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from the unique vantage point of the

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space shuttle Atlantis we can see the

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separation of two diverse environments

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all around us is the endless vacuum of

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space

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avoid where humans cannot survive

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without elaborate life-support systems

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and below us like a blue and white oasis

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in the middle of a lifeless desert is

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earth a place of abundant life

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separating these two extreme

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environments is a thin and fragile shell

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of gases we call our atmosphere in

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thickness the atmosphere is to the earth

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like the fuzz is to a tennis ball but in

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spite of its relative thinness the

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atmosphere is vitally important to life

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on earth it's the atmosphere that gives

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us the air we breathe it regulates our

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climate to make the earth habitable and

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it's a filter that screens out much of

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the sun's harmful radiation while

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allowing the radiation needed for life

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to pass through it should come as no

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surprise that life as we know it would

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cease to exist if our atmosphere didn't

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perform its unique functions but

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recently scientists have begun to detect

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that our atmosphere has been

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experiencing mysterious new changes

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changes that appear to be the result of

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human activity changes that could

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ultimately affect our lives in a major

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way many of you may have heard about

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ozone depletion the greenhouse effect

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and global warming all of these are

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related to the changes that are taking

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place in our atmosphere but do any of

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you know who or what is causing the

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changes

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as a scientist I've always considered

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myself a detective of sorts

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investigating the earth and its

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environment asking important questions

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that hopefully will lead to practical

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solutions join me now and let's see if

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let's begin our investigation by finding

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out what's happening to the ozone first

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we'll need to ask a few questions to get

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some background for starters what is

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ozone ozone is oxygen but not the kind

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we normally think of a regular oxygen

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molecule is formed by two oxygen atoms

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that are bonded together but ozone

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molecules are different they have three

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oxygen atoms bonded together ozone can

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be made in a laboratory on the ground

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where we can study its characteristics

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ozone is also made naturally in the

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upper atmosphere there ultraviolet light

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from the Sun breaks the bond in

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molecular oxygen to form two separate

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atoms these atoms may then join with

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other molecules to form ozone why is

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ozone so special well without ozone in

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our atmosphere I would probably need a

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sunscreen protection factor of five

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hundred and probably even that would not

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be enough you see ozone blocks

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ultraviolet radiation up in the

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stratosphere ozone forms a very thin

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layer so thin that for every 1 million

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gas molecules only 10 our ozone but even

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as thin as it is

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the ozone layer is able to screen out

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just having to cut back on the amount of

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sunscreen be happy to buy ozone is

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important to all life on earth because

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without it scientists believe cases of

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skin cancer and eye cataracts would

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increase and since sunscreen only helps

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humans animals would be unprotected

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crops and plant life would also be

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affected and that would upset the

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Earth's entire ecological system in fact

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the diversity of life as we know it

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would change drastically

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if ozone disappeared from the atmosphere

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by looking at the atmosphere of home

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space with just our eyes we can't tell

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if anything is happening to the ozone

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layer or not but scientific instruments

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carried on weather balloons sounding

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rockets and satellites show us revealing

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evidence that ozone levels are

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decreasing over much of the earth from

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September through November ozone levels

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decrease over Antarctica this is what's

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called the ozone hole the ozone hole

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allows more ultraviolet radiation to

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reach Antarctica than would otherwise do

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so but changes in ozone concentration

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are more complex than just the

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appearance of seasonal holes so now we

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know over many parts of the world are

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decreasing and we know some of the

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chemicals that play in this game but a

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good detective always has to look beyond

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the obvious we have to ask ourselves

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where do these chemicals come from two

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of the suspects are the chemical

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compounds chlorofluorocarbons also known

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as CFCs and oxides of nitrogen which

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have many faces here's why we suspect

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them in the upper atmosphere these

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compounds react with sunlight and are

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broken down into smaller parts

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the CFCs give off chlorine atoms while

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nitrogen oxides form nitric oxide there

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they are joined by other chemicals

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containing hydrogen sulfur and other

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atoms

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when these chemicals encounter ozone a

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reaction occurs that strips away an atom

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of oxygen from the ozone molecule the

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products of these reactions react with

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ozone also just a small amount of

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chlorine and nitric oxide can create a

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cycle that destroys many ozone molecules

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it looks like we may have some of the

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key players responsible for the ozone

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destruction but there are a lot more

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detail to be worked out a good detective

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I always looks beyond the obvious we've

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got to ask ourselves where are these

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chemicals coming from they come from

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many sources hydrogen compounds come

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from the gas methane that's formed by

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agricultural activities such as rice

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production and the cattle industry

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decaying vegetation and swamps also

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produces methane chlorofluorocarbons or

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CFCs are made by humans what form of

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this chemical is the gas used in our

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refrigerators and air-conditioning units

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to chill the air it's also used to blow

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insulating firm and clean electrical

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components nitrogen compounds come from

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many sources exhaust emission from

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high-flying supersonic aircraft is only

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one of them nitrogen is also released

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into the atmosphere during lightning

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storms in tropical regions many chemical

