and I hate weather.

我是氣候科學家，

I have spent too much time in California,

而我討厭天氣。

and I strongly feel that weather should be optional.

我花了太多時間在加州，

(Laughter)

我強烈認為， 天氣應該要是可選擇的。

So I don't want to experience clouds,

（笑聲）

let alone study them.

我並不想要體驗雲朵，

But clouds seem to follow me wherever I go.

更不用說研究它們了。

The thing is, clouds are a real challenge for climate science.

但不論我到哪裡去， 雲朵似乎都跟著我。

We don't know how they're going to react as the planet heats up,

重點是，對於氣候科學而言， 雲朵是非常有挑戰性的。

and hidden in that uncertainty

我們不知道當地球溫度上升時， 它們會如何反應，

might be hope.

而隱藏在那不確定性中的，

Maybe, just maybe,

可能是希望。

clouds could slow down global warming,

可能，只是可能，

and buy us a little bit more time to get our act together,

雲朵可能可以減緩全球暖化，

which would be very convenient right now.

幫我們爭取一些時間來努力想辦法，

I mean, even I could put up with a few more cloudy days

對現在會是非常好用的。

if clouds saved the planet.

我的意思是，即使是我 也願忍受多幾個陰天，

Now, we are sure about some things.

如果雲朵能拯救地球的話。

Carbon dioxide is a greenhouse gas,

我們能確定的有幾件事。

we're emitting a lot of it,

二氧化碳是溫室氣體，

and the planet is heating up.

我們排放了很多二氧化碳，

Case closed.

且地球溫度在上升。

But I still go to work every day.

結案。

It turns out that there is a lot that we don't understand

但我仍然每天都要工作。

about climate change.

結果發現，

In particular, we haven't answered

關於氣候改變，還有著很多 我們不了解的地方。

what seems to be a very fundamental question.

特別是，我們尚未回答

We know it's going to get hot,

一個似乎非常基礎的問題。

but we don't know exactly how hot it's going to get.

我們知道會越來越熱，

Now, this is a really easy question to answer

但我們不知道究竟會到多熱。

if one of you would like to give me a time machine.

這是個很容易回答的問題，

But I'm going to be honest with you:

只要有人能給我一台時光機器。

if I had a time machine,

但我得對各位說實話：

I would not be hanging out at this particular point in history.

如果我有一台時光機器，

So in order to see the future,

我不會在歷史上的這個時間點逗留。

we have to rely on the output of computer simulations --

所以，為了看到未來，

climate models, like this one.

我們要仰賴電腦模擬的輸出結果──

Now, in my line of work,

氣候模型，就像這一個。

I encounter many very charming people on the internet

在我的這個行業，

who like to tell me that climate models are all wrong.

我會在網上遇到許多非常迷人的人，

And I would just like to say:

他們會告訴我氣候模型都是錯的。

no kidding!

我只想要說：

Seriously? I get paid to complain about climate models.

別開玩笑了！

But we don't want models to be perfect.

當真嗎？我領薪水來抱怨氣候模型。

We want them to be useful.

但我們不要求模型完美，

I mean, think about it:

只要有用就好。

a computer simulation

想想看：

that's able to exactly reproduce all of reality.

能夠完全重製所有現實的電腦模擬。

That's not a climate model;

那不是氣候模型；

That's "The Matrix."

那是《駭客任務》。 （譯註：電影名稱）

So, models are not crystal balls.

所以，模型不是水晶球。

They're research tools,

它們是研究工具，

and the ways in which they're wrong can actually teach us a lot.

它們錯誤的方式 其實能教我們很多東西。

For example:

比如：

different climate models are largely able to capture

不同的氣候模型能捕捉到大部份

the warming that we've seen so far.

我們目前所看到的暖化現象。

But fast-forward to the end of the century

但快轉到這個世紀末，

under a business-as-usual scenario,

在一切照常的情況下，

and climate models don't really agree anymore.

氣候模型就不再一致了。

Yeah, they're all warming; that's just basic physics.

是的，它們都變暖， 那只是基本的物理。

But some of them project catastrophe --

但有些模型預測會有大災難──

more than five times the warming we've seen already.

暖化的程度是我們 目前已看到的五倍以上；

And others are literally more chill.

其他模型則預測稍微涼一些。

So why don't climate models agree on how warm it's going to get?

