改變飛行高度可減少影響氣候的飛機(jī)云

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.

人類(lèi)排放到大氣中的二氧化碳正改變著氣候，其中3%的碳排放來(lái)源于飛機(jī)。然而，飛機(jī)還正以另一種方式加劇全球變暖。倫敦帝國(guó)理工學(xué)院的工程師馬克·斯泰特勒介紹：“當(dāng)你仰望天空時(shí)，某個(gè)時(shí)刻可能會(huì)看到飛機(jī)。飛機(jī)后面拖著幾條毛絨絨的白色拉線(xiàn)，我們稱(chēng)之為飛機(jī)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.”

飛機(jī)云由冰晶組成，而這些冰晶則是由飛機(jī)引擎排放的廢氣遇冷空氣凝結(jié)而成。冰晶將太陽(yáng)的入射光反射回太空，對(duì)大氣產(chǎn)生冷卻效應(yīng)。但飛機(jī)云也阻止了地面熱量逃逸到太空中。“熱量被反射回地面。因此這是種升溫效應(yīng)。”

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，總的來(lái)說(shuō)，飛機(jī)云對(duì)大氣的升溫作用大于冷卻作用。“主要是因?yàn)榉瓷涮?yáng)光所產(chǎn)生的冷卻效應(yīng)只能在白天有太陽(yáng)時(shí)產(chǎn)生，而由于阻擋散發(fā)熱量所產(chǎn)生的升溫效應(yīng)則全天都在發(fā)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.

有些飛機(jī)云可以形成持續(xù)18小時(shí)不散的云團(tuán)。在這段時(shí)間里，這些云團(tuán)擴(kuò)散開(kāi)來(lái)，阻擋了更多熱量的散發(fā)。這一過(guò)程使飛機(jī)云給地球帶來(lái)的升溫效應(yīng)與飛機(jī)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，當(dāng)斯泰特勒及其團(tuán)隊(duì)分析從日本領(lǐng)空獲得的飛行數(shù)據(jù)時(shí)，他們發(fā)現(xiàn)飛機(jī)云產(chǎn)生的大部分升溫效應(yīng)僅由2%的航班造成。這些航班大多在傍晚起飛，隨著太陽(yáng)下山，飛機(jī)云的冷卻作用無(wú)法抵消其升溫作用。“升溫效應(yīng)從傍晚一直持續(xù)到深夜。”那如果對(duì)升溫作用最明顯的飛機(jī)云可以被消除呢？只要飛機(jī)避免在形成飛機(jī)云的潮濕薄層大氣中飛行，就可以實(shí)現(xiàn)這一改變。

“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.

“將飛行高度提升或降低幾千英尺，就不會(huì)再形成飛機(jī)云。因此，我們?cè)谶@項(xiàng)研究中發(fā)現(xiàn)，改變不到2%的航班的飛行高度就可以消除接近60%由飛機(jī)云引起的升溫效應(yīng)。”這項(xiàng)研究發(fā)表在《環(huán)境科學(xué)與技術(shù)》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.

這一研究使我們加深了認(rèn)識(shí)，了解到如何更好地控制飛機(jī)云的形成，也為航空業(yè)減少其對(duì)全球氣候的影響提供了機(jī)遇。正如烏云周邊都有一線(xiàn)光亮，我們也可以把這項(xiàng)成果視作是解決飛機(jī)云問(wèn)題的一絲希望吧！