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Threats to OurAtmosphere

A Reading A–Z Level W Leveled Reader

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Threats to Our AtmosphereLevel W Leveled Reader© 2005 Learning Page, Inc.Written by Shaun TaylorIllustrations by Craig Frederick

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Threats to OurAtmosphere

www.readinga-z.com

Written by Shaun Taylor CorrelationLEVEL W

Fountas & Pinnell SReading Recovery 26

DRA 44

Photo Credits:Front cover, back cover, title page, pages 3, 9, 12 (bottom), 13, 16, 18, 19, 20,22: © ArtToday; page 4: © NASA; page 21: © AcclaimImages; page 12 (top):© Hemera; page 11, 15: © NOAA; page 14: Photo courtesy of IISD

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Table of ContentsIntroduction . . . . . . . . . . . . . . . . . 4

The Earth’s Atmosphere . . . . . . . 5

The Ozone Layer . . . . . . . . . . . . . 6

Discovery of the Ozone Hole . . 10

The Cause of the Ozone Hole . . 12

The World Responds . . . . . . . . . 14

Global Warming . . . . . . . . . . . . . 15

Greenhouse Gases . . . . . . . . . . . 17

World Debate . . . . . . . . . . . . . . . 19

What You Can Do To Help . . . . 21

Conclusion . . . . . . . . . . . . . . . . . 22

Glossary . . . . . . . . . . . . . . . . . . . . 23

Index . . . . . . . . . . . . . . . . . . . . . . 24

Explore More . . . . . . . . . . . . . . . 24

IntroductionThere is a protective blanket around Earth

called the atmosphere. The atmosphere is amixture of many gases. The three most importantare nitrogen, oxygen, and carbon dioxide. Livingthings need these gases in order to live. Our Earth’satmosphere filters out the sun’s harmful rays andprevents heat from escaping too rapidly into space.

Living things on Earth survive within anarrow range of conditions. All living thingsneed the right amount of gases, the right range of temperature, and the right amount of sunlight.The atmosphere helps to maintain properconditions for life on Earth.

1981

1987

1993

1999

Antarctica

Antarctica

Antarctica

Antarctica

Earth’s atmosphere as seen from a satellite

The Earth’s AtmosphereEarth’s atmosphere is divided into five layers.

As you move up through the layers, conditionschange. The atmosphere gets colder and thinner as you move away from Earth’s surface.

The closest layer to the ground is the troposphere.This is where clouds form, and precipitationoccurs. The next layer is the stratosphere. It extendsabout 50 kilometers (30 miles) above the ground.Commercial airliners fly about 11 kilometers (6.84 miles) into the calmer, lower layers of the stratosphere. Next are the mesosphere andthermosphere, which are from 50 kilometers to above90 kilometers (30-56 miles) above the Earth’ssurface. The very thin, outermost layer of theEarth’s atmosphere is the exosphere.

65

Do You Know?Atoms are the tiny particles that make up all matter

in the universe. There are 101 natural substances onEarth called elements. Each element has its own type of atom. Atoms join together to makeall the things found on Earth.

Combinations of atoms arecalled molecules. For example,one molecule of the oxygen webreathe is made upof two atoms ofoxygen, or 02.Ozone is an oxygenmolecule made of three atoms of oxygen, or 03.

The Ozone LayerOzone is a special form of oxygen gas.

Different amounts of ozone are found in each ofthe five layers of the Earth’s atmosphere. There isa lot of ozone in the upper part of the stratosphereso it is considered a sublayer called the ozonelayer. This sublayer absorbs harmful ultravioletrays from the sun. This is called “good ozone”because it protects us.

Alti

tude

(km

)

120––

100––

80––

60 ––

40––

20––

0–

Thermosphere

Mesosphere

Stratosphere

Troposphere

Ozone Layer

Layers of theAtmosphere

Exosphere

EEaarrtthh’’ss ssuurrffaaccee

Oxygen

Ozone molecule

Oxygen

Oxygen

87

Ozone in the ozone layer is continuallycreated and destroyed. It is important that theamount of ozone remains fairly constant, whichmeans that the balance does not shift too greatlyone way or the other.

