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The Greenhouse Effect
Good or Bad?
Global Climate History
Geologic evidence clearly indicates relative long-term
climate stability that has allowed liquid H2O to exist for
most of geologic history.
Earth’s Atmosphere
77% N2, 21% O2, 1% Ar, + trace gases (CO2, CH4, H2O)
Absorbs incoming solar radiation and warms the planet.
Important component of global climate.
Without atmosphere, average Earth
temperatures would be a cool –17°C!!
Natural Greenhouse effect
The natural greenhouse effect causes the mean temperature of
the Earth's surface to be about 33oC warmer than it would be if
natural greenhouse gases were not present.
Greenhouse
Glass, the material
that greenhouse is
made of, 1) transmits
short-wavelength
visible light, 2)
absorbs and redirects
the longer
wavelengths of
energy. These two
aspects make the
greenhouse warmer
than outside air
temperature.
Greenhouse effect of the atmosphere
• Light from the sun includes the
entire visible region and smaller
portions of the adjacent UV and
infrared regions.
• Sunlight penetrates the atmosphere
and warms the Earth’s surface.
The gases in the
atmosphere that act
like glass in a
greenhouse are called
greenhouse gases.
• Longer wavelength infrared
radiation is radiated from the earth’s
surface.
• A considerable amount of the
outgoing IR radiation is absorbed by
gases in the atmosphere and reradiated back to Earth.
Greenhouse Effect & Global Warming
• The “greenhouse effect” & global
warming are not the same thing.
– Global warming refers to a rise in the
temperature of the surface of the earth

• An increase in the concentration of
greenhouse gases leads to an
increase in the the magnitude of the
greenhouse effect. (Called enhanced
greenhouse effect)
– This results in global warming
Enhanced greenhouse effect
When concentrations of greenhouse gases increase,
more infrared radiation is returned towards the Earth. 
The surface temperature rises.
Climate Change vs. Variability
Climate variability is natural.
Even in a stable climate regime, there will always
be some variation (wet/dry years, warm/cold
years) A year with completely “average” or
“normal” climate conditions is rare
The challenge for scientists is to determine
whether any increase/decrease in precipitation,
temperature, frequency of storms, sea level, etc.
is due to climate variability or climate change.
The Last Ice Age
30% of the land
surface was covered
by ice (only 10% is
covered today)
Northern Idaho was
covered by ~1 km
thick ice sheet
Selected Greenhouse Gases
• Carbon Dioxide (CO2)
– Source: Fossil fuel burning, deforestation
 Anthropogenic increase: 30%
 Average atmospheric residence time: 500 years

Methane (CH4)
– Source: Rice cultivation, cattle & sheep ranching, decay
from landfills, mining
 Anthropogenic increase: 145%
 Average atmospheric residence time: 7-10 years

Nitrous oxide (N2O)
– Source: Industry and agriculture (fertilizers)
 Anthropogenic increase: 15%
 Average atmospheric residence time: 140-190 years
What determines the contribution of a
greenhouse gas to global warming?
• Concentrations
– H2O and CO2 are the two biggest contributors to the
atmospheric warming because of their higher
concentrations.
• Lifetime
– The longer-lived a gas is, the higher the contribution.
e.g. N2O contribution > CH4
• Effectiveness as an infrared absorber
– For example, CFC-11 and CFC-12
CO2
Concentrations
at Mauna Loa,
Hawaii
The average atmospheric CO2 concentrations observed at Muana Loa,
Hawaii increased approximately 40 ppmv between 1958 and 1995.
The small fluctuations in the curve are seasonal variations due
primarily to the withdrawal and production of carbon dioxide by
terrestrial life. Notice that minimum values occur during the northern
hemisphere summers (when global photosynthetic activity is greatest)
and maximum values occur six months later.
The concentration of greenhouse gases, particularly
CO2, is important global climate regulation
What regulates the amount of CO2??
The Earth’s Climate System - very complex!!
Sources and sinks of CO2
• Sources
– Natural: respiration of vegetation and soil detritus
– Man-made: Fossil fuel combustion, deforestation
• Sinks:
slow exchange of carbon between surface waters and
deep layers of ocean.
(Seawater is alkaline while CO2 is acidic  The
oceans are a vast reservoir of CO2).
Methane
Rate of increase: 0.9% annually
Atmospheric methane has increased steadily to present day levels;
this increase is highly correlated with human population growth
and with related activities, including agricultural practices.
Sources and sinks of methane
• Sources
– Natural: end-product of the metabolism from an
anaerobic bacteria, methanogen.
Natural wetlands, enteric fermentation (wild animals),
termites, biomass burning, ocean/fresh water
– Man-made: rice paddies, gas drilling and transmission,
landfills, coal mining, biomass burning, enteric
fermentation (domestic animals)
• Sink: OH+ CH4 CH3. + H2O
Temperature over the past one century
The global air temperature at the Earth's surface has increased
about 0.5oC during the past century.
Temperature over the past 1000 years
Short-Term Climate Change
• Climate change over short time
scales (<1,000,000 years)
WARM
• Related to complex, poorly
understand interactions between
atmosphere, hydrosphere, and
lithosphere
COLD
Possible Causes
1.
Orbital Parameters of the Earth
2.
Changes in Atmospheric Composition
3.
Changes in Ocean Circulation
4.
Sunspot Activity
5.
Changes in Reflectivity (albedo)
Recent Global Warming
Consequences of global warming
• Sea level rise
– Beach erosion
– Coastal wetland loss
– Loss of low-lying territories
• Water resources change
– Precipitation pattern shift
– Increases instances of heavy precipitation
– New burdens on water capture, storage and
distribution system to be expected.
• Effects on agriculture
– Changes in the length of growing season
– Growth of undesirable plant species
Consequences of global warming (Continued)
• Effects on air quality
– Increase in reaction rates and concentrations of certain
atmospheric species increase in O3 in urban areas
– More droughts widespread forest fire worsen air quality
– Change in how pollutants are dispersed.
• Impacts on human health
– Changes in patterns of sickness and death.
– Respiratory problems affected by air quality change
• Biodiversity
– Some species may grow too quick and overshoot their
reproductive period (e.g. reef corals)
– Forest could be devastated if the rate of climate change
outpaced the rate at which forest species could migrate.
• Change in the pattern of ocean current