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[ music ]

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The Earth is a bright planet.

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From space, we can see why. More than half our world is covered with clouds

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at any one time. Those clouds reflect

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a lot of sunlight back to space, helping keep our planet relatively cool.

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But a NASA satellite instrument called MODIS is showing us

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that humans can change our planet's brightness.

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The pollution we put into the atmosphere actually alters clouds.

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The best way to see this is to look for signs of pollution in areas that have

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otherwise clean air, like the north Pacific, near the Aleutian islands.

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In clean ocean air, water vapor condenses

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around salt particles and marine sulfate particles, creating clouds.

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To the naked eye, the clouds in the north Pacific all look

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about the same. But MODIS' sensor reveals a different story...

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... long skinny trails of brighter clouds

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hidden within. As ships travel across the ocean,

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sulfate particles in their exhaust create more cloud drops that are smaller in size

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resulting in even brighter clouds. And, on clear days,

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ships can actually create new clouds.

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Water vapor condenses around particles of pollution, forming streamers

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of clouds as the ships travel on.

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Could air pollution actually curb global warming by making our planet brighter and more reflective?

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Scientists are studying the phenomenon, but

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scientists say it's not likely to significantly slow global warming.

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The heat-trapping effect of greenhouse gases, many of which lurk in the same pollution,

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will most likely keep temperatures on the rise.