The part of sunlight known as ultraviolet (UV)light is responsible for creating and destroyingozone. UV light creates ozone by splittingmolecules of oxygen gas (O2), into twoindividual oxygen atoms. If one of these oxygenatoms joins with a molecule of oxygen gas, athree-atom molecule called ozone (O3) forms.UV light can also change an existing ozonemolecule by removing one of its oxygen atoms.The freed oxygen atom then reacts with an ozonemolecule (O3) causing it to split into two oxygenmolecules (O2 + O2). violet indigo blue green yellow orange red

long wavelengths

ultraviolet

VISIBLE

LIGHT

UV

LIGHT

Ultraviolet lightwavelengths are

shorter than thoseof visible light and

cannot be seen.

The colors of therainbow make upthe range of visiblelight, or the lighthumans can see.

Light Wavelengths

short w

avele

ngths

Do You Know?Sunlight is actually a mixture of visible and invisible

light of various wavelengths. The visible light is madeof different colors from red to violet. Long wavelengthsare less powerful and produce red light. Shorterwavelengths are more powerful and produce blue andviolet light. Light eventually becomes invisible as thewavelengths decrease.

Invisible ultraviolet light is powerful and can causeskin cancer, damage the eyes and plants, and killocean life. Some biologists believe that increasedultraviolet light is bleaching the color out of coralsaround the world.

UV rays break down normal oxygen molecules into two separateatoms. Those atoms then combine with other oxygen molecules tomake ozone.

Oxygenmolecule

UV rays

Oxygenatom

Oxygenmolecule

Ozone(03)+ =

109

Discovery of the Ozone HoleIn the 1970s, scientists in Antarctica measured

an increase in the ultraviolet (UV) light reachingEarth. Later, satellites confirmed that UV light insome areas was not being absorbed by the ozonelayer as much as it had been in previous years.From the satellite data, scientists made maps that showed a hole in the ozone layer over theSouth Pole.

By 1994, the ozone level had dropped to onehalf of what it was in the 1970s. There were signsthat the ozone hole discovered above Antarcticawas expanding past the polar region toward theequator where more people lived. The ozone hole was becoming a threat to people and theenvironment.

This continual creation and destruction of ozonekeeps the amount of ozone in the ozone layer fairlyconstant. The layer of ozone created keeps harmfulUV light from reaching Earth’s surface.

Ozone also forms near the ground. This ozoneis harmful to plants and animals and is called“bad ozone.” It forms when cars and factoriesrelease chemicals called pollutants into the air.On hot days, sunlight starts a reaction betweenthe pollutants and oxygen causing the formationof bad ground-level ozone.

If levels of ground-level ozone rise todangerously high levels, a warning is sent out.People with breathing problems are told to stayinside.

Factory smoke stacks release chemicals into the air.

Math MinuteA one-percent decrease in ozone in the

stratosphere will cause a two-percent increase inUV-B light that reaches the ground. If ozone in thestratosphere decreases by ten percent, what is theincrease in the percentage of UV-B light reachingthe ground?

The Cause of the Ozone HoleScientists searched for

causes of the changingozone levels. Theydiscovered that somefactories releasechemicals called CFCs, orchlorofluorocarbons, thatcould destroy ozone. Theelement chlorine in CFCswas the main problem.Since CFCs were used in

air conditioners, insulating foams, and spraypaint, large amounts of chlorine were releasedinto the atmosphere.

Scientists also learned thatanother chemical, bromine, coulddestroy ozone. Bromine is foundin substances that are knownas ODCs, or Ozone DepletingChemicals. Bromine can destroy45 times more ozone than an equalamount of chlorine found in CFCs(chlorofluorocarbons). ODCs arefrequently used in chemicals usedto control fires.

Ozone destruction is greatest around theNorth and South Poles during winter due to thewinds and low temperatures common to polarregions. During spring and summer the ozonelayer rebuilds. (Winter in Antarctica, or the SouthPole, occurs during the summer for the Arctic, or North Pole.)

1211

Scientists in Antarctica launch an instrument that will measure the ozone layer.

refrigerator

fire extinguisher

The World Responds

Even after ozone destruction was connectedto CFCs and ODCs, many countries continued to produce them. These chemicals were so usefulthat nobody wanted to give them up. It tookcooperation between the governments of manynations to address this global problem.

Countries joined together in 1987 and signedthe Montreal Protocol. This agreement called forreducing and later banning the production ofCFCs and ODCs by 1996. This is a success storybecause it is the first time that many nations havetackled a environmental issue on a global scale.As a result, since the year 2000, CFCs and ODCsin the atmosphere have been decreasing.However, it may take years to tell whether or notthe ozone layer will fully recover.

