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Environmental Science
LECTURE NOTES FOR CHAPTER 13
ATMOSPHERE & CLIMATE CHANGE
I. Definitions
A. weather – the state of the atmosphere at a particular place at a particular moment
B. climate – the long-term prevailing weather conditions at a particular place based
upon records taken
II. Factors that determine climate
A. Latitude – the distance from the equator measured in degrees north or south
1. the most important factor determining climate
2. The amount of solar energy an area of Earth receives depends on its latitude
3. Low latitudes – areas near the equator
a. more sun falls on this area than others
b. night and day are both about 12 hours long throughout the year
c. temperatures are high throughout the year
d. no distinct summer or winter
4. High Latitudes – regions closer to the poles
a. sun is lower in the sky
b. sunlight hits Earth at an oblique angle and spreads over a larger surface area
than at the equator
c. Yearly average temperatures near the poles are lower than at the equator
d. Hours of daylight vary
1) 450 north and south latitude, there is 16 hours of daylight during the
summer and 8 hours of sunlight during the winter
2) Near the poles, sun sets for only a few hours each day in summer and
rises for only a few hours during the winter
3) Creates a large yearly temperature range
B. Atmospheric circulation
1. Three important properties of air illustrate how air circulation affects climate
a. cold air sinks because it is denser than warm air
1) as it sinks, it compresses and warms
b. warm air rises
1) it expands and cools as it rises
c. warm air can hold more water vapor than cold air
1) when warm air cools, the water vapor it contains may condense into
liquid and form rain, snow, or fog
2. Solar energy heats the ground which warms the air above it
3. Warm air rise & cooler air moves in to replace it
4. wind – the movement of air within the atmosphere created by the above (# 2 &
3)
5. pattern of global atmospheric circulation results because the Earth rotates &
because different latitudes receive different amounts of solar energy
a. circulation pattern determines Earth’s precipitation pattern
6. Global circulation patterns
a. Cool normally sinks
1) over equator cool air cannot descend because hot air is rising below the
cool air
2) the cool air is forced away from the equator and toward the poles
b. At 30º N & S latitudes air begins to accumulate in the upper atmosphere
1) some of the air sinks back to the Earth’s surface & becomes warmer as
it descends
2) Warm, dry air moves across the surface causing water to evaporate
from land below
a) creates dry conditions
3) Descending air either moves toward the equator or flows toward the
poles
a) air moving toward the poles warms while it is near Earth’s surface
c. At 60º N & S latitudes, this warmed air collides with cold air traveling
from the poles
1) the warm air rises
2) a small part of this rising air returns back to the circulation pattern
between 60º and 30º north and south latitudes
3) Most of the uplifted air is forced toward the poles
a) cold, dry air descends at poles (very cold desserts)
7. Prevailing winds – winds that blow predominantly in one direction throughout
the year
a. do not blow directly northward or southward
1) because or the rotation of the Earth
a) winds are deflected to right in Northern Hemisphere
b) winds are deflected to left in the Southern Hemisphere
b. trade winds – belts of prevailing winds in both hemispheres between 30º
north & south
1) blow from northeast in Northern Hemisphere
2) blow from southeast in the Southern Hemisphere
c. westerlies – prevailing winds produced between 30º and 60º north and south
latitudes
1) blow southwest in the Northern Hemisphere
2) blow northwest in the Southern Hemisphere
d. polar easterlies - blow from the poles to 60º north and south latitude
C. Oceanic circulation patterns
1. Surface ocean currents have a great effect on climate because water holds large
amounts of heat.
a. movement of surface ocean currents is caused by winds and the rotation of
the Earth
b. surface currents redistribute warm & cool masses of water around the planet
c. Some surface currents warm or cool coastal areas year round
d. Affect the climate in many parts of the world
2. El Nino-Southern Oscillation – the short-term (6-18 month period) periodic
change in the location of warm and cols water masses in the Pacific Ocean
a. Winds in the western Pacific which are usually weak, strengthen & push
warm water eastward
b. Rainfall follows and produces increased rainfall in southern U.S. and in
equatorial South America
c. Causes drought in Indonesia and Australia
d. La Nina – the water in the eastern Pacific Ocean is cooler than usual
e. El Nino & La Nina are opposite phases of the El Nino-Southern Oscillation
(ENSO) cycle
1) El Nino is the warm phase
2) La Nina is the cool phase
3. Pacific Decadal Oscillation (PDO) – a long term (20-30 year) change in the
location of warm and cold water masses in the Pacific
a. PDO influences the climate in the northern Pacific Ocean and North
America
b. Affects ocean surface temperatures, air temperatures, and precipitation
patterns
D. Topography
1. Elevation- height above sea level
a. temperatures fall about 11° F for every 1,000 m increase in elevation
2. Mountains and ranges also influence the distribution of precipitation
a. rain shadow- one side of the mountain gets rain from the ocean air while the
opposite side receives dry air
E. Other influences
1. Solar maximum- the sun emits an increased amount of UV radiation
a. UV radiation produces more ozone
b. the increase in ozone warms the stratosphere
c. increased solar radiation can also warm the lower atmosphere & surface of
the Earth
2. Volcanic eruptions – cause sulfur dioxide gas to reach the upper atmosphere
a. the sulfur dioxide can remain in the atmosphere for up to three years
b. reacts with smaller amounts of water vapor & dust in the atmosphere
c. this reaction forms a bright layer of haze that reflects enough sunlight to
cause the global temperature to decrease.
