Global Warming: the history

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Global Warming the history

• Why should we be worried about overall global
  climate change?

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What is global warming?

• Before we define global warming, we need to
  remember a few things about the atmosphere and
  climate.
• The atmosphere is defined as a thin layer of
  gases that surrounds our Earth. Without the
  atmosphere, organisms that survive on Oxygen
  would not be able to survive. This atmosphere
  also helps to distribute the heat gained from the
  suns rays.
• The atmosphere consists of
• 78 N2
• 21 O2
• 1 Ar
• And other trace amounts of permanent gases

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Our Climates History

• Since the time of Earths existence, the
  atmosphere has changed. Its composition began
  primarily as hydrogen and helium. As Earth
  processes took place such as volcanic
  eruptions, the atmosphere began to change. It is
  hypothesized that Earths atmosphere was very
  similar to Venus atmosphere primarily CO2,
  which made the Earth an unbearable place to live.

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First Atmosphere

• Composition - Probably H2, He
• These gases are relatively rare on Earth compared
  to other places in the universe and were probably
  lost to space early in Earth's history because
• Earth's gravity is not strong enough to hold
  lighter gases
• Earth still did not have a differentiated core
  (solid inner/liquid outer core) which creates
  Earth's magnetic field which deflects solar
  winds.
• Once the core differentiated the heavier gases
  could be retained

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Second Atmosphere

• Produced by volcanic out gassing.   Gases
  produced were probably similar to those created
  by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2,
  N2, H2) and NH3 (ammonia) and CH4 (methane)
• No free O2 at this time (not found in volcanic
  gases).
• Ocean Formation - As the Earth cooled, H2O
  produced by out gassing could exist as liquid in
  the Early Archean, allowing oceans to form.
• Evidence - pillow basalts, deep marine beds in
  greenstone belts.

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Addition of O2 to the Atmosphere

• Today, the atmosphere is 21 free oxygen.
• Oxygen Production
•   Photochemical dissociation - breakup of water
  molecules by ultraviolet
• Produced O2 levels approx. 1-2 current levels
• At these levels O3 (Ozone) can form to shield
  Earth surface from UV
• Photosynthesis - CO2 H2O sunlight organic
  compounds O2 - produced by cyanobacteria, and
  eventually higher plants - supplied the rest of
  O2 to atmosphere. Thus plant populations
• Oxygen Consumers
•   Chemical Weathering - through oxidation of
  surface materials (early consumer)
• Animal Respiration (much later)
• Burning of Fossil Fuels (much, much later)
• During the Proterozoic the amount of free O2 in
  the atmosphere rose from 1 - 10 . Most of this
  was released by cyanobacteria, which increase in
  abundance in the fossil record 2.3 Ga. Present
  levels of O2 were probably not achieved until
  400 Ma.

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Our Atmosphere

• Life on Earth is supported by the atmosphere,
  solar energy, and our planet's magnetic fields.
  The atmosphere absorbs the energy from the Sun,
  recycles water and other chemicals, and works
  with the electrical and magnetic forces to
  provide a moderate climate. The atmosphere also
  protects us from high-energy radiation and the
  frigid vacuum of space.

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The Troposphere

• From the Earths surface through the bottom layer
  of atmosphere, called the troposphere,
  temperature decreases with altitude. Weather
  occurs in this layer. Its also the layer we live
  in.

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Stratosphere

• The next layer up is called the stratosphere. In
  the stratosphere, temperature increases with
  altitude. This is because of ozone. When the
  ozone in this layer absorbs UV light from the
  sun, it increases in temperature.

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Mesosphere

• In the mesosphere, ozone concentration decreases.
  This means there is less absorption of UV light
  in this layer of atmosphere. Do you think the
  temperature would increase or decrease In this
  layer of the atmosphere?

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Thermosphere

• In the upper atmosphere, called the thermosphere,
  temperatures are HOT. This is because incoming
  energy from the sun heats the molecules up. Well,
  this occurs because short-wave, high-energy solar
  radiation is absorbed by the (relatively few)
  molecules of oxygen and nitrogen.

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Earth Naturally goes through a warming and
cooling periods.

• Serbian astronomer Milutin Milankovitch, who
  calculated the slow changes in the earth's orbit
  by careful measurements of the position of the
  stars, and through equations using the
  gravitational pull of other planets and stars.
• He determined that the earth "wobbles" in its
  orbit. The earth's "tilt" is what causes seasons,
  and changes in the tilt of the earth change the
  strength of the seasons. The seasons can also be
  accentuated or modified by the eccentricity
  (degree of roundness) of the orbital path around
  the sun, and the precession effect, the position
  of the solstices in the annual orbit.
• The Milankovitch or astronomical theory of
  climate change is an explanation for changes in
  the seasons which result from changes in the
  earth's orbit around the sun.

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What does this mean?

• The combination of the 41,000 year tilt cycle and
  the 22,000 year precession cycles, plus the
  smaller eccentricity signal, affect the relative
  severity of summer and winter, and are thought to
  control the growth and retreat of ice sheets.
• Cool summers in the northern hemisphere, where
  most of the earth's land mass is located, appear
  to allow snow and ice to persist to the next
  winter, allowing the development of large ice
  sheets over hundreds to thousands of years.

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Earths Natural Greenhouse Effect

• Greenhouse gases like water vapor, carbon
  dioxide, methane and nitrous oxide trap the
  infrared radiation released by the Earth's
  surface.
• The atmosphere acts like the glass in a
  greenhouse, allowing much of the shortwave solar
  radiation to travel through unimpeded, but
  trapping a lot of the longwave heat energy trying
  to escape back to space. This process makes the
  temperature rise in the atmosphere just as it
  does in the greenhouse. This is the Earth's
  natural greenhouse effect and keeps the Earth
  33C warmer than it would be without an
  atmosphere, at an average 15C.

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Warming the Earth Naturally

• The Sun, which is the Earth's only external form
  of heat, emits solar radiation mainly in the form
  of shortwave visible and ultraviolet (UV) energy.
  As this radiation travels toward the Earth, 25
  of it is absorbed by the atmosphere and 25 is
  reflected by the clouds back into space. The
  remaining radiation travels unimpeded to the
  Earth and heats its surface. The Earth releases a
  lot of energy it has received from the Sun back
  to space. However, the Earth is much cooler than
  the Sun, so the energy re-emitted from the
  Earth's surface is much weaker, in the form of
  invisible longwave infrared (IR) radiation,
  sometimes called heat.