How we look kilometers below the Antarctic ice sheet | Dustin Schroeder

譯者: Lilian Chiu 審譯者: Yanyan Hong

I'm a radio glaciologist.

我是無線電冰河學家。

That means that I use radar to study glaciers and ice sheets.

意思就是說，我用雷達 來研究冰河和大冰原。

And like most glaciologists right now,

和現在大部分的冰河學家一樣，

I'm working on the problem of estimating

我在努力解決的問題是估計

how much the ice is going to contribute to sea level rise in the future.

在未來，冰對於海平面 上升的影響會有多大。

So today, I want to talk to you about

所以，今天，我想和各位談的是

為什麼這麼難預測 海平面上升的數字，

why it's so hard to put good numbers on sea level rise,

and why I believe that by changing the way we think about radar technology

以及為什麼我相信藉由 改變我們對雷達技術

and earth-science education,

以及地球科學教育的看法，

we can get much better at it.

我們就能把預測做得更好。

When most scientists talk about sea level rise,

當大部分科學家談到海平面上升時，

they show a plot like this.

他們會展示這類的圖。

This is produced using ice sheet and climate models.

這張圖是用大冰原 和氣候模型產生出來的。

On the right, you can see the range of sea level

在右邊，各位能看見海平面的範圍，

predicted by these models over the next 100 years.

是用這些模型針對 未來一百年所做的預測。

For context, this is current sea level,

背景說明：這是目前的海平面，

and this is the sea level

海平面超過這個高度時，

above which more than 4 million people could be vulnerable to displacement.

有超過四百萬人會受到遷移的影響。

So in terms of planning,

所以，就規劃而言，

the uncertainty in this plot is already large.

在這張圖上的不確定性已經很高了。

However, beyond that, this plot comes with the asterisk and the caveat,

然而，在那之外，這張圖 還帶著星號和警告的訊息：

"... unless the West Antarctic Ice Sheet collapses."

「……除非西南極冰蓋崩解。」

And in that case, we would be talking about dramatically higher numbers.

若那狀況發生，我們要談的 數字又會明顯更高了。

They'd literally be off the chart.

它們會在這張圖的範圍之外。

And the reason we should take that possibility seriously

我們應該要認真看待 那種可能性的原因，

is that we know from the geologic history of the Earth

是我們從地球的地質史可以知道，

that there were periods in its history

在歷史上的某些時期，

when sea level rose much more quickly than today.

海平面上升的速度比現今還快很多。

And right now, we cannot rule out

現在，我們無法排除

the possibility of that happening in the future.

那種現象在未來發生的可能性。

So why can't we say with confidence

所以，為什麼我們無法有信心地說出

whether or not a significant portion of a continent-scale ice sheet

和大陸一樣大的一塊大冰原 是否有明顯的一部分

will or will not collapse?

將會或者將不會崩解？

Well, in order to do that, we need models

要做到這一點，我們需要模型，

that we know include all of the processes, conditions and physics

且模型必須要 含有與這類崩解相關的

that would be involved in a collapse like that.

過程、條件、物理學。

And that's hard to know,

那些資訊很難知道，

because those processes and conditions are taking place

因為那些過程和條件是發生在

beneath kilometers of ice,

冰底下數公里深的地方，

and satellites, like the one that produced this image,

而衛星，比如產出這張影像的衛星，

are blind to observe them.

無法觀察到它們。

In fact, we have much more comprehensive observations of the surface of Mars

事實上，我們對於火星表面的觀察，

than we do of what's beneath the Antarctic ice sheet.

還比南極冰蓋底下更全面。

And this is even more challenging in that we need these observations

更困難的是，我們需要的觀察資料

at a gigantic scale in both space and time.

在空間和時間的規模上都非常龐大。

In terms of space, this is a continent.

就空間來說，這是一塊大陸。

And in the same way that in North America,

就如同在北美洲，

the Rocky Mountains, Everglades and Great Lakes regions are very distinct,

落磯山脈、佛羅里達大沼澤、 五大湖區域是非常明顯的，

so are the subsurface regions of Antarctica.

