Download Radiation and Climate_Global Warming

Radiation and Climate
Greenhouse Gases and Global
Change
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Can we maintain our status?
• As long as concentrations of carbon dioxide and
other greenhouse gases in the atmosphere
remain relatively constant, the greenhouse effect
will comfortably maintain Earth’s average
temperature.
• The hydrologic cycle and the carbon cycle
maintain stable concentrations of water and
carbon dioxide in their respective reservoirs,
including the atmosphere.
• However, the effect of human activity must be
considered.
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“Spiraling-Up”
• If more CO2 is added to the atmosphere than can
be removed by natural processes, its
concentration will increase.
– If enough CO2 were added, the atmosphere could
retain enough additional IR radiation from the Sun to
increase Earth’s average surface temperature.
– CO2 stored in ice, water, and the frozen floors of
northern forests could also be released.
– A “spiraling-up” effect could occur, where warmer
temperatures produce more carbon dioxide, which
produces warmer temperatures, and so on.
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Hydrologic Cycle
• The hydrologic cycle must also be considered.
– The atmosphere contains about 12 trillion metric
tons of water vapor, a quantity so large that it
might seem impossible that human activity could
significantly affect it.
– However, if global temperatures increase, oceans
and other bodies of water will also become
warmer.
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Temperature and Water Vapor
• The amount of water vapor released increases as
temperature increases, so more of this slightly
warmed water will evaporate, increasing the
atmospheric concentration of water vapor.
• As a greenhouse gas, increased water vapor may
cause an even greater increase in global
temperatures due to absorption and the release
of infrared radiation, which causes another
“upward spiral.”
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Runaway Greenhouse Effect
• This spiraling-up effect is also commonly
known as a runaway greenhouse effect.
• However, by contrast, increased water vapor
concentration would also lead to increased
cloud cover, which would reflect more solar
radiation, thus counteracting some of the
predicted temperature increase.
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Other Greenhouse Gases
• Two other naturally occurring greenhouse gases
are also produced by human activity: nitrous
oxide (N2O) and methane (CH4).
• Many agricultural and industrial activities, as well
as the burning of solid waste and fossil fuels,
contribute to the concentration build up of N2O in
the atmosphere.
• CH4 occurs naturally as a decomposition product
of plant and animal wastes, but it is also
produced from refining fossil fuels and raising
livestock.
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In addition to carbon dioxide, atmospheric gases such as nitrous oxide (N2O)
and methane (CH4) are considered greenhouse gases. Raising cattle increases
methane concentrations, while burning solid waste adds nitrous oxide to the
atmosphere.
http://ecoki.com/increased-
/
nutrients-in-organic-cows
http://www.coldtruth.com/2009/children/risks-tochildren-children/epa%E2%80%99s-studies-on-thesafety-of-shredded-tires-on-children%E2%80%99s-
/
playgrounds-were-actually-never-conducted
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Non-natural Greenhouse Gases
• Some gases that do not occur naturally can
also contribute to the greenhouse effect.
– Especially fluorocarbons used in refrigeration and
air conditioning
– See next slide for a table that shows these gases
are much more effective than CO2 in retaining
heat at Earth’s surfaces.
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GREENHOUSE GAS EFFECTIVENESS
Greenhouse Gas
Relative Effectiveness
Percent Abundance in
Troposphere
Carbon dioxide (CO2)
1 (assigned value)
3.3 x 10-2
Methane (CH4)
30
1.7 x 10-4
Nitrous oxide (N2O)
160
3 x 10-4
Water vapor (H2O)
0.1
1
Ozone (O3)
2 000
4 x 10-6
Trichlorofluoromethane
(CCl3F)
21 000
2.8 x 10-8
Dichlorofluoromethane
(CCl2F2)
25 000
4.8 x 10-8
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Temperature Increases
• What are implications of increased
atmospheric concentrations of greenhouse
gases?
• Has any effect on Earth’s climate been noted
thus far?
• The 20th century’s 10 warmest years all
occurred within the last 15 years of that
century.
– Of these, 1998 was the warmest year on record.
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Global annual mean surface air temperature trends since 1880.
The 1951-1980 mean surface air temperature has been used as
the zero-point base for comparison.
