Transcript global ocean currents

Ocean Currents & Climate
•The ocean and its currents have a
major influence on weather and climate
on Earth.
•In this unit we will see how
interactions among the hydrosphere,
lithosphere, atmosphere, and the ocean
produce weather and climate changes.
•On the following slides, the green
sections are the most important.
Underline words = vocabulary!
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Global Warming Pre-Test
• Last week you took a global warming
pre-test to test your prior knowledge
on the subject of global warming.
• Let’s review your scores!
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Currents
• The major landmasses
on Earth are connected
by moving water called
ocean currents.
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• A current is a large mass of continuously moving ocean
water.
• The largest currents that move across the ocean are called
global ocean currents. These currents are like rivers that
travel great distances.
• Ocean currents are affected by global temperature,
freshwater glacial ice melt, and density differences due to
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salt concentrations and temperature differences.
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Greenhouse Effect
• The atmosphere of our Earth acts like a
greenhouse that traps heat; the energy
from the sun also heats up the oceans.
• 50% of radiation from the sun is
absorbed by the Earth’s surface and then
“bounces” back into the earth’s
atmosphere.
• Gases, such as carbon dioxide and water
vapor, can stop this energy from
escaping into space by keeping it here
on Earth.
• As a result, the Earth’s atmosphere stays
warm, this is termed the greenhouse
effect.
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Global Warming
• Scientists have noticed that the Earth is
experiencing a warming trend.
• In the past 100 years, the Earth’s mean
global temperature has increased more
than 1 degree Celsius and ocean levels
have risen approximately 10 cm.
• Global warming is the result, the gradual
increase in Earth’s temperature.
• Scientists are trying to measure polar ice
caps to determine if their rate of melting
continues to increase.
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Measuring the Melt
• Scientists around the world provide research based data
on the effects of increased global temperatures.
• Specific data includes measuring the levels of artic ice.
• The graph below shows total ice coverage since 1973.
• As glacial ice melts, sea levels rise and ocean currents
can change.
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Carbon Dioxide levels
• The amount of
carbon dioxide in
the atmosphere has
been steadily
increasing.
• As we continue to
cut down trees for
paper production,
we are decreasing
the plants that
convert CO2 to
oxygen, causing an
increase in CO2
levels.
• The burning of fossil fuels (oil, coal,
etc) also adds carbon dioxide to
the environment.
• Air pollution produces by humans
is adding to the problem of global
warming.
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Natural Air Pollution
• Even “clean” air is not
perfectly clean.
• It contains many pollutants
from natural sources like dust,
volcanic gases and ash,
smoke from forest fires,
pollen, etc.
• Most of the air pollution
mentioned in the news is a
result of human activities.
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Natural Cycle?
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• Throughout the history of Earth the
climate has gone through periods of
warmth and periods of extreme cold
(often known as an Ice Age). This is a
natural phenomenon.
• Some scientists claim that the warming
trend is part of a natural cycle that will
eventually reverse itself through CO2
uptake by photosynthetic marine and
terrestrial plant life.
• Others claim that the warming of
Earth’s atmosphere is a real problem
that can be reduced by decreasing the
use of fossil fuels and finding
alternative energy sources.
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Water’s Density
• Density is the process by which molecules are packed
closely together.
• Warm water has a higher density than cold water due to
the increased kinetic energy of the molecules (they are
moving fast, creating more pace – thus, they rise).
• Fresh water is less
dense than salty
water.
• Density is important to
the currents which
shape the planet’s
climate.
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Effect of Salinity
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• Salinity, or the
amount of salt
within a
solution,
changes the
density of the
water.
• Salty water will
sink while fresh
water will rise
because of
differences in
density.
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In the Mediterranean
• The Mediterranean Sea, for example, has a higher salinity than the
Atlantic Ocean, creating a current south of Spain that moves salty
water deep into the Atlantic Ocean.
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Global Ocean Currents
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• Observe the Image of the major global currents.
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Radiant Energy
• The sun, the source
of all energy on
Earth, gives off
radiant energy and
influences the
climate that we
experience.
• The amount of
radiant (or solar)
energy that reaches
any part of the
planet depends on
the angle at which
the rays of the sun
strike the surface.
(Angle of Isolation)
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• The Earth’s curved surface and the
tilt of its axis causes areas farthest
away from the sun’s rays (the
poles) to receive slanted rays with
a smaller angle, and are therefore
less intense.
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Ocean Temperature
• The uneven heating of the Earth due to the rays of the sun
causes ocean temperatures to vary with latitude.
• The ocean is warmest at the equator.
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Coriolis Effect
• The coriolis effect states that the spinning Earth causes the
winds and surface waters to move in a specific directions.
• In the northern
hemisphere, the
currents deflect
clockwise to the east.
• In the southern
hemisphere currents
move in the opposite
direction, counter
clockwise to the west.
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Gyres
• The water moves and hits the continent which deflect the
currents, causing them to move in giant circles called gyres.
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Gulf Stream
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• The gulf stream current flows
from the southwestern Atlantic
to the northeastern; it is the
major factor in favorable
(warm) weather on the eastern
coast of the United States.
• Benjamin Franklin was the first
to chart the temperature and
speed of the gulf stream back
in the 1700s.
• You can see that the gulf stream flows northeast up the
coast of the United States. The satellite image shows it
carries with it very warm water.
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Hurricanes
• A hurricane is a coastal storm
with a wind velocity exceeding
120 km per hour.
• Hurricanes form in warm tropical
seas where there is hot, moist air.
Such conditions contain the heat
needed to fuel a hurricane.
• As hot, moist air rises, it
cools in the upper
atmosphere and
condenses into ring
shaped clouds. During
condensation, a great deal
of heat energy is released,
which causes more hot air
to rise even quicker. This
whirlwind of rising air
moves in a spiral direction
around calm air knows as
the “eye” of a hurricane.
• View the animation from
NASA by clicking the
graphic.
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El Nino
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• Droughts in Australia,
famine in Africa, floods in
California, and other
climate disturbances in
recent years have all been
caused by changes in the
warm ocean currents
around the globe.
• Oceanic warming is called
El Nino.
• El Nino begins in the
western Pacific Ocean.
• Warm currents are
normally carried
northwest due to trade
winds.
• El Nino reverses the currents because
of a decline in southeast trade winds
and causes a change in the climate
of South America (bringing floods
and stormy weather).
• Follow the arrows in the image
above.
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La Nina
• Unusually cold currents causing cooler surface temperatures is
known as La Nina.
• During La Nina years (when ocean currents are unusually cool in
the mid-Pacific) winters are cooler than normal in the northwest
United states and warmer than normal in the southeast.
• The cycles for El Nino/La Nina often last 1 to 2 years and occur
every 4 to 6 years. Click on the graphic to view an animation
depicting the differences between El Nino and La Nina.
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Conclusion
• Ocean currents on planet Earth drive the weather and
stabilize the climate.
• Changing of ocean currents and related factors such as
trade winds can have devastating effects (El Nino, La
Nina, rising sea levels, etc).
• In order to understand the complex factors that create
Earth’s climate you need to understanding the forces of
density, salinity, and Earth’s temperature as they relate to
ocean currents.
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Possible Effects
Journal: Future of Global
Warming
Using the political cartoon at
the left, predict earth in the
future and explain why the
cartoonist chose to use the
image to image a future earth
after global warming. Is this a
possible effect of an increase
in global temperatures?
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