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Chapter 4
Global Climates and Biomes
Earth’s climate system is composed of
atmosphere/ocean interactions (driven by sun)
Earth's Atmosphere
Layers of the Atmosphere
• Troposphere- the layer closest to Earth's surface and
is the layer where we live; most of the atmosphere’s
oxygen is found here.
• The troposphere extends upwards 5 to 9 miles
from the Earth’s surface at sea level.
• Most weather occurs in the troposphere.
• The troposphere is the most dense layer of the
atmosphere (more molecules per unit of volume)
Earth's Atmosphere
Stratosphere- the layer directly above the troposphere.
• The stratosphere extends from 9 to 31 miles from
the Earth’s surface at sea level.
• Stratospheric ozone is vital to trapping and
scattering ultraviolet (UV) radiation from the sun.
• This layer is drier and less dense than the
troposphere.
• The troposphere and stratosphere make up the
lower atmosphere. 99% of all atmospheric air is
found here.
Earth's Atmosphere
• Mesosphere lies directly above the stratosphere from
31-53 miles above the Earth’s surface at sea level.
• Thermosphere is directly above the mesosphere,
extending from 53-372 miles above the Earth’s
surface.
• Together the mesosphere and thermosphere are
sometimes called the ionosphere.
• Exosphere is the outermost layer of Earth’s
atmosphere and acts as the transition zone between
Earth’s atmosphere and outer space. Has the lowest
atmospheric pressure of all layers.
The
Silly
Mouse
Tried to
Escape
Earth's Atmosphere
• Composition of the Atmosphere
• The atmosphere is made up of gases:
Atmospheric gas
Nitrogen (N)
Oxygen (O)
Water Vapor (H2O)
Carbon Dioxide (CO2)
Ozone (O3)
% of the Earth’s Atmosphere
78%
21%
0-7% (varies by climate)
0.01-0.1% (varies by location)
0-0.01% (varies by location)
Greenhouse Effect: The temperature of the Earth’s atmosphere is
maintained by the absorption of incoming infrared radiation (heat) by
atmospheric gases such as CO2 (carbon dioxide), CH4(methane), N2O
(nitrous oxide) and O3 (ozone).
Earth's Tilt and the Seasons
• The Earth's axis of rotation is tilted 23.5 ˚.
• When the Northern Hemisphere is tilted
toward the Sun, the Southern Hemisphere is
tilted away from the Sun, and vice versa.
Earth's Rotation and the Coriolis Effect
• As Earth rotates, its surface moves much faster at the
equator than in mid-latitude and polar regions.
• The faster rotation speeds closer to the equator cause a
deflection of objects that are moving directly north or
south.
• Coriolis Effect- the deflection of an object's path due to
Earth's rotation.
Global Processes Determine Weather
and Climate
• Weather- the short term conditions of the
atmosphere in a local area. These include
temperature, humidity, clouds,
precipitation, wind speed and atmospheric
pressure.
• Climate- The average weather that occurs
in a given region over a long periodtypically several decades.
Unequal Heating of Earth
• As the Sun's energy passes through the atmosphere and
strikes land and water, it warms the surface of Earth.
But this warming does not occur evenly across the
planet.
Unequal Heating of Earth
• This unequal heating is because:
• The variation in angle at which the Sun's rays strike
• The amount of surface area over which the Sun's
rays are distributed
• Some areas of Earth reflect more solar energy than
others. (Albedo – the measure of the degree of
reflection of heat from the sun off of a surface.
Darker substances tend to absorb more heat and
have a lower albedo while lighter substances tend to
reflect more heat have a higher albedo)
Atmospheric Convection Currents
• Air has four properties that determines its movement:
• Density- less dense air rises, denser air sinks.
• Water vapor capacity- warm air has a higher
capacity for water vapor than cold air.
• Adiabatic heating or cooling- as air rises in the
atmosphere its pressure decreases and the air
expands. Conversely, as air sinks, the pressure
increases and the air decreases in volume.
• Latent heat release- when water vapor in the
atmosphere condenses into liquid water and energy
is released.
The differences in temperature, density, and
pressure of air/water determine movement
patterns
• Warm air/water rises
& expands (low
pressure)
• Cold air/water is
denser & sinks (high
pressure)
• Air’s saturation point
for water falls as it
cools (precipitation is
“squeezed” out)
Formation of Convection Currents
• Atmospheric convection currents are global
patterns of air movement that are initiated by
the unequal heating of Earth.
• Hadley cells- the convection currents that
cycle between the equator and 30˚ north and
south.