所以，為什麼氣候模型對於 將來有多暖的預測會不一致呢？

Well, to a large extent,

有很大的程度，

it's because they don't agree on what clouds will do in the future.

是因為它們對於雲朵在未來 扮演什麼角色的看法不一致。

And that is because, just like me,

那是因為，就跟我一樣，

computers hate clouds.

電腦也討厭雲朵。

Computers hate clouds because they're simultaneously very large

電腦討厭雲朵

and very small.

是因為它們同時可大可小。

Clouds are formed

雲朵的形成，

when microscopic water droplets or ice crystals coalesce

是顯微鏡才看得到的小水滴或冰晶體

around tiny particles.

包圍在小粒子的周圍結合。

But at the same time, they cover two-thirds of the earth's surface.

但同時，它們覆蓋了 三分之二的地球表面。

In order to really accurately model clouds,

為了要真正精確地建立雲朵的模型，

we'd need to track the behavior of every water droplet and dust grain

我們必須要追蹤整個大氣當中

in the entire atmosphere,

每個水滴與塵粒的行為，

and there's no computer powerful enough to do that.

沒有電腦強大到可以做到這一點。

So instead, we have to make a trade-off:

因此，我們得要做取捨：

we can zoom in and get the details right,

我們可以放大一小塊範圍， 以求細節的正確，

but have no idea what's going on worldwide;

但就不知道全世界發生什麼事；

or, we could sacrifice realism at small scales

或者，我們可以犧牲 小規模的真實性，

in order to see the bigger picture.

以求看到更大更整體的狀況。

Now, there's no one right answer,

沒有正確的答案，

no perfect way to do this,

沒有完美的方式，

and different climate models make different choices.

不同的氣候模型會做不同的選擇。

Now, it is unfortunate

很不幸的是，

that computers struggle with clouds,

電腦很難處理雲朵，

because clouds are crucially important

因為雲朵在調節地球溫度上，

in regulating the temperature of the planet.

扮演非常重要的角色。

In fact, if all the clouds went away,

事實上，如果所有的雲朵都沒了，

we would experience profound climate changes.

我們會經歷到很劇烈的氣候改變。

But without clouds,

但若沒有雲朵，

would it be warmer or colder?

會比較溫暖或比較寒冷？

The answer is both.

答案是，都會。

So I'm going to be honest with you, I am not a cloud spotter.

老實告訴各位，我不是賞雲者。

My favorite type of cloud is none.

我最喜歡晴朗無雲。

But even I know that clouds come in all shapes and sizes.

但即使是我這種人， 也知道雲朵有各種形狀大小。

Low, thick clouds like these are really good at blocking out the sun

像這樣的低厚雲層很能夠阻擋陽光，

and ruining your barbecue,

讓你的烤肉活動泡湯；

and high, wispy clouds like these cirrus

而像這些卷雲的高雲，

largely let that sunlight stream through.

會讓大部份的陽光穿過。

Every sunny day is the same,

晴天全都一樣，

but every cloudy day is cloudy in its own way.

但每個陰天有它自己的多雲方式。

And it's this diversity

正是這種多樣性，

that can make the global impact of clouds very hard to understand.

讓雲朵的全球性影響變得難以了解。

So to see this global effect of clouds,

要了解雲朵的全球性效應，

it really helps to take a selfie.

拍張自拍照是很有幫助的。

It will never cease to blow my mind

我們能夠從外太空來看我們的星球， 這點總是讓我感到不可思議，

that we can see our planet from outer space,

但我們無法看到它的全部。

but we can't see all of it.

雲朵會阻擋視線。

Clouds are blocking the view.

這是它們的功能之一。

That's what they do.

低空的厚雲層是非常有效的遮陽板。

These low, thick clouds are extremely effective sunshades.

雲朵反射回去 20% 的陽光，

They turn back about 20 percent of everything the sun sends us.

浪費掉許多的太陽能。

That is a lot of wasted solar power.

所以，低雲是很強大的遮陽板，

So, low clouds are powerful sunshades,

讓地球比較涼快。

making the planet cooler.

但雲朵的效應不只如此。

But that's not the only effect of clouds.

我們的星球有熱度，

Our planet has a temperature,

就像所有有熱度的東西一樣，

and like anything with a temperature,

它會散熱。

it's giving off heat.

