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Why is the world warming up?

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

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Every second, a huge amount of energy[br]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[br]and heats everything up.

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Much of that heat[br]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[br]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[br]of our greenhouse thicker.

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Thicker glass means heat escapes[br]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[br]just as quickly as before.

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The result is a planet with temperatures[br]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[br]at COUNTDOWN.TED.COM]