Chapter 18: Climate and Climate Change,
18-1: What Causes Climate?
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“Weather” is the condition of the atmosphere at
a certain place and time
Climate is the average year-after-year
conditions of temperature, precipitation, winds,
and clouds in an area
Two main factors determine the climate of a
region: temperature and precipitation
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18-1 Factors affecting temperature
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The main factors that influence
temperature are latitude, altitude,
distance from large bodies of water,
and ocean currents.
Latitude is the distance from the equator,
measured in degrees.
Climates of areas farther from the equator
tend to be cooler than areas close to the
equator.
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18-1 Factors affecting temperature: Latitude
Earth’s temperature zones based on latitude
• Tropical zone: Near the equator, between 23.5°
North and 23.5° South, climates are warm.
Frequent direct sunlight
• Temperate zones: Between tropical and polar
zones (23.5°-66.5°North, and also 23.5°66.5°South). Climates in these areas vary from
having warm or hot summers to having cool or
cold winters
• Polar zones: Near poles, from 66.5° to 90°
North and from 66.5° to 90° South, climates are
cold
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Climate Zones
http://www.cgrove417.org/fry/Science/Climate/climate%20graphics/Climatezones.jpg
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Climate Zones
http://www.iteachbio.com/Life%20Science/Ecology/ClimateZones.png
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18-1Factors affecting temperature
Altitude
• The temperature of the troposphere
decreases about 6.5° Celsius for every 1kilometer increase in altitude.
*Highland areas everywhere have cool
climates
* Mount Kilimanjaro is 39° Celsius
cooler at it’s peak than the air at sea level
at the same latitude
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Mount Kilamanjaro
http://www.destination360.com/africa/tanzania/images/s/mount-kilimanjaro.jpg
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18-1 Factors affecting temperature:
Distance from large bodies of water
• Oceans or large lakes can affect temperatures
• Oceans/large lakes moderate (make less
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extreme) temperatures of nearby land
Water heats up more slowly and cools
down more slowly than land
Winds from the ocean keep coastal areas from
reaching extreme temperatures
Marine climates have warm winters and cool
summers
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18-1 Factors affecting temperature:
Ocean currents
• Mary marine climates are influenced by
ocean currents
• Generally, warm currents from tropics
carry warm water toward poles while cold
currents from poles carry cold water
towards the equator
• The air over these currents is warmed or
cooled and affects the land nearby
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Gulf Stream & Europe
http://www.johnchaple.co.uk/images/le-gulf-stream.jpg
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Global Average Temperatures
http://www.climate-charts.com/images/world-temperature-map.png
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18-1 Factors affecting Precipitation
• The main factors that affect
precipitation are prevailing winds and
the presence of mountains.
• Air masses are moved by prevailing
winds. The characteristics of the air in an
air mass will determine how much rain or
snow can fall.
• Prevailing westerlies air masses across
the United States.
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18-1 Factors affecting precipitation:
Mountain Ranges
• A mountain range in the path of prevailing
winds can influence where precipitation
falls
* When humid winds blow from the
ocean toward a mountain range the air is
forced to rise up to pass the mountains.
The warm humid air cools and condenses
this forms clouds and maybe rain or snow
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Eisenhower Tunnel in Colorado
p://images.travelpod.com/users/chmk11/1.1263678962.i---70-entering-eisenhower-tunnel.jpg
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Eisenhower Tunnel in Colorado
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http://images.travelpod.com/users/chmk11/1.1263678962.the-easy-route-is-boring.jpg
Sierra Nevada Mountains
http://www.atmos.umd.edu/~dankd/MesDes3/images/SierraNevada5.jpg
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18-1 Factors affecting precipitation:
Mountain Ranges
• Rain or snow tends to fall on the
windward side of the mountain, the side
that oncoming wind hits
• The leeward side of the mountain which is
downwind from the windward side is in a
“rain shadow”. The air on the leeward side
tends to be drier than the windward side
where the rain or snow falls, after being
removed from the humid wind
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18-1 Microclimates
 A microclimate is a small area with
specific climate conditions that may be
different from the surrounding area
 Inland mountains, lakes, forests, and
other natural features can influence the
climate nearby, resulting in a
microclimate
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Global AverageTemperatures
http://www.climate-charts.com/images/world-temperature-map.png
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18-1 Seasons
 Most places on Earth outside of the
tropics have four seasons: winter, spring,
summer and autumn
 The seasons are caused by the tilt of
Earth’s axis as Earth travels around
the sun. Earth is tilted at an angle of
23.5° on its axis.
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