I'm a radio glaciologist. That means that I use radar to study glaciers and ice sheets. And like most glaciologists right now, I'm working on the problem of estimating how much the ice is going to contribute to sea level rise in the future. So today, I want to talk to you about 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 and earth-science education, we can get much better at it.
我是無線電冰河學家。 意思就是說,我用雷達 來研究冰河和大冰原。 和現在大部分的冰河學家一樣, 我在努力解決的問題是估計 在未來,冰對於海平面 上升的影響會有多大。 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, 以及為什麼我相信藉由 改變我們對雷達技術 以及地球科學教育的看法, 我們就能把預測做得更好。
When most scientists talk about sea level rise, they show a plot like this. This is produced using ice sheet and climate models. On the right, you can see the range of sea level predicted by these models over the next 100 years. For context, this is current sea level, and this is the sea level above which more than 4 million people could be vulnerable to displacement. So in terms of planning, the uncertainty in this plot is already large.
當大部分科學家談到海平面上升時, 他們會展示這類的圖。 這張圖是用大冰原 和氣候模型產生出來的。 在右邊,各位能看見海平面的範圍, 是用這些模型針對 未來一百年所做的預測。 背景說明:這是目前的海平面, 海平面超過這個高度時, 有超過四百萬人會受到遷移的影響。 所以,就規劃而言, 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, "... unless the West Antarctic Ice Sheet collapses." And in that case, we would be talking about dramatically higher numbers. They'd literally be off the chart. And the reason we should take that possibility seriously is that we know from the geologic history of the Earth that there were periods in its history when sea level rose much more quickly than today. And right now, we cannot rule out the possibility of that happening in the future. So why can't we say with confidence whether or not a significant portion of a continent-scale ice sheet will or will not collapse?
然而,在那之外,這張圖 還帶著星號和警告的訊息: 「……除非西南極冰蓋崩解。」 若那狀況發生,我們要談的 數字又會明顯更高了。 它們會在這張圖的範圍之外。 我們應該要認真看待 那種可能性的原因, 是我們從地球的地質史可以知道, 在歷史上的某些時期, 海平面上升的速度比現今還快很多。 現在,我們無法排除 那種現象在未來發生的可能性。 所以,為什麼我們無法有信心地說出 和大陸一樣大的一塊大冰原 是否有明顯的一部分 將會或者將不會崩解?
Well, in order to do that, we need models that we know include all of the processes, conditions and physics that would be involved in a collapse like that. And that's hard to know, because those processes and conditions are taking place beneath kilometers of ice, and satellites, like the one that produced this image, are blind to observe them. In fact, we have much more comprehensive observations of the surface of Mars than we do of what's beneath the Antarctic ice sheet. And this is even more challenging in that we need these observations at a gigantic scale in both space and time.
要做到這一點,我們需要模型, 且模型必須要 含有與這類崩解相關的 過程、條件、物理學。 那些資訊很難知道, 因為那些過程和條件是發生在 冰底下數公里深的地方, 而衛星,比如產出這張影像的衛星, 無法觀察到它們。 事實上,我們對於火星表面的觀察, 還比南極冰蓋底下更全面。 更困難的是,我們需要的觀察資料 在空間和時間的規模上都非常龐大。
In terms of space, this is a continent. And in the same way that in North America, the Rocky Mountains, Everglades and Great Lakes regions are very distinct, so are the subsurface regions of Antarctica. And in terms of time, we now know that ice sheets not only evolve over the timescale of millennia and centuries, but they're also changing over the scale of years and days. So what we want is observations beneath kilometers of ice at the scale of a continent, and we want them all the time.
