Ahh. The chain reaction.
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You know when you are surfing the web, your parents tell you, or you surf the web, that you see some things like "STOP GLOBAL WARMING?"
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Yep, I have, at least.
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Well, let's see about the chain reaction...
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You see, where does our energy come from?
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Yes, windmills and solar cells...
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but also nuclear and power plants, no?
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The power plants emit carbon dioxide that contribute to global warming.
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Now, cars do the same. One car may not seems like a lot of carbon dioxide...
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But... this many cars multiplied by 9 trillion times 9 trillion and much more... is...
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Well, you know the difference.
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They contribute to global warming over a period of time, slowly, because they emit carbon monoxide/dioxide.