在南極的表面區域亦是如此。

And in terms of time, we now know

就時間來說，我們現在知道

that ice sheets not only evolve over the timescale of millennia and centuries,

大冰原的演化並不只能從 千年和百年才看得出來，

but they're also changing over the scale of years and days.

它們其實每年、每天都在改變。

So what we want is observations beneath kilometers of ice

所以我們想要的是： 觀察在冰底下數公里深的地方，

at the scale of a continent,

範圍規模要和一塊大陸一樣大，

and we want them all the time.

且所有時間點的資料都要有。

So how do we do this?

所以，我們要怎麼做？

Well, we're not totally blind to the subsurface.

我們並非完全看不見 表層以下的地方。

I said in the beginning that I was a radio glaciologist,

在一開始我有提到 我是無線電冰河學家，

and the reason that that's a thing

這一點之所以很重要，

is that airborne ice-penetrating radar is the main tool we have

是因為空載且能穿透冰的雷達，

是我們用來看大冰原 裡面的主要工具。

to see inside of ice sheets.

So most of the data used by my group is collected by airplanes

所以，我的小組所用的大部分資料， 都是用飛機搜集的資料，

like this World War II-era DC-3,

像這架二次大戰時期的 DC-3，

that actually fought in the Battle of the Bulge.

它真的打過突出部之役。

You can see the antennas underneath the wing.

你們可以看到在機翼下面的天線。

These are used to transmit radar signals down into the ice.

它們是用來把雷達訊號 向下傳輸到冰裡面。

And the echos that come back contain information

反射回來的電波資訊就能說明

about what's happening inside and beneath the ice sheet.

在大冰原內部和底下發生的狀況。

While this is happening,

在進行的同時，

scientists and engineers are on the airplane

科學家和工程師會在飛機上，

for eight hours at a stretch,

八小時完全不休息，

making sure that the radar's working.

確保雷達的運作順利。

And I think this is actually a misconception

我認為，人們對於這種 實地調查工作有一種誤解，

about this type of fieldwork,

where people imagine scientists peering out the window,

把這種工作想像成 科學家從窗戶向外窺視，

contemplating the landscape, its geologic context

凝視著地景以及其地質環境，

and the fate of the ice sheets.

深思著大冰原的命運。

We actually had a guy from the BBC's "Frozen Planet" on one of these flights.

其實在飛機上有一個 BBC 《冰凍星球》節目的人同行。

And he spent, like, hours videotaping us turn knobs.

他花了數小時的時間 在拍攝我們轉動旋鈕。

(Laughter)

（笑聲）

And I was actually watching the series years later with my wife,

多年後，我和我太太 一起看這系列節目，

and a scene like this came up, and I commented on how beautiful it was.

出現了一個像這樣的景， 我說著它有多麼美麗。

And she said, "Weren't you on that flight?"

她說：「你不是在那台飛機上嗎？」

(Laughter)

（笑聲）

I said, "Yeah, but I was looking at a computer screen."

我說：「是啊， 但我都在看電腦螢幕。」

(Laughter)

（笑聲）

So when you think about this type of fieldwork,

所以，別把這類的實地調查工作

don't think about images like this.

想像成這樣的畫面。

Think about images like this.

而是要想成這樣的畫面。

(Laughter)

（笑聲）

This is a radargram, which is a vertical profile through the ice sheet,

這是雷達圖像， 整個大冰原的垂直剖面，

kind of like a slice of cake.

有一點像一片蛋糕。

The bright layer on the top is the surface of the ice sheet,

上方亮色的那一層 是大冰原的表面，

the bright layer on the bottom is the bedrock of the continent itself,

底下亮色的那一層 是大陸本身的床岩，

and the layers in between are kind of like tree rings,

中間的各層有點像是年輪，

in that they contain information about the history of the ice sheet.

