Transcript Understanding Our Environment

Air, Weather, and Climate
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Outline
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The Atmosphere and Climate
 Greenhouse Effect
 Convection Currents
Weather
 Coriolis Effect
 Cyclonic Storms
Climate
 El Nino
 Climate Change
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THE ATMOSPHERE AND CLIMATE
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Weather - A description of physical conditions
of the atmosphere.
Climate - A description of the long-term
weather pattern in a particular area.
 Weather and climate are primary
determinants of biomes and ecosystem
distribution.
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The Atmosphere and Climate
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Troposphere
 Ranges in depth from 18 km over the
equator to 8.0 km over the poles.
- All weather occurs here.
- Composition is relatively uniform.
- Air temperature drops rapidly with
increasing altitude.
 Tropopause - Transition boundary that
limits mixing between the troposphere
and upper zones.
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The Atmosphere and Climate
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Stratosphere
 Extends from troposphere to about 50 km.
- Air temperature is stable, or increases
with altitude.
 Has almost no water vapor and ozone
is 1000x more than in the
troposphere.
- Relatively calm
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The Atmosphere and Climate
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Mesosphere
 Middle Layer
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Thermosphere
 Begins at 80 km.
- Ionized gases and high temperatures.
 Lower Thermosphere
 Aurora borealis (northern lights)
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Energy and the Greenhouse Effect
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Of the solar energy that reaches the outer
atmosphere:
 About one-quarter is reflected by clouds and
the atmosphere.
 Another quarter is absorbed by carbon
dioxide, water vapor, ozone and a few other
gases.
 About half reaches the earth’s surface.
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Energy Balance
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Energy and the Greenhouse Effect
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Surfaces that reflect energy have a high
albedo (Reflectivity).
Fresh clean snow
 Dark soil
 Net average of earth

80-85%
3%
30%
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Energy and the Greenhouse Effect
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Most solar energy reaching the earth is
visible light.
 Energy reemitted by the earth is mainly
infrared radiation (heat energy).
- Longer wavelengths are absorbed in the
lower atmosphere, trapping heat close to
the earth’s surface.
 Greenhouse Effect
 Increasing atmospheric CO2 due to
human activities appears to be
causing global warming.
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Convection and Atmospheric Pressure
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Lighter air rises and is replaced by cooler,
heavier air, resulting in vertical convection
currents.
 Transport energy and redistribute heat.
Much of solar energy absorbed by the earth
is used to evaporate water.
 Energy stored in water vapor as latent
heat.
- If condensation nuclei are present, or if
temperatures are low enough,
condensation will lead to precipitation.
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Convection Currents
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Releasing latent heat causes air to rise, cool,
and lose more water vapor.
 Rising, expanding air creates an area of
relatively high pressure at the top of the
convection column.
- Air flows out of high-pressure zone
towards areas of low-pressure, where
cool, dry air is subsiding.
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Convection Currents
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Subsiding air is compressed as it
approaches the earth’s surface where it piles
up and creates an area of high pressure at
the surface.
 Air flows out of this region back towards
low pressure, closing the cycle.
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Coriolis Effect
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As air warms at the equator, rises, and
moves northward, it sinks and rises in
several intermediate bands, forming
circulation cells.
 Surface flows do not move straight North
and South, but are deflected due to
Coriolis Effect.
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Coriolis Effect
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Major zones of subsidence occur at about
30o north and south latitude.
 Where dry, subsiding air falls on
continents, it creates broad, subtropical
desert regions.
- Winds directly under regions of
subsiding air are often light and variable.
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Jet Streams
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Jet Streams - Large-scale upper air flows.
 Generally follow undulating paths where
Hadley and Ferrell cells meet.
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Ocean Currents
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Warm and cold ocean currents strongly
influence climate conditions on land.
 As surface water moves, deep water wells
up to replace it.
- Ocean circulation also driven by
differences in water density.
 Gyres
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Seasonal Winds and Monsoons
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Monsoon - Seasonal reversal of wind
patterns caused by differential heating and
cooling rates of oceans and continents.
 Most prevalent in tropical countries where
large land area is cut off from continental
air masses by mountain ranges and
surrounded by a large volume of water.
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Frontal Weather
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Cold Front - Boundary formed when cooler
air displaces warmer air.
 Cold air is more dense, thus hugs ground
and pushes under warm air.
- Warm air cooled adiabatically.
Warm Front - Boundary formed when warm
air displaces cooler air.
 Warm air is less dense and slides over
cool air, creating a long wedge-shaped
band of clouds.
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Cyclonic Storms
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When rising air is laden with water vapor,
latent energy released by condensation
intensifies convection currents and draws up
more warm air and water vapor.
 Storm cell will exist as long as temperature
differential exists.
- Hurricanes (Atlantic)
- Typhoons (Western Pacific)
- Cyclones (Indian Ocean)
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Cyclonic Storms
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Tornadoes - Swirling funnel clouds.
 Rotation not generated by Coriolis forces.
 Generated by “supercell” frontal systems
where strong dry cold fronts collide with
warm humid air.
- Greater air temperature differences in
Spring thus more tornadoes.
 Spinning - Rolling vortex tubes.
 Downbursts - Disorganized supercells.
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Tornadoes
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CLIMATE
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Driving Forces and Patterns
 Periodic weather cycles detected.
- Solar magnetic cycles
- Milankovitch Cycles - Periodic shifts in
earth’s orbit and tilt.
 Change distribution and intensity of
sunlight reaching the earth.
 Ice cores show drastic changes
may have occurred over short
periods of time (decades).
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El Nino Southern Oscillation
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Large pool of warm surface water in Pacific
Ocean moves back and forth between
Indonesia and South America.
 Most years, the pool is held in western
Pacific by steady equatorial trade winds.
- Every three-five years the Indonesian
low collapses and the mass of warm
surface water surges back east.
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El Nino Southern Oscillation
During an El Nino year, the northern jet
stream pulls moist air from the Pacific over
the U.S..
- Intense storms and heavy rains.
 During intervening La Nina years, hot,
dry weather is often present.
 Pacific Decadal Oscillation - Very large
pool of warm water moving back and forth
across the North Pacific every 30 years.