就空間來說,這是一塊大陸。 就如同在北美洲, 落磯山脈、佛羅里達大沼澤、 五大湖區域是非常明顯的, 在南極的表面區域亦是如此。 就時間來說,我們現在知道 大冰原的演化並不只能從 千年和百年才看得出來, 它們其實每年、每天都在改變。 所以我們想要的是: 觀察在冰底下數公里深的地方, 範圍規模要和一塊大陸一樣大, 且所有時間點的資料都要有。
So how do we do this? Well, we're not totally blind to the subsurface. I said in the beginning that I was a radio glaciologist, and the reason that that's a thing is that airborne ice-penetrating radar is the main tool we have to see inside of ice sheets. So most of the data used by my group is collected by airplanes like this World War II-era DC-3, that actually fought in the Battle of the Bulge. You can see the antennas underneath the wing. These are used to transmit radar signals down into the ice. And the echos that come back contain information about what's happening inside and beneath the ice sheet. While this is happening, scientists and engineers are on the airplane for eight hours at a stretch, making sure that the radar's working. And I think this is actually a misconception about this type of fieldwork, where people imagine scientists peering out the window, contemplating the landscape, its geologic context and the fate of the ice sheets. We actually had a guy from the BBC's "Frozen Planet" on one of these flights. And he spent, like, hours videotaping us turn knobs.
所以,我們要怎麼做? 我們並非完全看不見 表層以下的地方。 在一開始我有提到 我是無線電冰河學家, 這一點之所以很重要, 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。 所以,我的小組所用的大部分資料, 都是用飛機搜集的資料, 像這架二次大戰時期的 DC-3, 它真的打過突出部之役。 你們可以看到在機翼下面的天線。 它們是用來把雷達訊號 向下傳輸到冰裡面。 反射回來的電波資訊就能說明 在大冰原內部和底下發生的狀況。 在進行的同時, 科學家和工程師會在飛機上, 八小時完全不休息, 確保雷達的運作順利。 我認為,人們對於這種 實地調查工作有一種誤解, 把這種工作想像成 科學家從窗戶向外窺視, 凝視著地景以及其地質環境, 深思著大冰原的命運。 其實在飛機上有一個 BBC 《冰凍星球》節目的人同行。 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, and a scene like this came up, and I commented on how beautiful it was. And she said, "Weren't you on that flight?"
多年後,我和我太太 一起看這系列節目, 出現了一個像這樣的景, 我說著它有多麼美麗。 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, don't think about images like this. Think about images like this.
所以,別把這類的實地調查工作 想像成這樣的畫面。 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, kind of like a slice of cake. The bright layer on the top is the surface of the ice sheet, the bright layer on the bottom is the bedrock of the continent itself, and the layers in between are kind of like tree rings, in that they contain information about the history of the ice sheet. And it's amazing that this works this well. The ground-penetrating radars that are used to investigate infrastructures of roads or detect land mines struggle to get through a few meters of earth. And here we're peering through three kilometers of ice. And there are sophisticated, interesting, electromagnetic reasons for that, but let's say for now that ice is basically the perfect target for radar, and radar is basically the perfect tool to study ice sheets.
這是雷達圖像, 整個大冰原的垂直剖面, 有一點像一片蛋糕。 上方亮色的那一層 是大冰原的表面, 底下亮色的那一層 是大陸本身的床岩, 中間的各層有點像是年輪, 包含了大冰原歷史的資訊。 能有這麼好的結果, 是很不可思議的。 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, 要穿過幾公尺的陸地都很困難了。 在這裡,我們能穿過三公里的冰。 這背後有著很複雜 且有趣的電磁理由, 但在這裡我們姑且就說 冰是雷達的完美目標, 而基本上雷達也是研究 大冰原的完美工具。
These are the flight lines of most of the modern airborne radar-sounding profiles collected over Antarctica. This is the result of heroic efforts over decades by teams from a variety of countries and international collaborations. And when you put those together, you get an image like this, which is what the continent of Antarctica would look like without all the ice on top. And you can really see the diversity of the continent in an image like this. The red features are volcanoes or mountains; the areas that are blue would be open ocean if the ice sheet was removed. This is that giant spatial scale. However, all of this that took decades to produce is just one snapshot of the subsurface. It does not give us any indication of how the ice sheet is changing in time. Now, we're working on that, because it turns out that the very first radar observations of Antarctica were collected using 35 millimeter optical film. And there were thousands of reels of this film in the archives of the museum of the Scott Polar Research Institute at the University of Cambridge.