包含了大冰原歷史的資訊。

And it's amazing that this works this well.

能有這麼好的結果， 是很不可思議的。

The ground-penetrating radars that are used

能夠穿透地面的雷達，

用來調查道路基礎設施 或是偵測地雷的那種，

to investigate infrastructures of roads or detect land mines

struggle to get through a few meters of earth.

要穿過幾公尺的陸地都很困難了。

And here we're peering through three kilometers of ice.

在這裡，我們能穿過三公里的冰。

And there are sophisticated, interesting, electromagnetic reasons for that,

這背後有著很複雜 且有趣的電磁理由，

but let's say for now that ice is basically the perfect target for radar,

但在這裡我們姑且就說 冰是雷達的完美目標，

and radar is basically the perfect tool to study ice sheets.

而基本上雷達也是研究 大冰原的完美工具。

These are the flight lines

這些是飛行路線，

of most of the modern airborne radar-sounding profiles

沿這些路線，我們從 南極各地取得大部分的

collected over Antarctica.

現代空載雷達探測數據。

This is the result of heroic efforts over decades

這是來自不同國家的團隊

by teams from a variety of countries and international collaborations.

以及國際合作，投入 數十年努力的結果。

And when you put those together, you get an image like this,

把這些都整合起來， 就會得到像這樣的影像，

which is what the continent of Antarctica would look like

這就是把南極大陸上面的冰

without all the ice on top.

去除後的樣子。

And you can really see the diversity of the continent in an image like this.

在這樣的影像中， 可以真正看到大陸的多樣性。

The red features are volcanoes or mountains;

紅色區域代表火山或山岳；

the areas that are blue would be open ocean

藍色區域是開放海洋，

if the ice sheet was removed.

如果把冰除去的話。

This is that giant spatial scale.

那是巨大的空間尺度。

However, all of this that took decades to produce

然而，要花數十年時間才能

is just one snapshot of the subsurface.

產出一張表面底下的快照。

It does not give us any indication of how the ice sheet is changing in time.

這樣還無法看出大冰原 如何隨著時間改變。

Now, we're working on that, because it turns out

我們正在努力，因為結果發現，

that the very first radar observations of Antarctica were collected

最早的南極雷達觀測資料

using 35 millimeter optical film.

是用 35 毫米的光學底片收集的。

And there were thousands of reels of this film

這種底片有數千卷之多，

in the archives of the museum of the Scott Polar Research Institute

都存放在史考特 極地研究中心的博物館中，

at the University of Cambridge.

位在劍橋大學內。

So last summer, I took a state-of-the-art film scanner

所以，去年夏天， 我拿了最先進的掃瞄器，

that was developed for digitizing Hollywood films and remastering them,

它是為了將好萊塢電影 給數位化和重製而設計的，

and two art historians,

與兩位藝術歷史學家

and we went over to England, put on some gloves

一同前往英國，戴上手套，

and archived and digitized all of that film.

把所有那些底片都建檔和數位化。

So that produced two million high-resolution images

結果產出了兩百萬張 高解析度的影像，

that my group is now working on analyzing and processing

現在我的小組正在 努力分析和處理它們，

for comparing with contemporary conditions in the ice sheet.

來和同時期大冰原內的狀況做比較。

And, actually, that scanner -- I found out about it

其實，那台掃瞄器──我是從

from an archivist at the Academy of Motion Picture Arts and Sciences.

電影藝術與科學學院的 檔案保管員那裡得知的。

So I'd like to thank the Academy --

所以，我要感謝影藝學院── （註：模仿奧斯卡得主致辭）

(Laughter)

（笑聲）

for making this possible.

讓這一切得以成真。

(Laughter)

（笑聲）

And as amazing as it is

我們能夠看到五十年前，

that we can look at what was happening under the ice sheet 50 years ago,

在冰底下發生的狀況， 雖然這是很了不起的事，

this is still just one more snapshot.

