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  • Every summer when I was growing up,

    譯者: Lilian Chiu 審譯者: 易帆 余

  • I would fly from my home in Canada to visit my grandparents,

    在我成長過程中,每年夏天,

  • who lived in Mumbai, India.

    我會從我在加拿大的家, 搭飛機去看我的祖父母,

  • Now, Canadian summers are pretty mild at best --

    他們住在印度孟買。

  • about 22 degrees Celsius or 72 degrees Fahrenheit

    現在加拿大的夏天很暖和,

  • is a typical summer's day, and not too hot.

    最高大約攝氏 22 度或華氏 72 度,

  • Mumbai, on the other hand, is a hot and humid place

    這是典型的夏日,不算太熱。

  • well into the 30s Celsius or 90s Fahrenheit.

    另一方面,孟買 是個又熱又濕的地方,

  • As soon as I'd reach it, I'd ask,

    會超過攝氏 30 度或華氏 90 度。

  • "How could anyone live, work or sleep in such weather?"

    一抵達孟買,我就會問:

  • To make things worse, my grandparents didn't have an air conditioner.

    「怎麼可能有人在這種天氣 生活、工作,或睡覺?」

  • And while I tried my very, very best,

    更糟的是,我的祖父母沒有冷氣。

  • I was never able to persuade them to get one.

    我已經盡了我最大的努力,

  • But this is changing, and fast.

    但我始終無法 說服他們裝一台冷氣。

  • Cooling systems today collectively account for 17 percent

    但這狀況在改變,且改變得很快。

  • of the electricity we use worldwide.

    現今的冷卻系統所用的電量加總起來

  • This includes everything from the air conditioners

    佔全世界用電量的 17%。

  • I so desperately wanted during my summer vacations,

    包括從我暑假

  • to the refrigeration systems that keep our food safe and cold for us

    超想要的冷氣,

  • in our supermarkets,

    到超級市場中確保我們的食物安全

  • to the industrial scale systems that keep our data centers operational.

    且存放於低溫的冷藏系統,

  • Collectively, these systems account for eight percent

    到確保我們資料儲存中心 能順利運作的工業規模冷卻系統。

  • of global greenhouse gas emissions.

    這些系統所排放的溫室氣體加起來

  • But what keeps me up at night

    佔全球總排放的 8%。

  • is that our energy use for cooling might grow sixfold by the year 2050,

    但,讓我睡不著覺的,

  • primarily driven by increasing usage in Asian and African countries.

    是我們用在冷卻上的能量, 到 2050 年時可能會增為六倍,

  • I've seen this firsthand.

    主要的原因是亞洲 和非洲國家的用量增加。

  • Nearly every apartment in and around my grandmother's place

    我親眼見過。

  • now has an air conditioner.

    幾乎我祖母家附近的每一間公寓,

  • And that is, emphatically, a good thing

    現在都有冷氣了。

  • for the health, well-being and productivity

    那很明顯是件好事,

  • of people living in warmer climates.

    就溫暖氣候地區居民的健康、

  • However, one of the most alarming things about climate change

    幸福,以及生產力而言。

  • is that the warmer our planet gets,

    然而關於氣候變遷最大的警訊之一,

  • the more we're going to need cooling systems --

    就是當地球變得更暖和,

  • systems that are themselves large emitters of greenhouse gas emissions.

    我們就會更需要冷卻系統,

  • This then has the potential to cause a feedback loop,

    這些系統本身就是 溫室氣體排放的來源。

  • where cooling systems alone

    這就有可能會形成一個惡性循環,

  • could become one of our biggest sources of greenhouse gases

    光是冷卻系統

  • later this century.

    就能在這個世紀後期變成最大的

  • In the worst case,

    溫室氣體來源。

  • we might need more than 10 trillion kilowatt-hours of electricity every year,

    在最糟的狀況中,

  • just for cooling, by the year 2100.

    到 2100 年時, 光為了冷卻,我們可能每年

  • That's half our electricity supply today.

    就會需要超過 十兆千瓦小時的電力。

  • Just for cooling.

    那是現今我們電力總供應量的一半。

  • But this also point us to an amazing opportunity.

    光為了冷卻。

  • A 10 or 20 percent improvement in the efficiency of every cooling system

    但這也為我們點出了 一個很棒的機會。

  • could actually have an enormous impact on our greenhouse gas emissions,

    如果每一種冷卻系統在效能上 都能有 10%~20% 的改善,

  • both today and later this century.

    就會對溫室氣體的排放 有非常大的影響,

  • And it could help us avert that worst-case feedback loop.

    對於現今以及本世紀後期都是如此。

  • I'm a scientist who thinks a lot about light and heat.

    且它能協助我們避免發生 最糟狀況的惡性循環。

  • In particular, how new materials allow us to alter the flow

    我是一位常常在思考 光和熱的科學家。

  • of these basic elements of nature

    我特別著重研究新材料 如何能協助我們改變

  • in ways we might have once thought impossible.

