0:00:00.844,0:00:04.744
I'm here to talk to you about something[br]important that may be new to you.

0:00:05.259,0:00:06.645
The governments of the world

0:00:06.669,0:00:08.933
are about to conduct[br]an unintentional experiment

0:00:08.957,0:00:10.712
on our climate.

0:00:10.736,0:00:16.046
In 2020, new rules will require ships[br]to lower their sulfur emissions

0:00:16.070,0:00:18.178
by scrubbing their dirty exhaust

0:00:18.202,0:00:20.153
or switching to cleaner fuels.

0:00:20.705,0:00:23.338
For human health, this is really good,

0:00:23.362,0:00:25.696
but sulfur particles[br]in the emission of ships

0:00:25.720,0:00:28.481
also have an effect on clouds.

0:00:28.981,0:00:31.482
This is a satellite image of marine clouds

0:00:31.506,0:00:34.028
off the Pacific West Coast[br]of the United States.

0:00:34.482,0:00:37.789
The streaks in the clouds[br]are created by the exhaust from ships.

0:00:38.139,0:00:41.013
Ships' emissions include[br]both greenhouse gases,

0:00:41.037,0:00:43.872
which trap heat over long periods of time,

0:00:43.896,0:00:47.111
and particulates like sulfates[br]that mix with clouds

0:00:47.135,0:00:48.968
and temporarily make them brighter.

0:00:49.672,0:00:52.963
Brighter clouds reflect[br]more sunlight back to space,

0:00:52.987,0:00:54.276
cooling the climate.

0:00:55.260,0:00:56.642
So in fact,

0:00:56.666,0:00:59.579
humans are currently running[br]two unintentional experiments

0:00:59.603,0:01:00.753
on our climate.

0:01:01.188,0:01:05.230
In the first one, we're increasing[br]the concentration of greenhouse gases

0:01:05.254,0:01:07.324
and gradually warming the earth system.

0:01:07.712,0:01:11.148
This works something like a fever[br]in the human body.

0:01:11.172,0:01:14.558
If the fever remains low,[br]its effects are mild,

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but as the fever rises,[br]damage grows more severe

0:01:17.480,0:01:19.439
and eventually devastating.

0:01:19.748,0:01:21.629
We're seeing a little of this now.

0:01:22.739,0:01:23.962
In our other experiment,

0:01:23.986,0:01:26.606
we're planning to remove[br]a layer of particles

0:01:26.630,0:01:29.864
that brighten clouds and shield us[br]from some of this warming.

0:01:30.306,0:01:33.512
The effect is strongest[br]in ocean clouds like these,

0:01:33.536,0:01:39.005
and scientists expect the reduction[br]of sulfur emissions from ships next year

0:01:39.029,0:01:42.402
to produce a measurable increase[br]in global warming.

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Bit of a shocker?

0:01:45.687,0:01:49.877
In fact, most emissions contain sulfates[br]that brighten clouds:

0:01:49.901,0:01:53.467
coal, diesel exhaust, forest fires.

0:01:54.149,0:01:57.848
Scientists estimate that the total[br]cooling effect from emission particles,

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which they call aerosols[br]when they're in the climate,

0:02:01.156,0:02:05.724
may be as much as all of the warming[br]we've experienced up until now.

0:02:05.748,0:02:08.756
There's a lot of uncertainty[br]around this effect,

0:02:08.780,0:02:13.106
and it's one of the major reasons[br]why we have difficulty predicting climate,

0:02:13.130,0:02:17.139
but this is cooling that we'll lose[br]as emissions fall.

0:02:17.968,0:02:21.944
So to be clear, humans[br]are currently cooling the planet

0:02:22.896,0:02:26.617
by dispersing particles[br]into the atmosphere at massive scale.

0:02:26.641,0:02:29.673
We just don't know how much,[br]and we're doing it accidentally.

