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
• Earth is surrounded by a mixture of gases known as the
atmosphere
• Nitrogen, oxygen, carbon dioxide and other gases are all parts of
this mixture
• The atmosphere changes constantly as these gases are added
and removed (ex: animals take in O2, give off CO2; plants take in
CO2 and give off O2; volcanic eruptions add gases; cars add and
remove gases)
• Our atmosphere (this layer of gases) is what makes life possible
on the Earth by insulating Earth’s surface, slowing the rate at
which heat from the sun is lost, thus allowing us to survive
• Extends from the surface of Earth to hundreds of kilometers
above the surface
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
Composition of the Atmosphere
• AIR = 78% nitrogen (entering when volcanoes erupt,
dead plants and animals decay) and 21% oxygen
(primarily produced by plants); remaining 1% is made up
of water vapor, argon, carbon dioxide, methane and
other gases
• Most important gases for organisms is oxygen (cellular
respiration) and carbon dioxide for plants
(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
Air Pressure
• Earth’s atmosphere is pulled toward Earth’s surface by
gravity making the atmosphere denser near the surface
• Almost the entire mass of Earth’s atmospheric gases are
located with 30 km of the surface; fewer gas molecules
are found at altitudes above 30 km (less pressure to
push downward)
• Air becomes less dense as elevation increases;
breathing becomes more difficult the higher you go
The Layers of the Atmosphere
• Atmosphere is divided into 4 individual layers (less
dense the farther away from Earth) based on
temperature changes that occur at different distances
above the Earth’s surface
• Troposhere – closest to the earth; extends from surface
outward about 18 km; contains 90% of atmosphere’s
gases; layer where weather occurs; most dense
atmospheric layer; temperature decreases as altitude
increases
The Layers of the Atmosphere…continued
• Stratosphere – extends from 18 km to about 50 km
(about 30 miles); temperature rise as altitude increases
as a result of ozone in the stratosphere absorbing the
sun’s ultraviolet energy and warming the air
• Ozone (O3) is a molecule made up of three oxygen;
almost all O3 is concentrated in ozone layer in the
stratosphere; Because ozone absorbs UV radiation, it
reduces the amount of UV radiation that reaches the
Earth. UV rays cause damage to living cells
The Layers of the Atmosphere…continued
• Mesosphere – extends from 50 to 80 km; coldest layer of the
atmosphere, measured as low as -93 degrees C.
• Thermosphere – extends from 80 to 550 km; located farthest
from Earth’s surface; nitrogen and oxygen absorb solar
radiation which results in temperatures above 2000 degrees
C. (wouldn’t feel hot because air particles are so far apart
they never collide, so little heat is transferred)
• Nitrogen and oxygen (lower region of thermosphere) absorb
harmful radiation (x-rays, gamma rays) causing them to
become electrically charged (called ions). The lower region
of the atmosphere is sometimes called the ionosphere.
These ions radiate energy as light and oftentimes glow in
spectacular colors in the night sky (North and South poles)
Energy in the Atmosphere
• Energy from the sun is transferred in Earth’s atmosphere
by three mechanisms: radiation, convection, and
conduction
• Radiation is the transfer of energy across space and in
the atmosphere; ex: when you stand near a fire, the
warmth you feel is from radiation
• Conduction is the flow of heat from a warmer object to a
colder object when in direct contact
• Convection is the transfer of heat by air currents; hot air
rises, cold air sinks. Ex: if you hold your hand above a
hot iron, you will feel the heat because it is rising off the
iron
Heating of the Atmosphere
• Solar energy reaches Earth as electromagnetic radiation
(includes visible light, infrared radiation and ultraviolet light); sun
releases vast amounts of radiation, Earth receives about 2
billionths of that energy
• The small amount of radiation we receive amounts to a lot of
energy; about half of the solar energy ever reaches the Earth’s
surface, the rest is absorbed or reflected in the atmosphere by
clouds, gases and dust
• If the Earth would continually absorb that energy, it would grow
hotter and hotter; however, the oceans and the land radiate the
energy they have absorbed back into the atmosphere
• Dark colored objects absorb more energy than light colored
objects, therefore they release more heat; cities are hotter that
country sides because of this.