    大自然這些基本元素的流動方式,

  • So, while I always understood the value of cooling

    用我們以前認為 不可能的方式來做到。

  • during my summer vacations,

    所以,我一直都懂

  • I actually wound up working on this problem

    暑假降溫的重要性,

  • because of an intellectual puzzle that I came across about six years ago.

    由於六年前我遇到的智力難題,

  • How were ancient peoples able to make ice in desert climates?

    我實際上已經完成了 解決這個問題的工作。

  • This is a picture of an ice house,

    古人怎麼能在沙漠氣候下製冰?

  • also called a Yakhchal, located in the southwest of Iran.

    這張照片中的是一間冰室,

  • There are ruins of dozens of such structures throughout Iran,

    也叫做「Yakhchal」, 位在伊朗西南部。

  • with evidence of similar such buildings throughout the rest of the Middle East

    在伊朗各地,有數十個 這類建築物的遺跡,

  • and all the way to China.

    有證據顯示,這類建築物 還遍及了中東其它地區,

  • The people who operated this ice house many centuries ago,

    一路延伸到中國。

  • would pour water in the pool you see on the left

    幾百年前使用這些冰室的人

  • in the early evening hours, as the sun set.

    會把水倒入照片左側的池子中,

  • And then something amazing happened.

    時機是太陽下山, 剛剛進入傍晚的時候。

  • Even though the air temperature might be above freezing,

    接著,神奇的事就會發生。

  • say five degrees Celsius or 41 degrees Fahrenheit,

    雖然空氣中的溫度還在冰點以上,

  • the water would freeze.

    比如攝氏 5 度,或華氏 41 度,

  • The ice generated would then be collected in the early morning hours

    水卻會結冰。

  • and stored for use in the building you see on the right,

    一大清早,產出的冰 就會被收集起來,

  • all the way through the summer months.

    儲存放在右邊的建築物裡備用,

  • You've actually likely seen something very similar at play

    夏季的所有月份就是這樣渡過。

  • if you've ever noticed frost form on the ground on a clear night,

    你們其實有可能見過 類似的現象發生,

  • even when the air temperature is well above freezing.

    如果你有注意過,在晴天晚上, 即使空氣溫度在冰點以上,

  • But wait.

    地面也會形成霜,就是類似的現象。

  • How did the water freeze if the air temperature is above freezing?

    但,等等。

  • Evaporation could have played an effect,

    如果空氣溫度沒有低於冰點, 為什麼水會結冰?

  • but that's not enough to actually cause the water to become ice.

    蒸發的效應就很重要了,

  • Something else must have cooled it down.

    但光是這點還不夠讓水變成冰。

  • Think about a pie cooling on a window sill.

    還要有其他東西來將水冷卻。

  • For it to be able to cool down, its heat needs to flow somewhere cooler.

    想像一個派,在窗臺上冷卻。

  • Namely, the air that surrounds it.

    若要讓它冷下來, 就要讓熱流到比較冷的地方。

  • As implausible as it may sound,

    也就是,流到它周圍的空氣中。

  • for that pool of water, its heat is actually flowing to the cold of space.

    雖然這聽起來很不合情理,

  • How is this possible?

    一池水的熱怎麼可能 流到低溫的外太空中。

  • Well, that pool of water, like most natural materials,

    這怎麼有可能發生?

  • sends out its heat as light.

    嗯,那池水和大部分的 自然材料一樣,

  • This is a concept known as thermal radiation.

    以光的方式將熱發送出去。

  • In fact, we're all sending out our heat as infrared light right now,

    這概念就是大家所知的「熱輻射」。

  • to each other and our surroundings.

    事實上,我們現在都在 用紅外線光的方式把我們的熱

  • We can actually visualize this with thermal cameras

    發送給彼此和周遭的環境。

  • and the images they produce, like the ones I'm showing you right now.

    使用熱感攝影機 就能將這現象視覺化,

  • So that pool of water is sending out its heat

    它們所產出的影像, 就會類似各位現在看到的這一張。

  • upward towards the atmosphere.

    所以,這一池水把它的熱

  • The atmosphere and the molecules in it

    向上發送到大氣中。

  • absorb some of that heat and send it back.

    大氣以及大氣中的分子

  • That's actually the greenhouse effect that's responsible for climate change.

    會吸收其中一些熱,再發送回來。

  • But here's the critical thing to understand.

    那其實就是造成 氣候變遷的溫室效應。

  • Our atmosphere doesn't absorb all of that heat.

    但在這裡要了解一個關鍵。

  • If it did, we'd be on a much warmer planet.

    我們的大氣並不會吸收所有的熱。

  • At certain wavelengths,

    如果會的話,地球就會更暖和許多。

  • in particular between eight and 13 microns,

    在某些波長,

  • our atmosphere has what's known as a transmission window.

    特別是在 8~13 微米之間,

  • This window allows some of the heat that goes up as infrared light

    我們的大氣有個所謂的傳送窗口。

  • to effectively escape, carrying away that pool's heat.