我們向太空輻射熱能。

We are radiating thermal energy away into space,

這現象用紅外線就可以看到。

and we can see this in the infrared.

同樣的，雲朵會阻擋視線。

Once again, clouds are blocking the view.

那是因為高雲位在大氣的上層，

That's because high clouds live in the upper reaches of the atmosphere,

那裡非常寒冷。

where it's very cold.

這意味著它們本身 散失到太空的熱能很少。

And this means that they lose very little heat to space themselves.

但同時，它們阻擋了 下方的地球向上散熱。

But at the same time, they block the heat coming up from the planet below.

地球試著冷卻自己，

The earth is trying to cool itself off,

而高雲卻從中作梗。

and high clouds are getting in the way.

結果就是非常強大的溫室效應。

The result is a very powerful greenhouse effect.

所以，雲朵在氣候系統中

So, clouds play this very large and dual role

扮演著非常大的雙重角色。

in the climate system.

我們有低雲當遮陽板，

We've got low clouds that act like a sunshade,

冷卻地球，

cooling the planet,

也有高雲當溫室，

and high clouds which act like a greenhouse,

暖化地球。

warming the planet.

現今，這兩種效應並不會互相抵消。

Right now, these two effects -- they don't cancel out.

遮陽的力量稍大一些些。

That sunshade -- it's a little bit more powerful.

所以，如果我們明天 就清除所有的雲朵──

So if we got rid of all the clouds tomorrow,

聲明一下，我沒在提倡這件事喔──

which, for the record, I am not advocating,

那麼地球就會暖化。

our planet would get warmer.

所以很顯然，雲不會消失。

So clearly, all of the clouds are not going away.

但氣候改變就是改變。

But climate change is change.

所以我們可以問：

So we can ask:

全球暖化會如何改變雲朵？

How will global warming change clouds?

但切記雲朵

But remember, clouds are so important

在調節地球溫度的重要角色，

in regulating the earth's temperature,

它們會冷卻也會暖化地球。

and they both warm and cool the planet.

所以即使雲朵的覆蓋稍微變了，

So even small changes to cloud cover

也可能會造成深切的影響。

could have profound consequences.

所以我們也可以問：

So we might also ask:

雲朵會如何改變全球暖化？

How will clouds change global warming?

那可能是能找到希望的地方。

And that is where there might be space for hope.

如果全球暖化觸發了雲朵的改變，

If global warming triggers cloud changes

導致溫室變弱、 或遮陽板變得更有效，

that make for a less powerful greenhouse or a more effective sunshade,

那麼那就會強化雲朵的冷卻力。

then that would enhance the cooling power of clouds.

它的功能就會和全球暖化正好相反，

It would act in opposition to global warming,

那就是那些預測暖化將會緩和的

and that's what's happening in those climate models

氣候模型中所發生的現象。

that project relatively muted warming.

但，氣候模型很難處理雲朵，

But climate models struggle with clouds,

而這不確定性是雙向的。

and this uncertainty -- it goes both ways.

雲朵能協助我們處理全球暖化，

Clouds could help us out with global warming.

也可能讓它惡化。

They could also make it worse.

現在，我們知道氣候改變正在發生，

Now, we know that climate change is happening

因為我們看見：

because we can see it:

氣溫上升、冰山溶化、 降雨模式轉變。

rising temperatures, melting icecaps, shifts in rainfall patterns.

你可能會認為，我們也能 在雲朵上看到改變。

And you might think that we could also see it in the clouds.

但還有件不幸的事：

But here's something else unfortunate:

雲朵真的很難看見。

clouds are really hard to see.

我看見來自太平洋西北地區的每個人

I see everybody from the Pacific Northwest

都像在說：「我想給你些建議。」

is like, "I have some suggestions for you."

（笑聲）

(Laughter)

各位，我們有試過抬頭向上看了。

And you guys, we have tried looking up.

（笑聲）

(Laughter)

但為了要做氣候科學，

But in order to do climate science,

我們得要看見各處的所有雲朵， 且持續很長一段時間。

we need to see all of the clouds, everywhere, for a very long time.

那就是困難之處。

And that's what makes it hard.

