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Why is the world warming up?

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Let's think of Earth
for just a moment as a greenhouse.

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Every second, a huge amount of energy
smashes into our greenhouse.

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Our atmosphere, the glass roof and walls,

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reflects some of that energy,

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but most of it passes right through
and heats everything up.

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Much of that heat
used to escape back into space,

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keeping us at a stable, warm temperature.

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But then something changed.

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Humans began to spew enough carbon dioxide
to fill billions of greenhouses each day.

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What does all that greenhouse gas do?

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It makes the glass
of our greenhouse thicker.

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Thicker glass means heat escapes
into space much more slowly.

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And don't forget, energy from the sun

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is still streaming in
just as quickly as before.

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The result is a planet with temperatures
too hot for our liking

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and, eventually...

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living.

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[Countdown

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Take action on climate change
at COUNTDOWN.TED.COM]