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Chapter 2
The Greenhouse Effect
• The Earth’s atmosphere is compared
to the glass walls and roof of a
greenhouse
– Traps the sun’s warmth for
growing plants
• Solar Radiation reaches the Earth’s
atmosphere
• Some radiation reflects back into
space
• Other radiation remains to warm the
Earth’s surface
• Not all places on the Earth get the
same amount of heat from the sun
– This depends on the relative
position of the sun and the Earth
Rotation
• The Earth rotates on an axis
as it moves through space
– The axis is an invisible line
through the center of the
Earth from pole to pole
• The Earth completes one
rotation in 24 hours
• The side that faces the sun
it is daytime, and the side
that is turned away from the
sun is night
Revolution
• The Earth also revolves around the sun in a orbit
• The Earth completes one revolution every 365 ¼ days (one year)
• To account for the ¼ a day, every 4 years we have an extra day,
known as Leap Year
• The Earth’s position to the sun is tilted at a 23 ½ degree axis
– The Tropic of Cancer is at 23 ½ degrees North
– The Tropic of Capricorn is at 23 ½ degrees South
– These places receive the most direct sunlight
Solstices and Equinoxes
• Because of the Earth’s tilt, sunlight hits the
surface differently at certain times of the year
– As the Earth moves halfway around the sun, the
Northern and Southern Hemispheres tilt closer or
farther from the sun
– These changes are marked by summer and winter
solstices
• June 21 and December 21
• For the equinox, at noon the sun appears
directly overhead at the Equator
– March 21 and September 23
Influences on Climate
• The angle of the sun’s rays affect weather and
climate in certain areas of the Earth
• Wind
– Rising warm air creates areas of low pressure
– Falling cool air causes areas of high pressure
– Winds move from areas of high pressure into areas of
low pressure
– The movement of winds distributes the sun’s heat
over the earth’s surface
– If the earth were not moving, winds would blow in a
straight line, because the earth moves, the winds
blow in different directions
Influences on Climate
• Currents
– Ocean currents carry warm water from the tropics to
the poles
– Other currents return cold water to the Equator
Influences on Climate
• Precipitation
– Forms as air temperature changes
– Warm, less-dense air absorbs more moisture than cool air
– When the air cools, it cannot retain all of its water vapor, so the
excess water vapor condenses into a liquid
– Tiny droplets of water gather together to form clouds
– Precipitation occurs when more water collects in clouds than
they can hold
– Precipitation is divided into three types: convectional, orographic,
and frontal
Influences on Climate
• Convectional Precipitation
– Occurs when hot, humid air rises from the earth’s
surface and cools. It then losses its ability to hold
much water
– Common near the Equator and in the tropics
– Produces nourishing rainfalls that feed lush, tropical
forests
Influences on Climate
• Orographic Precipitation
– Sometimes warm, moist air is forced upward when passing over
high landforms
– This is common on seacoasts where moist, ocean winds blow
toward coastal mountains
– The warm winds cool as they rise up over the mountains
– Clouds form and rain or snow falls
– The air is cool and dry by the time it reaches the other side of the
mountains
Influences on Climate
• Frontal Precipitation
– The most common kind of precipitation
– Occurs when two fronts (or air masses) of different
temperatures meet
– The warm air is forced upward by the heavier cool air
– The rising warm air cools, and frontal precipitation
forms
Influences on Climate
• Nearby Bodies of Water
– Bodies of water temperatures change much
more slowly then land temperatures
– Because of this difference, large bodies of
water affect the surrounding climates
– Winds blow over the water take on the water’s
temperature
Influences on Climate
• Elevation
– Elevation has a dramatic effect on climate in highland
areas throughout the world
– Air temperature decreases at a rate of 3.5 degrees for
every 1000 feet
– Hikers must use caution because of this
Influences on Climate
• Nearby Landforms
– All landforms affect climate
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Coastal mountains
Lakes
Forests
Tall buildings
Pavement – absorbs large amounts of solar energy
Plant Communities
• Plants usually don’t live alone. Most plants
are in groups that depend on each other
– Nourishment, shade, support
• A Plant community is a mix of
interdependent plants that naturally grow
in one place
• Similar environments tend to produce
similar plant communities
Biomes and Vegetation Regions
• Biome describes a region in which the
environment, plants, and animal life are
suited to one another
• Regions are classified by their natural
vegetation – or the typical plant life in
areas where humans have not altered the
landscape significantly