Transcript Margaret Mead, American Anthropologist

Chapter 7:
Atmosphere and Climate
“The atmosphere is the key symbol of global
interdependence.”
Margaret Mead, American Anthropologist
7.1 The Atmosphere
• Our atmosphere (this layer of gases) is what makes life
possible on the Earth
• Extends from the surface of Earth to hundreds of
kilometers above the surface
• AIR = 78% nitrogen and 21% oxygen; remaining 1% is
made up of water vapor, argon, carbon dioxide, neon,
helium and other gases
• Most important gases for organisms is oxygen (cellular
respiration) and carbon dioxide (photosynthesis)
• Atmosphere protects Earth’s organisms by: protecting
from sun’s ultraviolet radiation, allows light to reach the
surface and keeps the Earth’s temperatures stable
How Photosynthesis Changed the
Atmosphere
• Earth’s early atmosphere probably contained very little
oxygen; early organisms (bacteria) evolved the ability to
perform photosynthesis
• During photosynthesis, some oxygen from water and
carbon dioxide formed oxygen gas, which entered the air
• As plants multiplied, oxygen in the air increased
• Organisms, during cellular respiration, release carbon
dioxide into the atmosphere, creating the balance
between the two; thus, sustaining the balance for life on
Earth and keeping the planet within a temperature range
for life to exist
The Five Layers
• Atmosphere is divided into 5 individual layers (less
dense the farther away from Earth)
• Troposhere – extends from surface outward about 10 km
(about 6 miles); contains 90% of atmosphere’s gases;
layer where weather occurs
• Stratosphere – extends from 10 km to about 50 km
(about 30 miles)
• Mesosphere – extends from 50 to 80 km (50 miles)
• Thermosphere – extends from 80 to 500 km (310 miles)
• Exosphere – extends out and merges with outer space
7.2: Climate
• Weather is happening at a particular place at a particular
moment; climate is the average weather in an area over
a long period of time
• Important aspects of climate are: temperature, humidity,
wind and precipitation (rain, snow, hail and sleet)
• Climate determines what type of organisms are able to
live in a region
What Determines Climate?
• Climate is determined by a variety of factors, including
latitude, air circulation, ocean currents and the local
geography of the area
• The most important factor is climate
Latitude
• Latitude is the distance from the equator; measured in
degrees north or south of the equator
• Equator is 0°; most northerly latitude is 90° north (North
Pole); most southerly latitude is 90° south (South Pole)
• Latitude influences climate: equator receives the most
direct solar energy because it is directly overhead and is
concentrated on a smaller area; poles receive less
energy because the sun is lower in the sky and the
sunlight is spread out over a larger area
Atmosphere Circulation Patterns
• Three (3) important properties of air affect climate: cold
air sinks and warms as it sinks, warm air rises and cools
as it rises, warm air holds more water vapor than cold air
can
• Heating of the atmosphere causes wind; different
latitudes get different amounts of solar energy resulting
in global circulation which, in turn, determines the
amount of precipitation at different latitudes
• Equator (0°) gets heavy rain (450 cm per year or 177
inches); at 30° north and south are generally warm and
dry (most deserts found here); at 60° winds are
beginning to rise again and drop again around 90°
causing very cold deserts
Ocean Circulation Patterns
• Ocean currents have a great affect on climate because
water holds a large amount of heat
• Movement of currents is a result of winds and rotation of
Earth
• Oceans make climates more moderate; coastal areas
usually have warmer winters/cooler summers
• Coastal areas will usually get more precipitation than
inland areas
Local Geography
• Latitude does affect climate; however, height above sea
level also has an effect on climate. Ex: Mt. Kilimanjaro
(Tanzania) is 3° south of the equator but has snow
covered peaks year round
• Plants and animals living in the mountains will resemble
those living in cold, northern climates
• Mountains and mountain ranges also affect precipitation
ex: Sierra Nevada mountains (California) – coastal side
is very moist and receives a great deal of rain; the
eastern side is the Great Basin Desert
Seasonal Changes in Climate
• Temperature and precipitation change with the seasons,
but what causes the seasons? The Earth’s orbit around
the sun and the tilt on its axis
• During spring and summer in the Northern Hemisphere,
it is tilted toward the sun, receiving more concentrated,
direct sunlight; Southern Hemisphere is tilted away
receiving less concentrated sunlight. During fall and
winter, the situation is reversed
• Our four seasons do not occur in the tropics (close to the
equator) They have high constant temperatures
throughout the year and receive the most direct sunlight
year round
7.3 Greenhouse Earth
• When you get into a car in the summer, you may notice
that it is hotter in the car than outside the car. This
occurs when light energy from the sun streams in
through the glass (absorbed by the carpet and
upholstery and is changed into heat energy. Heat
energy cannot flow back out through the glass, it gets
trapped by the glass and continues to heat up
• This is the same principle which is applied when building
a greenhouse for growing plants
The Greenhouse Effect
• Earth is similar to a greenhouse; outer space is icy cold,
Earth’s atmosphere acts like the glass of a greenhouse
trapping the heat from the sunlight
• Heat radiates up from the Earth, some escapes into
space but most is trapped by the gases in the
troposphere and warms the air
• Not all gases trap this heat, but the ones that do are
called greenhouse gases (water vapor, carbon dioxide,
chlorofluorocarbons (CFC’s), methane and nitrous oxide)
• Water vapor and carbon dioxide are the most important
More Carbon Dioxide in Our Atmosphere
• 1958, Scientist, Charles Keeling installed instruments in
Hawaii to measure the amount of CO2 in the air;
determined that CO2 levels in summer fall, winter they
rise (314 ppm)
• By 1994, those levels had more drastic differences,
summer levels did not fall as low as in 1958 and winter
levels were higher (358 ppm)
Where is the Extra Carbon Dioxide Coming
From?