The Movement of Energy in the Atmosphere
• Air that moves up, down and sideways causes Earth’s
weather
• In the troposphere. Currents of less dense air rise into
the atmosphere, begin cooling and then sink back to the
Earth’s surface
• The continual process of warm air rising and cool air
sinking moves air in a circular motion, called a
convection current
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, solar activity and volcanic activity
• The most important factor of climate is distance from the
equator
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
more 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
Low Latitudes
• Latitude strongly influences climate because amounts of
solar energy an area on Earth receives depends on its
latitude
• More solar energy falls on areas near the equator and is
more concentrated on a small surface area
• Regions near the equator have about 12 hours daylight
and 12 hours of night year round
• Temperatures are high year-round, with no summers or
winters
High Latitudes
• Regions closer to the poles, the sun is lower in the sky;
this causes a reduction in the amount of energy arriving
on the surface of the Earth
• Northern and Southern latitudes, sunlight hits Earth at an
oblique angle and spreads out over a larger surface area
• Yearly temperatures near the poles are much lower than
they are at the equator; the range is very large
• Hours of sunlight vary depending on the season;
summers (at 45 degrees N or S) can be as long as 16
hours; winters as little as 8 hours.
• Near the poles, the sun sets for only a few hours each
day during summer and rises only for a few hours in
winter
Atmosphere Circulation Patterns
• Three (3) important properties of air affect climate: cold air
(denser) sinks and warms as it sinks, warm air rises and cools
as it rises, warm air holds more water vapor than cold air can;
as it cools it condenses and forms a liquid (rain, snow or fog)
• Solar energy heats the ground, which warms the air above it;
warm air rises, cooler air moves in to replace it = wind (the
movement of air within the atmosphere)
• With different latitudes getting different amounts of solar energy
results 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
Global Circulation Patterns
• Cool air normally sinks, but cool air over the equator cannot descend
because hot air is rising below the cool air
• Cool air is then forced away from the equator toward the poles
• At 30 degrees north latitude and 30 degrees south latitude, air
accumulates in the upper atmosphere; some air sinks back to Earth’s
surface (gradually getting warmer) which moves across the surface,
causing water to evaporate from the land, creating dry conditions
• Air ascending at 30 degrees north and 30 degrees south latitude
move toward the equator or flow to the poles, air moving toward
poles warms while near the surface; at 60 degrees north and south
latitude, the air collides with cold air traveling from the poles; the
warm air rises, reaching the top of the troposphere, where a small
part returns back into the circulation pattern between 60 degrees and
30 degrees north and south latitude. However, most of this uplifted
air is forced toward the poles.
Prevailing Winds
• Winds that blow predominantly in one direction throughout the
year are called prevailing winds
• Because of rotation of the Earth, they do not blow directly north or
south but to the right in the Northern Hemisphere and to the left in
the Southern Hemisphere
• Primarily produced between 30 degrees north and south latitude
and the equator; these belts of winds are called trade winds; blow
from northeast in the Northern Hemisphere; blow from the
southeast in the Southern Hemisphere
• Prevailing winds known as westerlies are produced between 30
and 60 degrees north and south latitude; in Northern Hemisphere
these westerlies are southwest winds; in Southern Hemisphere
they are northwest winds
• Polar easterlies blow from the poles to 60 degrees north and south
latitude
Ocean Circulation Patterns
• Ocean currents have a great effect on climate because
water holds a large amount of heat
• Movement of surface ocean 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
El Nino – Southern Oscillation
• El Nino is the name given to the short-term (6 – 18
month period) periodic change in the location of warm
and cold water masses in the Pacific Ocean; weak
western Pacific Ocean winds strengthen and push warm
water eastward; rainfall follows the warm water eastward
and produces increased rainfall in the southern half of
the US and in equatorial S. America; drought in
Indonesia and Australia
• During La Nina, water in the eastern Pacific Ocean is
cooler than usual
• El Nino and La Nina are opposite phases: El Nino is the
warm phase of the cycle and La Nina is the cold phase
Pacific Decadal Oscillation
• This is the long term (20-30 year) change in the location
of warm and cold water masses in the Pacific Ocean.
• Influences the climate in the northern Pacific Ocean and
North America
• Affects ocean surface temperatures, air temperature and
precipitation patterns
Topography
• 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; this effect is
called a rain shadow
Other Influences on Earth’s Climate
• Both sun and volcanic eruptions influence Earth’s
climate; at a solar maximum the sun emits an increased
amount of UV radiation, producing more ozone; this
increase warms the stratosphere as well as the lower
atmosphere and surface of the Earth
• Large-scale volcanic eruptions spews sulfur dioxide into
the upper atmosphere, which can remain there for up to
3 years; it reacts with smaller amounts of water vapor
and dust forming a bright layer of haze that reflects
enough sunlight to cause global temperatures to
decrease.
