Theme: The Air We Breathe
Topic 6. Global warming
A. Greenhouse effect

Solar energy from the sun heats the earth and the latter radiates energy back to the space.

Atmospheric greenhouse gases are responsible for the natural greenhouse effect:
— Trap some of the outgoing energy, and
— Retain heat that maintains a constant range of temperatures for the planet.

The atmosphere (contains greenhouse gases) acts like the glasses in a greenhouse,
—
Light (radiation) passes through the glass and absorbed by the objects inside the greenhouse.
— Objects are warmed and emit heat energy that mostly cannot pass through glass.
— The temperature inside the greenhouse rises.

Without greenhouse gases, the average temperature of the earth will be much lower than
now (minus >10°C and uninhabitable for the living organisms).
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The following figure shows how a greenhouse retains heat energy:
Figure 1. The planet traps incoming radiant energy to keep warm as a greenhouse.

The greenhouse gases include carbon dioxide, methane, nitrous oxide (N2O),
chlorofluorocarbons (CFCs) and Ozone (O3), etc.
B. Global warming and the evidence
Global warming

It means the gradual heating up of the earth (increase in temperature).

There is evidence of global warming from polar icecap including:
— National Snow and Ice Data Center (NSIDC) claimed that examination of springtime
ice thickness in the Arctic Ocean indicates that the mean ice thickness decreased 1.5
meters between the mid-1980s and early 1990s.

According to the National Academy of Sciences, the Earth's surface temperature has risen
by about 1ºF (0.375ºC) in the past century.
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
Figure 2 shows the change in global average temperature in the past century.
Figure 2. The global average temperature changes in the past century.

Global surface temperatures have increased since the late 19th century. Warming has been
recorded in both the northern and southern hemispheres, and over the oceans.

In the past century, the temperature increased faster.
C. Causes of global warming

International Panel on Climate Change (IPCC) claimed that:
— The recorded global warming is not likely as the result of natural variability alone.
— Human activities are at least partially responsible.

Human activities have been increasing the concentrations of greenhouse gases.
— Increase in atmospheric greenhouse gases strengthens greenhouse effect.
— The major greenhouse gas responsible for the global warming is carbon dioxide. The
sources are:

Power stations, motor vehicles and industry that burn fossil fuels in producing
electricity. For example:
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Combustion
C (in fossil fuel)
+
O2 (g)
CO2 (g)
360
355
Parts per million (ppm) carbon dioxide
350
345
340
335
330
325
320
315
1955
1960
1965
1970
1975
year
1980
1985
1990
1995
2000
Figure 3. The tropospheric carbon dioxide concentrations from 1960 – 1995 (Data from
Electric Power Research Institute, U.S.A.).
— The increasing trend may be partially related to the global temperature increases in
the past twenty years.
— Experts of United Nations predicted that:

Carbon dioxide emissions may reach as high as 100 Giga tonnes by 2100, a
five-fold increase of current level if no measures are taken.
— Figure 4 shows the concentrations of tropospheric nitrous oxide (N2O) from 1976 to
1990.
— Nylon production, burning of nitrogen containing fossil fuel and breakdown of
nitrogen fertilizer release the gas and responsible for the increase.
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Changes of tropospheric nitrous oxide concentration in 1976 - 1990
310
309
Parts per billion (ppb) Nitrous oxide
308
307
306
305
304
303
302
301
300
299
1974
1976
1978
1980
1982
year
1984
1986
1988
1990
1992
Figure 4. The tropospheric nitrous oxide concentrations from 1960 – 1995 (Data from
Electric Power Research Institute, U.S.A.).

Deforestation
- decreases the number of vegetation that can convert the atmospheric carbon dioxide to
oxygen, which keeping the atmospheric concentration in a constant range.
Suggested Student Activity：
Investigate the effect of carbon dioxide on plant growth.
Is Global warming a natural phenomenon?

Global warming has been a serious environmental issue for years.

There are arguments on the issue and some scientists claim that global warming is a
natural phenomenon and we do not need to worry about it.
Suggested Student Activity：
Information search and report on ‘controversy on global warming’.
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D. Consequence of global warming

Agriculture, forests, water resources, wildlife and our health are vulnerable to global
warming and the consequent climatic changes.

The IPCC concluded “climate change is likely to have wide–ranging and mostly adverse
impacts on human health with significant loss of life”.
— A few degrees of warming can cause more heat–related death and illness.

Global warming would double or triple heat–related diseases among the elderly
and people with heart diseases.
— Increases the spread of tropical diseases, such as malaria northward in some areas of
the world.
— Intensifies the Earth’s hydrological cycle:

Some areas receive more rain while other areas will be drier.

Flooding and drought will be more frequent and they may cause disasters.
— Warming causes glaciers to melt and oceans to expand. IPCC projects that sea level
will rise 0.16 – 0.94 m (½ foot to 3 feet) over the next century. This may threaten
costal areas.
— Disturbing the harmony of the ecosystems in the planet. The temperature rise affects
the flow of energy and materials in ecosystems.
Suggested Student Activity：
Debate on the impact of global warming on Hong Kong.
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E. What can we do about global warming?

Government formulates and implements measures to mitigate climate changes and its
possible impacts, and to limit greenhouse emissions.

Reduce greenhouse gases emission
— Cut down the industrial emission of greenhouse gases by applying environmental
friendly technologies, and promote the sustainable use of energy.

For example, higher energy efficient and energy saving machines and electrical
appliances applied.

Replacing fossil fuels with renewable energy including hydroelectric energy and solar
energy, etc.
— To cut down the emission of carbon dioxide, water vapor and nitrous oxide in
combustion.

Implement reforestation program that intensifies the nature’s ability in purifying air
pollutants, and converting carbon dioxide to oxygen.
Reference:
1. Johansen, B. E. (2002). The Global Warming Desk Reference. Greenwood Press.
2. McWhirter, S. (2001) Global Warming & the Greenhouse Effect [video recording].
Huntsville, Tex.: Educational Video Network, Inc.
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3. Moore, T. G. (1995) Global Warming: a Boon to Humans and other Animals. Stanford,
California: Stanford University.
4. Roleff, T. L., Barbour, S. and K. L. Swisher (1997) Global Warming: Opposing
Viewpoints. San Diego, California: Greenhaven Press.
5. U.S. Environmental Protection Agency (USEPA). USEPA web site, global warming. Web
address: http://yosemite.epa.gov/oar/globalwarming.nsf/content/index.html
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