III. The Ozone Shield
A. ozone layer – an area in the stratosphere where ozone is highly concentrated
1. ozone – molecule made of three oxygen molecules
2. ozone layer absorbs most of the ultraviolet (UV) light from the sun
a. UV light can damage genetic material in living organisms
B. Ozone depletion
1. chlorofluorocarbons (CFCs) – class of human-made chemicals; can damage
ozone
a. nonpoisonous, nonflammable, & non-corrosive to metals
b. used as coolants in refrigerators & air conditioners, in making plastic
foams, & as propellants in spray cans
c. are chemically stable at Earth’s surface
d. break apart in stratosphere & absorb UV radiation which destroys ozone
1) each CFC molecule contains one – four chlorine atoms
2) a single chlorine atom can destroy 1000,000 ozone molecules
2. ozone hole – a thinning of stratospheric ozone that occurs over the poles
during the spring
a. First reported in 1985 above the South Pole
1) ozone had thinned 50-98%
b. NASA went back and looked at data from 1979 and discovered the first
signs of ozone thinning
c. Ozone thinning is also occurring over the Arctic
d. in 1997 ozone levels over part of Canada were 45% below normal
3. How ozone holes form
a. polar vortex – strong circulating winds over Antarctica during winter
1) isolates cold air from surrounding warmer air
2) air inside vortex grows extremely cold & fall below -80° C
3) form polar stratospheric clouds – high-altitude clouds made of water
and nitric acid
b. on surface of polar stratospheric clouds, the products of CFCs are
changed to chlorine
1) when sunlight returns in spring, chlorine is split into two chlorine
atoms by UV rays
2) chlorine atoms rapidly destroy ozone
3) destruction of ozone causes a thin spot or ozone hole that lasts
several months
a) some estimate that 70% of ozone layer can be destroyed during
this time
c. ozone produced as air pollution does not repair the ozone hole
1) ozone produced by pollution breaks down or combines with other
substances in troposphere before it can reach the stratosphere
4. Effects of ozone thinning on humans
a. more UV light reaches Earth’s surface which damages DNA
b. makes body more susceptible to skin cancer
c. may cause other damaging effects to human body
5. Effects of ozone thinning on plants and animals
a. higher UV light can kill phytoplankton
1) disrupts ocean food chains
2) increases amount of CO2 in atmosphere
b. higher UV light is damaging to amphibians
1) kills eggs which do not have shells
2) amphibians are indicator species – species used to indicate
environmental changes
c. higher UV light can damage plants by interfering with photosynthesis
1) results in lower crop yields
6. Protecting the Ozone layer
a. Montreal Protocol of 1987
1) meeting of nations in Canada which agreed to take action against
ozone depletion
2) Agreed to limit the production of CFCs
b. A second Conference was held in Copenhagen, Denmark in 1992
1) developed countries agreed to eliminate most CFCs by 1995
2) U.S. pledge to ban all substances that endanger the ozone layer by
2000
c. Chemical companies have developed CFC replacements
1) spray cans no longer use CFCs as propellants
2) air conditioners are becoming CFC free
d. There has been a decline in CFC production since Montreal Protocol
e. CFC molecules remain active in stratosphere for 60-120 years
1) CFC released 30 years ago are still destroying ozone today
2) it will be many years before the ozone layer recovers
IV. Global Warming
A. Greenhouse effect – the process of heat absorption in which sunlight streams
through the atmosphere and heats the Earth.
1. Some of the heat escapes into space
2. Some of the heat is absorbed by gases in the troposphere & warms the air
3. greenhouse gases – gases that absorb and radiate heat
a. water vapor
b. carbon dioxide,
c. chloroflourocarbons
d. methane
e. nitrous oxide
f. water vapor and carbon dioxide account for most of the absorption of heat
that occurs in the atmosphere
B. Measuring Carbon Dioxide in the Atmosphere
1. First measured in 1958 by Charles David Keeling in Mauna Loa in Hawaii
a. 1st measurement was 314 parts per million of carbon dioxide in air or
.0314%
1) levels fell and rose seasonally
b. By 2000 the average level of carbon dioxide was about 368 parts per
million
1) in 42 years, carbon dioxide increased 54 parts per million
2) 17% increase
3) Largely due to burning of fossil fuels
C. Greenhouse gases & Earth’s temperature
1. Scientists believe that greenhouse gases trap heat near the Earth’s surface and
increase the temperature
2. Comparisons of carbon dioxide and average global temperatures for past
400,000 years support this view
3. Today we are releasing more carbon dioxide than another other greenhouse
gas
a. Results of power plants and vehicles
b. we are also releasing CFCs, methane, and nitrous oxide
D. Global warming- predicted increase in global temperatures
1. Earth’s average global temperature increased in the 20th century
2. Most agree it will continue during 21st century
3. Not all scientist agree that it is caused by greenhouse gases
a. some believe that the warming is due to part of natural climatic variability
b. this type of fluctuations in temperature have occurred throughout time
E. Modeling global warming
1. Scientist cannot make accurate predictions about the rate of global warming
a. climatic patterns are too complex
b. too many variables
V. Consequences of a Warmer Earth