from the unique vantage point of the
space shuttle Atlantis we can see the
separation of two diverse environments
all around us is the endless vacuum of
space
avoid where humans cannot survive
without elaborate life-support systems
and below us like a blue and white oasis
in the middle of a lifeless desert is
earth a place of abundant life
separating these two extreme
environments is a thin and fragile shell
of gases we call our atmosphere in
thickness the atmosphere is to the earth
like the fuzz is to a tennis ball but in
spite of its relative thinness the
atmosphere is vitally important to life
on earth it's the atmosphere that gives
us the air we breathe it regulates our
climate to make the earth habitable and
it's a filter that screens out much of
the sun's harmful radiation while
allowing the radiation needed for life
to pass through it should come as no
surprise that life as we know it would
cease to exist if our atmosphere didn't
perform its unique functions but
recently scientists have begun to detect
that our atmosphere has been
experiencing mysterious new changes
changes that appear to be the result of
human activity changes that could
ultimately affect our lives in a major
way many of you may have heard about
ozone depletion the greenhouse effect
and global warming all of these are
related to the changes that are taking
place in our atmosphere but do any of
you know who or what is causing the
changes
as a scientist I've always considered
myself a detective of sorts
investigating the earth and its
environment asking important questions
that hopefully will lead to practical
solutions join me now and let's see if
together we can solve our responsible
let's begin our investigation by finding
out what's happening to the ozone first
we'll need to ask a few questions to get
some background for starters what is
ozone ozone is oxygen but not the kind
we normally think of a regular oxygen
molecule is formed by two oxygen atoms
that are bonded together but ozone
molecules are different they have three
oxygen atoms bonded together ozone can
be made in a laboratory on the ground
where we can study its characteristics
ozone is also made naturally in the
upper atmosphere there ultraviolet light
from the Sun breaks the bond in
molecular oxygen to form two separate
atoms these atoms may then join with
other molecules to form ozone why is
ozone so special well without ozone in
our atmosphere I would probably need a
sunscreen protection factor of five
hundred and probably even that would not
be enough you see ozone blocks
ultraviolet radiation up in the
stratosphere ozone forms a very thin
layer so thin that for every 1 million
gas molecules only 10 our ozone but even
as thin as it is
the ozone layer is able to screen out
most of the sun's harmful UV rays
just having to cut back on the amount of
sunscreen be happy to buy ozone is
important to all life on earth because
without it scientists believe cases of
skin cancer and eye cataracts would
increase and since sunscreen only helps
humans animals would be unprotected
crops and plant life would also be
affected and that would upset the
Earth's entire ecological system in fact
the diversity of life as we know it
would change drastically
if ozone disappeared from the atmosphere
by looking at the atmosphere of home
space with just our eyes we can't tell
if anything is happening to the ozone
layer or not but scientific instruments
carried on weather balloons sounding
rockets and satellites show us revealing
evidence that ozone levels are
decreasing over much of the earth from
September through November ozone levels
decrease over Antarctica this is what's
called the ozone hole the ozone hole
allows more ultraviolet radiation to
reach Antarctica than would otherwise do
so but changes in ozone concentration
are more complex than just the
appearance of seasonal holes so now we
know over many parts of the world are
decreasing and we know some of the
chemicals that play in this game but a
good detective always has to look beyond
the obvious we have to ask ourselves
where do these chemicals come from two
of the suspects are the chemical
compounds chlorofluorocarbons also known
as CFCs and oxides of nitrogen which
have many faces here's why we suspect
them in the upper atmosphere these
compounds react with sunlight and are
broken down into smaller parts
the CFCs give off chlorine atoms while
nitrogen oxides form nitric oxide there
they are joined by other chemicals
containing hydrogen sulfur and other
atoms
when these chemicals encounter ozone a
reaction occurs that strips away an atom
of oxygen from the ozone molecule the
products of these reactions react with
ozone also just a small amount of
chlorine and nitric oxide can create a
cycle that destroys many ozone molecules
it looks like we may have some of the
key players responsible for the ozone
destruction but there are a lot more
detail to be worked out a good detective
I always looks beyond the obvious we've
got to ask ourselves where are these
chemicals coming from they come from
many sources hydrogen compounds come
from the gas methane that's formed by
agricultural activities such as rice
production and the cattle industry
decaying vegetation and swamps also
produces methane chlorofluorocarbons or
CFCs are made by humans what form of
this chemical is the gas used in our
refrigerators and air-conditioning units
to chill the air it's also used to blow
insulating firm and clean electrical
components nitrogen compounds come from
many sources exhaust emission from
high-flying supersonic aircraft is only
one of them nitrogen is also released
into the atmosphere during lightning
storms in tropical regions many chemical
fertilizers that we use to grow our food
are nitrogen based and they lead to
