Atmosphere, Climate and Global Warming

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Atmosphere, Climate and Global Warming
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Whats In the Atmosphere?

• Nitrogen gas 78.
• Oxygen 21.
• Remaining 1
• Argon (0.9)
• Carbon dioxide (0.03)
• Trace gases and particulates (0.07).

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Whats in the Atmosphere?

• Water vapor constitutes from 1-4 of the
  troposphere.
• Life on Earth depends on three basic physical
  conditions of the atmosphere
• Gases at the right ratio and pressure
• Appropriate atmospheric temperature range
• Relative humidity.

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Relative Humidity

• The measure of the actual amount of water vapor
  in the atmosphere relative to the potential
  amount it can contain.
• A saturated air mass has a relative humidity of
  100.
• A rapid drop in temperature lowers the saturation
  point and the water vapor condenses (dew).

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Atmospheric Conditions

• Troposphere Lowest stratum of the atmosphere
  range from the Earths surface to 10-12 km.
• Air temperature and pressure decrease with
  increasing altitude.
• Stratosphere Extends from the troposphere to
  50 km in altitude.
• Temperature is constant ( -55o C).
• The stratospheric ozone layer between 20 km and
  25 km protects the Earth from uV radiation.

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Vertical Structure of the Atmosphere
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Global Air Circulation

• Air moves from areas of high pressure to areas of
  low pressure.
• The stronger the gradient, the higher the wind
  speed.
• Differential heating and cooling of the land
  surface creates the differences in air pressure.

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Global Air Circulation

• Air at the equator is warmed and rises, creating
  a low pressure area.
• Air masses move horizontally from north to south
  toward the equator to compensate for the low
  pressure area.
• In the upper troposphere, warm air move toward
  the poles and descends at 25 degrees to 30
  degrees latitude.
• Similar cells are established in the temperate
  and polar zones.

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Global Air Circulation

• Directionality is given to global wind patterns
  as a result of the CORIOLIS EFFECT.
• The rotational speed at the equator is faster
  than at higher latitudes. This deflects the
  surface winds in the northern hemisphere to the
  right and to the left in the southern hemisphere.

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Global Air Circulation

• Global wind belts
• Doldrums Equatorial, low pressure, ascending
  air, little horizontal air movement.
• Horse latitudes 30o N and S, high pressure,
  descending air, little horizontal movement.
• Trade winds Tropical zone, horizontal movement
  to the east.
• Westerlies Temperate zones, horizontal movement
  to the west.
• Polar easterlies Polar zones, horizontal
  movement to the east.

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Weather and Climate

• Weather Short-term conditions.
• Climate Long-term, characteristic weather
  patterns.
• Both are dynamic conditions, they change over
  time, but climatic conditions change slowly.
• Precipitation and temperature are the two factors
  that most strongly influence climate.

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Urban Microclimate

• Cities alter local weather and climate.
• Urban islands concept
• Tall buildings, asphalt and concrete, few trees
  and high fossil fuel emissions.
• Stagnant polluted air develops over cities.

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Global Climate Change

• Numerous changes throughout geologic time (4-5
  billion years).
• Major climatic changes have occurred during the
  past 2 million years
• Appearances and retreats of glaciers
• During the past 100 years, the mean global annual
  temperature ahs increased by .5 degrees Celsius.

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Global Warming and Greenhouse Effects

• Global warming A natural or human-induced
  increase in average global temperature.
• The temperature on Earth depends on
• Amount of solar energy received
• Amount of solar energy reflected by the
  atmosphere and surface
• Amount of solar energy retained by the
  atmosphere
• Amount of solar energy transferred in evaporation
  amd condensation.

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Global Warming and Greenhouse Effects

• Greenhouse effects A natural phenomenon.
• Atmospheric gases, primarily water vapor, trap
  radiant heat in the lower atmosphere.
• Moderates daily and seasonal temperature
  fluctuations.
• Of concern are man-made gases that reach the
  troposphere.

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Anthropogenic Greenhouse Gases
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Status of Atmospheric CO2

• Carbon dioxide concentrations can be measured in
  glacial ice to determine long term trends.
• Prior to the Industrial Revolution background CO2
  were 200-300 ppm.
• In 1860, concentrations were 280 ppm.
• Today, concentrations are 400 ppm.
• Rate of increase 0.5 per year.
• Total carbon emissions increased by 4.3 annually.

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Status of Atmospheric Methane

• Methane increasing by 1 per year.
• Sources Termites, wetlands, rice cultivation,
  biomass, and fossil fuel use.

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Status of Atmospheric CFCs

• Increasing at a rate of 5 per year.
• Long residence time.
• Absorbs uV wavelengths that would normally exit
  the atmosphere.

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Status of Atmospheric Nitrous Oxide

• Increasing at a rate of 5 per year.
• Sources Fertilizers and fossil fuels.
• Long residence time.

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Is Global Warming Occurring?

• Cycles are always underway in climate and
  precipitation, so it is hard to say if any
  changes that occur in one year are due to global
  climate change.
• There are three apparent facts
• Greenhouse effect is an understood atmospheric
  phenomenon
• Man-made sources increase concentrations of
  greenhouse gases
• There is a correlation between CO2 and global
  temperature.

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Models of Global Warming

• Positive Feedback
• Increased global warming increases evaporation
  and increases water vapor which leads to
  increased greenhouse effects and higher global
  warming
• Increases permafrost melting and methane
  production
• Increased burning of fossil fuels to cool
  buildings.

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Models of Global Warming

• Negative Feedback
• Increased carbon dioxide increases oceanic algae
  or terrestrial plant uptake, therefore global
  warming would decrease
• Increased carbon dioxide increases evaporation
  rates causing increased cloud cover, therefore
  less solar energy reaches the ground and cooling
  occurs.

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Models of Global Warming

• Global Circulation Models
• Use atmospheric temperature, relative humidity
  and wind conditions to predict regional effects
  of global warming.
• North America Increased winter precipitation and
  decreased summer rainsless crop production
• Sea level will rise with global warming. It is
  already rising at a rate of 2.5-3.0 mm per year.

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Effects of Global Warming

• Changes in climatic patterns
• Rise in sea level
• Changes in biosphere

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Variables That Need Further Study

• Sunspot cycles Correlation exists today, but we
  do not know if there is a cause-effect
  relationship.
• Aerosols (Particles lt 10 um) Condensation sites
  for water vapor. Increased cloud cover can result
  and cause a cooling trend.
• El Nino Reduces the amount of carbon dioxide
  outgased from the ocean, thereby altering global
  carbon cycling.

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What We Need To Know

• Uncertainties
• Will global temperature increases continue?
• Will the continual burning of fossil fuels and
  increased carbon dioxide concentrations cause
  global warming?
• Will policy decisions and actions taken to reduce
  greenhouse gas emissions have a beneficial effect?

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What We Need To Know

• Based on these uncertainties, we have two basic
  options
• Attempt to mitigate the severity of global
  warming by reducing greenhouse gas emissions
  (erring on the side of caution)
• Accept that change will occur and adapt to the
  new conditions.

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