Transcript Understanding Our Environment

Chapter 15
Lecture Outline*
William P. Cunningham
University of Minnesota
Mary Ann Cunningham
Vassar College
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Air, Weather, and Climate
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Outline
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The Atmosphere and Climate
 Convection Currents
 Greenhouse Effect
Weather
 Winds
 Frontal Systems
 Cyclonic Storms
Climate
 El Nino
 Climate Change
 Kyoto Protocol
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The Atmosphere and Climate
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Weather - daily temperature and moisture
conditions in a place
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Climate - a description of the long-term weather
pattern in a particular area
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The Atmosphere and Climate
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Troposphere
 Ranges in depth from 18 km over the equator to
8 km over the poles.
- All weather occurs here.
- Convection currents redistribute heat and
moisture around the globe.
- 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
 From tropopause up to about 50 km
- Has almost no water vapor, but 1000X more
ozone than the troposphere
- Ozone absorbs ultraviolet light, which warms
upper part of stratosphere.
- Ozone protects all life on Earth since UV
radiation damages living tissues.
- Ozone being depleted
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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 has ions which are
struck by high energy radiation.

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
80-85%
•
Surfaces that absorb energy have low albedo.
 Dark soil
3%
Net average of earth
30%
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•
Absorbed energy evaporates water and runs
photosynthesis. Absorbed energy released as heat.
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Energy and the Greenhouse Effect
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Most solar energy reaching the Earth is near
infrared (short wavelength).
 Energy reemitted by the earth is mainly far
infrared radiation (long wavelength, heat)
- Longer wavelengths are absorbed in the
lower atmosphere, trapping heat close to the
earth’s surface.
 Greenhouse Effect
 Atmosphere transmits sunlight while
trapping heat.
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Greenhouse Effect




Gases in the atmosphere, especially carbon
dioxide and water vapor, are the substances
that retain heat.
Burning fossil fuels releases extra carbon
dioxide.
Deforestation destroys carbon sinks.
Positive feedback loop - poles covered with ice
reflect solar radiation back into space. Now that
ice is melting, open water is absorbing more
heat, which in turn is melting more ice, leading to
more warming.
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Convection and Atmospheric Pressure
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Much of solar energy absorbed by the Earth is
used to evaporate water.
 Energy stored in water vapor as latent heat.
 When water vapor condenses, heat energy is
released.
 Heat and water move from warmer areas near
the equator towards cooler areas at poles. Heat
redistribution prevents extreme temperature
fluctuation.
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Circulation Patterns
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Convection Currents
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Releasing latent heat causes air to rise, cool, and
lose more water vapor as precipitation.
Warm air close to equator vs. cold air at poles also
produces pressure differences that cause weather.
 Air near surface warms and becomes less dense
than the air above it; rises above cool air
creating vertical convection currents.
- Low pressure - air is rising
- High pressure - air is sinking
 Pressure differences cause winds.
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Convection Currents
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Weather Happens
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Weather - physical conditions in the atmosphere
(humidity, temperature, air pressure, wind and
precipitation) over short time scales
 Rain
- Air cools as it rises, and water condenses as
air cools.
- Cooling occurs because pressure decreases
as air rises.
- Condensation nuclei (tiny particles) must also
be present to have precipitation.
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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.
The curving pattern results from the fact that the
earth rotates in an eastward direction as winds
move above it.
 Winds and currents move clockwise in Northern
Hemisphere and counterclockwise in the
Southern Hemisphere.
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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 subtropical deserts.
On a regional scale, the Coriolis effect produces
cyclonic winds, which spiral clockwise out of an
area of high pressure in the Northern Hemisphere
and counterclockwise into an area of low pressure.
You can see these on weather maps.
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Jet Streams
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Jet streams - hurricane
force winds at the top
of the trophosphere
which follow an
undulating path
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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 due to temperature and
saltiness of water
 Gyres - huge cycling currents carrying
water north and south
 Currents can shift abruptly.
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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 subtropical and tropical areas.
 Tilt of Earth’s axis changes location where the
Sun is most intense over the course of the year.
Places where the Sun shines most directly have
evaporation and convection currents which bring
thunderstorms.
 Seasonal rains support tropical forests and fill
great rivers such as Ganges and Amazon.
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Summer Monsoons in India
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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 warm air up.
- Warm air cooled adiabatically (without loss or
gain of energy), precipitation.
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
and precipitation.
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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)
 Katrina in 2005 caused greatest natural
disaster in North American history.
- 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 the
spring, thus more tornadoes
 Downbursts - disorganized supercells that cause
downdrafts and straight line winds
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Cyclonic Storms
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Studying Climate
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Ice cores - collected from glaciers reveal light and
dark bands caused by annual snow accumulation
on glacier
 Gas bubbles can be analyzed for atmospheric
composition.
 Ash and sulfur deposits correlate with volcanic
eruptions.
 Vostok ice core gives us a record back 420,000
years.
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Climate
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Data show that:
 Abrupt climatic change has catastrophic effect on
living things as organisms are unable to adjust
before conditions exceed their tolerance limits.
Species may become extinct.
 There is a close correlation between carbon
dioxide concentration and temperature of the
atmosphere.
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Climate
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What causes climate change?
 Sunspot cycles
 Solar magnetic cycles
 Cycle of shift in angle of moon alters tides and
currents.
 Milankovitch Cycles - periodic shifts in Earth’s
orbit and tilt which change distribution and
intensity of sunlight
- Ice cores show drastic changes may have
occurred over short periods of time (years to
decades).
 Volcanic eruptions can cool planet suddenly.
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Milankovitch Cycles
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El Nino/Southern Oscillation
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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.
 Surface waters driven westward by trade winds
are replaced by upwelling of cold, nutrient rich
waters off west coast of South America.
Nutrients supply food for fisheries.
 Every three-five years the Indonesian low
collapses and the mass of warm surface water
surges back east and we call this an El Nino.
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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 from
California to the Midwest
- During intervening La Nina years, hot, dry
weather is often present.
- ENSO events are becoming stronger and
more irregular due to global warming.
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El Nino/Southern Oscillation

