Download 45:211: Environmental Geography

Module 8
Atmosphere and Climate
45:211: Environmental Geography
Learning Objectives
• Explain what is meant by the term “global
warming”
– Know the major greenhouse gases and their main
sources
– Describe the objectives of the Kyoto Agreement
– Describe examples of climate change impacts
• Explain the link between CFCs and ozone
depletion
– Describe the objectives of the Montreal Protocol
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Atmosphere
• The layers of air masses surrounding the
Earth are collectively referred to as the
atmosphere.
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How is atmosphere important?
• The atmosphere controls climate - which
keeps us comfortable and safe
– Ozone depletion and increasing GHGs are a
current concern
• We use it to dispose of wastes
– within the past century, the composition of the
atmosphere has been changed on the scale of
human time
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Atmospheric Layers
• Troposphere
– Where weather is.
– Where most of the
pollutants are.
– Thickness - 15 km at
the equator, and about
8 km over the poles.
– It is well mixed by air
motions which disperse
pollutants
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Atmospheric Layers
• Stratosphere
– Extends from about 20-50
km. The ozone layer.
• This “good” ozone protects
us from solar UV radiation
– Very thin air with virtually
no weather or turbulence.
– Compared to Troposphere,
the volume of water vapor
is 1000 x less, and volume
of ozone is 1000 x greater.
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Ozone: the Good and the Bad
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Climate Control and Atmospheric
Composition
• Earth’s surface absorbs incoming solar radiation,
and converts it into heat.
– Some of this heat escapes into space
– Some is absorbed by greenhouse gases in the
atmosphere, warming the air
 Heat is radiated back to Earth, warming it by about 33oC
– This trapping of heat is called the Greenhouse
Effect
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Greenhouse Effect
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Trace Gases
• Most of Earth’s
atmosphere is
climatically
neutral
– the important
gases are present
in trace amounts
only
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Anthropogenic Climate Change
• The Greenhouse Effect that warms the surface
of the Earth occurs because of a few minor
constituents of the atmosphere (GHGs) that
absorb IR radiation very efficiently.
– As a result of human activities, the concentrations
of GHGs is increasing.
– This will lead to a warmer Earth, the amount
depending on other climate effects.
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Main Greenhouse Gases
• Carbon Dioxide - fossil fuel burning (80%
of emissions), deforestation (20%).
• Methane - breakdown of organic material
by anaerobic bacteria.
• Nitrous Oxide - biomass burning,
breakdown of nitrogen-rich products.
• Chlorofluorocarbons - refrigerants.
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What is Global Warming
• The term Global Warming is widely used to
describe a potentially dramatic rise in the
average global temperature as a result of the
continuing and accelerating buildup of
greenhouse gases in the atmosphere.
– It is different to the problem of ozone depletion
in the Stratosphere, although this also arises
from atmospheric pollution
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Atmospheric carbon dioxide
(CO2):1750 to present
370
parts per million volume
360
350
340
Siple Station (1750-1970)
330
Mauna Loa (1958-present)
320
310
300
290
280
270
1750
1800
1850
1900
1950
2000
Data Source: C.D. Keeling and T.P. Whorf, Atmospheric CO2 Concentrations (ppmv) derived from in situ air samples collected at Mauna Loa
Observatory, Hawaii, Scripps Institute of Oceanography, August 1998. A. Neftel et al, Historical CO2 Record from the Siple Station Ice
Core, Physics Institute, University of Bern, Switzerland, September 1994. See http://cdiac.esd.ornl.gov/trends/co2/contents.htm
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The Historical Data
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Cumulative Radiative Forcing of
GHG Emissions
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Temperature Change, 1400-2000
(Northern Hemisphere)
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Global climate change …..
• We frequently view
climate change in
terms of a global
average - but nobody
lives in a global
average climate.
– Location (geography)
is important.
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… is spatial
Climate change is not uniform
over the Earth.
Magnitude varies with location
And with season ….
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Canada: Temperature Changes
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Possible Effects of A Warmer
World
• Higher temperatures (wider extremes?)
• Changes in precipitation - wetter and drier
• Rising sea level (e.g. Fig. 17.16 in text) and
melting of ice bodies
• Changes in food production and ecosystems
– Longer growing seasons
– Range of tolerance
– See Figure 17.18 in text
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Ecozones
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Rising Seas: The Future
• One of the most
striking
consequences of
global warming
will be the
associated rise in
global mean sea
level.
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Change in Arctic Ocean:
Summer Ice Cover
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Permafrost in Canada
Present
2xCO2
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Good or Bad?
• Whether global warming is “good” or “bad”
is a matter of perspective (and self-interest)
– There will be “winners” and “losers”
– This is not a scientific issue but social and
economic
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Slowing Global Warming
• Reduce emissions - the quickest, cheapest,
most effective way to reduce emissions is to
use energy more efficiently.
• Slow population growth - if we cut per
capita greenhouse gas emissions in half, but
double the population - we do not help the
problem.
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Cumulative carbon emissions,
1950-1996
15,715
China
11,651
Germany
8,504
Japan
7,415
United Kingdom
India
4,235
Canada
4,054
South Africa
2,331
Mexico
2,118
Australia
2,080
Brazil
1,557
Korea, Rep.
1,361
966
Indonesia
50,795
United States
0
10,000
20,000
30,000
40,000
50,000
60,000
Million tons of carbon
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Data Source: Marland et al, 1999. Carbon Dioxide Information Analysis Center.
How much will the Kyoto Protocol
reduce emissions?
Business-as-usual
Kyoto Protocol scenario
Billion tons of carbon
8
6
8.0
7.6
6.4
5.8
4
2
0
1990
1995
2000
2005
Data Sources: United States Department of Energy, Energy Information Administration, International
Energy Outlook, 1998 and 1999.
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2010
Ozone Depletion
• Ozone is formed in the Stratosphere when
high-energy solar ultraviolet radiation splits
molecular oxygen (O2) into atomic oxygen
(O+O).
– The atomic oxygen may then combine with
another oxygen molecule to form triatomic
oxygen (O3, ozone).

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Problem:
• In the 1970s, it was discovered that CFCs
were reducing the concentration of ozone in
the stratosphere.
– CFCs take 10-20 years to diffuse up into the
stratosphere, but they are long-lived.

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• In the stratosphere, UV radiation breaks down
CFC molecules, releasing atomic chlorine. A free
chlorine atom reacts with an ozone molecule,
converting it from O3 to O2.
Cl + O3 = ClO + O2
Unstable
Cl + O
Cl + O3 = ClO + O2
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Consequences of Ozone Loss
• More UV radiation will reach Earth’s
surface.
– More/worse sunburns - leading to increased
rates of skin cancers
– Suppression of immune system
– Lower crop yields
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Montreal Protocol (1987)
• Reduce production of CFCs and phase out
their use by 2000
– 82 nations have signed the agreement
– U.S. stopped production of CFCs in 1996.
• As a result of these efforts, the levels of
CFCs in the atmosphere will stabilize and
should decline in the future.
– But CFCs will remain in the atmosphere for
several decades (residence time)
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Summary
• Global warming is due to increased levels
of greenhouse gases.
– Impacts of climate change are varied and may
be viewed as positive and negative.
– Kyoto Treaty calls for emissions reductions.
• CFC’s are thought to lead to the destruction
of the ozone layer.
– Increase of UV radiation poses a health risk.
– Their use is being curtailed through the
Montreal Protocol.
45:211: Environmental Geography