Climate 101: Ozone Depletion | National Geographic

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- [Narrator] 15 to 35 kilometers above Earth's surface

a gas called ozone surrounds the planet.

The ozone layer acts as a barrier

between Earth and ultraviolet radiation from the Sun.

However, pollution has caused the ozone layer to thin

exposing life on Earth to dangerous radiation.

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Earth's atmosphere is made up of six layers.

The second layer, called the stratosphere,

contains the ozone layer.

The ozone layer is made up of a highly

reactive molecule called ozone

which contains three oxygen atoms.

Ozone is a trace gas in the atmosphere.

There are only about three molecules for every

10 million molecules of air

but it does a very important job.

The ozone layer acts as Earth's sunscreen,

absorbing about 98% of damaging ultraviolet or UV light.

But the ozone layer has gotten thinner.

Chemicals called chlorofluorocarbons or CFCs

are the primary culprits in ozone layer breakdown.

A CFC is a molecule that contains the elements

carbon, chlorine and fluorine.

CFCs are mostly found in refrigerants,

aerosols and plastic products.

When CFCs are exposed to ultraviolet rays

in the atmosphere, they break down

into substances that include chlorine.

The chlorine reacts with the oxygen atoms

in ozone and rips apart the ozone molecule.

Areas of damage in the ozone layer are often

called ozone holes but that name is misleading.

Ozone layer damage is more like a thin patch

with the thinnest areas near the poles.

The ozone layer above the Antarctic in particular

has been impacted by pollution since the mid-1980s.

There the region's low temperatures speed up

the conversion of CFCs to ozone-damaging chlorine.

About 90% of CFCs currently in the atmosphere

were emitted by industrialized countries

in the northern hemisphere.

In 1989 the Montreal Protocol banned the production

of ozone-depleting substances.

Since then the amount of chlorine

and other ozone-depleting elements

in the atmosphere have been falling.

Scientists estimate that chlorine levels will return

to their natural state in about 50 years.

By then the Antarctic ozone hole will shrink

to smaller than eight million square miles.

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