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Climate Change
• Over the last four million years there have
been at least 30 “Ice Ages” - glacial periods
lasting 90,000 years or more.
• They were separated by relatively short
interglacial period, each about 10,000 to
15,000 years long.
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Temperature/900,000 yrs ago
Figure 9.11a
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Source: Data from National Climate Data Center/NESDIS/NOAA, 1998.
• About 110,000 years ago, an interglacial
period ended and a new ice age began.
Planetary ice caps expanded, oceans fell,
and ice sheets advanced. In North America
this was known as the Laurentide glaciation,
which reached its maximum extension
approximately 18,000 years ago.
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Temperature/10,000 yrs ago
Figure 9.11b
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Ice sheets reached
as far south as
London, England
and St. Louis,
Missouri. Some
continental
ice sheets
became as
thick as
3km (~1.9 miles)
Then about 15,000 years ago a warming period
began marking the end of the ice age and the
beginning of the current interglacial period.
• In the last thousand years, there was a
Medieval Warm period between about
1000CE and 1450CE. Following this was a
“Little Ice Age” when temperatures fell,
glaciers advanced once again, and winters
were severe. The Little Ice Age ended
about 1900 and a new warming trend began.
Settlement
of North
America
18,000
years ago
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Temperature/1,000 yrs ago
Figure 9.11c
Start of Industrial Revolution
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Ice Cores
At the Vostok station in Antarctica, scientists are obtaining
ice core samples down to ice depths exceeding 3600 m.
(Courtesy Claude Lorius, LLGE)
• For the past 100 years temperatures have
been directly measured at over 2,000
meteorological stations around the world
IPCC
• In 1988 the World Meteorological
Organization (WMO) and the United
Nations Environment Program (UNEP)
formed an Intergovernmental Panel on
Climate Change (IPCC).
• The panel analyzed the available data and
came to the consensus that worldwide
average temperatures have significantly
increased over the past century.
Three conclusions
1. Over very long periods of time, global
temperatures have varied greatly, rising as
much as 8°C between glacial and
interglacial periods
Three conclusions
2. During the past 118 years, average global
temperatures have tended to increase and
are continuing to increase.
Three conclusions
3. On average, the earth’s atmosphere is
warmer now than at any other time in the
last 1,000 years. Furthermore, the rate of
atmospheric warming is greater now than
at any earlier time during the past 1,000
years.
Why ?
• Some people argue that because the average
global temperature during the Medieval
Warm period was approximately 1°C
(~1.8°F) than those recorded during 1951 1980, the current temperature increase of
0.8°C (~1.4°F) is “natural” and not due to
human influence at all.
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Climate change (earth's orbit)
Figure 9.12a
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However
1. The current global warming trend appears
to have started at the time of the Industrial
Revolution
2. Analyses show that pre-industrial CO2
levels were about 280ppmv and that they
have risen by 1998 to 365 ppmv, an
increase of ~30%
3. Carbon dioxide levels are at their highest
level in 160,000 years
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Global warming and CO2
Figure 9.1
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Source: Data from Dave Keeling and Tim Whorf, Scripps Institute of Oceanography.
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Greenhouse diagram
Figure 9.3
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Carbon dioxide emissions
Figure 9.16
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Source: Data from World Resources 1998-99, World Resources Institute.
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Greenhouse gases
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Climate changes and species
Figure 9.15
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Source: Data from Margaret Davis and Catherine Zabriskie in Global Warming and Biological Diversity, ed. by Peters and
Lovejoy, 1991, Yale University Press.
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Greenhouse precipitation
Figure 9.14
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Temperature/120 yrs ago
Figure 9.11d
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