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That's worrying,

0:02:32.553,0:02:35.971
but it could mean that we have[br]a fast-acting way to reduce warming,

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emergency medicine[br]for our climate fever if we needed it,

0:02:39.634,0:02:42.411
and it's a medicine[br]with origins in nature.

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This is a NASA simulation[br]of earth's atmosphere,

0:02:47.140,0:02:49.724
showing clouds and particles[br]moving over the planet.

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The brightness is the Sun's light[br]reflecting from particles in clouds,

0:02:54.947,0:02:58.670
and this reflective shield[br]is one of the primary ways

0:02:58.694,0:03:01.076
that nature keeps the planet[br]cool enough for humans

0:03:01.100,0:03:02.756
and all of the life that we know.

0:03:03.665,0:03:08.546
In 2015, scientists assessed possibilities[br]for rapidly cooling climate.

0:03:09.002,0:03:12.236
They discounted[br]things like mirrors in space,

0:03:12.260,0:03:17.101
ping-pong balls in the ocean,[br]plastic sheets on the Arctic,

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and they found[br]that the most viable approaches

0:03:19.523,0:03:23.590
involved slightly increasing[br]this atmospheric reflectivity.

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In fact, it's possible that reflecting[br]just one or two percent more sunlight

0:03:28.790,0:03:30.743
from the atmosphere

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could offset two degrees Celsius[br]or more of warming.

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Now, I'm a technology executive,[br]not a scientist.

0:03:39.259,0:03:42.068
About a decade ago,[br]concerned about climate,

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I started to talk with scientists about[br]potential countermeasures to warming.

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These conversations grew[br]into collaborations

0:03:50.027,0:03:52.351
that became the Marine[br]Cloud Brightening Project,

0:03:52.375,0:03:54.657
which I'll talk about momentarily,

0:03:54.681,0:03:58.734
and the nonprofit policy organization[br]SilverLining, where I am today.

0:03:59.483,0:04:03.070
I work with politicians, researchers,

0:04:03.094,0:04:05.070
members of the tech industry and others

0:04:05.094,0:04:07.233
to talk about some of these ideas.

0:04:08.039,0:04:11.284
Early on, I met British[br]atmospheric scientist John Latham,

0:04:11.308,0:04:14.315
who proposed cooling the climate[br]the way that the ships do,

0:04:14.339,0:04:16.654
but with a natural source of particles:

0:04:16.678,0:04:19.316
sea-salt mist from seawater

0:04:19.340,0:04:22.572
sprayed from ships into areas[br]of susceptible clouds over the ocean.

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The approach became known[br]by the name I gave it then,

0:04:26.253,0:04:27.820
"marine cloud brightening."

0:04:27.844,0:04:32.302
Early modeling studies suggested[br]that by deploying marine cloud brightening

0:04:32.326,0:04:35.914
in just 10 to 20 percent[br]of susceptible ocean clouds,

0:04:35.938,0:04:40.579
it might be possible to offset[br]as much as two degrees Celsius's warming.

0:04:41.200,0:04:44.129
It might even be possible[br]to brighten clouds in local regions

0:04:44.153,0:04:48.738
to reduce the impacts caused[br]by warming ocean surface temperatures.

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For example, regions[br]such as the Gulf Atlantic

0:04:51.598,0:04:54.218
might be cooled in the months[br]before a hurricane season

0:04:54.242,0:04:56.583
to reduce the force of storms.

0:04:56.607,0:05:00.530
Or, it might be possible to cool waters[br]flowing onto coral reefs

0:05:00.554,0:05:02.158
overwhelmed by heat stress,

0:05:02.182,0:05:04.236
like Australia's Great Barrier Reef.

0:05:04.260,0:05:07.006
But these ideas are only theoretical,

0:05:07.030,0:05:10.158
and brightening marine clouds[br]is not the only way

0:05:10.182,0:05:13.483
to increase the reflection[br]of the sunlight from the atmosphere.

0:05:14.063,0:05:19.016
Another occurs when large volcanoes[br]release material with enough force

0:05:19.040,0:05:22.245
to reach the upper layer[br]of the atmosphere, the stratosphere.