High sea surface temperatures cause hurricanes
to be more violent.

Pacific Decadal Oscillation - very large pool of
warm water moving back and forth across the
North Pacific every 30 years. Affects fishing
harvest.
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Global Warming is Happening
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Most important environmental issue of our time
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In 2007, the Intergovernmental Panel on Climate
Change released its fourth report.
 Represents a consensus by more than 90% of
all scientists working on climate
 Gives a probability value of 90% that the
warming we are now seeing is caused by
humans
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Global Warming
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Range of temperature increase predicted to be
from 1.1 to 6.4°C (2 to 11.5°F) by 2100 depending
on population growth, energy conservation, etc.
Best estimate is 1.8 to 4°C (3.2 to 7.8°F)
 To put that in perspective, there has been a 5
degree C rise since the middle of the last ice age
(about 20,000 years ago).
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Global Warming
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Most people will experience more extreme weather
including droughts, floods, heat waves and
hurricanes. These extremes have increased
significantly in the last decade.
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In the worst outcome, we could see millions of
human deaths.
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Sea levels are projected to rise 17-57 cm (7 to 23
in). If we do nothing, Greenland’s ice will melt and
raise sea levels 20 ft.
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Global Warming
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If Greenland’s ice melts, a great deal of land will be
flooded including:
 Most of Florida
 Some of the Gulf Coast
 Most of Manhattan
 Shanghai
 Hong Kong
 Tokyo
Bush administration praised the report but said it
opposes mandatory cuts in greenhouse gas
emissions as too costly.
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Sources of Greenhouse Gases
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Carbon Dioxide - fossil-fuel burning
- Atmospheric levels increasing steadily
- Most important cause of warming
Methane - ruminants, rice paddies
- Absorbs more infrared than CO2 .
Chlorofluorocarbons (CFC’s) - refrigerants
- Declined in developed countries, but now
produced in developing nations.
Nitrous Oxide - burning organic material
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Carbon Dioxide Concentrations on Mauna Loa
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Sources of Greenhouse Gases
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U.S. has less than 5% of world’s population but
produces 28% of carbon dioxide.
China, with 1.3 billion people, is second.
Japan and Europe produce half as much carbon
dioxide per person as the U.S.
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Evidence of Climate Change is Overwhelming
“As best as can be determined, the world is now
warmer than it has been at any point in the last two
millennia, and, if current trends continue, by the end
of the century it will likely be hotter than at any point
in the last two million years.”
American Geophysical Union
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Evidence of Climate Change is Overwhelming
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Ave. global temperature climbed 0.6°C (1°F) in last
century.
 19 of 20 warmest years in the past 150 yrs have
occurred since 1980.
 Hottest year since temperature records were
begun was 2005; 2007 is expected to surpass it.
 Poles are warming fastest (4°C, 7°F over past 50
years). Permafrost is melting in Alaska and
Canada and houses, pipelines and trees are
being toppled.
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Evidence of Climate Change is Overwhelming
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Arctic Sea ice is half as thick as it was 30 years
ago, and the ocean area covered by ice has
decreased by 1 million sq. km. in 30 yr.
 Polar bears are dying.
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Antarctic ice shelves are disappearing.
 Penguins declined 50% in last 50 yrs.
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Glaciers are melting all over the world.
