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4-1 Climate
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THINK ABOUT IT
When you think about climate, you might
think of dramatic headlines: “Hurricane
Sandy Devastates the East Coast!” or
“Rain Causes Flooding in the West!”
But big storms and seasonal droughts
are better described as weather rather than
climate.
What is climate, and how does it differ
from weather? How do climate and
weather affect organisms and
ecosystems?
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4-1 The Role of Climate
What Is Climate?
What Is Climate?
Weather is the day-to-day condition of Earth's
atmosphere at a particular time and place.
Climate refers to the average year-after-year
conditions of temperature and precipitation in a
particular region.
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4-1 The Role of Climate
Climate is rarely uniform even within a
region. Environmental conditions can vary
over small distances, creating
microclimates.
For example, in the Northern
Hemisphere, south-facing sides of trees and
buildings receive more sunlight, and are often
warmer and drier, than north-facing sides.
These differences can be very important to
many organisms.
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Plants and animals vary in their
adaptations to temperature, rainfall, and
other environmental conditions.
All species have a low tolerance for
conditions outside their normal ranges.
Alligators, for example, cannot tolerate
extreme cold and cannot survive in areas
where there is a prolonged winter.
The climate of their ecosystems is very
important to alligators.
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4-1 The Role of Climate
What Is Climate?
Climate is shaped by:
1.
Solar energy trapped in the biosphere
2.
latitude
3.
transport of heat by winds and ocean currents
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4-1 The Role of Climate
The Greenhouse Effect
The main force that shapes climate is solar energy
that arrives as sunlight that strikes the Earth’s
surface.
Some of the energy is reflected by the atmosphere
right back into space but some of it is absorbed by
the gases in the atmosphere and is converted into
heat.
Atmospheric gases that trap the heat energy of
sunlight and maintain Earth's temperature range
include:
• carbon dioxide
• methane
• water vapor
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4-1 The Role of Climate
This natural
situation in which
heat is retained in
Earth’s
atmosphere by this
layer of gases is
called the
greenhouse
effect.
The Greenhouse Effect
Sunlight
Some heat
escapes
into space
Greenhouse
gases trap
some heat
Atmosphere
Earth’s Surface
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4-1 The Role of Climate
These “greenhouse gases” function like glass
in a greenhouse, allowing visible light to
enter but trapping heat.
The heat that stays in the biosphere
determines Earth’s average temperature.
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4-1 The Role of Climate
Global Climate Change
An increase in the amount of “greenhouse gases” has
occurred since the late 19th century. This increase is
primarily due to human activity – increases in
manufacturing, transportation, and power generation.
As a result, scientists have tracked an increase in the
average temperature of the biosphere. They call it
global warming.
Global warming can have catastrophic effects on many
ecosystems – droughts, floods, and intense storms are
likely to occur. The polar bear, for example, is
threatened with extinction due to the melting of the polar
ice caps.
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4-1 The Role of Climate
The Effect of Latitude on Climate
The Effect of Latitude
on Climate
At the equator, energy from
the sun strikes Earth almost
directly. Since solar energy is
intense, equatorial regions
are generally very warm.
The curvature of Earth
causes the same amount of
solar energy to spread out
over a much larger area from
the poles to the equator.
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4-1 The Role of Climate
The Effect of Latitude on Climate
Earth’s polar areas annually receive less intense
solar energy, and therefore heat, from the sun.
As a result of differences in heat distribution,
Earth has three main climate zones:
• polar,
• temperate, and
• tropical
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The Effect of Latitude on Climate
The tropical zone, or tropics, is near the equator,
between 23.5° North and 23.5° South latitudes.
The tropics receive direct or nearly direct sunlight
year-round, making the climate almost always warm.
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4-1 The Role of Climate
The Effect of Latitude on Climate
The temperate zones sit between the polar zones
and the tropics. The polar zones are located in the
areas around the North and South poles, between
66.5° and 90° North and South latitudes.
Temperate and polar zones receive very different
amounts of solar energy at different times of the year
because Earth’s axis is tilted.
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4-1 The Role of Climate
As Earth revolves around the sun, solar radiation
strikes different regions at angles that vary from
summer to winter.
During winter in the temperate and polar zones, the
sun is much lower in the sky, days are shorter, and
solar energy is less intense.
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4-1 The Role of Climate
Heat Transport in the Biosphere
Heat Transport in the Biosphere
The unequal heating of Earth’s surface creates
wind and ocean currents, which transport heat and
moisture.
Earth has winds because warm air is less dense
and rises, and cool air is more dense and sinks.
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4-1 The Role of Climate
Warm air over the equator
rises, expands, and spreads
north and south. It carries
heat with it and loses it along
the way.
As the warm air loses heat
and cools, it sinks. When it
sinks, it pushes the air below
it outward. This air then
warms as it travels over the
surface of the Earth towards
the equator.
When warm, it rises again!
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The upward and downward movement of
air creates air currents, or winds, that
move heat through the atmosphere, from
the equator to the north or south.
The prevailing winds, then, bring warm or
cold air to a region, affecting its climate.
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4-1 The Role of Climate
In addition, Earth’s rotation causes winds to
blow generally from west to east over the
temperate zones and from east to west over
the tropics and the poles.
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Heat Transport in the Biosphere
Similar patterns of heating
and cooling occur in Earth’s
oceans. Cold water near the
poles sinks, then flows
parallel to the ocean bottom,
and rises in warmer regions.
This water rising in warmer regions is a process called
upwelling.
Water is also moved at the surface by winds.
In both cases, the movement of the water creates
ocean currents, which, like air currents, transport heat
energy throughout the biosphere.
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4-1 The Role of Climate
In addition, ocean currents add moisture and heat
to air that passes over them.
Cool surface currents cool the air that passes over
them.
In this way, ocean currents can affect the weather
and climate of landmasses as air currents do.
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