云彩怎样影响地球的气候

Their shade cools the planet and their water vapor traps heat from the sun.

云彩的阴影使地球变得凉爽，云彩中的水蒸气则留住了来自太阳的热量。

THE GIST

摘要：

·Clouds have both cooling and warming effects on Earth's surface. Figuring how they balance is tricky.

*云彩对地表有降温和保温的双重作用。但至于云彩如何平衡这两种作用，我们还很难解释。

·Determining global cloud cover over time is a major aspect of understanding climate change.

*随时测定出全球云量的多少，是了解气候变化的一个主要角度。

（image illustration）Clouds play a crucial role in regulating Earth's climate.

Some clouds help cool the Earth, but other clouds help keep Earth warm – in part depending on how high up they are in our atmosphere. That’s according to Steven Platnick, a satellite researcher with NASA. He studies clouds and how they connect with Earth’s climate. He said that low, fluffy clouds keep us cooler.

（插图说明文字）云彩对地球气候的调节有关键作用。

有些云彩能为地球降温，也有些云彩能为地球保暖——某种程度上取决于云彩在大气层中的高度。这一观点是由美国国家航空航天局的卫星研究学者Steven Platnick（史蒂芬·普兰尼克）提出来的。他负责研究云彩以及它们与地球气候的关系。他曾经说过，低空的絮状云更能使我们感到凉爽。

SP: You can appreciate that if you go out on a hot and sunny day, and a cloud passes by overhead, it’s a great relief from the heat. And the reason of course is because the cloud is reflecting sunlight.

SP:如果你在一个晴朗又炎热的日子出门，若一片云彩从头顶飘过时，你就会顿时觉得凉快很多，这时你就得谢谢云彩了。这是因为云彩反射了太阳光。

But it’s a different story for clouds that are high up in the atmosphere, said Platnick. Those high, wispy clouds actually keep Earth warm, like a blanket, by preventing heat from escaping into space. Platnick uses NASA’s Aqua satellite to determine the height of clouds, and other properties of clouds as well -- like what’s inside them, how much water they have, and whether a cloud is primarily liquid or ice. The satellite also tracks the amount of cloud cover all over the world.

但是Platnick说，对于处在高空大气层中的云彩来说，情况就不一样了。实际上，那些高空的束状云是为地球保暖的，它们的作用很像地毯，阻止了热量流失到太空中。Platnick利用国家航空航天局的水文气象卫星来测定云层的高度，也能用它测出云层其他的性质——比如云层的成分、含水量，再如某片云彩主要是液态水还是固态冰。这个卫星还能测出全世界总的云量。

Steven Platnick: The most important thing to trying to understand their effect on global climate is we need to know how they’re globally distributed and how they vary over the course of a year. And you need satellites to really obtain the statistics over those scales. It’s really impossible for most of those quantities to get the same statistics from ground-based or aircraft observations.

SP:要搞清楚云层对地球气候的影响，最重要的是，我们需要了解云层在全球的分布规律和在一年中的变化规律。你需要使用卫星，因为只有利用卫星能够获取有关云层全球分布和时节变化方面的统计数据。其中大部分数据，通过地面观测站或者空中观测站是根本收集不到的。

Platnick explained to EarthSky what scientists mean when they talk about climate.

Platnick在“天地（EarthSky）”节目中解释了科学家所论的气候的含义。

SP: When scientists talk about climate, what we’re talking about is the statistics of weather. And normally we’re talking about that on multi-decadal time scales, and longer, even centuries and millennium. An example might be the average surface temperatures, something that most people can relate to. Or also, the minimum and maximum surface temperatures. And there’s other examples -– precipitation, the amount of rainfall during the month, or snowfall, or snow pack. But when we talk about recent climate change, and the causes of recent climate change, and that’s over the last several decades including the last several centuries since the start of the industrial revolution, then we start to study the effect of human activities, and how humans can directly modify climate.

SP:科 学家们在谈论气候时，实际都是在谈论关于天气的统计数据。一般来说，我们谈论的这些数据的时间跨度有的几十年，有的几百年，有的甚至长达几千年。比如平均 地表温度，很多人谈论时都会提到它，有的人还会谈到最高地表温度和最低地表温度。其他例子如降水量、月降雨量、降雪量、积雪量等等。但当我们谈到近年来的 气候变化和变化的原因时，由于最近这几十年涵盖了工业革命以来的几个世纪，我们就需要开始研究人类活动对气候的影响以及人类怎样直接改变了气候。

Platnick said that there are several ways that humans can directly impact climate. The best understood of these, he said, and what’s likely the most important in the long run, is the release of greenhouse gases into the atmosphere.

根据Platnick的说法，人类直接改变气候的方式有好几种。在他看来，向大气中排放温室气体这一方式是其中最需要充分理解的，并且从长远来看还可能是最重要的一种影响方式。

SP: And that includes not just carbon dioxide, but methane, ozone, there’s other gases as well. And these greenhouse gases perturb the radiation balance of climate. And what they do is move the climate system to a warmer state. And it does that because of the way that gases reduce the emissions of infrared radiation to space by the Earth and its atmosphere. And this so-called greenhouse gas forcing on the climate system is well-understood.

SP:温 室气体不仅包括二氧化碳，还包括甲烷、臭氧等其他气体。这些温室气体会扰乱气候的辐射平衡。它们会使气候系统进入一种增温状态。这一现象的产生是因为这些 气体使地球及其大气层散入到太空的红外线辐射减少了。这些所谓的温室气体，对气候系统施加强迫性，这一点已经得到了很好的理解。

He said that what’s less well-understood is how the climate responds to this forcing.

但他说，还有一个问题没有被充分理解，那就是气候是如何对这种强迫性作用作出回应的。

SP: And that is the focus of much climate modeling research today. It’s certainly the motivation behind many of NASA’s satellite observations and the modeling studies that we do, and that’s in fact what a large part of my own work involves.

SP:这一问题是现今大多数气候模拟研究的核心问题。当然，它也为美国国家航空航天局许多卫星观测项目和我们所进行的模拟研究提供了动力；事实上，我的工作有一大部分就是围绕这一问题展开的。新物理？基本的宇宙常数现在显得不确定

Platnick told EarthSky what he thought was the most important thing people should know about Earth’s clouds and climate.

关于地球上云彩与气候的关系，人们应该了解的最重要的信息是什么？Platnick在“天地”节目中谈了自己对这一问题的看法。

SP: Earth is a dynamic system of components. On the largest scales you have the atmosphere, the land, the ocean, snow and ice on the ground. And these systems connect with each other in different ways, through the exchange of water, and energy, and chemistry, such as the exchange of carbon. We need to be able to better understand the consequences of these connections. Clouds are the prime example of this interconnection, because they play a key role in these systems, especially in the water and energy connections.

SP:地 球是一个由不同成分组成的动态系统。从最大的范围来看，大气、土地、海洋、地面冰雪都包括在内。此外，通过交换水分、能量和化学元素（如碳元素），这些系 统还以不同的方式互相联系着。我们需要更好地把这些联系带来的影响弄懂。在这个互相联系的系统网络中，云彩是个典型的例子，因为云彩在这一联系网络中发挥 着关键作用，特别是水和能量之间的联系。

NASA satellites and instruments, along with our international partners are helping us to get better observations we need to understand these cloud physical processes and to enable cloud model improvements as well.

具备了美国国家航空航天局的卫星和仪器，再加上我们的国际合作伙伴的帮助，我们就能更容易得到我们所需要的更充分的观测数据，以便解决关于云层的物理变化过程的问题，也能使我们的云模型得到改进。