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Global warming case study
A case study is a story about an issue or problem. The case presents the information, facts, and data needed to analyze the problem and to consider the possible consequences and solutions. The purpose of this case study is to help you connect what you already know about global warming and climate change with the knowledge scientists have about the way that global warming and climate change affect the Earth. As you work through the case study, answer the questions and complete the global warming issue analysis worksheet. Think about the causes of global warming and its
effects on the environment, where global warming is located, and how the problem of
global warming might be solved.
Does the Earth’s Temperature Vary Over Time?
Geologists and climatologists are scientists who study
global warming and climate change. These specialists
who study the Earth’s climate have concluded that the
Earth’s temperature has varied over the past four million
years, and that at least 30 glacial periods have
occurred. These glacial periods can be described as
time periods when the Earth’s temperature was cooler
than it is today, and many continental glaciers occurred.
These glacial periods were separated by time periods
when the Earth’s temperature became warmer, known
as interglacial periods. During these cooler time
periods, the polar ice caps expanded, ocean levels fell, and glaciers advanced over the
continents. The last glacial period in North America started about 18,000 years ago and
extended from Canada south to St. Louis, Missouri. As the Earth entered a warming
period (about 15,000 years ago), this glacier began to melt and retreat. The advancing,
melting, and retreating resulted in the formation of the Great Lakes. With the glacial
periods, the Earth’s temperature was cooler, and with the melting periods, the Earth’s
temperature was warmer.
One way scientists estimate the changes in the Earth’s temperature is through the
physical and chemical analysis of ice core samples taken from the polar ice caps in the
Arctic and Antarctic regions. Based on ice core samples, scientists have been able to
estimate the Earth’s temperature as far back as 160,000 years. The variations in the
Earth’s temperature for the past 140 years and the past 1,000 years are shown below in
Figure 1.
Case Study
NASA
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Carbon Dioxide and Global Warming Case Study
- Based on the data in Figure 1, what can you say about the Earth’s
temperature during the past 1,000 years?
Figure 1. The Earth’s Past Temperature.
Source: IPCC
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Carbon Dioxide and Global Warming Case Study - Based on the data in Figure 1, what can you say about the Earth’s
temperature during the past 100 years? - Based on the data in Figure 1 is the Earth entering a cool or warm period?
What evidence supports your view?
Has the Earth’s Temperature Increased?
Today, scientists are able to measure the Earth’s actual temperature from over 2,000
meteorological stations around the world. In 1995, this data was analyzed by the United
Nations Intergovernmental Panel on Climate Change (IPCC). The IPCC scientists
concluded that the Earth’s temperature had increased during the last century. The
average temperatures from 1880 and on are shown in Figure 2.
Figure 2. Changes in the Earth’s Temperature. Source: NOAA - How does the data in Figure 2 support the idea that the Earth’s
temperature is increasing? Why?
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Carbon Dioxide and Global Warming Case Study
Based on the ice core data and the actual temperature data, scientists have concluded
that:
ï‚· Global temperatures have varied over time with cool (glacial) periods and
warm periods.
ï‚· Over the past 100 years, global temperatures have tended to increase and
now appear to be continuing to increase.
 The Earth’s temperature is warmer today than at any other time in the past
1,000 years.
Could an Increase in Atmospheric Carbon Dioxide Be the Cause of Global
Warming?
Atmospheric carbon dioxide levels have mostly
been measured at the Mauna Loa Observatory in
Hawaii. The data collected since 1958 shows a
trend toward increasing atmospheric carbon
dioxide levels, as well as seasonal variation—
peaks during the winter, and valleys or troughs
during the summer (Figure 3). Scientists have
also measured air bubbles in the Vostok ice core
in order to estimate the level of atmospheric
carbon dioxide before 1958 (Figure 4). Scientists
call ice core data proxy data because it is not a
direct measure of carbon dioxide levels or
temperature (see box). The analysis of this data
shows that carbon dioxide levels have increased from about 220 parts per million (ppm)
to about 380 ppm today.
