 1960. The
measurements, which naturally fluctuate,
show the warming trend of the past several
decades. The dip in global temperatures in
the early 1990s was caused by the eruption
of Mount Pinatubo in 1991.