    這扇窗會讓其中一些 以紅外線方式向上發送的熱

  • And it can escape to a place that is much, much colder.

    有效地發散傳送,將池水的熱給帶走。

  • The cold of this upper atmosphere

    這些熱會發散到一個更冷的地方 :

  • and all the way out to outer space,

    大氣上層的低溫當中,

  • which can be as cold as minus 270 degrees Celsius,

    以及一路到外太空中,

  • or minus 454 degrees Fahrenheit.

    外太空的溫度可以 低到攝氏 -270 度,

  • So that pool of water is able to send out more heat to the sky

    或華氏 -454 度。

  • than the sky sends back to it.

    所以那池水發送到天空中的熱

  • And because of that,

    就多於天空發送回來的熱。

  • the pool will cool down below its surroundings' temperature.

    基於這個理由,

  • This is an effect known as night-sky cooling

    那池水會冷卻到比環境更低的溫度。

  • or radiative cooling.

    那就是一般所知的夜空冷卻,

  • And it's always been understood by climate scientists and meteorologists

    或稱輻射冷卻。

  • as a very important natural phenomenon.

    氣候科學家和氣象學家一直都知道

  • When I came across all of this,

    這是個非常重要的自然現象。

  • it was towards the end of my PhD at Stanford.

    當我接觸到這些資訊時,

  • And I was amazed by its apparent simplicity as a cooling method,

    我已經快要拿到 史丹佛的博士學位了。

  • yet really puzzled.

    這種冷卻方法表面是如此簡單, 背後卻又是個複雜的謎,

  • Why aren't we making use of this?

    這讓我感到困惑。

  • Now, scientists and engineers had investigated this idea

    我們為什麼不好好利用它?

  • in previous decades.

    在過去數十年,科學家和工程師

  • But there turned out to be at least one big problem.

    都在研究這個機制。

  • It was called night-sky cooling for a reason.

    但結果發現,至少有一個大問題。

  • Why?

    它被稱為夜空冷卻,是有原因的。

  • Well, it's a little thing called the sun.

    為什麼?

  • So, for the surface that's doing the cooling,

    因為有個小東西,叫做太陽。

  • it needs to be able to face the sky.

    要進行冷卻的表面,

  • And during the middle of the day,

    必需要能夠面向天空。

  • when we might want something cold the most,

    在日正當中時,

  • unfortunately, that means you're going to look up to the sun.

    我們最希望的就是能冷到最低點,

  • And the sun heats most materials up

    很不幸的,在那時候 你得要向上看向太陽。

  • enough to completely counteract this cooling effect.

    而太陽會把大部分的物質加熱,

  • My colleagues and I spend a lot of our time

    熱到足以完全抵消掉這種冷卻效應。

  • thinking about how we can structure materials

    同事和我花了很多時間思考

  • at very small length scales

    要如何建構出波長極短的材料,

  • such that they can do new and useful things with light --

    讓它們能與光反應 產生新的、有用的東西——

  • length scales smaller than the wavelength of light itself.

    波長要小於光本身的波長。

  • Using insights from this field,

    使用這個領域的洞見,

  • known as nanophotonics or metamaterials research,

    也就是一般所知的 奈米光子或超材料研究,

  • we realized that there might be a way to make this possible during the day

    我們首次發現可能有種辦法 能夠在白天實現這一點,

  • for the first time.

    我為此設計了一種多層的光學材料,

  • To do this, I designed a multilayer optical material

    在這張顯微鏡影像中可以看見。

  • shown here in a microscope image.

    它比一般人髮的 40 分之一還要薄。

  • It's more than 40 times thinner than a typical human hair.

    它能夠同時做兩件事。

  • And it's able to do two things simultaneously.

    首先,它能精準地把熱發送到大氣層

  • First, it sends its heat out

    達到最佳的降溫效果。

  • precisely where our atmosphere lets that heat out the best.

    我們對準了通往太空的窗戶。

  • We targeted the window to space.

    第二是它能避免被太陽加溫。

  • The second thing it does is it avoids getting heated up by the sun.

    它是面很好的太陽光反射鏡。

  • It's a very good mirror to sunlight.

    我第一次測試它時, 是在史丹佛的屋頂上,

  • The first time I tested this was on a rooftop in Stanford

    各位在照片上可以看見。

  • that I'm showing you right here.

    我把這個裝置留在那裡一陣子,

  • I left the device out for a little while,

    幾分鐘之後,我走向它,

  • and I walked up to it after a few minutes,

    在幾秒鐘之內,我就知道它有用。

  • and within seconds, I knew it was working.

    如何知道的?

  • How?

    我摸了它,摸起來是冷的。

  • I touched it, and it felt cold.

    (掌聲)

  • (Applause)

    再強調一下這個現象 有多怪異且和直覺不符:

  • Just to emphasize how weird and counterintuitive this