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 and Global Warming
• 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; this process is called the
greenhouse effect.
• 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
Measuring Carbon Dioxide in Our Atmosphere
• 1958, Scientist, Charles Keeling installed instruments in Hawaii
(Mauna Loa volcano) to measure the amount of CO2 in the air;
winds blow pretty steady and have come thousands of miles
across the Pacific Ocean
• 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)
• During photosynthesis, plants take in carbon dioxide, release
oxygen; carbon is not returned to the air until the plant dies or the
leaves fall
• Most of the CO2 released into the air dissolves in the ocean or is
used by plants for photosynthesis; causing CO2 levels in the air
to vary with the seasons; summer, CO2 levels decrease (plants
use it), in winter, CO2 levels naturally rise
Rising Carbon Dioxide Levels
• In less than 50 years, CO2 levels in the atmosphere have
risen by over 20%
• 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
• They have been able to determine CO2 levels in the
atmosphere for thousands of years by analyzing ice
cores drilled from ice sheets; much higher levels today
than they have been for probably the last 20 million
years.
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 400,000 years supports that view
• Today, we are releasing more carbon dioxide into the
atmosphere than any other greenhouse gas; power plants burn
coal or oil, cars burn gasoline, millions of trees are being
burned in tropical rainforests…all this is contributing to the
increase of CO2 in our atmosphere
• 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 (global
warming)
Global Warming
• The average temperature of Earth’s surface has increase
during the 20th century; also known as global warming
• The temperature has been rising at a similar rate as the
increase in greenhouse gases, scientists believe the
greenhouse gases have caused the increase in temperature;
thousands of experiments and computer models support this
hypothesis
• Increase in temperatures is predicted to continue throughout
the 21st century; does not mean temps are rising at a
constant rate or that they are rising in all parts of the world.
• We do, however, experience natural climatic variability,
which means that temperatures change naturally over the
centuries; so this change cannot be ruled out.
Modeling Global Warming
• Computer models are used to predict future changes in
climate; equations are written by scientist that represent
the atmosphere and oceans, then CO2 levels, prevailing
winds and other variables are entered into it; the
resulting models are used to predict factors like
temperature and sea levels will be affected
• Weather forecasters use similar programs; as you know,
programs and models are not always accurate (ex: get
rained on when it was predicted to be dry)
• Computer models are becoming more reliable as more
data is available and additional variables are added
The Consequences of 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
• In North America, tree swallows, Baltimore orioles and robins are
nesting about 11 days earlier than they did 50 years ago; In Britain, at
least 200 species of plants are flowering up to 55 days earlier in the
year than 40 years ago
• There is no evidence that global warming is the cause but the nesting
of birds and flowering of plants are influenced by temperature
• Scientists cannot predict how quickly Earth will warm or how severe
the effects will be; different computer models give different predictions
• However, the possible effects of global warming can create a number
of potentially serious environmental problems (ex: changes in weather
patterns, rising sea levels)
Melting Ice and Rising Sea Level
• As polar regions warm, icebergs may break and melt in
the sea resulting in a rise in the sea level
• The result of the rise in the sea level will cause coastal
areas to become covered with water; coastal wetlands
and other low-lying areas will become flooded, people
will lose their homes and sources of income, beaches
will be eroded, salinity levels of bays and estuaries will
increase and affect marine fisheries, and coastal
freshwater aquifers could become too salty to be used
as sources of fresh water.