CFCs and ODCs rise into the stratospherewhere sunlight breaks these molecules intochlorine and bromine atoms. The chlorine andbromine then break down ozone molecules. One chlorine atom can destroy 100,000 ozonemolecules. The process stops when the chlorineand bromine drift into space.

Natural sources of chemicals also can destroyozone. One source is erupting volcanoes, whichspread hydrochloric acid high into the stratospherewhere it breaks down into ozone-destroyingchlorine gas. While volcanoes and other naturalcauses do destroy the ozone, CFCs and ODCsfrom industry cause most of the damage.

1413

Delegates from around the world get together each year to makesure countries are doing what they promised.

Erupting volcanoes are one natural source of chemicals thatdestroy ozone.

The Earth has warmed by one degree over the last one hundred years. That may not seemlike a lot, but scientists do not want globalwarming to become a trend that over time mightcause the temperature to rise higher and higher.

A hotter Earth may lead to the melting of thepolar ice caps. This would cause the world’soceans to rise. The rising water levels wouldflood land near the coast and destroy habitats of living things. A warmer Earth would alsocreate changes in weather patterns that could lead to habitat destruction and the deaths of someplants and animals. Some living things, such asthe oceans’ corals, would find it hard to findother places to live. The destruction of coral reefswould destroy the habitat of many ocean animals.

Global Warming

Engineers quickly developed alternativechemicals to CFCs and ODCs in hopes ofrestoring the ozone layer. However, some of thealternative gases that are ozone friendly are alsopowerful greenhouse gases. Greenhouse gasessuch as carbon dioxide and methane, whenreleased into the atmosphere, are able to trapheat near Earth’s surface in the same way glasstraps heat in a greenhouse. The result is acondition known as the “greenhouse effect.”Some scientists think that the greenhouse effecthas caused the temperature of the air aroundEarth to gradually rise.

1615

If the Earth becomes hotter, there is a possibility that polar iceand icebergs will melt, raising the ocean’s water level.

Earth

Atmosphere

GreenhouseGases

Sun

Sun’s rays

heat

from

Ear

th

trapped

heat

How Greenhouse Gases Trap HeatHow Greenhouse Gases Trap Heat

Methane is responsible for about 13 percent ofglobal warming. Methane is produced naturallyin swamps and by livestock passing gas. It is alsoa product of rotting garbage.

Nitrous oxide is the third-worst contributorto global warming. Nitrous oxide is found mostlyin fertilizers. The nitrogen in fertilizers is animportant plant food, but when it mixes with soilit produces nitrous oxide. Nitrous oxide also isproduced when animal waste decomposes.

The final contributor to global warming isfluorocarbon gases. Fluorocarbons also contributeto the destruction of ozone. Fluorocarbons rarelyoccur in nature. They are almost totally human-made so their production can be prevented.

Greenhouse Gases

There are four gases that cause global warmingwhen they are released into the atmosphere. Theyare called greenhouse gases—carbon dioxide,methane, nitrous oxide, and fluorocarbons.

Some scientists believe carbon dioxide causesabout three-fourths, or 76 percent, of the increasein global warming. Cars and other machines thatuse gas-powered motors, as well power plants,produce carbon dioxide by burning fossil fuelssuch as coal, oil, and natural gas. As more cars,planes, trucks, and trains are driven, more carbondioxide is released into the atmosphere. All ofthis leads to greater global warming.

1817

Rotting garbage at landfills produces methane, a greenhouse gas.Some scientists think these four gases are responsible for currenttrends in global warming.

Carbon dioxide 76%

Methane 13%

Greenhouse GasesFluorocarbons 5%Nitrous

oxide 6%

further breakdown of the ozone layer. So, if wecan learn how to decrease the production ofgreenhouse gases, we might prevent furtherdestruction of the ozone layer.

There are no definite answers to the globalwarming problem, but some scientists aroundthe world are looking into solutions. They feelit is in everyone’s best interest to understand asmuch as possible about decreasing the release of greenhouse gases.

World Debate

Not everyone agrees on the seriousness of the global warming problem. Some say that a one-percent rise is nothing to be concernedabout. Others think that the problem will worsenand that people ought to take steps now toprevent future global warming. These peoplebelieve that we should find ways to reducegreenhouse gas production before it is too late.