0:05:22.705,0:05:25.984
When Mount Pinatubo erupted in 1991,

0:05:26.008,0:05:28.008
it released material[br]into the stratosphere,

0:05:28.032,0:05:32.494
including sulfates that mix[br]with the atmosphere to reflect sunlight.

0:05:33.309,0:05:36.355
This material remained[br]and circulated around the planet.

0:05:36.996,0:05:40.968
It was enough to cool the climate[br]by over half a degree Celsius

0:05:40.992,0:05:42.658
for about two years.

0:05:44.011,0:05:50.027
This cooling led to a striking increase[br]in Arctic ice cover in 1992,

0:05:50.051,0:05:54.325
which dropped in subsequent years[br]as the particles fell back to earth.

0:05:54.349,0:05:58.167
But the volcanic phenomenon[br]led Nobel Prize winner Paul Crutzen

0:05:58.191,0:06:01.492
to propose the idea that dispersing[br]particles into the stratosphere

0:06:01.516,0:06:05.111
in a controlled way might be[br]a way to counter global warming.

0:06:05.960,0:06:08.882
Now, this has risks[br]that we don't understand,

0:06:08.906,0:06:11.636
including things like[br]heating up the stratosphere

0:06:11.660,0:06:13.691
or damage to the ozone layer.

0:06:13.715,0:06:18.231
Scientists think that there could be[br]safe approaches to this,

0:06:18.255,0:06:19.851
but is this really where we are?

0:06:19.875,0:06:22.628
Is this really worth considering?

0:06:23.494,0:06:24.779
This is a simulation

0:06:24.803,0:06:27.407
from the US National Center[br]for Atmospheric Research

0:06:27.431,0:06:31.866
global climate model showing,[br]earth surface temperatures through 2100.

0:06:31.890,0:06:35.883
The globe on the left visualizes[br]our current trajectory,

0:06:35.907,0:06:39.575
and on the right, a world where particles[br]are introduced into the stratosphere

0:06:39.599,0:06:40.994
gradually in 2020,

0:06:41.018,0:06:43.636
and maintained through 2100.

0:06:43.660,0:06:47.946
Intervention keeps surface temperatures[br]near those of today,

0:06:47.970,0:06:52.221
while without it, temperatures rise[br]well over three degrees.

0:06:52.245,0:06:56.152
This could be the difference[br]between a safe and an unsafe world.

0:06:57.854,0:07:01.718
So, if there's even a chance[br]that this could be close to reality,

0:07:01.742,0:07:04.354
is this something[br]we should consider seriously?

0:07:06.234,0:07:07.965
Today, there are no capabilities,

0:07:07.989,0:07:10.607
and scientific knowledge[br]is extremely limited.

0:07:11.342,0:07:15.888
We don't know whether these types[br]of interventions are even feasible,

0:07:15.912,0:07:17.959
or how to characterize their risks.

0:07:18.761,0:07:21.888
Researchers hope to explore[br]some basic questions

0:07:21.912,0:07:26.071
that might help us know[br]whether or not these might be real options

0:07:26.095,0:07:27.769
or whether we should rule them out.

0:07:28.689,0:07:32.109
It requires multiple ways[br]of studying the climate system,

0:07:32.133,0:07:35.245
including computer models[br]to forecast changes,

0:07:35.269,0:07:37.548
analytic techniques like machine learning,

0:07:37.572,0:07:39.610
and many types of observations.

0:07:40.595,0:07:42.380
And though it's controversial,

0:07:42.404,0:07:46.540
it's also critical that researchers[br]develop core technologies

0:07:46.564,0:07:49.984
and perform small-scale,[br]real-world experiments.

0:07:51.186,0:07:54.519
There are two research programs[br]proposing experiments like this.