Global 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)
Human Health Problems
• Warmer average global temperatures pose potential
threats to human health
• Greater numbers of heat related deaths could occur;
very young and very old city dwellers are at the greatest
risk during heat waves
• People with allergies to pollen would suffer more as a
result of the increase in growing time for flowering plants
• Warmer and longer summers could allow mosquitoes to
establish themselves in areas which are too cold for
them now (ex: bring diseases like malaria, dengue fever
and encephalitis)
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
• We would see decreased crops yields and higher
demand for irrigation, further depleting aquifers
Effects on Plants and Animals
• Climate change could alter both the range of plant
species and the composition of plant communities; trees
colonizing cooler areas, forest could shrink in the warmer
part of their range, lose of diversity
• Could cause a shift in the geographical range of some
animals (ex: migrating birds may not have to go as far
south for winter, warm surface water in the ocean might
cause a reduction in zooplankton, and warming in
tropical waters may kill the algae that nourish corals,
killing the coral reefs)
Recent Findings
• Intergovernmental Plan on Climate Change (IPCC) is a
network of about 2,500 of the world’s leading
climatologists from 70 countries; they provide future
estimates about the state of the global climate system
• Findings have included: the average global surface
temperatures have increases by 0.6 degrees C during
the 20th century, snow cover and ice extent have
decreased and average global sea level has risen
• They also have reported that atmospheric greenhouse
gases have continued to increase as a result of human
activities and predict that human influences will continue
to change the composition of the Earth’s atmosphere
throughout the 21st century
Reducing the Risk
• In 1997, representative from 160 countries met and set
timetables for reducing emissions of greenhouse gases;
this treaty is called the Kyoto Protocol (ratified by 55% of
the attending nations)
• Kyoto Protocol requires developed countries to decrease
emissions of carbon dioxide and other greenhouse
gases by an average of 5% below their 1990 levels by
2012; US decided not to ratify the Kyoto Protocol.
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
Chemicals That Cause Ozone Depletion
• During the 1970’s scientists believed Chlorofluorocarbons (CFC’s)
might be damaging the ozone shield; CFC’s are nonpoisonous,
noncorrosive (do not corrode metals) 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)
• CFC’s are chemically stable at the Earth’s surface; break apart high
in the stratosphere where UV radiation is powerful enough to break
down CFC molecules
• Over a period of 10 – 20 years, CFC molecules released at the
Earth’s surface make their way into the stratosphere, each CFC
molecule contain between one and four chlorine atoms; one single
chlorine atom can destroy 10,000 ozone molecules.
The Ozone Hole
• 1985, scientists reported a study about the ozone layer
near Antarctica and how it had thinned by 50% to 98%;
this was the first news about the ‘ozone hole’ thinning
the stratospheric ozone over the poles during the spring
• This “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
How Does the Ozone Hole Form?
• During the dark polar winter, strong circulating winds over Antarctica,
called the polar vortex, isolate cold air from surrounding warmer air.
The air within the vortex grows extremely cold; when temperatures fall
below about -80 degrees C, high altitude clouds made of water and
nitric acid begin to form (polar stratospheric clouds)
• On the surface of these clouds, the products of CFCs are converted to
molecular chlorine; when sunlight returns to S Pole in spring, molecular
chlorine splits into two chlorine atoms by UV radiation; chlorine atoms
destroy ozone causing a thin spot, or ozone hole, which can last
several months (up to 70% of ozone layer can be destroyed during
spring)
• Ozone is produced by air pollution so why doesn’t the ozone repair this
hole? Because ozone is very chemically reactive. Ozone produced by
pollution breaks down or combines with other substances in the
troposphere long before it can reach the stratosphere to replace the
ozone that is being destroyed
The Effects of Ozone Thinning on Humans
• As ozone decreases in the stratosphere, more UV light is
able to pass through atmosphere to Earth’s surface
causing an increase in skin cancer, cataracts (damages
DNA)
Effects of Ozone Thinning on Animals and
Plants
• High levels of UV light can kill single-celled organisms called
phytoplankton that live near the surface of the ocean; disrupts
the ocean food chain and reduces fish harvest
• The reduction of phytoplankton would also increase the amount
of CO2 in the atmosphere
• Scientists believe the increased UV light will be especially
damaging to amphibians (toads and salamanders); lay eggs that
lack shells in shallow water of ponds and streams
• UV light at natural levels already kill many eggs of some species
by damaging the unprotected DNA; higher levels might kill more
eggs and put amphibian populations at risk
• Ecologists oftentimes use the health of amphibian populations
as environmental indicators of environmental changes
(sensitive)
Protecting the Ozone Layer
• 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 Copenhagen, Denmark in 1992;
developed countries 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
• After develop countries banned most uses of CFCs, chemical companies
developed CFC replacements ( aerosol can no longer use CFCs as
propellants and air conditioners are becoming CFC-free)
• Battle to protect the ozone is not over, some countries still make and use
CFC’s; CFC molecules stay active for decades (for 60 -120 years) so it
will take decades for the ozone to recover