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Global Warming


Global Warming 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 ... – PowerPoint PPT presentation

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Title: Global Warming

Global Warming
  • The name given to the increase in the average
    temperature of the Earths 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 thing-without it the Earth
    would be cold and life (a least as we know it)
    would not be possible

  • 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
  • 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 (T860F)

Greenhouse Gasses in order of importance
  • water vapor
  • carbon dioxide
  • methane
  • nitrous oxide
  • ozone
  • CFCs

Changes in greenhouse gas concentrations
  • 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 re-crystallized 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

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
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What do the ice cores tell us?
  • Natural variations occur in the greenhouse gas

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
  • 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
  • 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
  • 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

Sources of Feed back
  • Positive
  • 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
  • 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 ice-more 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 diatoms-diatoms 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
  • Worlds 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
  • Observations-Earths 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. Thats 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)
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