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Global Warming: the history


Global Warming: the history Why should we be worried about overall global climate change? – PowerPoint PPT presentation

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Title: Global Warming: the history

Global Warming the history
  • Why should we be worried about overall global
    climate change?

What is global warming?
  • Before we define global warming, we need to
    remember a few things about the atmosphere and
  • 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

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.

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
  • Once the core differentiated the heavier gases
    could be retained

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
  • 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.

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.

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

  • 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.

  • 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?

  • 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.

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
  • 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.

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.