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

33,504 views ・ 2018-03-22

TED


Please double-click on the English subtitles below to play the video.

00:12
I'm a radio glaciologist.
0
12929
2087
00:15
That means that I use radar to study glaciers and ice sheets.
1
15397
3872
00:19
And like most glaciologists right now,
2
19705
2023
00:21
I'm working on the problem of estimating
3
21752
2068
00:23
how much the ice is going to contribute to sea level rise in the future.
4
23844
4160
00:28
So today, I want to talk to you about
5
28367
1775
00:30
why it's so hard to put good numbers on sea level rise,
6
30166
3737
00:33
and why I believe that by changing the way we think about radar technology
7
33927
4040
00:37
and earth-science education,
8
37991
1388
00:39
we can get much better at it.
9
39403
1754
00:42
When most scientists talk about sea level rise,
10
42030
2302
00:44
they show a plot like this.
11
44356
1381
00:45
This is produced using ice sheet and climate models.
12
45761
2786
00:48
On the right, you can see the range of sea level
13
48966
2341
00:51
predicted by these models over the next 100 years.
14
51331
3198
00:54
For context, this is current sea level,
15
54553
2952
00:57
and this is the sea level
16
57529
1398
00:58
above which more than 4 million people could be vulnerable to displacement.
17
58951
3554
01:02
So in terms of planning,
18
62863
1770
01:04
the uncertainty in this plot is already large.
19
64657
3182
01:07
However, beyond that, this plot comes with the asterisk and the caveat,
20
67863
4674
01:12
"... unless the West Antarctic Ice Sheet collapses."
21
72561
2921
01:15
And in that case, we would be talking about dramatically higher numbers.
22
75506
3563
01:19
They'd literally be off the chart.
23
79093
1968
01:21
And the reason we should take that possibility seriously
24
81671
3065
01:24
is that we know from the geologic history of the Earth
25
84760
2580
01:27
that there were periods in its history
26
87364
2158
01:29
when sea level rose much more quickly than today.
27
89546
2641
01:32
And right now, we cannot rule out
28
92211
2025
01:34
the possibility of that happening in the future.
29
94260
2452
01:37
So why can't we say with confidence
30
97625
3136
01:40
whether or not a significant portion of a continent-scale ice sheet
31
100785
5197
01:46
will or will not collapse?
32
106006
2101
01:48
Well, in order to do that, we need models
33
108799
1985
01:50
that we know include all of the processes, conditions and physics
34
110808
3581
01:54
that would be involved in a collapse like that.
35
114413
2398
01:57
And that's hard to know,
36
117206
1460
01:58
because those processes and conditions are taking place
37
118690
2734
02:01
beneath kilometers of ice,
38
121448
1839
02:03
and satellites, like the one that produced this image,
39
123311
2550
02:05
are blind to observe them.
40
125885
1425
02:07
In fact, we have much more comprehensive observations of the surface of Mars
41
127713
4284
02:12
than we do of what's beneath the Antarctic ice sheet.
42
132021
2662
02:15
And this is even more challenging in that we need these observations
43
135829
3207
02:19
at a gigantic scale in both space and time.
44
139060
3196
02:22
In terms of space, this is a continent.
45
142687
2248
02:25
And in the same way that in North America,
46
145322
2120
02:27
the Rocky Mountains, Everglades and Great Lakes regions are very distinct,
47
147466
4040
02:31
so are the subsurface regions of Antarctica.
48
151530
2991
02:34
And in terms of time, we now know
49
154545
1643
02:36
that ice sheets not only evolve over the timescale of millennia and centuries,
50
156212
4341
02:40
but they're also changing over the scale of years and days.
51
160577
3786
02:44
So what we want is observations beneath kilometers of ice
52
164387
4309
02:48
at the scale of a continent,
53
168720
1929
02:50
and we want them all the time.
54
170673
1645
02:53
So how do we do this?
55
173014
1400
02:54
Well, we're not totally blind to the subsurface.
56
174814
4056
02:58
I said in the beginning that I was a radio glaciologist,
57
178894
2670
03:01
and the reason that that's a thing
58
181588
1878
03:03
is that airborne ice-penetrating radar is the main tool we have
59
183490
3770
03:07
to see inside of ice sheets.