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Sea level has risen 6 to 8 inches in last century.
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Evidence of Climate Change is Overwhelming
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Oceans have been absorbing some of the extra
CO2 but that is acidifying the ocean and damaging
coral.
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Growing seasons are lengthening in Northern
hemisphere. Some animals are breeding earlier or
extending their range. Others are disappearing.
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Droughts are more frequent and widespread and
storms more severe.
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Global Warming will be Expensive
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At present, reducing greenhouse gas emissions
would cost 1% of world GDP according to Stern
report. (IPCC report says less than that.)
If we delay, it could cost as much as 20% of world
GDP.
Energy production will need to be 80%
decarbonized by 2050 to stabilize climate.
 Ethical issue
 Poor will suffer the most; at least 200 million
people will become refugees of flood and
drought.
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Steps For Combating Climate Change
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Emissions trading
 markets already exist
Technology sharing
Reducing deforestation
Helping poorer countries adapt to climate change
 Tropical areas will not change as much as
middle and high latitudes.
 If both Greenland and Antarctica melt, 1/3 of
Earth’s population will be displaced.
- South Pacific island nation of Tuvalu already
abandoned due to climate change
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Combating Climate Change
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Insurance companies have $2 trillion in insured
properties along U.S. coastlines at risk from
flooding or severe storms.
Infectious diseases will increase as insects that
spread them are able to move to places where
they could not live before.
 West Nile, malaria, and dengue fever have
appeared in North America.
Melting of permafrost may release stores of
methane hydrate. Uncertainty about whether that
would increase warming or cooling.
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Predicted Warming for 2090-2099
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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.
took a leading role in the 1990s, but Bush
declined to honor U.S. commitments.
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Kyoto Protocol
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Bush claimed reducing carbon emissions would be
too costly for the U.S.
 But in 2007, the CEOs of the 10 largest business
conglomerates in the U.S. called for legislation to
reduce greenhouse gases.
 A single national standard would be better for
business than a patchwork of state and local
rules.
 Companies engaged in international business
will have to modify their products anyway to
compete abroad.
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Controlling Greenhouse Emissions
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Reducing carbon dioxide levels
 Renewable energy sources
- Double average fuel economy
- Switch to efficient lighting and appliances
- Wind turbines
- Biofuels
 Capture and store carbon dioxide
- Planting vegetation
- Injection into wells
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Progress Made
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United Kingdom has rolled back its CO2 emissions
to 1990 levels and is aiming for a 60% reduction by
2050.
Germany has reduced CO2 by 10%.
Denmark gets 20% of its electricity from windmills,
and plans to increase that to 50%.
China reduced its emissions 20% between 1997
and 2005.
(At its present rate, U.S. will be 25% above 1990
emissions in 5 years. No progress.)
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Carbon Management
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Capturing and storing carbon dioxide
Build “trees” in which calcium hydroxide solution
would absorb carbon dioxide
Plant forests
Fertilize the oceans with iron to permit
phytoplankton growth, which would take up carbon
dioxide
Inject carbon dioxide underground or in ocean
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Synthetic “Trees” that Capture Carbon Dioxide
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