但這也只是多看到一張快照而已。

It doesn't give us observations

它還沒辦法提供我們

of the variation at the annual or seasonal scale,

每年或每季的變化觀測資料，

that we know matters.

我們知道這些資料很重要。

There's some progress here, too.

還是有一些進展。

There are these recent ground-based radar systems that stay in one spot.

最近有些地面雷達系統 可以固定在一個地點。

So you take these radars and put them on the ice sheet

所以你可以把這類的 雷達放到大冰原上，

and you bury a cache of car batteries.

並貯藏許多汽車電池來供電。

And you leave them out there for months or years at a time,

你可以把它們留在那裡 數個月或數年，

and they send a pulse down into the ice sheet

它們每分鐘或每小時就會將脈衝

every so many minutes or hours.

向下發送到大冰原裡。

So this gives you continuous observation in time --

這樣就能得到 連續時間的觀測資料──

but at one spot.

但只是單點的。

So if you compare that imaging to the 2-D pictures provided by the airplane,

如果你把那成像結果放到 飛機提供的二維圖片上，

this is just one vertical line.

其實只是一條垂直線。

And this is pretty much where we are as a field right now.

大致上，這就是我們 目前在努力的領域。

We can choose between good spatial coverage

我們可以選擇涵蓋很大的空間面積，

with airborne radar sounding

用空載雷達探測；

and good temporal coverage in one spot with ground-based sounding.

或選擇涵蓋長時間範圍、 單一地點，用陸基雷達探測。

But neither gives us what we really want:

但兩個選項都無法提供我們想要的：

both at the same time.

我們想同時得到兩者。

And if we're going to do that,

如果我們要那麼做，

we're going to need totally new ways of observing the ice sheet.

我們會需要用全新的 方式來觀察大冰原。

And ideally, those should be extremely low-cost

理想上，那些方式的 成本應該要極低，

so that we can take lots of measurements from lots of sensors.

這樣我們才能從許多 感測器取得許多測量值。

Well, for existing radar systems,

就目前既有的雷達系統而言，

the biggest driver of cost is the power required

最耗成本的部分是在電力，

to transmit the radar signal itself.

用來發射雷達訊號。

So it’d be great if we were able to use existing radio systems

所以，如果我們 能用在環境中既有的

or radio signals that are in the environment.

雷達系統或雷達訊號，那就很棒了。

And fortunately, the entire field of radio astronomy

不幸的是，整個無線電天文學領域

is built on the fact that there are bright radio signals in the sky.

都建立在一個基礎事實上： 天空中有明亮的無線電訊號。

And a really bright one is our sun.

而最明亮的訊號就是太陽。

So, actually, one of the most exciting things my group is doing right now

所以，我的小組現在正在進行的 最讓人興奮的事情之一，

is trying to use the radio emissions from the sun as a type of radar signal.

就是嘗試使用太陽放射的 無線電來當作一種雷達訊號。

This is one of our field tests at Big Sur.

這是我們在大索爾的實地測試之一。

That PVC pipe ziggurat is an antenna stand some undergrads in my lab built.

聚氯乙烯管做成的塔是個天線架， 我的實驗室中的一些大學生打造的。

And the idea here is that we stay out at Big Sur,

這裡的想法是， 我們在大索爾待在戶外，

and we watch the sunset in radio frequencies,

我們去看日落的無線電頻率，

and we try and detect the reflection of the sun off the surface of the ocean.

並試著偵測太陽照在 海洋表面所形成的反射。

Now, I know you're thinking, "There are no glaciers at Big Sur."

我知道你們在想： 「在大索爾沒有冰河。」

(Laughter)

（笑聲）

And that's true.

的確如此。

(Laughter)

（笑聲）

But it turns out that detecting the reflection of the sun

但結果發現，偵測太陽 照射在海洋表面的反射，

off the surface of the ocean

和偵測大冰原底部的反射，

and detecting the reflection off the bottom of an ice sheet

在地球物理學上是極度相似的。

are extremely geophysically similar.