60
187284
1596
03:09
So most of the data used by my group is collected by airplanes
61
189212
3846
03:13
like this World War II-era DC-3,
62
193082
2225
03:15
that actually fought in the Battle of the Bulge.
63
195331
2452
03:17
You can see the antennas underneath the wing.
64
197807
2580
03:20
These are used to transmit radar signals down into the ice.
65
200411
3730
03:24
And the echos that come back contain information
66
204165
2453
03:26
about what's happening inside and beneath the ice sheet.
67
206642
2937
03:30
While this is happening,
68
210530
1317
03:31
scientists and engineers are on the airplane
69
211871
2285
03:34
for eight hours at a stretch,
70
214180
1487
03:35
making sure that the radar's working.
71
215691
1869
03:37
And I think this is actually a misconception
72
217996
2541
03:40
about this type of fieldwork,
73
220561
1444
03:42
where people imagine scientists peering out the window,
74
222029
3147
03:45
contemplating the landscape, its geologic context
75
225200
2914
03:48
and the fate of the ice sheets.
76
228138
1718
03:50
We actually had a guy from the BBC's "Frozen Planet" on one of these flights.
77
230327
3623
03:53
And he spent, like, hours videotaping us turn knobs.
78
233974
2722
03:57
(Laughter)
79
237046
2603
03:59
And I was actually watching the series years later with my wife,
80
239673
3376
04:03
and a scene like this came up, and I commented on how beautiful it was.
81
243073
3423
04:07
And she said, "Weren't you on that flight?"
82
247001
2930
04:09
(Laughter)
83
249955
1159
04:11
I said, "Yeah, but I was looking at a computer screen."
84
251138
2945
04:14
(Laughter)
85
254107
1256
04:15
So when you think about this type of fieldwork,
86
255387
2207
04:17
don't think about images like this.
87
257618
2023
04:19
Think about images like this.
88
259665
1691
04:21
(Laughter)
89
261380
1163
04:22
This is a radargram, which is a vertical profile through the ice sheet,
90
262567
3342
04:25
kind of like a slice of cake.
91
265933
1484
04:27
The bright layer on the top is the surface of the ice sheet,
92
267768
2849
04:30
the bright layer on the bottom is the bedrock of the continent itself,
93
270641
3330
04:33
and the layers in between are kind of like tree rings,
94
273995
2526
04:36
in that they contain information about the history of the ice sheet.
95
276545
3207
04:39
And it's amazing that this works this well.
96
279776
2230
04:42
The ground-penetrating radars that are used
97
282321
2018
04:44
to investigate infrastructures of roads or detect land mines
98
284363
2928
04:47
struggle to get through a few meters of earth.
99
287315
2159
04:49
And here we're peering through three kilometers of ice.
100
289498
2756
04:52
And there are sophisticated, interesting, electromagnetic reasons for that,
101
292278
3840
04:56
but let's say for now that ice is basically the perfect target for radar,
102
296142
4151
05:00
and radar is basically the perfect tool to study ice sheets.
103
300317
3228
05:04
These are the flight lines
104
304641
1279
05:05
of most of the modern airborne radar-sounding profiles
105
305944
3044
05:09
collected over Antarctica.
106
309012
1714
05:10
This is the result of heroic efforts over decades
107
310750
2970
05:13
by teams from a variety of countries and international collaborations.
108
313744
3625
05:17
And when you put those together, you get an image like this,
109
317672
2857
05:20
which is what the continent of Antarctica would look like
110
320553
2706
05:23
without all the ice on top.
111
323283
1346
05:25
And you can really see the diversity of the continent in an image like this.
112
325958
4532
05:30
The red features are volcanoes or mountains;
113
330514
2412
05:32
the areas that are blue would be open ocean
114
332950
2110
05:35
if the ice sheet was removed.
115
335084
1580
05:36
This is that giant spatial scale.
116
336688
2634
05:39
However, all of this that took decades to produce
117
339807
3001
05:42
is just one snapshot of the subsurface.
118
342832
3002
05:46
It does not give us any indication of how the ice sheet is changing in time.
