The Earth*s Atmosphere

The Earth’s Atmosphere
The Atmosphere
The atmosphere is made up of an
envelope of gases whose composition has
remained relatively stable through most of
Earth’s history. Degree of difference in heating
and rotation of our planet contribute to the
dynamic nature of our atmosphere, and the
consequent changes in force, pressure, and
temperature create climate zones, weather
patterns, and storms on our planet.
Misconceptions About the Earth’s
• A common misconception is that land plants
generate most of the oxygen in the
• Most people falsely believe that direct
sunlight heats the atmosphere.
• Another common misconception is that
greenhouse gases make up a major portion of
the atmosphere.
Radiative Balance
• Earth's surface temperature has been remarkably
constant over geologic time.
• Earth exchanges energy with its environment
primarily through transfers of electromagnetic
• The most abundant gases in the atmosphere—
nitrogen, oxygen, and argon—neither absorb nor
emit terrestrial or solar radiation.
– But clouds, water vapor, and some relatively rare
greenhouse gases (GHGs) such as carbon dioxide,
methane, and nitrous oxide in the atmosphere can
absorb long-wave radiation
Major GHGs
• Carbon dioxide (CO2), the most significant
GHG directly affected by anthropogenic
activity, is the product of the oxidation of
carbon in organic matter.
• Methane (CH4) is produced by anaerobic
decay of organic material.
• Nitrous oxide (N2O) is produced by fertilizer
use, animal waste management, fossil fuel
combustion, and industrial activities.
Major GHGs
• Hydrofluorocarbons (HFCs) and
perfluorocarbons (PFCs) are synthetic
chemicals that are used in a variety of
industrial production processes such as
semiconductor manufacturing. PFCs are also
produced as a by-product of aluminum
The Carbon Cycle
Carbon Cycle Activity
Atmosphere •1 black
Land Biomass •4 black
•1 red; 2 black
Fossil Fuel
•7 black
•1 white
The Carbon Cycle
Do you agree
with the number
of balloons in
each location?
Use this diagram
to guide your
The Carbon Cycle
1. Describe two important “sinks” (parts of Earth that
store carbon), two important “sources” (parts of Earth
that release carbon), and one important “release agent”
(conditions that trigger release) for carbon.
2. Currently it seems that CO2 sources are out of balance
with CO2 sinks. If more CO2 is produced than sinks can
remove, CO2 in the atmosphere increases. What might
happen if the reverse were true and sinks took up more
CO2 than sources released?
3. Why is knowledge about the carbon cycle important
for helping scientists understand global climate change?
Vertical Motion in the Atmosphere
• What causes motion in the atmosphere?
• When a column of air is heated, it becomes
less dense which increases its buoyancy and
convection occurs.
• Water vapor reported as relative humidity is
the total amount of water vapor that can be
held in the air at a given temperature.
– Consequently, atmospheric water vapor
concentrations are highest in warm regions and
decrease toward the poles
Contribution of H2O
• Atmospheric water vapor contributes to
weather patterns in several ways
• First, adding water vapor to the air reduces its
• Secondly, moist air carries latent energy.
• The dew point, another key weather variable,
denotes the temperature to which air would
have to cool to reach 100 percent relative
How Clouds Form
When conditional instability exists, air parcels are stable if they are dry and
unstable if they are saturated. Conditional instability can help to generate storms
by causing parcels of moist air to rise and form towering clouds.
Movement of Air Mass
• Convection is not the only process that lifts air
from lower to higher altitudes.
• Convergence occurs when air masses run
together, pushing air upward.
• When warm and cold air fronts collide, the
denser cold air slides underneath the warm air
layer and lifts it. In each case, if warm air is
lifted high enough to reach its dew point,
clouds will form.
Atmospheric Circulation Patterns
Sea breezes are caused by temperature differences between land at the surface and
adjoining water, which cause air to flow in opposite directions during the day and at
Atmospheric Circulation Patterns
• Winds that move over very long distances
appear to curve because of the Coriolis force,
an apparent force caused by Earth's rotation.
• This phenomenon occurs because all points
on the planet's surface rotate once around
Earth's axis every 24 hours, but different
points move at different speeds
Atmospheric Circulation Patterns
Atmospheric Circulation Patterns
Climate, Weather and Storms
Climate vs. Weather
• Climate refers to long-term weather trends
and the range of variations that can be
detected over decades.
• Specific weather trends describe annual
meteorological happenings in a given area.
• The global air circulation patterns create
predictable regional climate zones.
Global Air Circulation
• Because the Coriolis effect prevents mass and
heat from moving readily to polar latitudes,
temperatures decline and pressures increase
sharply between middle latitudes and the
polar regions, creating currents in the
atmosphere known as the “jet stream”.
• Hurricanes form over tropical waters
(between 8° and 20° latitude) in areas with
high humidity, light winds, and warm sea
surface temperatures, typically above 26.5°C
• At the ocean's surface a feedback loop
sometimes develops: falling pressure pulls in
more air at the surface, which makes more
warm air rise and release latent heat, which
further reduces surface pressure.
Hurricane wind speeds range from 74 miles per hour (the minimum for a Category 1
storm on the Saffir/Simpson scale) to more than 155 miles per hour for Category 5
Mid-latitude Cyclones
Mid-latitude cyclones occur when warm and cold air masses collide
around a center of low pressure.
Mid-latitude Cyclones
• Mid-latitude cyclones cause most of the
stormy weather in the United States,
especially during the winter season.
• They occur when warm tropical and cold polar
air masses meet at the polar front (coincident
with the jet stream).
The Global Carbon Cycle
• One of the key issues in current atmospheric
science research is understanding how GHG
emissions affect natural cycling of carbon
between the atmosphere, oceans, and land.
• Today, human intervention in the carbon cycle
is disturbing this natural balance.
• Two processes remove CO2 from the
atmosphere: photosynthesis by land plants
and marine organisms, and dissolution in the
Carbon Reservoir
• The residence time of carbon varies widely
among different reservoirs.
– A carbon atom spends about 5 years in the
– It spends 10 years in terrestrial vegetation.
– It spends 380 years in intermediate and deep
ocean waters.
– Carbon can remain locked up in ocean sediments
or fossil fuel deposits for millions of years.
Feedbacks in the Atmosphere
• Feedbacks are interactions between climate
variables such as temperature, precipitation, and
vegetation and elements that control the
greenhouse effect.
• Positive feedbacks amplify temperature change
by making the greenhouse effect stronger.
• Negative feedbacks have a dampening effect on
temperature change, making the climate system
less sensitive to the factors that trigger them.
Feedbacks in the Atmosphere
• Water vapor feedback (positive).
• Cloud feedback on terrestrial radiation
• Cloud feedback on solar radiation (negative).
• Vegetation feedback on solar radiation
• Ice-albedo feedback on solar radiation
Feedbacks in the Atmosphere
• Feedbacks cause much of the uncertainty in
today's climate change models, and more
research is needed to understand how these
relationships work.
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