increased releases of nitrous oxide into
the atmosphere too so now we know that
mother nature and humans both contribute
to the decreasing ozone but does that
mean that one of them is more
responsible than the other well we don't
know for certain that part of the
mystery requires more investigation and
that's why we're here during this
spaceflight we are observing the
atmosphere in the Sun with several
sophisticated instruments the data we
gather will not only improve our
knowledge of the amounts of ozone
depleting chemicals found in the
atmosphere it will also help us to
better understand
the rolled the sun's radiation
when the facts are all in we'll have a
better understanding of the distribution
of ozone depleting chemicals in the
atmosphere now let's turn our attention
to another mystery of the changing
atmosphere below you know summers here
in Houston can be pretty hot it's hard
to imagine they could get much hotter
but some scientists say it's actually
happening actually Earth's climate has
changed many times over millions of
years we've had ice ages and we've had
warmer periods that's because several
factors that affect the climate of the
earth vary over tonight one of these is
the concentration of carbon dioxide a
gas present in the atmosphere in very
small quantities here's how it works
picture a primeval setting with lots of
volcanic activity as the volcanoes erupt
they spew large amounts of carbon
dioxide into the atmosphere carbon
dioxide is what we call a greenhouse gas
that's because it blankets the earth and
traps heat much the same as a greenhouse
does in a greenhouse incoming radiation
from the Sun passes through the
translucent roof unhindered
but the heat radiated back from the
earth is trapped by the glass
this trapped heat causes the temperature
in the greenhouse to rise the same thing
happens in the atmosphere if carbon
dioxide increases heat becomes trapped
under the atmospheric blanket and global
temperatures will rise by a few degrees
so what's a few degrees the earth's
temperature changes every day when the
sun goes down
well the slightly warmer global
temperatures can cause other changes to
happen polar ice caps and mountain
glaciers begin to melt adding fresh
water to the oceans and ocean water
itself expands as it warms together
these two changes can cause ocean levels
to rise flooding lowlands warmer
temperatures along with sufficient
rainfall also mean that more green
plants grow but to some extent ocean
water and vegetation both naturally
absorb carbon dioxide from the air so
with more ocean surface and more
vegetation more carbon dioxide is
removed from the atmosphere eventually
enough carbon dioxide may be removed
from the atmosphere so that the
greenhouse effect begins to diminish and
the earth begins to cool again of course
climate change is not that simple there
are a lot of other factors too some of
the same chemicals that are hurting the
ozone layer contribute to global warming
also things like photosynthesis
respiration ocean currents forest fires
and fluctuations in the amount of energy
generated by the Sun so if the earth's
temperature varies a few degrees what's
the big mystery measurements of co2 and
air samples trapped in ice indicate that
levels of carbon dioxide are increasing
our planet appears to be warming more
than normal this is another mystery of
where and who where is this excess
carbon dioxide coming from and who or
what is responsible for it parent space
we can see some natural sources of
carbon dioxide
volcanoes and naturally caused forest
fires
but many human activities are also
releasing carbon dioxide for more than
100 years the fossil fuel burning
machines of the Industrial Revolution
have dumped millions of tons of carbon
dioxide into the atmosphere
at the same time the harvesting of
forests and clearing land for
cultivation is reducing vegetation color
vegetation uses carbon dioxide for
growth and in doing so tends to limit
atmospheric increases of carbon dioxide
so once again we fight both nature and
humans are causing our atmosphere to
change these relatively rapid changes
leading to a major warming that part
investigation is still underway in 1991
the upper atmospheric research satellite
or urs was launched from the space
shuttle Discovery you ours is using 10
highly sophisticated sensors to conduct
a long-term study of the atmosphere it
will compile the most complete data ever
collected on energy input from the Sun
winds and atmospheric composition this
information will add to the clues we
have for solving the mystery of ozone
depletion and global warming but another
part of the investigation is happening
right here on space shuttle Atlantis our
atmospheric laboratory for applications
and science is gathering important
information about the atmosphere such as
what trace gases and chemicals are
present in the atmosphere and in what
quantities and what is the ultraviolet
radiation output of the Sun the URS
satellite and this mission are the start
of a long term investigation of the
interaction of the sun's energy with
Earth's atmosphere the goal is to better
understand how chemicals in the
atmosphere reacting with the sun's
changing energy levels are affecting our
environment
there are obviously a lot more questions
that need to be asked and answered
before we can completely solve the
mysteries of our changing atmosphere
it's going to take far more than a
single satellite or a single shuttle
mission to solve this puzzle this
investigation is going to take long term
study by many dedicated scientists some
of the people who ultimately will
unravel all these clues inside the
mystery are probably sitting right
beside you at this very moment now the
question is will you be one of them