CLIMATE CHANGE

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CLIMATE CHANGE

• Global Temperatures
• Past, Present, and Future

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Mean Temperature

• Mean Temperature of the Earths surface is 15
  degrees Celsius
• Locations with the same mean annual temperature
  can have very different climates, however.
• Eg. Beijing and San Francisco, both have a mean
  annual T of 50 degrees F and 15 inches of rain
  per year, but climates are very different
• Beijung has large T range, most rain falls in
  Summer San Francisoc, very small temperature
  range and most rain falls in Winter

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CLIMATE BASICS

• The Earth receives radiation from the Sun, which
  is called irradiance
• The average irradiance, also known as the Solar
  Constant 1367 wm-2
• The amount varies with
• Latitude
• Time of Year
• Time of Day
• Sunspot Activity
• Orbital Variations

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CLIMATE CHANGE

• Earth History has seen numerous Ice ages and Warm
  periods

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CO2 Concentration and Global Temperatures for
last 160,000 years
From air bubbles in ice cores
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Last 130,000 years
Warming starts 18-15 ka
Oxygen isotopes from ice cores in Greenland (Camp
Century) and Antarctica (Byrd) can be used to
determine sea surface temperatures for the last
160,000 years. A decrease of 1ppm in d O18
equals a 1.50C reduction in Temp.
Cooling starts 60ka
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Climate Monitors
Levels of naturally occurring methane and carbon
dioxide both increase with increasing
temperatures Notice the high values at
about 120ka
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Evidence for Past Climates
Notice in c the period of sudden cooling about
10ka that lasted about 700 years
About 1000 AD, climate was warm and Dry the
Medieval Warm Period About 1300 to 1800 AD a
cooling trend resulted in the Little Ice Age
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CLIMATE CHANGE

• CONTROLLED BY
• Long-term
• Plate Tectonics 107-108 yr
• Placement and sizes of continents
• Convection rates (generate more volcanic
  activity)
• Solar output increased 30 in last 3 billion
  years
• Medium-term
• Orbital Changes 104-105 yr
• -- Volcanic Eruptions long-term increase
  releases more CO2 and increases temps
• Short-term
• Increases in explosive volcanic eruptions
  increase particulates in atmosphere resulting in
  cooling 100.5-101 yr
• Changes in Solar output of 0.1 to 0.2 22-yr
  cycle
• Fossil Fuel emissions 101 to 102 yr

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During the last 2.3 billion years, there have
been 7 major Ice Ages with many more minor
variations. Most were controlled by the
positions of the continents and by the intensity
of volcanic eruptions
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Plate Tectonics affects the positions and sizes
of continents
TODAY
300 m.y. ago
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Volcanic Eruptions
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AXIAL TILT
At present, we are near maximum tilt, which makes
polar regions have more contrast. Not especially
likely to promote cooling.
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Eccentricity
Periodicity of 100,000 years
We are near minimum eccentricity, so seasonal
contrasts are minimized. Minimum seasonal
contrasts promote cooling.
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Precession

• Changes in precession occur on a time scale of
  23,000 years.

Presently, earth is near maximum tilt of 23.50
(range is 21.5-24.5) So maximizes seasonal
contrasts Preceesion effect presently earth is
closest to sun in January, farthest in July
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Milankovitch Cycles
Combined result is a difference of /- 60 C
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The combined Milankovitch curves form an
asymmetric curve. Notice how temperature
increases are gradual, but cooling can be very
rapid.
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Triggering Mechanisms and Feedback

• Massive, explosive volcanic eruptions can
  introduce huge amounts of ash into the
  atmosphere. This blocks out some of the sun,
  increases cloudiness as water vapor nucleates
  around the particles, and increases precipitation
  and possible snowfall.
• Albedo snow and ice on ground reflect sunlight
  much more than vegetation or bare rock. This
  cools the earths surface and favors more ice and
  snow accumulation.

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CO2 Budget
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Temperature Change in Last 150 years
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CO2 in Atmosphere for last 50 Years
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A business as usual Means current rate
of INCREASE of use of Fossil fuels continues D
CO2 emissions decreased drastically thru
conservation, technology, and alternative sources
B,C partial changes using other models
Climate Models predict increases of 4 degrees
over the next 100 years. The prediction depends
on assumptions about the fossil fuel consumption
rate.
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Sealevel is rising at 2 mm/yr at present
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CONSEQUENCES OF GLOBAL WARMING

• CO2 has increased 50 ppm in the last 40 years to
  reach 365 ppm.
• If CO2 doubles in the atmosphere, much of the
  earth will become hotter, with larger increases
  with increasing Latitude.
• Some climate models say increased evaporation
  will result in drier climates, while others say
  increased T will result in increased
  precipitation.

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