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Other things have changed too - we’ve chopped

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down tropical forests,

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caused the ozone hole, and

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filled the air with soot, smog and

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other kinds of air pollution.

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And this is on top of natural variations

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caused by the dynamics of the oceans, or volcanoes,

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or variations in the Sun’s activity.

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And so we can ask whether

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it’s human activities warming our planet.

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At NASA, we have some big and

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powerful computers,

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able to make 6.8 trillion calculations per second.

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We put these huge supercomputers

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to work to recreate Earth’s climate.

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So, we have thousands of ideas of

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what could naturally cause climate change.

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We have 4 billion years of history
where nearly

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anything and everything

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you could imagine has impacted Earth's climate!

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But each of those events have

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their own distinct fingerprint which we can

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identify a pattern of behavior with natural variability.

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Using supercomputers, we can run
simulations of natural climate drivers,

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solar energy changes, wobbles in Earth’s orbits, ocean turnover,

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volcanic eruptions....

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And we can run simulations of human effects.

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And what we've seen is...

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It's us.  There's no way around it.

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Looking at the evidence, we're the force
that's enacting these changes.

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I am so proud of our ability to understand

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the climate, but I'm terrified of what we found.