• During photosynthesis, plants take in carbon dioxide,
release oxygen; carbon is not returned to the air until the
plant dies or the leaves fall
• The ones that do not decay but are covered by sand or
silt (after millions of years underground) become coal, oil
or natural gas
• Carbon is released into the air when burning these fossil
fuels and when burning plants; millions of tons of carbon
dioxide is released into the air from power plants
Greenhouse Gases and the Earth’s
Temperature
• Greenhouse gases are trapped near the Earth’s surface;
scientists feel this will result in a warmer Earth.
• Data collect over the last 160,000 years supports that
view
• Today, we are releasing more carbon dioxide into the
atmosphere than any other greenhouse gas; we are also
releasing significant amounts of other greenhouse gases
like CFC’s, methane and nitrous oxide
• Scientist feel that with the increased gases we will be
raising the Earth’s temperature by at least 2° by 2050
(called global warming)
A Warmer Earth
• Earth’s climate has dramatically changed in the past; ice
ages came and went
• These changes occur over hundreds or thousands of
years
• Scientists don’t know how quickly the Earth will warm or
how severe the effects will be
Weather Patterns
• If it heats up significantly, oceans will absorb more heat
energy resulting in an increase of hurricanes and
typhoons
• Scientists are concerned about changes in ocean current
patterns if there are changes in the world’s weather;
some areas may get more rain (flooding) than normal
and other areas may get even less (severe droughts)
Agriculture
• Agriculture will be greatly affected if there are severe
weather changes
• Some of the most fertile, productive areas may get hotter
and drier resulting in a shift northward for farming rather
than the areas where farming is prevalent today
Sea Levels
• As polar regions warm, icebergs may break and melt in
the sea resulting in a rise in the sea level
• Water expands as it melts
• The result of the rise in the sea level will cause coastal
areas to become covered with water
Slowing the Temperature Change
• How can we slow down global warming?
• Use less fossil fuels will lessen the release of carbon
dioxide into the atmosphere
• Preserve Earth’s existing forests and plant more trees;
this will help remove carbon dioxide from the
atmosphere
• Limit greenhouse gas emissions
7.4: The Ozone Shield
• The Ozone Shield is located in the stratosphere; ozone
is a form of oxygen made up of 3 oxygen atoms
• Ozone absorbs most of the UV (ultraviolet) rays from the
sun
• UV rays damage the genetic material in living cells
• The ozone shield acts like a sunscreen for the Earth and
the inhabitants
Ozone Eaters
• Chlorofluorocarbons (CFC’s) might be damaging the
ozone shield; nonpoisonous, noncorrosive and
nonflammable, man-made chemicals (thought to be the
miracle chemical) used in refrigerators and air
conditioners (coolants)
• Also used as a gassy “fizz” when making plastic foams
(styrofoam) and as a propellant in spray cans
(deodorants, insecticides and paints)
Breaking Apart CFC’s
• CFC’s are chemically stable at the Earth’s surface; break
apart high in the statosphere where UV radiation is
powerful enough to break down CFC molecules
• CFC molecules contain between one and four chlorine
atoms; one single chlorine atom can destroy 10,000
ozone molecules
The Effects of Ozone Thinning
• As ozone decreases, more UV light is able to pass
through stratosphere to Earth’s surface causing an
increase in skin cancer, cataracts
• High levels can kill one-celled organisms that live near
the surface of the ocean (can disrupt the balance of food
chains), reduce microscopic photosynthesizers,
increasing CO2 in the atmosphere
The Ozone Hole
• 1985, scientists reported a study about the ozone layer
near Antarctica and how it had tinned by 50% to 98%;
first news about the ‘ozone hole’
• Hole fluctuates depending on the time of year; greater
during the summer months when the UV light is breaking
apart the CFC molecules, less during winter when they
are building up
• 1997, ozone over Canadian Arctic was down to 45%
below normal
Stopping the Ozone Eaters
• In 1987, A group of nations met to take action against ozone
depletion (Montreal Protocol); decided to sharply limit their
production of CFC’s
• A second conference was held in Denmark in 1992; decided to:
•
1. Eliminate most CFC’s by 1995; U.S. pledged to ban all
•
substances by 2000
•
2. Set up a fund to help developing countries switch to
•
substitutes for CFC’s
•
3. Ban other substances that harm the ozone
• Battle to protect the ozone is not over, some countries still make and
use CFC’s; CFC molecules stay active for decades (up to 30 years)
so it will take decades for the ozone to recover