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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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TPO 23-L2 .Earth Radiation Budget 点击收藏

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    Listen to part of a lecture in an environmental science class.

    Basically, a cloud either contributes to the cooling of Earth's surface or to its heating.

    Earth climate system is constantly trying to strike a balance between the cooling and warming effects of clouds.

    It's very close, but overall the cumulative effects of cloud is to cool Earth rather than heat it.

    And this balance between the amount of solar radiation, energy from the Sun, that's absorbed by Earth, and the amount that's reflected back into space, we call this "Earth's radiation budget".

    And one way we keep track of the "radiation budget" is by looking at the "albedo" of the different surfaces on the planets.

    A surface's "albedo" is the percentage of incoming solar energy, sunlight, that's reflected off the surface back into space.

    Oceans have a low albedo, because they reflect very little energy.

    Most of the solar energy that reaches the ocean gets absorbed and heats the water.

    Um, rain forests also have low albedo.

    Well, by contrast, deserts and areas covered by ice and snow, these places have high albedos.

    And clouds, in general, clouds also have high albedos.

    That means that a large percentage of the solar energy clouds recieve is reflected back into space.

    OK, now when we say that clouds have a high albedo, we are talking about the effect of all the clouds on Earth averaged together.

    But different types of clouds have different reflective properties, they have different albedos.

    So which type of clouds cool Earth, and which type heat it?

    Well, high thin clouds contribute to heating while low thick clouds cool Earth.

    High thin clouds are very transparent to solar radiation.

    Like clear air.

    So, they mostly transmit incoming solar energy down to Earth, there is not much reflection going on at all.

    At the same time, these clouds trap in some of the Earth's heat, because of trapped heat, these clouds have an overall heating effect.

    Oh, OK, so since low thick clouds are not transparent the radiation...

    Exactly, they block much of the solar energy, so it never reaches Earth's surface, they reflect much of it back out into space.

    So that's how clouds contribute to cooling?

    Yep, and as I said earlier, this cooling affect predominates.

    Now what if there was a process that could control the type of clouds that form?

    Are you talking about controlling the weather?

    Well, I am not sure I would go that far.

    But we recently noticed an increasing cloud cover over an area of the ocean waters around Antarctica.

    An increased area of low thick clouds, the type that reflects a large portion of the solar energy back to space and cools the Earth.

    Well, the reason for this increased cloud cover, it turns out, is the exceptionally large amount of microscopic marine plants.

    Well the current hypothesis is that these microorganisms produce a chemical, dimethyl sulfide that interacts with the oxygen in the air, creating conditions that lead to the formation of the low thick clouds we observed.

    Well, that's true. It could have huge implications.

    So maybe we are talking about controlling the weather, perhaps if the microorganism in Antarctica really are responsible, perhaps we can accelerate the process somehow.

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