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					Physical Forces of Climate
           The climate system
The climate system includes the
    •   Atmosphere
    •   Hydrosphere
    •   Geosphere
    •   Biosphere
    •   Cryosphere (ice and snow)
The climate system

                     Fig. 1
   Earth’s atmosphere and climate
A. Overview
  1. study of global change is the study of changes in
     the atmosphere and linkages to other systems
  2. climate: characteristic atmospheric conditions
     over time scales of seasons to decades
  3. major climatic zones (Figure 2)
B. The atmosphere
  1. Earth’s atmosphere is complex, with many little-
     understood reactions taking place
  2. troposphere: lower 10 km of atmosphere, where
     dramatic water vapor variations occur
Climates of the world.

                         Fig. 2
     Some atmospheric basics (1)
A. Composition of the atmosphere
  1. Air is a mixture of many discrete gases
  2. Composition varies over time and distances
  3. After water vapor, dust, and other variable
     components are removed, nitrogen and oxygen
     make up 99% of the clean dry air
  4. CO2, although present in minute amounts
     (0.038%), greatly influences the heating of the
  Composition of
Earth’s atmosphere

      Fig. 3
   Some atmospheric basics (2)
A. Composition of the atmosphere (cont)
  1. Two important variable components of air
     are water vapor and aerosols
    a. Water vapor absorbs ultraviolet radiation
       given off by Earth similar to CO2
    b. Aerosols (tiny solid and liquid particles) are
       important because they act as surfaces for
       condensation and also are good absorbers and
   Some atmospheric basics (3)
A. Energy from the Sun
  1. Electromagnetic radiation is energy
     emitted in the form of rays, or waves
    a. Key difference among electromagnetic waves is
       their wavelength
  2. Some basic laws governing radiation
    a. All objects emit radiant energy
    b. Hotter objects radiate more total energy than
       do colder objects
    c. The hotter the radiating body, the shorter the
       wavelengths of maximum radiation
    d. Objects that are good absorbers of radiation
       are good emitters as well
    Earth-Sun Energy Relationship

Idealized diagram comparing the emission of energy from the Sun with that from Earth. Notice that the solar
emissions have a relatively short wavelength, whereas those from Earth have a relatively long wavelength.
    Some atmospheric basics (4)
A. The fate of incoming solar energy
    1. Less than 50% of the solar energy that
       strikes the atmosphere reaches Earth’s
       a. Approximately 30% is reflected back to
       b. 20-25% is absorbed by clouds and the
          atmosphere’s gases
Annual energy flow to Earth from the Sun
Atmosphere Energy Balance
Global Warming
Anthropogenic Greenhouse Effect.
           Global warming (1)
A. The greenhouse effect
  1. three factors determine temperature of Earth:
     amount of sunlight received, amount of sunlight
     reflected, atmospheric retention of heat
  2. trapping of heat by atmospheric gases including
     water vapor,carbon dioxide, methane and CFCs
  3. natural versus anthropogenic warming?
  4. carbon dioxide records from Antarctic ice sheet
B. Global temperature records
  1. Pleistocene ice ages
  2. last 1000 years
  3. last 250 years
Carbon dioxide in the atmosphere. (1)

Concentration of atmospheric carbon dioxide for the past 160,000 years, based on evidence from Antarctica.
Carbon dioxide in the atmosphere. (2)

      Average concentration of atmospheric carbon dioxide from 1500 to 2000.
Carbon dioxide in the atmosphere. (3)

      Atmospheric concentration of carbon dioxide at Mauna Loa, Hawaii.
    Carbon dioxide and temperature

Inferred concentration of atmospheric
carbon dioxide and temperature change
for the past 160,000 years. The relation
is based on evidence from Antarctica and
indicates a high correlation between
temperature and CO2
          Global warming (2)
C. Why does climate change?
  1. Link to Milankovitch cycles (Use ESC to
     exit the program)
  2. ocean conveyor belt
Ocean conveyor belt.
           Global warming (3)
D. Solar forcing - variability of solar energy
  1. Cool and warm periods in N. America and Europe
     seem to coincide with 11-year sunspot cycle
  2. Western N. America experiences droughts that
     coincide with 22-year cycle of magnetic reversals
     of sunspots
  3. However, records from other parts of the globe
     show no susnpot correlation
E. Medieval warm period and Little Ice Age
   correspond with increased and decreased
   solar energy output. However, the
   difference between high and low solar
   energy is only ~0.25%
                  Global warming (4)
E.    Volcanic forcing -
      volcanic aerosols
      and cooling
     The eruption of Mt.
         Pinatubo in the
         Philippines in 1991
         injected vast
         amounts of volcanic
         ash and sulfur
         dioxide up to about
         30 km (19 mi) into
         the atmosphere
         Global warming (5)
F. Anthropogenic forcing
  1. natural variability of last 1000 years
     cannot explain late 20th century warming
  2. agreement with models of greenhouse gas
  3. global warming as a result of human
     activity is occurring
  How is climate change detected?
A. Techniques for analyzing Earth’s climate
  1. Seafloor sediments – numbers and types of
     organic remains are indicative of past sea-surface
  2. Oxygen isotope analysis – ratio of O18/O16 in
     shells of microorganisms reflect past
B. Other sources of data for studying past
   climates include
  1. Growth of tree rings
  2. Pollen contained in sediment and coral reefs
  3. Information found in historical documents
Climate-feedback mechanisms (1)
A. When any component in the climate
   system is altered, scientists must
   consider many possible outcomes
B. These possible outcomes are called
   climate-feedback mechanisms
Climate-feedback mechanisms (2)
A. Climate-feedback mechanisms
  1.   Changes that reinforce the initial change are
       called positive-feedback mechanisms
       a.   Example – warmer surface temperatures cause an
            increase in evaporation, which further increases
            temperatures as water vapor absorbs more radiation
  2. Negative-feedback mechanisms produce results
     that are the opposite of the initial change and
     tend to offset it
       a.   Example – negative effect of increased cloud cover on
            the amount of solar energy available to heat the
   Other examples of global change
           feedback loops
A. Changes in albedo (reflection of sunlight)
  1. caused by melting of Arctic sea ice
  2. leads to more water absorbing more sunlight,
     warming the Arctic and melting more sea ice
B. Melting of tundra/permafrost
  1. release of methane otherwise trapped in
  2. Methane enhances greenhouse effect causing
     more warming and more melting of permafrost
 Tools for studying global change
A. The geologic record (PAST)
  1. sediments
  2. organic material
  3. glacial ice
B. Real-time monitoring (PRESENT)
  1. regular collection of data for a specific purpose
  2. methods vary with subject being measured
C. Mathematical models (FUTURE)
  1. numerical methods to represent real-world
     phenomena and linkages between processes
  2. Global (General) Circulation Models
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