現在，能看見最多雲朵的就是衞星，

Now, nothing sees more clouds than a satellite --

連英國人都看不到那麼多。

not even a British person.

（笑聲）

(Laughter)

幸運的是，我們的確有 衛星觀測雲朵的資料，

And fortunately, we do have satellite observations of clouds

就像我，可追溯到 1980 年代。

that, like me, date back to the 1980s.

但這些衛星是為了天氣設計的，

But these satellites were designed for weather,

不是氣候。

not climate.

它們無法持久。

They weren't in it for the long haul.

若要取得長期趨勢的資訊，

So to get that long-term trend information,

我們必須要做氣候科學。

we need to do climate science.

我們得把不同視角、運行軌道，

We have to stitch together the output of multiple satellites

帶著不同照相設備的多個衛星

with different viewing angles and orbits

所輸出的資料結合起來。

and carrying different camera equipment.

而結果和我們的知識有差距。

And as a result,

但即使是從這像多雲一樣 非常朦朧的狀況中，

there are gaps in our knowledge.

我們也開始得到些關於 可能發生之未來的暗示。

But even from this very cloudy picture,

當我們看這些觀測資料時，

we're starting to get hints of a possible future.

有一點引起了我們的注意：

When we looked at the observations,

雲朵在移動。

one thing jumped out at us:

隨著地球溫度上升，

the clouds are moving.

高雲會上升。

As the planet's temperature increases,

它們移向大氣中更上層更冷的地方，

high clouds rise up.

這意味著，即使地球在變暖，

They move to the colder upper reaches of the atmosphere,

高雲卻不會。

and this means that even as the planet heats up,

它們的溫度大致上維持相同。

high clouds don't.

所以它們並沒有散失更多熱到太空。

They remain at roughly the same temperature.

但同時卻圈住了更多

So they are not losing more heat to space.

在下方暖化中的地球的熱能。

But at the same time, they're trapping more heat

這會讓溫室效應加劇。

from the warming planet below.

高雲會讓全球暖化的情況更糟。

This intensifies the greenhouse effect.

雲朵也向其他維度移動。

High clouds are making global warming worse.

大氣環流，

Clouds are moving in other dimensions, too.

大氣中空氣和水的大規模移動

The atmospheric circulation, that large-scale motion

正在改變，

of air and water in the atmosphere,

而雲朵也隨之移動。

is changing,

大規模來看，

and clouds are going with it.

雲朵似乎是從熱帶移向極地。

On large scales,

這有點像是你的祖父母返老還童。

clouds seem to be moving from the tropics toward the poles.

這有其重要性，

It's kind of like your grandparents in reverse.

因為如果你要阻擋太陽光射進來，

And this matters,

你身在熱帶會有效許多，

because if your job is to block incoming sunlight,

熱帶的太陽非常強烈，

you are going to be much more effective in the tropics

在較高的緯度就比較沒效。

under that intense tropical sun

所以如果繼續這樣下去，

than you are in higher latitudes.

這也會讓全球暖化再惡化。

So if this keeps up,

儘管花了數年在尋找，

this will also make global warming worse.

我們仍然尚未發現

And what we have not found,

任何顯示相反情況的徵兆。

despite years of looking,

觀察到的證據未能證明

is any indication of the opposite.

雲朵在本質上能減緩全球暖化。

There is no observational evidence

地球並不會治好它自己的發燒。

that clouds will substantially slow down global warming.

這裡仍然有著不確定性。

The earth is not going to break its own fever.

我們不能確定

Now, there are still uncertainties here.

未來會怎樣。

We don't know for sure

但我們的孩子正朝向未來的不歸路。

what the future holds.

我警告他們，對將要 面臨的狀況要有心理準備，

But we are sending our kids there,

因此，非常重要的事就是要讓那些

and they are never coming back.

觀察地球的衛星能繼續在天上運行，

I want them to be prepared for what they'll face,

並要僱用多樣化、聰明有才華的人，

and that is why it is so important

不討厭雲朵的人，

to keep our earth-observing satellites up there

來改善氣候模型。

and to hire diverse and smart and talented people

但不確定性並不等同無知。

who do not hate clouds

我們並非全知，

to improve the climate models.

但也不是全然無知，

But uncertainty is not ignorance.

且我們知道二氧化碳的影響。

We don't know everything,

我最初的職業是天體物理學家，