Graph referenced from NASA website on http://jouleblog.com/
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Global Warming
• An international panel of climate scientists has predicted
that under a business-as-usual scenario, in which no steps
are taken to control the release of human-generated CO2
and other greenhouse gases, the average global surface
temperature could rise 0.8°C to 2.9°C in the next 50 years
and 1.4°C to 5.8 °C in the next 100 years, with significant
regional variation.
• This prediction can be compared to evidence that Earth has
warmed only 3°C to 5°C since the depths of the last Ice Age,
some 20 000 years ago.
• These observed and predicted increases in average global
surface temperatures are often referred to as global
warming.
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IPCC
• The 2001 report of the United Nations
Intergovernmental Panel on Climate Change
(IPCC) reported that Earth’s average global
surface air temperature increased by 0.4°C to
0.8°C over the past 100 years.
• The 2000-page report was prepared by 500
climate scientists and reviewed by another
500 climate experts.
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Disagreement Among Scientists
• Although most climate specialists agree that Earth’s
average temperature will increase, there is still some
disagreement about causes of this predicted warming.
• New data indicate that the lower atmosphere may not
be warming at the same rate as Earth’s surface, which
suggests that additional factors contribute to the
buildup of greenhouse gases and to the warming trend.
– Ocean currents, such as El Niño and La Niña, transport
thermal energy within the oceans and can affect climates
when this energy is transferred to he land and to the
atmosphere.
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Possible Impact
• What are the projected effects of global warming?
• Based on the assumption that the average temperature increases
0.5°C per decade, the oceans are predicted to rise about 5 cm each
decade over this century.
– Due to the major effect of melting polar ice caps and very small
contribution of expansion of ocean water from warming
– Such changes could produce an approximately 15-cm increase in
ocean levels by 2030, a situation that could cause flooding in coastal
cities, such as Miami and New York.
• Possible regional climate changes, including reduced summer
precipitation and soil moisture in North America, might be
expected.
– Northern regions might benefit from lengthened growing seasons,
while growers in southern regions would probably shift to crops that
can benefit from warmer winters.
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The glacier on Mt. Kilimanjaro as photographed
in February 1993 (top) and February 2003
(bottom).
http://en.wikipedia.org/wiki/
Mount_Kilimanjaro
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What Can Be Done?
• Scientists today understand the influence of CO2 and other greenhouse
gases on world climate better than they did even a decade ago.
– Sophisticated computer modeling has enhanced their research efforts.
– This new understanding supports the idea of a surface global warming trend.
• In 1992, representatives of more than 150 nations developed the
Framework Convention on Climate Change, where they agreed to develop
policies and procedures to reduce greenhouse gas emissions.
• In 1997, the third meeting of parties to this agreement, held in Kyoto,
Japan, resulted in a protocol to address climate change.
– By late 2004, 126 nations had signed the protocol; thus, this international
agreement entered into force in 2005.
– As of 2005, some industrialized nations, including the United States and
Australia, still have not ratified the Kyoto Protocol.
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Kyoto Protocl
• The Kyoto Protocol sets ambitious goals for
reducing greenhouse gas emissions.
• For industrialized nations, this involves
developing energy-efficient technologies,
relying more heavily on renewable energy, and
applying alternative processes that do not
release greenhouse gases into the
atmosphere.
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Kyoto Protocol Examples
• An alternative process has been developed for producing the
polystyrene foam used to make such items such as plastic egg
cartons and meat trays.
– This process uses CO2 that would normally be released during the
production of ammonia.
– The captured CO2 replaces chlorofluorocarbons (CFCs) that had been
used in this foam-producing process, this reducing greenhouse gases
in two ways.
• First, CO2 that would normally be released by another industry is used.
• Second, CO2 replaces CFCs which have a global-warming potential much
greater than that of CO2.
• In an application of green chemistry principles, Hangers Cleaners, a
chain of dry-cleaning stores, also uses liquid carbon dioxide (formed
by compressing the gas under high pressure) and special detergents
to replace potentially harmful dry-cleaning solvents.
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HOMEWORK (review)
1) If you see considerable black exhaust emitted by
a bus, what might that indicate about the
combustion processes in the engine?
2) a. What would be the effect on the average
global temperature if significant atmospheric
increases occurred in
i. Carbon dioxide?
ii. Methane?
iii. Water vapor?
b. How would such global temperature changes,
in turn, affect Earth’s atmosphere? Explain.
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