And if this works,

如果這是可行的，

we should be able to apply the same measurement principle in Antarctica.

我們應該可以把同樣的 測量原則應用到南極。

And this is not as far-fetched as it seems.

這並沒有看起來得那麼牽強。

The seismic industry has gone through a similar technique-development exercise,

地震產業就已經完成了 一個類似的技術發展實做，

where they were able to move from detonating dynamite as a source,

他們從將引爆炸藥當作來源，

to using ambient seismic noise in the environment.

變成是用環境中的震測雜波。

And defense radars use TV signals and radio signals all the time,

防禦雷達也總是在用 電視訊號以及廣播訊號，

so they don't have to transmit a signal of radar

這樣他們就不用發出一個雷達訊號，

and give away their position.

暴露出他們的所在位置。

So what I'm saying is, this might really work.

所以，我的意思是， 這很有可能是可行的。

And if it does, we're going to need extremely low-cost sensors

如果可行，我們就會 需要極低成本的感測器，

so we can deploy networks of hundreds or thousands of these on an ice sheet

才能在大冰原上部署含有 數百或數千個感測器的網路，

to do imaging.

來進行成像。

And that's where the technological stars have really aligned to help us.

那對我們而言，可說是 科技上的天時地利人和。

Those earlier radar systems I talked about

我先前談到的早期雷達系統，

were developed by experienced engineers over the course of years

是由有經驗的工程師， 花了數年時間，

at national facilities

在國家提供的場所中， 用昂貴的專門設備開發出來的。

with expensive specialized equipment.

But the recent developments in software-defined radio,

但因為近期開發出了軟體無線電，

rapid fabrication and the maker movement,

加上快速製造，以及自造者運動，

make it so that it's possible for a team of teenagers

讓在我實驗室中工作的 一個青少年團隊，

working in my lab over the course of a handful of months

能夠花短短幾個月的時間，

to build a prototype radar.

就建造出一個原型雷達。

OK, they're not any teenagers, they’re Stanford undergrads,

好吧，他們不是隨便的青少年， 他們是史丹佛大學生，

but the point holds --

但重點不變──

(Laughter)

（笑聲）

that these enabling technologies are letting us break down the barrier

這些科技賦予我們能力， 讓我們能夠突破擋在

between engineers who build instruments and scientists that use them.

打造工具的工程師和 使用工具的科學家之間的障礙。

And by teaching engineering students to think like earth scientists

透過教導工程學生 用地球科學家的方式思考，

and earth-science students who can think like engineers,

教導地球科學學生 用工程師的方式思考，

my lab is building an environment in which we can build custom radar sensors

我的實驗室建立出了一個環境， 讓我們可以針對手上的每個問題，

for each problem at hand,

打造訂製的雷達感測器，

that are optimized for low cost and high performance

為該問題找出低成本高效能的

for that problem.

最佳化解決方案。

And that's going to totally change the way we observe ice sheets.

那將會完全改變我們 觀察大冰原的方式。

Look, the sea level problem and the role of the cryosphere in sea level rise

海平面問題以及冰凍圈在 海平面上升中所扮演的角色

is extremely important

是極度重要的，

and will affect the entire world.

且會影響整個世界。

But that is not why I work on it.

但那並非我投身這個領域的原因。

I work on it for the opportunity to teach and mentor

我這麼做是為了 有機會能夠教導和指導

extremely brilliant students,

極聰明的學生，

because I deeply believe that teams of hypertalented,

因為我深信， 由超有才華、超有動力、

hyperdriven, hyperpassionate young people

超有熱情的年輕人所組成的團隊，

can solve most of the challenges facing the world,

能夠解決世界面臨的大部分難題，

and that providing the observations required to estimate sea level rise

我也深信，提供估計 海平面上升所需要的觀測值，

is just one of the many such problems they can and will solve.

也只是他們能夠且將會解決的 許多此類問題當中的一個。

Thank you.

謝謝。

(Applause)

（掌聲）