[00:00.00]NARRATOR: Listen to part of a lecture in an environmental science class.
[00:05.09]MALE PROFESSOR: Basically, a cloud either contributes to the cooling of Earth's surface or to its heating.[00:12.51]Earth's climate system is constantly trying to strike a balance between the cooling and warming effects of clouds.
[00:19.26] It's very close, but overall, the cumulative effect of clouds is to cool Earth rather than heat it. [00:26.41]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, [00:36.38]we call this Earth's "radiation budget."[00:39.55]And one way we keep track of the radiation budget is by looking at the albedo of the different surfaces on the planet.
[00:47.67]A surface's albedo is the percentage of incoming solar energy...sunlight...that's reflected off that surface back into space. [00:59.22]Oceans have a low albedo, because they reflect very little energy; [01:04.34]most of the solar energy that reaches the ocean gets absorbed and heats the water. [01:09.17]Um?rain forests also have low albedos.
[01:13.32]Well, by contrast, deserts and areas covered by ice or snow, these places have high albedos. [01:20.48] And clouds—in general—clouds also have high albedos. [01:25.71]That means that a large percentage of the solar energy clouds receive is reflected back into space.[01:31.77]OK?now when we say that clouds have a high albedo, [01:36.54]we're talking about the effect of all the clouds on Earth averaged together. [01:41.44]But different types of clouds have different reflective properties—they have different albedos.[01:47.17]FEMALE STUDENT: So which type of clouds cools Earth? [01:52.04]And which type heat it? [01:53.34]MALE PROFESSOR: Well, high, thin clouds contribute to heating, while low, thick clouds cool Earth. [02:00.27]High, thin clouds are very transparent to solar radiation, like, eh, clear air. [02:05.82]So, they mostly transmit incoming solar energy down to Earth; [02:10.50]there's not much reflection going on at all. [02:12.34]At the same time, these clouds trap in some of Earth's heat. [02:16.45]Because of the trapped heat, these clouds have an overall heating effect.
[02:20.80]MALE STUDENT: Oh, OK, so since low, thick clouds are not transparent to radiation?[02:26.95]MALE PROFESSOR: ...exactly, they block much of the solar energy so it never reaches Earth's surface. [02:32.30]They reflect much of it back out in to space.
[02:35.48]FEMALE STUDENT: So that's how clouds contribute to cooling.[02:38.13]MALE PROFESSOR: Yep. And as I said earlier, this cooling effect predominates. [02:42.39]Now, what if there was a process that could control the types of clouds that form?[02:47.79]MALE STUDENT: Are you talking about controlling the weather?[02:50.48]MALE PROFESSOR: Well, I'm not sure I would go that far. [02:53.23]But, we recently noticed an increase in cloud cover over an area of the ocean waters around Antarctica—[02:59.81]an increased area of low, thick clouds, the type that reflects a large portion of solar energy back to space and cools the Earth.
[03:07.85]Well, the reason for this increased cloud cover, it turns out, is the exceptionally large amount of microscopic marine plants. [03:16.91]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've observed.
[03:30.32]Well, that's true. [03:32.09]It could have huge implications.[03:34.48]So, maybe we are talking about controlling the weather.[03:37.78]Perhaps, if the microorganisms near Antarctica really are responsible, perhaps we can accelerate the process somehow.
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