Climate Determines
Global Patterns in the
Biosphere
34.2
Uneven Heating of Earth’s
Surface
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Energy from the sun
warms Earth's surface.
But because of Earth's
spherical shape,
different locations on
Earth's surface receive
different amounts of
solar energy.
Near the equator, the
sun's rays strike the
surface most directly.
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Earth's surface can be
divided into different
temperature zones
based on lines of
latitude.
The region that lies
between 23.5° N
latitude (the Tropic of
Cancer) and 23.5° S
latitude (the Tropic of
Capricorn), called the
tropics, is the warmest
temperature zone.
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The region north of the
Arctic Circle (66.5° N)
and the region south of
the Antarctic Circle
(66.5° S), called the
polar zones, receive
the least amount of
direct sunlight yearround.
The polar zones are the
coldest temperature
zones.
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The latitudes in
between the tropics
and the polar zones
in each hemisphere
are called the
temperate zones.
Most of the United
States is located
within the northern
temperate zone.
Wind, Precipitation, and Ocean
Currents
The uneven heating of Earth's surface
by the sun is also a driving force
behind global patterns of winds and
precipitation (rain, snow, and sleet).
 When air is warmed it can absorb more
moisture, and it also tends to rise.
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Thus air near the equator, heated by the
direct rays of the sun, absorbs moisture and
rises.
Higher in the atmosphere the air cools again,
forming clouds that produce rainfall.
This pattern means that many areas of Earth
close to the equator tend to have warm
temperatures and heavy rainfall year-round.
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After losing moisture
over the equator, air
masses spread away
from the tropics.
The dry air descends
again and warms at
latitudes of about 30° N
and 30° S.
Some of the world's
largest deserts are
found in these regions.
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The rising and falling of air masses,
combined with Earth's rotation, produce
predictable wind patterns.
These wind patterns combine with the
uneven heating of Earth's surface, the
rotation of the Earth, and the shapes of the
continents, producing surface currents.
A current is a river-like flow pattern within
a body of water.
Surface currents can greatly affect
regional climates.
 For instance, the Gulf Stream carries
warm water northward from the
tropics.
 This makes the climate in western
Europe warmer than other areas at
similar latitudes.
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Local Climate
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On an August day, people in Los Angeles'
San Fernando Valley might face
temperatures of 38°C (100°F), while just 30
kilometers away, people at the beach are
enjoying the comfortable 24°C (75°F)
outdoor air.
Local climate variations may be influenced
by nearby large water bodies.
Oceans and large lakes affect climate
because water tends to absorb and release
heat more gradually than most other
substances
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Mountains also affect local climate. First, air
temperature declines by about 6°C with
every 1000-meter increase in elevation.
This is why it becomes cooler as you hike
up a mountain.
Second, mountains near a coast can block
the flow of cool, moist air from the ocean,
causing different climates on opposite sides
of the mountain range.
Microclimate
Organisms living in the same climate
region may be exposed to different
conditions created by shade, snow
cover, or windbreaks.
 Such small-scale differences in
climate result in a microclimate, the
climate in a specific area that varies
from the surrounding climate region.
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