119
346220
4213
05:51
Now, we're working on that, because it turns out
120
351338
2417
05:53
that the very first radar observations of Antarctica were collected
121
353779
3449
05:57
using 35 millimeter optical film.
122
357252
2378
06:00
And there were thousands of reels of this film
123
360021
2191
06:02
in the archives of the museum of the Scott Polar Research Institute
124
362236
3254
06:05
at the University of Cambridge.
125
365514
1502
06:07
So last summer, I took a state-of-the-art film scanner
126
367040
2581
06:09
that was developed for digitizing Hollywood films and remastering them,
127
369645
3556
06:13
and two art historians,
128
373225
1151
06:14
and we went over to England, put on some gloves
129
374400
2218
06:16
and archived and digitized all of that film.
130
376642
2514
06:19
So that produced two million high-resolution images
131
379744
3095
06:22
that my group is now working on analyzing and processing
132
382863
3198
06:26
for comparing with contemporary conditions in the ice sheet.
133
386085
2944
06:29
And, actually, that scanner -- I found out about it
134
389458
2392
06:31
from an archivist at the Academy of Motion Picture Arts and Sciences.
135
391874
3386
06:35
So I'd like to thank the Academy --
136
395284
2524
06:37
(Laughter)
137
397832
2245
06:40
for making this possible.
138
400101
1318
06:41
(Laughter)
139
401443
1055
06:42
And as amazing as it is
140
402522
1697
06:44
that we can look at what was happening under the ice sheet 50 years ago,
141
404243
3636
06:47
this is still just one more snapshot.
142
407903
2682
06:50
It doesn't give us observations
143
410609
2117
06:52
of the variation at the annual or seasonal scale,
144
412750
3173
06:55
that we know matters.
145
415947
1336
06:57
There's some progress here, too.
146
417926
1564
06:59
There are these recent ground-based radar systems that stay in one spot.
147
419514
3524
07:03
So you take these radars and put them on the ice sheet
148
423062
2613
07:05
and you bury a cache of car batteries.
149
425699
1890
07:07
And you leave them out there for months or years at a time,
150
427613
2810
07:10
and they send a pulse down into the ice sheet
151
430447
2112
07:12
every so many minutes or hours.
152
432583
1498
07:14
So this gives you continuous observation in time --
153
434105
2407
07:16
but at one spot.
154
436958
1150
07:18
So if you compare that imaging to the 2-D pictures provided by the airplane,
155
438418
4390
07:22
this is just one vertical line.
156
442832
1857
07:25
And this is pretty much where we are as a field right now.
157
445498
2856
07:28
We can choose between good spatial coverage
158
448378
2658
07:31
with airborne radar sounding
159
451060
1493
07:32
and good temporal coverage in one spot with ground-based sounding.
160
452577
3809
07:36
But neither gives us what we really want:
161
456410
2311
07:38
both at the same time.
162
458745
1341
07:40
And if we're going to do that,
163
460753
1437
07:42
we're going to need totally new ways of observing the ice sheet.
164
462214
3007
07:45
And ideally, those should be extremely low-cost
165
465245
2721
07:47
so that we can take lots of measurements from lots of sensors.
166
467990
3235
07:51
Well, for existing radar systems,
167
471871
2143
07:54
the biggest driver of cost is the power required
168
474038
3044
07:57
to transmit the radar signal itself.
169
477106
2297
08:00
So it’d be great if we were able to use existing radio systems
170
480187
3295
08:03
or radio signals that are in the environment.
171
483506
2722
08:06
And fortunately, the entire field of radio astronomy
172
486252
2849
08:09
is built on the fact that there are bright radio signals in the sky.
173
489125
3785
08:12
And a really bright one is our sun.
174
492934
2301
08:15
So, actually, one of the most exciting things my group is doing right now
175
495259
3460
08:18
is trying to use the radio emissions from the sun as a type of radar signal.
176
498743
3587
08:22
This is one of our field tests at Big Sur.
177
502354
2187
08:24
That PVC pipe ziggurat is an antenna stand some undergrads in my lab built.
178
504565
4158
08:29
And the idea here is that we stay out at Big Sur,
179
509100
2983
08:32
and we watch the sunset in radio frequencies,
180
512107
2438
08:34
and we try and detect the reflection of the sun off the surface of the ocean.