這些是飛行路線, 沿這些路線,我們從 南極各地取得大部分的 現代空載雷達探測數據。 這是來自不同國家的團隊 以及國際合作,投入 數十年努力的結果。 把這些都整合起來, 就會得到像這樣的影像, 這就是把南極大陸上面的冰 去除後的樣子。 在這樣的影像中, 可以真正看到大陸的多樣性。 紅色區域代表火山或山岳; 藍色區域是開放海洋, 如果把冰除去的話。 那是巨大的空間尺度。 然而,要花數十年時間才能 產出一張表面底下的快照。 這樣還無法看出大冰原 如何隨著時間改變。 我們正在努力,因為結果發現, 最早的南極雷達觀測資料 是用 35 毫米的光學底片收集的。 這種底片有數千卷之多, 都存放在史考特 極地研究中心的博物館中, 位在劍橋大學內。
So last summer, I took a state-of-the-art film scanner that was developed for digitizing Hollywood films and remastering them, and two art historians, and we went over to England, put on some gloves and archived and digitized all of that film. So that produced two million high-resolution images that my group is now working on analyzing and processing for comparing with contemporary conditions in the ice sheet. And, actually, that scanner -- I found out about it from an archivist at the Academy of Motion Picture Arts and Sciences. So I'd like to thank the Academy --
所以,去年夏天, 我拿了最先進的掃瞄器, 它是為了將好萊塢電影 給數位化和重製而設計的, 與兩位藝術歷史學家 一同前往英國,戴上手套, 把所有那些底片都建檔和數位化。 結果產出了兩百萬張 高解析度的影像, 現在我的小組正在 努力分析和處理它們, 來和同時期大冰原內的狀況做比較。 其實,那台掃瞄器──我是從 電影藝術與科學學院的 檔案保管員那裡得知的。 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 that we can look at what was happening under the ice sheet 50 years ago, this is still just one more snapshot. It doesn't give us observations of the variation at the annual or seasonal scale, that we know matters. There's some progress here, too. There are these recent ground-based radar systems that stay in one spot. So you take these radars and put them on the ice sheet and you bury a cache of car batteries. And you leave them out there for months or years at a time, and they send a pulse down into the ice sheet every so many minutes or hours. So this gives you continuous observation in time -- but at one spot. So if you compare that imaging to the 2-D pictures provided by the airplane, this is just one vertical line. And this is pretty much where we are as a field right now. We can choose between good spatial coverage with airborne radar sounding and good temporal coverage in one spot with ground-based sounding.
我們能夠看到五十年前, 在冰底下發生的狀況, 雖然這是很了不起的事, 但這也只是多看到一張快照而已。 它還沒辦法提供我們 每年或每季的變化觀測資料, 我們知道這些資料很重要。 還是有一些進展。 最近有些地面雷達系統 可以固定在一個地點。 所以你可以把這類的 雷達放到大冰原上, 並貯藏許多汽車電池來供電。 你可以把它們留在那裡 數個月或數年, 它們每分鐘或每小時就會將脈衝 向下發送到大冰原裡。 這樣就能得到 連續時間的觀測資料── 但只是單點的。 如果你把那成像結果放到 飛機提供的二維圖片上, 其實只是一條垂直線。 大致上,這就是我們 目前在努力的領域。 我們可以選擇涵蓋很大的空間面積, 用空載雷達探測; 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: both at the same time. And if we're going to do that, we're going to need totally new ways of observing the ice sheet. And ideally, those should be extremely low-cost so that we can take lots of measurements from lots of sensors. Well, for existing radar systems, the biggest driver of cost is the power required to transmit the radar signal itself. So it’d be great if we were able to use existing radio systems or radio signals that are in the environment. And fortunately, the entire field of radio astronomy is built on the fact that there are bright radio signals in the sky. And a really bright one is our sun.
但兩個選項都無法提供我們想要的: 我們想同時得到兩者。 如果我們要那麼做, 我們會需要用全新的 方式來觀察大冰原。 理想上,那些方式的 成本應該要極低, 這樣我們才能從許多 感測器取得許多測量值。 就目前既有的雷達系統而言, 最耗成本的部分是在電力, 用來發射雷達訊號。 所以,如果我們 能用在環境中既有的 雷達系統或雷達訊號,那就很棒了。 不幸的是,整個無線電天文學領域 都建立在一個基礎事實上: 天空中有明亮的無線電訊號。 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 is trying to use the radio emissions from the sun as a type of radar signal. This is one of our field tests at Big Sur. That PVC pipe ziggurat is an antenna stand some undergrads in my lab built. And the idea here is that we stay out at Big Sur, and we watch the sunset in radio frequencies, and we try and detect the reflection of the sun off the surface of the ocean. Now, I know you're thinking, "There are no glaciers at Big Sur."
