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Concept Review
The Atmosphere and Climate
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Weather is the daily temperature and moisture conditions. Weather is the
combination of humidity, temperature, pressure, wind, and precipitation.
Climate is the long-term weather pattern for an area.
The early atmosphere probably consisted of hydrogen and helium.
Over time, volcanic eruptions added carbon, nitrogen, oxygen, and sulfur.
Photosynthetic organisms, plants and algae, produced molecular
oxygen (O2).
Other minute particles in the air are referred to as aerosols.
The atmosphere has four distinct layers absorbing solar energy in different
amounts and therefore having different temperatures.
The troposphere is the layer closest to the earth, varying in depth from
8 km to 18 km.
o Within the troposphere, air circulates in convection currents, which
redistribute heat and moisture.
o The troposphere is the densest layer of the atmosphere, accounting
for about 75 percent of the total mass.
The stratosphere extends from the troposphere up to about 50 km.
o There is almost no water vapor in this layer and the ozone
concentration is nearly 1,000 times greater than in the troposphere.
o There is very little mixing of the atmosphere in this layer, so
particles remain suspended for many years.
o Stratospheric ozone absorbs UV-B radiation from the sun, thereby
protecting life on the surface of the earth.
The mesosphere is the next layer, where temperature diminishes to -80°
Celsius.
The fourth layer is the thermosphere, which begins at about 80 km. Highly
energized gases are ionized as they are heated by solar and cosmic
radiation.
About one-fourth of the sun’s energy is reflected by clouds and
atmospheric gases.
About one-fourth of the sun’s energy is absorbed by carbon dioxide, water
vapor, methane, and ozone.
The remaining energy is absorbed by the earth’s surface or is reflected by
light-colored surfaces.
o The term albedo refers to the reflective property.
o The wavelength of the energy determines if and how the energy is
absorbed or reflected.
o Longer wavelengths are absorbed by the atmosphere.
o Shorter wavelengths pass through the atmosphere to the earth’s
surface.
The atmosphere traps the heat energy as the sunlight is transmitted. This
phenomenon is referred to as the greenhouse effect.
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Water vapor absorbs energy as latent heat.
As the water vapor condenses, heat energy is released
The circulation pattern of the air in the form of convection cells
redistributes heat and water vapor. These convection currents cause
precipitation as the air cools as it rises and cannot hold the same amount
of water vapor.
The movement of the earth and the circulation of the air form a wind
pattern known as the Coriolis effect.
o These atmospheric wind currents influence climate conditions on
land and ocean water currents.
o If the circulation of the air mass becomes stalled, weather patterns
stabilize, resulting in droughts in some areas and excess rain in
others.
Ocean currents also modify the climate conditions on land as water
temperature moderates the temperature and rainfall patterns.
Seasonal changes in the global wind pattern, known as monsoons or rainy
seasons, are essential for maintaining ecosystems. The main reason for
rainy seasons is the change in solar heating and evaporation as the
earth’s axis of rotation is at an angle.
Air masses form on the basis of temperature and the amount of moisture
they contain. When two air masses meet, the boundary between them is
called a front.
 Cold air is denser than warm air, so it stays closer to the
ground.
 As warm air is forced upward, it is cooled.
The interactions between the air masses cause weather patterns.
Air pressure differs with the temperature of the air.
o Warm air rises, causing low-pressure areas.
o Cool air sinks, and high-pressure areas result.
Hurricanes form as rising warm air swirls upward, releasing latent energy.
As long as there is a temperature difference to feed the rising, swirling air
mass, the storm will intensify as energy is released.
Tornadoes occur over land when cold fronts collide with warm, humid air
moving north. The greater the temperature difference, the stronger the air
currents.
Climate
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Climate is the pattern of weather in a region over a period of time.
o Scientists study ice cores from glaciers to learn about climate
history.
o Gas bubbles trapped in the ice provide information on climate;
atmospheric disturbances, such as volcanic eruptions; CO2
concentration; and temperature variations.
Major climatic changes can drastically affect living organisms. The Ice
Ages and the mass extinction of dinosaurs that occurred at the end of the
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Cretaceous period are the most well-known examples of catastrophic
climatic changes.
Some of the changes are associated with the 11-year sunspot cycle or the
22-year solar magnetic cycles.
The periodic changes in the earth’s orbit and tilt, known as Milankovitch
cycles, change the distribution and intensity of the solar energy reaching
the earth.
The oceans and the atmosphere produce cycles, which greatly affect
climate.
o The El Nino and La Nina Southern Oscillation Cycles (ENSO) affect
global weather and wind patterns, which in turn affect rainfall and
temperature across the globe.
o Every 3 to 5 years these cycles alternate, although there is
evidence that the cycles are becoming more irregular and stronger
than they were in the past.
o During El Nino, moist air and rain are pulled across the United
States by the jet stream.
o During La Nina, the same geographic areas have hot, dry weather.
o Studies suggest these weather patterns are part of earth’s cooling
effect as a release from a portion of global warming temperatures.
Human activities also cause global climatic change, mostly through our
burning of fossil fuels and burning of forests and grasslands.
o Through these activities, atmospheric concentrations of CO2, CH4,
and N2O have risen dramatically.
o As global warming increases, ice caps and glaciers melt, which
changes climate and ecosystems, as well as causing more storms
and raising sea levels.
In an attempt to stabilize greenhouse gas emissions, an international
conference constructed the Kyoto Protocol in 1997. Only four countries
(the United States being one) have not ratified the agreement.
Progress is being made toward reducing greenhouse gas emissions by
changing fuels and technologies in order to manage CO2 and methane
levels.