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fertilizers that we use to grow our food

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are nitrogen based and they lead to

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increased releases of nitrous oxide into

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the atmosphere too so now we know that

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mother nature and humans both contribute

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to the decreasing ozone but does that

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mean that one of them is more

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responsible than the other well we don't

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know for certain that part of the

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mystery requires more investigation and

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that's why we're here during this

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spaceflight we are observing the

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atmosphere in the Sun with several

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sophisticated instruments the data we

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gather will not only improve our

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knowledge of the amounts of ozone

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depleting chemicals found in the

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atmosphere it will also help us to

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better understand

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when the facts are all in we'll have a

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better understanding of the distribution

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of ozone depleting chemicals in the

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atmosphere now let's turn our attention

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to another mystery of the changing

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atmosphere below you know summers here

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in Houston can be pretty hot it's hard

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to imagine they could get much hotter

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but some scientists say it's actually

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happening actually Earth's climate has

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changed many times over millions of

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years we've had ice ages and we've had

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warmer periods that's because several

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factors that affect the climate of the

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earth vary over tonight one of these is

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the concentration of carbon dioxide a

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gas present in the atmosphere in very

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small quantities here's how it works

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picture a primeval setting with lots of

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volcanic activity as the volcanoes erupt

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they spew large amounts of carbon

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dioxide into the atmosphere carbon

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dioxide is what we call a greenhouse gas

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that's because it blankets the earth and

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traps heat much the same as a greenhouse

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does in a greenhouse incoming radiation

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from the Sun passes through the

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translucent roof unhindered

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but the heat radiated back from the

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earth is trapped by the glass

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this trapped heat causes the temperature

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in the greenhouse to rise the same thing

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happens in the atmosphere if carbon

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dioxide increases heat becomes trapped

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under the atmospheric blanket and global

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so what's a few degrees the earth's

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temperature changes every day when the

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sun goes down

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well the slightly warmer global

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temperatures can cause other changes to

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happen polar ice caps and mountain

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glaciers begin to melt adding fresh

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water to the oceans and ocean water

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itself expands as it warms together

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these two changes can cause ocean levels

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to rise flooding lowlands warmer

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temperatures along with sufficient

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rainfall also mean that more green

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plants grow but to some extent ocean

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water and vegetation both naturally

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absorb carbon dioxide from the air so

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with more ocean surface and more

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vegetation more carbon dioxide is

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removed from the atmosphere eventually

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enough carbon dioxide may be removed

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from the atmosphere so that the

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greenhouse effect begins to diminish and

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the earth begins to cool again of course

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climate change is not that simple there

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are a lot of other factors too some of

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the same chemicals that are hurting the

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ozone layer contribute to global warming

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also things like photosynthesis

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respiration ocean currents forest fires

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and fluctuations in the amount of energy

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generated by the Sun so if the earth's

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temperature varies a few degrees what's

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the big mystery measurements of co2 and

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air samples trapped in ice indicate that

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levels of carbon dioxide are increasing

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our planet appears to be warming more

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than normal this is another mystery of

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where and who where is this excess

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carbon dioxide coming from and who or

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what is responsible for it parent space

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we can see some natural sources of

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volcanoes and naturally caused forest

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fires

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but many human activities are also

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releasing carbon dioxide for more than

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100 years the fossil fuel burning

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machines of the Industrial Revolution

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have dumped millions of tons of carbon

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dioxide into the atmosphere

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at the same time the harvesting of

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forests and clearing land for

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cultivation is reducing vegetation color

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vegetation uses carbon dioxide for

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growth and in doing so tends to limit

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atmospheric increases of carbon dioxide

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so once again we fight both nature and

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humans are causing our atmosphere to

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change these relatively rapid changes

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leading to a major warming that part

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investigation is still underway in 1991

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the upper atmospheric research satellite

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or urs was launched from the space

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shuttle Discovery you ours is using 10

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highly sophisticated sensors to conduct

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a long-term study of the atmosphere it

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will compile the most complete data ever

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collected on energy input from the Sun

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winds and atmospheric composition this

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information will add to the clues we

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have for solving the mystery of ozone

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depletion and global warming but another

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part of the investigation is happening

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right here on space shuttle Atlantis our

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atmospheric laboratory for applications

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and science is gathering important

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information about the atmosphere such as

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what trace gases and chemicals are

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present in the atmosphere and in what

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quantities and what is the ultraviolet

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radiation output of the Sun the URS

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satellite and this mission are the start

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of a long term investigation of the

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interaction of the sun's energy with

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Earth's atmosphere the goal is to better

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understand how chemicals in the

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atmosphere reacting with the sun's

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changing energy levels are affecting our

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environment

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there are obviously a lot more questions

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that need to be asked and answered

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before we can completely solve the

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mysteries of our changing atmosphere

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it's going to take far more than a

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single satellite or a single shuttle

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mission to solve this puzzle this

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investigation is going to take long term

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study by many dedicated scientists some

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of the people who ultimately will

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unravel all these clues inside the

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mystery are probably sitting right