181
514569
4561
08:39
Now, I know you're thinking, "There are no glaciers at Big Sur."
182
519585
3796
08:43
(Laughter)
183
523405
1085
08:44
And that's true.
184
524514
1158
08:45
(Laughter)
185
525696
1180
08:46
But it turns out that detecting the reflection of the sun
186
526900
3700
08:50
off the surface of the ocean
187
530624
1358
08:52
and detecting the reflection off the bottom of an ice sheet
188
532006
2802
08:54
are extremely geophysically similar.
189
534832
1741
08:56
And if this works,
190
536597
1199
08:57
we should be able to apply the same measurement principle in Antarctica.
191
537820
3405
09:01
And this is not as far-fetched as it seems.
192
541249
2040
09:03
The seismic industry has gone through a similar technique-development exercise,
193
543313
3753
09:07
where they were able to move from detonating dynamite as a source,
194
547090
3130
09:10
to using ambient seismic noise in the environment.
195
550244
2489
09:12
And defense radars use TV signals and radio signals all the time,
196
552757
3833
09:16
so they don't have to transmit a signal of radar
197
556614
2579
09:19
and give away their position.
198
559217
1651
09:21
So what I'm saying is, this might really work.
199
561280
2598
09:23
And if it does, we're going to need extremely low-cost sensors
200
563902
3202
09:27
so we can deploy networks of hundreds or thousands of these on an ice sheet
201
567128
3589
09:30
to do imaging.
202
570741
1151
09:31
And that's where the technological stars have really aligned to help us.
203
571916
3606
09:35
Those earlier radar systems I talked about
204
575546
2404
09:37
were developed by experienced engineers over the course of years
205
577974
3633
09:41
at national facilities
206
581631
1349
09:43
with expensive specialized equipment.
207
583004
1976
09:45
But the recent developments in software-defined radio,
208
585354
2890
09:48
rapid fabrication and the maker movement,
209
588268
2246
09:50
make it so that it's possible for a team of teenagers
210
590538
2952
09:53
working in my lab over the course of a handful of months
211
593514
2642
09:56
to build a prototype radar.
212
596180
1445
09:58
OK, they're not any teenagers, they’re Stanford undergrads,
213
598045
2809
10:00
but the point holds --
214
600878
1647
10:02
(Laughter)
215
602549
1424
10:03
that these enabling technologies are letting us break down the barrier
216
603997
3303
10:07
between engineers who build instruments and scientists that use them.
217
607324
3811
10:11
And by teaching engineering students to think like earth scientists
218
611590
3941
10:15
and earth-science students who can think like engineers,
219
615555
2678
10:18
my lab is building an environment in which we can build custom radar sensors
220
618257
4233
10:22
for each problem at hand,
221
622514
1610
10:24
that are optimized for low cost and high performance
222
624148
3437
10:27
for that problem.
223
627609
1468
10:29
And that's going to totally change the way we observe ice sheets.
224
629101
3477
10:32
Look, the sea level problem and the role of the cryosphere in sea level rise
225
632998
5081
10:38
is extremely important
226
638103
1585
10:39
and will affect the entire world.
227
639712
1674
10:41
But that is not why I work on it.
228
641815
2088
10:44
I work on it for the opportunity to teach and mentor
229
644458
3115
10:47
extremely brilliant students,
230
647597
1787
10:49
because I deeply believe that teams of hypertalented,
231
649804
3109
10:52
hyperdriven, hyperpassionate young people
232
652937
2492
10:55
can solve most of the challenges facing the world,
233
655453
2547
10:58
and that providing the observations required to estimate sea level rise
234
658577
4012
11:02
is just one of the many such problems they can and will solve.
235
662613
3690
11:06
Thank you.
236
666768
1152
11:07
(Applause)
237
667944
2642
About this website

This site will introduce you to YouTube videos that are useful for learning English. You will see English lessons taught by top-notch teachers from around the world. Double-click on the English subtitles displayed on each video page to play the video from there. The subtitles scroll in sync with the video playback. If you have any comments or requests, please contact us using this contact form.

https://forms.gle/WvT1wiN1qDtmnspy7