改变飞行高度可减少影响气候的飞机云

Changing the altitude of flights decreases contrails that affect the weather

林晓洁 供稿

Airplanes account for about 3 percent of the climate-altering carbon dioxide emissions we add to the atmosphere. But planes are warming the planet in another way. “So if you look up in the sky, you probably see, at some point, an aircraft. And behind that aircraft are white, fluffy streaks. And that’s what we call a contrail.” said Imperial College London engineer Marc Stettler.

人类排放到大气中的二氧化碳正改变着气候，其中3%的碳排放来源于飞机。然而，飞机还正以另一种方式加剧全球变暖。伦敦帝国理工学院的工程师马克·斯泰特勒介绍：“当你仰望天空时，某个时刻可能会看到飞机。飞机后面拖着几条毛绒绒的白色拉线，我们称之为飞机云。”

Contrails are made up of ice crystals that form when aircraft engines emit exhaust that hits the cold air. The ice crystals reflect incoming light from the sun back into space, which has a cooling effect on the atmosphere. But the contrails also stop heat coming up from the ground from escaping into space. “It’s reflected back down toward the ground. And so that’s a warming effect.”

飞机云由冰晶组成，而这些冰晶则是由飞机引擎排放的废气遇冷空气凝结而成。冰晶将太阳的入射光反射回太空，对大气产生冷却效应。但飞机云也阻止了地面热量逃逸到太空中。“热量被反射回地面。因此这是种升温效应。”

Stettler says, on balance, contrails warm the atmosphere more than they cool it. “And that’s primarily because the cooling effect due to reflecting of sunlight can only happen during the day, when the sun’s shining, whereas the warming effect due to trapping of outgoing heat happens all of the time.” 

斯泰特勒表示，总的来说，飞机云对大气的升温作用大于冷却作用。“主要是因为反射太阳光所产生的冷却效应只能在白天有太阳时产生，而由于阻挡散发热量所产生的升温效应则全天都在发生。”

Some contrails can form clouds that last for up to 18 hours. During that time, they spread out, trapping even more heat. This process allows contrails to warm the planet about as much as the carbon dioxide emissions from aircraft.

有些飞机云可以形成持续18小时不散的云团。在这段时间里，这些云团扩散开来，阻挡了更多热量的散发。这一过程使飞机云给地球带来的升温效应与飞机排放的二氧化碳基本持平。

But when Stettler and his team analyzed flight data they obtained of Japan airspace, they found that most contrail warming was caused by just 2 percent of flights. And most of those flights originated in the late afternoon because as the sun goes down, cooling can no longer offset the warming. “And the warming effect persists throughout the evening, into the night.” But what if the contrails that contribute the most to warming could be eliminated? Such a change could be achieved if aircraft avoided flying in the thin layers of humidity where contrails form.

然而，当斯泰特勒及其团队分析从日本领空获得的飞行数据时，他们发现飞机云产生的大部分升温效应仅由2%的航班造成。这些航班大多在傍晚起飞，随着太阳下山，飞机云的冷却作用无法抵消其升温作用。“升温效应从傍晚一直持续到深夜。”那如果对升温作用最明显的飞机云可以被消除呢？只要飞机避免在形成飞机云的潮湿薄层大气中飞行，就可以实现这一改变。

“By changing the altitude only by couple of thousand feet, either up or down, it would no longer form contrail. And so what we found in this study was that by changing the altitude of less than 2 percent of flights, we could actually get rid of just under 60 percent of the warming effect due to contrails.” The study is in the journal Environmental Science & Technology.

“将飞行高度提升或降低几千英尺，就不会再形成飞机云。因此，我们在这项研究中发现，改变不到2%的航班的飞行高度就可以消除接近60%由飞机云引起的升温效应。”这项研究发表在《环境科学与技术》期刊上。

This improved understanding of how to manage contrails presents an opportunity for the aviation industry to reduce its global environmental impact. Think of it as a silver lining in those contrail clouds.

这一研究使我们加深了认识，了解到如何更好地控制飞机云的形成，也为航空业减少其对全球气候的影响提供了机遇。正如乌云周边都有一线光亮，我们也可以把这项成果视作是解决飞机云问题的一丝希望吧！

【VOCABULARY】

1. fluffy n. 毛绒绒的；松软的；蓬松的

2. emit v. 排放；排出

3. exhaust n. 废气；排放物

4. contrails n. 飞机云；凝结尾（飞机飞过留下的尾迹）

5. originate v. 起驶；起航

6. humidity n. 湿度；湿气

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