0:07:55.408,0:07:59.496
At Harvard, the SCoPEx experiment[br]would release very small amounts

0:07:59.520,0:08:04.996
of sulfates, calcium carbonate and water[br]into the stratosphere with a balloon,

0:08:05.020,0:08:07.956
to study chemistry and physics effects.

0:08:08.956,0:08:10.295
How much material?

0:08:10.867,0:08:13.552
Less than the amount released[br]in one minute of flight

0:08:13.576,0:08:15.027
from a commercial aircraft.

0:08:15.654,0:08:18.312
So this is definitely not dangerous,

0:08:18.336,0:08:19.939
and it may not even be scary.

0:08:21.114,0:08:23.179
At the University of Washington,

0:08:23.203,0:08:27.337
scientists hope to spray[br]a fine mist of salt water into clouds

0:08:27.361,0:08:29.945
in a series of land and ocean tests.

0:08:29.969,0:08:32.780
If those are successful,[br]this would culminate in experiments

0:08:32.804,0:08:36.048
to measurably brighten[br]an area of clouds over the ocean.

0:08:36.738,0:08:40.666
The marine cloud brightening effort[br]is the first to develop any technology

0:08:40.690,0:08:44.721
for generating aerosols for atmospheric[br]sunlight reflection in this way.

0:08:45.166,0:08:47.953
It requires producing[br]very tiny particles --

0:08:47.977,0:08:52.445
think about the mist that comes[br]out of an asthma inhaler --

0:08:52.469,0:08:55.669
at massive scale -- so think[br]of looking up at a cloud.

0:08:56.500,0:08:58.713
It's a tricky engineering problem.

0:08:59.420,0:09:01.032
So this one nozzle they developed

0:09:01.056,0:09:03.698
generates three trillion[br]particles per second,

0:09:03.722,0:09:05.740
80 nanometers in size,

0:09:05.764,0:09:07.499
from very corrosive saltwater.

0:09:08.681,0:09:12.293
It was developed by a team[br]of retired engineers in Silicon Valley --

0:09:12.317,0:09:13.859
here they are --

0:09:13.883,0:09:18.887
working full-time for six years,[br]without pay, for their grandchildren.

0:09:19.334,0:09:22.222
It will take a few million dollars[br]and another year or two

0:09:22.246,0:09:25.690
to develop the full spray system[br]they need to do these experiments.

0:09:26.754,0:09:30.353
In other parts of the world,[br]research efforts are emerging,

0:09:30.377,0:09:34.710
including small modeling programs[br]at Beijing Normal University in China,

0:09:34.734,0:09:37.063
the Indian Institute of Science,

0:09:37.087,0:09:41.778
a proposed center for climate repair[br]at Cambridge University in the UK

0:09:41.802,0:09:44.007
and the DECIMALS Fund,

0:09:44.031,0:09:46.730
which sponsors researchers[br]in global South countries

0:09:46.754,0:09:49.715
to study the potential impacts[br]of these sunlight interventions

0:09:49.739,0:09:51.135
in their part of the world.

0:09:51.946,0:09:56.048
But all of these programs,[br]including the experimental ones,

0:09:56.072,0:09:57.672
lack significant funding.

0:09:58.601,0:10:01.512
And understanding[br]these interventions is a hard problem.

0:10:01.536,0:10:03.958
The earth is a vast, complex system

0:10:03.982,0:10:06.901
and we need major investments[br]in climate models, observations

0:10:06.925,0:10:08.474
and basic science

0:10:08.498,0:10:12.315
to be able to predict climate[br]much better than we can today

0:10:12.339,0:10:16.204
and manage both our accidental[br]and any intentional interventions.

0:10:17.521,0:10:18.728
And it could be urgent.

0:10:20.107,0:10:24.104
Recent scientific reports[br]predict that in the next few decades,

0:10:24.128,0:10:26.932
earth's fever is on a path to devastation:

0:10:26.956,0:10:28.781
extreme heat and fires,

0:10:29.875,0:10:32.001
major loss of ocean life,

0:10:32.812,0:10:34.676
collapse of Arctic ice,

0:10:35.779,0:10:39.382
displacement and suffering[br]for hundreds of millions of people.