所以,我的小組現在正在進行的 最讓人興奮的事情之一, 就是嘗試使用太陽放射的 無線電來當作一種雷達訊號。 這是我們在大索爾的實地測試之一。 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。 這裡的想法是, 我們在大索爾待在戶外, 我們去看日落的無線電頻率, 並試著偵測太陽照在 海洋表面所形成的反射。 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 off the surface of the ocean and detecting the reflection off the bottom of an ice sheet are extremely geophysically similar. And if this works, we should be able to apply the same measurement principle in Antarctica. And this is not as far-fetched as it seems. The seismic industry has gone through a similar technique-development exercise, where they were able to move from detonating dynamite as a source, to using ambient seismic noise in the environment. And defense radars use TV signals and radio signals all the time, so they don't have to transmit a signal of radar and give away their position. So what I'm saying is, this might really work. And if it does, we're going to need extremely low-cost sensors so we can deploy networks of hundreds or thousands of these on an ice sheet to do imaging.
但結果發現,偵測太陽 照射在海洋表面的反射, 和偵測大冰原底部的反射, 在地球物理學上是極度相似的。 如果這是可行的, 我們應該可以把同樣的 測量原則應用到南極。 這並沒有看起來得那麼牽強。 地震產業就已經完成了 一個類似的技術發展實做, 他們從將引爆炸藥當作來源, 變成是用環境中的震測雜波。 防禦雷達也總是在用 電視訊號以及廣播訊號, 這樣他們就不用發出一個雷達訊號, 暴露出他們的所在位置。 所以,我的意思是, 這很有可能是可行的。 如果可行,我們就會 需要極低成本的感測器, 才能在大冰原上部署含有 數百或數千個感測器的網路, 來進行成像。
And that's where the technological stars have really aligned to help us. Those earlier radar systems I talked about were developed by experienced engineers over the course of years at national facilities with expensive specialized equipment. But the recent developments in software-defined radio, rapid fabrication and the maker movement, make it so that it's possible for a team of teenagers working in my lab over the course of a handful of months to build a prototype radar. OK, they're not any teenagers, they’re Stanford undergrads, but the point holds --
那對我們而言,可說是 科技上的天時地利人和。 我先前談到的早期雷達系統, 是由有經驗的工程師, 花了數年時間, 在國家提供的場所中, 用昂貴的專門設備開發出來的。 但因為近期開發出了軟體無線電, 加上快速製造,以及自造者運動, 讓在我實驗室中工作的 一個青少年團隊, 能夠花短短幾個月的時間, 就建造出一個原型雷達。 好吧,他們不是隨便的青少年, 他們是史丹佛大學生, 但重點不變──
(Laughter)
(笑聲)
that these enabling technologies are letting us break down the barrier between engineers who build instruments and scientists that use them. And by teaching engineering students to think like earth scientists and earth-science students who can think like engineers, my lab is building an environment in which we can build custom radar sensors for each problem at hand, that are optimized for low cost and high performance for that problem. And that's going to totally change the way we observe ice sheets.
這些科技賦予我們能力, 讓我們能夠突破擋在 打造工具的工程師和 使用工具的科學家之間的障礙。 透過教導工程學生 用地球科學家的方式思考, 教導地球科學學生 用工程師的方式思考, 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, 打造訂製的雷達感測器, 為該問題找出低成本高效能的 最佳化解決方案。 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 is extremely important and will affect the entire world. But that is not why I work on it. I work on it for the opportunity to teach and mentor extremely brilliant students, because I deeply believe that teams of hypertalented, hyperdriven, hyperpassionate young people can solve most of the challenges facing the world, and that providing the observations required to estimate sea level rise is just one of the many such problems they can and will solve.
海平面問題以及冰凍圈在 海平面上升中所扮演的角色 是極度重要的, 且會影響整個世界。 但那並非我投身這個領域的原因。 我這麼做是為了 有機會能夠教導和指導 極聰明的學生, 因為我深信, 由超有才華、超有動力、 超有熱情的年輕人所組成的團隊, 能夠解決世界面臨的大部分難題, 我也深信,提供估計 海平面上升所需要的觀測值, 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)