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 is:

這種材料及其它相似的材料

this material and others like it

如果離開陰影反而會變得更冷，

will get colder when we take them out of the shade,

即使是被陽光直射著。

even though the sun is shining on it.

各位現在看到的 是我們第一次實驗的資料，

I'm showing you data here from our very first experiment,

當時那材料的溫度比空氣的溫度

where that material stayed more than five degrees Celsius,

低攝氏 5 度或華氏 9 度，

or nine degrees Fahrenheit, colder than the air temperature,

即使太陽光直射在它上面。

even though the sun was shining directly on it.

實際量產這種材料的方法已然存在。

The manufacturing method we used to actually make this material

我非常興奮，

already exists at large volume scales.

因為我們不只是 發明出了很酷的東西，

So I was really excited,

我們可能真的有機會 做出很有用的東西來。

because not only do we make something cool,

那就帶出了下一個大問題。

but we might actually have the opportunity to do something real and make it useful.

要如何用這個點子，來節省能源？

That brings me to the next big question.

我們相信，若要用這項技術 來節省能源，最直接的方式

How do you actually save energy with this idea?

就是對現今的冷氣

Well, we believe the most direct way to save energy with this technology

和冰箱系統進行效能的提升。

is as an efficiency boost

為此，我們打造了液態的冷卻板，

for today's air-conditioning and refrigeration systems.

就像畫面上的這種。

To do this, we've built fluid cooling panels,

它們的外型和太陽能熱水器很相似，

like the ones shown right here.

差別在於功能相反，

These panels have a similar shape to solar water heaters,

它們能用我們的特殊材料 被動地讓水冷卻。

except they do the opposite -- they cool the water, passively,

這些冷卻板可以和一個元件整合，

using our specialized material.

幾乎所有冷卻系統 都有這個元件：冷凝器，

These panels can then be integrated with a component

目的是要改善系統的根本效率。

almost every cooling system has, called a condenser,

我們的新創公司叫 SkyCool Systems，

to improve the system's underlying efficiency.

目前已經在加州戴維斯 完成了實地測試，如照片所示。

Our start-up, SkyCool Systems,

在那次展示中，

has recently completed a field trial in Davis, California, shown right here.

我們展現了我們在實做上真的能夠

In that demonstration,

改善冷卻系統的效率達 12%。

we showed that we could actually improve the efficiency

在接下來的一、兩年，

of that cooling system as much as 12 percent in the field.

我很興奮地期待能看到 商業規模的測試開始進行，

Over the next year or two,

用在包括冷氣以及冰箱上。

I'm super excited to see this go to its first commercial-scale pilots

在未來，我們可能可以 把這些冷卻板整合到

in both the air conditioning and refrigeration space.

更高效能的建築冷卻系統中，

In the future, we might be able to integrate these kinds of panels

將這些系統所需要使用的 能源減少三分之二。

with higher efficiency building cooling systems

最終，我們可能可以打造一個完全

to reduce their energy usage by two-thirds.

不需要電力輸入的冷卻系統。

And eventually, we might actually be able to build a cooling system

要做到這點，第一步，

that requires no electricity input at all.

我和史丹佛的同事

As a first step towards that,

已經讓大家看到，確實可以

my colleagues at Stanford and I

將物體維持在比空氣溫度 低攝氏 42 度的狀態，

have shown that you could actually maintain

用更好的工程方式就能做到。

something more than 42 degrees Celsius below the air temperature

謝謝。

with better engineering.

（掌聲）

Thank you.

想像一下，

(Applause)

在炎熱的夏日，有低於冰點的東西。

So just imagine that --

所以，雖然我對於我們 能為冷卻做出的貢獻感到很興奮，

something that is below freezing on a hot summer's day.

但我認為還有很多還沒完成的，

So, while I'm very excited about all we can do for cooling,

身為科學家，我也被 這項發明所強調出來的

and I think there's a lot yet to be done,

深刻機會給深深吸引著。

as a scientist, I'm also drawn to a more profound opportunity

我們可以利用太空的寒冷黑暗

that I believe this work highlights.

來改善地球上

We can use the cold darkness of space

每一項與能源有關過程的效能。

to improve the efficiency

我想要特別提出來的 其中一種過程，就是太陽能板。

of every energy-related process here on earth.

在太陽下，它們會被加溫，

One such process I'd like to highlight are solar cells.

當它們本身越熱，就越沒沒效率。

They heat up under the sun

2015 年，我們展示出在太陽能板上方

and become less efficient the hotter they are.

刻意加上微結構，

In 2015, we showed that with deliberate kinds of microstructures

就能夠更善加利用這種冷卻效應，

on top of a solar cell,

來被動地將太陽能板保持在較低的溫度。

we could take better advantage of this cooling effect

這樣太陽能板就能更有效地運作。

to maintain a solar cell passively at a lower temperature.

我們還在進一步研究這些機會。

This allows the cell to operate more efficiently.

我們在問的問題是， 我們是否能用太空的低溫

We're probing these kinds of opportunities further.

來協助我們做水資源保存。

We're asking whether we can use the cold of space

或許協助我們不再使用電網。

to help us with water conservation.

我們甚至可以直接用這低溫來發電。