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Human-Caused Global Climate Change
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In 1988, the Intergovernmental Panel on
Climate Change (IPCC) was formed.
 Released third climate report in February
2001.
- Recent changes in world’s climate have
had discernable impacts on physical and
biological systems.
 Human activities must be at least
partially responsible.
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CO2 Concentrations on Mauna Loa
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Sources of Greenhouse Gases
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Carbon Dioxide - Fossil-fuel burning.
- Atmospheric levels increasing steadily.
Methane - Ruminants, Coal-mines.
- Absorbs more infrared than CO2.
Chlorofluorocarbons (CFC’s) - Refrigerants
- Declined in recent years.
Nitrous Oxide - Burning organic material.
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Aerosol Effects
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Aerosols have a tendency to reflect sunlight
and cool surface air temperatures.
 Short-lived, thus effects are temporary.
 Mt. Pinatubo erupted in 1991 and ejected
enough ash and sulfate particles to cool
global climate about 1o C for nearly a year.
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Current Evidence of Climate Change
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Global average surface temperature rose 0.6o C
during 20th century.
Droughts are more frequent and widespread.
Severe weather events have increased
dramatically.
Polar regions have warmed much faster than the
rest of the world.
Ice shelves on Arctic peninsula are disappearing.
Many animals breeding earlier and extending their
ranges.
Amphibians disappearing.
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Current Evidence of Climate Change
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Retreating alpine glaciers.
 Mt. Kilimanjaro
 Glacier National Park
Coral reefs are “bleaching.”
Northern growing seasons are longer.
Sea level has risen.
Arctic sea ice is 40% thinner.
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Winners and Losers
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Residents of extreme northern areas would
enjoy warmer temperatures and longer
growing-seasons.
Plant growth patterns may be altered.
One-third of population living in areas likely
flooded by rising seas.
More evaporation may cause severe storms.
 Infectious disease likely to spread faster.
 Circulation patterns may cause more
snowfall at poles - New ice age ?
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Predicted Warming for CO2 Doubling in 2100
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International Climate Negotiations
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Kyoto Protocol (1997)
 160 nations agreed to roll back carbon
dioxide, methane, and nitrous oxide
emissions about 5% below 1990 levels by
2012.
- Sets different limits for different
countries, depending on prior output.
 Developing countries exempted.
 126 countries have ratified the Protocol.
U.S. has not.
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Controlling Greenhouse Emissions
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Reducing carbon dioxide levels.
 Renewable energy sources may offer a
better solution to climate problems.
Capturing and storing carbon dioxide.
 Carbon Management
- Planting vegetation
- Emissions trading system
- Deep water injection
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Summary
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The Atmosphere and Climate
 Greenhouse Effect
 Convection Currents
Weather
 Coriolis Effect
 Cyclonic Storms
Climate
 El Nino
 Climate Change
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