Scientists generally mark the beginning of the Industrial Revolution in 1750 with the first
burning of coal (a fossil fuel) as an energy source. The burning of coal releases carbon
dioxide into the atmosphere. Most scientists agree that the burning of fossil fuels (coal,
petroleum, and natural gas) is the primary cause for the increase in atmospheric
carbon dioxide levels. Today about 85% of the total energy used in the United States
is derived from fossil fuels, and this use contributes about 97% of the carbon dioxide
released by the US into the Earth’s atmosphere. Utilities emit about 35% of the total
carbon dioxide released into the atmosphere followed by the transportation (about
31%), industrial (about 21%), commercial (5%), and residential (7%) sectors. The
average annual increase in atmospheric carbon dioxide levels from fossil fuel use in the
United States is about 1%. Since the Industrial Revolution global atmospheric carbon
dioxide levels have increased about 30%.
Proxy Data
Scientists collect proxy data
from natural sources such as
tree rings, ice cores, fossil
pollen, ocean sediments, and
corals. By analyzing these
proxy sources, scientists can
construct a picture of the
Earth’s climate beyond the
years of actual measurement.
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Carbon Dioxide and Global Warming Case Study
Figure 3: Carbon Dioxide Levels, Mauna Loa Observatory, Hawaii
Figure 4. Vostok CO2 and Temperature Data
10.Based on the data in Figure 4, how would you explain the relationship between
the Earth’s temperature and the level of atmospheric carbon dioxide?
The top red line is carbon dioxide
The bottom blue line is temperature
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Carbon Dioxide and Global Warming Case Study
IPCC scientists and others, using computer models and different world population
growth rates and economic development scenarios projected an increase in
atmospheric carbon dioxide levels (Figure 5). The high-emission scenario assumes
current rates of population growth, high economic growth, and the continued use of
fossil fuels. The mid-range scenario assumes that world population growth will slow,
economic activity will increase, and the use of fossil fuels will continue. The lowemission scenario assumes that the world population and economic development will
stabilize and that fossil fuel use will decline. All three scenarios project an increase in
atmospheric carbon dioxide levels, ranging from about 470 ppm for the low-emission
scenario to almost 900 ppm for the high-emission scenario.
11.Why was it important for the IPCC to include world population growth and
economic development in their model for projecting carbon dioxide levels?
12.Based on these projections what might happen to the Earth’s temperature
in the future?
Figure 5. CO2 Projections. Source: IPCC
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Carbon Dioxide and Global Warming Case Study
How is the Increase in Atmospheric Carbon Dioxide Linked to Global Warming?
Carbon dioxide, water vapor,
nitrous oxide, and methane are
naturally occurring gases in the
Earth’s atmosphere. These gases
work together as a type of filter that
lets some of the sun’s energy (visible
light) pass through the atmosphere
and reach the Earth’s surface where
the light is absorbed and changed
into heat (infrared radiation). This
heat then radiates back upwards into
the Earth’s atmosphere. The carbon
dioxide, water vapor, nitrous oxide,
and methane in the atmosphere
work again as a filter and trap some
of this heat, and re-radiate it back
towards the Earth’s surface, warming
the Earth with the earth’s own heat
(Figure 6). This natural process is
known as radiative forcing and is
similar to the way the glass walls and
ceilings of a greenhouse work to let light in, but to prevent heat loss. Since carbon
dioxide, water vapor, nitrous oxide, and methane work like the glass ceilings of a
greenhouse, letting the light through and keeping the Earth’s reflected heat in, these
gasses are known as greenhouse gases, and this natural heating process is called the
greenhouse effect. Naturally occurring levels of carbon dioxide, water vapor, nitrous
oxide, and methane are essential to life on earth. Without these greenhouse gases to
hold in the warmth of the sun, the Earth’s temperature would be much cooler.
The atmospheric content, or concentration, of greenhouse gases has naturally varied
over time. Since the Industrial Revolution, human activities such as burning fossil fuels
(oil, natural gas, and coal) and cutting down trees have added greenhouse gases,
especially carbon dioxide, to the atmosphere