• Intertropical convergence- the area of Earth
that receives the most intense sunlight and
where the ascending branches of the two
Hadley cells converge.
• Polar cells- the convection currents that are
formed by air that rises at 60˚ north and south
and sinks at the poles (90˚ north and south)
• Look at the equator – as the air is warmed by the sun’s radiation, it rises and
cools. As the warm, moist air rises and cools, the water vapor it contains
condenses and falls as rain. This is why tropical rainforests are common
along the equator
• At 30º lat (N/S of the equator) notice that now cool air falls toward the
earth. As that air falls and warms, it has a greater capacity for holding
water and it absorbs water from the Earth's surface.
• At 60º lat, the warm, moist air once again rises and cools dropping water
toward Earth’s surface and causing temperate rainforest to be common in
this location.
• The final rotation of the cells results in cool, dry air descending over the
poles, warming and pulling water from the land and leading to polar
deserts.
Ocean Currents
• Ocean currents are driven by a combination of
temperature, gravity, prevailing winds, the
Coriolis effect, and the locations of continents.
• Warm water, like warm air, expands and rises.
• Gyres- the large-scale patterns of water
circulation. The ocean surface currents rotate in
a clockwise direction in the Northern
Hemisphere and a counterclockwise direction in
the Southern Hemisphere.
Upwelling
• Upwelling- as the surface currents separate from one another,
deeper waters rise and replace the water that has moved away.
• This upward movement of water brings nutrients from the ocean
bottom that supports the large populations of producers, which in
turn support large populations of fish.
• Thermohaline circulation- another oceanic circulation that drives
the mixing of surface water and deep water.
• Scientists believe this process is crucial for moving heat and
nutrients around the globe.
Ocean surface currents (~10% of water movement):
Subsurface thermohaline circulation ocean currents
(90% of water movement)
El Nino-Southern Oscillation
• The El Niño-Southern Oscillation (ENSO) is a climate
shift found in the tropical equatorial Pacific Ocean.
• El Niño occurs when the trade winds blowing east to
west across the equatorial Pacific Ocean slacken or
reverse.
This causes surface water to be
warmer and suppresses nutrient
rich upwelling off the northwest
coast of South America (near
Peru).
If the upwellings are halted for
more than 12 mths, population of
plankton, seabirds, fish, etc. find it
difficult to find enough nutrients
to survive. As a result, their
populaiton numbers decline.
• ENSO events occur every three to seven years and last from a
few months (normal) to as long as 4 years (extreme).
• A strong ENSO can affect weather patterns over most of the Earth.
• Warmer, dry weather may be found across much of the northern US,
Canada, Brazil, Indonesia, Australia, India and southeast Africa leading
to:
Less snow, causing decreased snowmelt in the spring to
replenish snow-fed rivers; severe droughts; increased wildfires;
increased transmission of diseases due to stagnant warm water
and lack of winter kill-off of insect vectors (malaria, dengue
fever) and deterioration of fresh water in times of drought.
• Significantly higher rainfall may occur across much of the southern US,
Cuba, northern Peru, Ecuador, Bolivia, southeast Argentina, and
equatorial east Africa leading to:
suppression of hurricanes in
the Caribbean and Atlantic Ocean; flooding which is often followed by
landslides; increased transmission of diseases due to contamination of
water sources because of flooding and standing water (mosquito
breeding).
•
Variations in Climate Determine the
Dominant Plant Growth Forms of
Terrestrial Biomes
• Climate affects the distribution of species
around the globe.
• Organisms possess distinct growth forms
due to adaptations to local temperature and
precipitin patterns.
• Biomes- The presence of similar plant
growth forms in areas possessing similar
temperature and precipitation patterns.
BIOME DISTRIBUTION
Lakes and Ponds
Lakes and Ponds
• Littoral zone- the shallow area of soil and water near the
shore where algae and emergent plants grow.
• Limnetic zone- open water, where rooted plants can no
longer survive. Phytoplankton are the only
photosynthetic organisms. This zone extends to as deep
as sunlight can penetrate.
• Profundal zone- the zone where sunlight cannot
penetrate and therefore producers cannot survive.
• Benthic zone- the muddy bottom of a lake or bond
beneath the limnetic and profundal zone.
The Open Ocean
• The depth that light can penetrate in the open
ocean is dependent on the amount of sediment
and algae suspended in the water.
• Photic zone- the zone that receives enough light
to allow photosynthesis to occur.
• Aphotic zone- the deeper water that lacks
sufficient light for photosynthesis.
• Chemosynthesis- The process that occurs in the
aphotic zone when some species of bacteria use
methane and hydrogen sulfide to generate
energy.