Reducing the amount of greenhouse gasesmay also slow down the destruction of the ozonelayer. Global warming of the lower atmosphereactually cools the upper atmosphere. Thiscooling leads to conditions that can cause

2019

Using bicycles instead of cars helps decrease the amount ofgreenhouse gases being produced.

Carpooling and taking public transportation would reduce theamount of carbon dioxide released into the atmosphere by gas-powered cars and trucks.

Conclusion

Factories and certain products we use releasechemicals that are destroying part of the protectiveblanket surrounding Earth. The chemicals beingreleased into the air may be causing Earth’satmosphere to warm up. Actions taken bygovernments from all around the world havehelped ban certain chemicals. However, moreaction is needed to prevent future harm to ouratmosphere.

The ozone problem has taught us manythings. We now know that we need to control theuse of certain chemicals. It has brought scientists,politicians, and concerned citizens together towork on common goals. Perhaps the mostimportant thing it has taught us is that we needto start thinking about how our current activitiesmight affect not only people today, but also ourfuture well-being and the health of our planet.

What You Can Do To Help

Governments and industries around the worldhave taken steps to reduce ozone-destroyingchemicals. There are also things that we can doas individuals to protect the atmosphere. We can stop producing more ground-level ozone by reducing the use of automobiles. We can walk,car pool, ride buses, and shop for fuel-efficientvehicles. We can use newspapers to startbarbecues instead of using lighter fluid, and use hand-powered mowers.

Protecting the upper-level ozone layer meanstrying to avoid releasing CFCs and ODCs into theatmosphere. Recycle the chemicals that cool oldrefrigerators and air conditioners. Avoid foampackaging if possible. Write letters to industriesthat still use CFCs and ODCs, and ask them whatthey are doing to find alternatives.

2221

Using public transportation helps decrease ozone depletion.

Index

Antarctica, 10, 11

atmosphere, 4–6, 12, 14, 15, 17, 19, 21, 22exosphere, 5mesosphere, 5stratosphere, 5, 10thermosphere, 5troposphere, 5

atom(s), 6, 7

breathe, 6

bromine, 12, 13

carbon dioxide, 4, 15, 17, 19

chlorine, 12, 13

chlorofluorocarbons (CFCs),12–15, 21

damage, 13

element, 6

fluorocarbons, 17,18

fossil fuels, 17

global warming, 15, 17-20

greenhouse gases, 17, 18

invisible light, 8

Glossary

atmosphere the gas surrounding a celestial body,such as Earth (p. 4)

atoms the smallest particles of elements that canexist alone (p. 7)

chemicals substances of a certain kind that areformed when two or more substances actupon one another (p. 9)

constant steady, not changing (p. 7)

contributor someone or something that has a share insomething (p. 18)

decomposes breaks down in decay (p. 18)

fossil fuels organic substances, such as coal and oil,found underground and used as a sourceof energy (p. 17)

global warming increase in the temperature of Earth’satmosphere, especially a rise greatenough to change the climate (p. 17)

greenhouse effect process by which heat is trapped insideEarth’s atmosphere by an excess of gases(p. 15)

molecules smallest parts of a substance that areformed when two or more elements actupon one another (p. 7)

pollutants things that cause something to no longerbe pure (p. 9)

precipitation different forms of water that fall to theground, such as hail, sleet, rain, snow, ormist (p. 5)

ultraviolet a short-wavelength form of light energythat cannot be seen (p. 6)

2423

Explore MoreOn the Internet use www.google.com to find out more

about topics presented in this book. Use terms from thetext, or try searching for glossary or index words.

Some searches to try: global warming, ozone hole, or CFCs.

methane, 15, 17, 18

molecule(s), 6, 7

Montreal Protocol, 14

nitrogen, 4, 18

North Pole, 11

oxygen, 4, 6, 7, 9

ozone, 6, 7, 9–15, 18–22

hole, 10, 12

layer, 4, 7, 9–11, 14, 15, 19–21

Ozone Depleting Chemicals (ODCs), 12–15, 21

satellites, 10

skin cancer, 8

South Pole, 10

ultraviolet (UV), 6–10UV-B, 10

visible light, 8

volcanoes, 13

wavelength(s), 8