Transcript Global Warming

Global Warming
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The name given to the increase in the
average temperature of the Earth’s
near surface temperature and oceans
that has occurred since the middle of
the 20th century.
In the graph to the right, panel a
gives the Earth's surface temperature
is shown year by year (red bars) and
approximately decade by decade
(black line, panel b gives the year by
year (blue curve) and 50 year average
(black curve) variations of the
average surface temperature of the
Northern Hemisphere for the past
1000 years have been reconstructed
from "proxy" data calibrated against
thermometer data.
Greenhouse effect
• Main culprit behind global
warming
• Sunlight enters the atmosphere
and warms the Earth (UV, visible,
IR)
• At night, Earth radiates heat
energy it gained during the
day(mostly at IR wavelengths)
• Not all of this energy escapes the
atmosphere-some of it is
absorbed and re-emitted back
into the atmosphere, warming
the atmosphere and the Earth.
• Not necessarily a bad thingwithout it the Earth would be
cold and life (a least as we know
it) would not be possible
Venus
• Hottest planet in the solar
system
• But not the closest to the sun
• Atmosphere is 96.5% carbon
dioxide
• Venus once had immense
amounts of water, but no
ozone layer-the UV radiation
broke up the water molecules
• Unfortunate, water absorbs
carbon dioxide wand mitigates
the greenhouse effect
• Resulted in an extreme
greenhouse effect
Greenhouse effect-What could happen
• Global temperatures rise until boiling point of
water is reached
• As water boils away, it becomes water vapor in
the atmosphere, accelerating the heat rise (called
positive feedback).
• At a few hundred degrees celsius, carbon dioxide
would be released from the rocks (sublimation),
accelerating the heating again
• Eventually the Earth would stabilize at surface
temperatures similar to Venus (T=860F)
Greenhouse Gasses –in order of
importance
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water vapor
carbon dioxide
methane
nitrous oxide
ozone
CFCs
Changes in greenhouse gas
concentrations
Gas
Preindustrial Level Current Level
Increase since 1750
Carbon dioxide
280 ppm
387ppm
104 ppm
Methane
700 ppb
1,745 ppb
1,045 ppb
Nitrous oxide
270 ppb
314 ppb
44 ppb
CFC-12
0
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• Historical variations can be tracked via analysis of ice cores
– Ice core - a core sample (a cylindrical section of a naturally occurring
medium consistent enough to hold a layered structure) from the
accumulation of snow and ice over many years that have recrystallized and have trapped air bubbles from previous time periods.
– The composition of these ice cores provides a picture of the climate at
the time.
– Record for over 800,000 years
What do the ice cores tell us?
• Natural variations occur in the greenhouse gas
concentrations
Post industrial revolution
Man made sources of greenhouse
gasses
• Also called Anthropogenic, which designates an effect or object resulting
from human activity
• burning of fossil fuels and deforestation leading to higher carbon dioxide
concentrations.
– Account for one third of total anthropogenic CO2 emissions.
• livestock enteric fermentation and manure management, paddy rice
farming, land use and wetland changes, pipeline losses, and covered
vented landfill emissions leading to higher methane atmospheric
concentrations. Many of the newer style fully vented septic systems that
enhance and target the fermentation process also are sources of
atmospheric methane.
• use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs
and halons in fire suppression systems and manufacturing processes.
• agricultural activities, including the use of fertilizers, that lead to higher
nitrous oxide (N2O) concentrations.
What are we seeing?
• Since 1860-1900, global
surface temperatures
have increased by 1.35 F
• Urban heat island effect
only accounts for 0.02 C
rise
• Since 1979 land T have
increased twice as fast as
ocean Temperatures
• Temperatures on the
lower troposphere have
have increased by 0.62
between 1979 and 2000.
Hold on, could it be the sun?
• No overall increase in solar brightness in over
1000 years
• Solar cycles do cause small variations in
brightness, but not enough to account for
what has been seen
• No its not the sun
Feedback-making the problem worse
(or better)
• Positive feedback-when the warming induces
further warming
• Negative feedback – when the warming
induces a cooling
Sources of Feed back
• Positive
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Water vapor
Clouds
Ice albedo
Arctic methane release
Reduced carbon dioxide
absorption in the oceans
• Negative
– Lapse rate
Negative feedback
• Lapse Rate
• Increased heating means increased IR
emission
• Global warming reduces the rate of
Temperature decrease with height, which
means more long wavelength radiation will be
emitted by the upper atmosphere
• This will weaken the greenhouse effect
Positive feedback
• Water vapor
– Warming increases the amount of water vapor in the atmosphere,
which increases the warming since water vapor is also a greenhouse
gas
• Clouds
– Act as a blanket, reflect IR radiation downward toward the surface
• Ice albedo
– Melting ice reveals land and water, both reflect less light than icemore warmth is absorbed increasing warming
• Arctic methane release
– Warming releases sources of carbon dioxide
• Reduce carbon dioxide absorption in oceans
– Warm waters favor the growth of plankton rather than diatomsdiatoms are more efficient carbon dioxide absorbers
Global dimming
• An effect that has been counteracting some of
global warming from about 1960 forward
• Aerosols produced by volcanoes and
pollutants such as sulfur dioxide reflect
incoming sunlight
• Soot –suspended in the atmosphere, it can
absorb solar radiation and heat the
atmosphere, but cool the surface
What are we seeing:
• Besides the increases in Temperature:
– World’s glaciers are melting
– Arctic sea ice is reducing in both extent ( 9% reduction in area per
decade) and thickness (15-40% in thickness in the last 30 years)
– Ocean levels are rising-both due to melting of Antarctic ice and
thermal expansion of sea water
– Longer growing seasons
– Thawing of permafrost in Alaska
– Coral reef bleaching-whitening of reefs due to increased temperature
– Earlier plant flowering
– Earlier bird arrivals
– Shifting of animal ranges poleward
– More frequent EL Nino-warming of the Pacific ocean surface
temperatures-causes changes in local weather patterns
Global warming-the debate
• The fact that the Earth is warming is not a
matter of debate, the evidence is clear
• The fact that global carbon dioxide levels have
increased is also clear
• The debate centers around how much of it is
caused by human involvement vs a natural
cycle
• Think about it in terms of the steps in the
scientific method:
Global warming in the context of the
scientific method
• Observations-Earth’s temperature is warming
• Hypothesis-due to a man-made increase in green house
gases
• Testing the hypothesis-many scientists hold different views
and interpret data differently, but the consensus is that it is
due to increases in greenhouse gasses from man made
sources.
• Until the data is incontrovertible, there will always be
naysayers. That’s ok, they keep us honest and push the
method forward
• Lots of examples like this in modern science (evolution, big
bang, cosmological interpretations of galaxy redshifts)