0:10:40.277,0:10:43.977
The fever could even reach tipping points[br]where warming takes over

0:10:44.001,0:10:46.238
and human efforts are no longer enough

0:10:46.262,0:10:49.166
to counter accelerating changes[br]in natural systems.

0:10:49.848,0:10:52.115
To prevent this circumstance,

0:10:52.139,0:10:54.783
the UN's International Panel[br]on Climate Change predicts

0:10:54.807,0:10:58.314
that we need to stop[br]and even reverse emissions by 2050.

0:10:59.108,0:11:03.841
How? We have to quickly and radically[br]transform major economic sectors,

0:11:03.865,0:11:08.104
including energy, construction,[br]agriculture, transportation and others.

0:11:08.898,0:11:13.403
And it is imperative that we do this[br]as fast as we can.

0:11:13.427,0:11:15.460
But our fever is now so high

0:11:15.484,0:11:17.692
that climate experts say[br]we also have to remove

0:11:17.716,0:11:20.668
massive quantities of CO2[br]from the atmosphere,

0:11:20.692,0:11:24.295
possibly 10 times[br]all of the world's annual emissions,

0:11:24.319,0:11:26.150
in ways that aren't proven yet.

0:11:27.031,0:11:31.086
Right now, we have slow-moving solutions[br]to a fast-moving problem.

0:11:32.015,0:11:34.126
Even with the most optimistic assumptions,

0:11:34.150,0:11:37.428
our exposure to risk[br]in the next 10 to 30 years

0:11:37.452,0:11:39.896
is unacceptably high, in my opinion.

0:11:40.809,0:11:44.492
Could interventions like these[br]provide fast-acting medicine if we need it

0:11:44.516,0:11:48.060
to reduce the earth's fever[br]while we address its underlying causes?

0:11:48.621,0:11:51.222
There are real concerns about this idea.

0:11:51.246,0:11:54.610
Some people are very worried[br]that even researching these interventions

0:11:54.634,0:11:58.786
could provide an excuse to delay efforts[br]to reduce emissions.

0:11:58.810,0:12:01.140
This is also known as a moral hazard.

0:12:02.013,0:12:03.894
But, like most medicines,

0:12:03.918,0:12:07.175
interventions are more dangerous[br]the more that you do,

0:12:07.199,0:12:09.692
so research actually[br]tends to draw out the fact

0:12:09.716,0:12:12.786
that we absolutely,[br]positively cannot continue

0:12:12.810,0:12:15.631
to fill up the atmosphere[br]with greenhouse gases,

0:12:15.655,0:12:18.132
that these kinds of alternatives are risky

0:12:18.156,0:12:20.527
and if we were to use them,

0:12:20.551,0:12:22.926
we would need to use[br]as little as possible.

0:12:24.746,0:12:26.677
But even so,

0:12:26.701,0:12:29.405
could we ever learn enough[br]about these interventions

0:12:29.429,0:12:31.005
to manage the risk?

0:12:31.444,0:12:35.210
Who would make decisions[br]about when and how to intervene?

0:12:35.720,0:12:38.249
What if some people are worse off,

0:12:38.273,0:12:40.101
or they just think they are?

0:12:40.537,0:12:42.386
These are really hard problems.

0:12:43.506,0:12:48.488
But what really worries me[br]is that as climate impacts worsen,

0:12:48.512,0:12:51.973
leaders will be called on to respond[br]by any means available.

0:12:52.836,0:12:56.018
I for one don't want them to act[br]without real information

0:12:56.042,0:12:57.883
and much better options.

0:12:58.758,0:13:01.092
Scientists think it will take[br]a decade of research

0:13:01.116,0:13:03.265
just to assess these interventions,

0:13:03.289,0:13:05.685
before we ever were[br]to develop or use them.

0:13:06.392,0:13:10.796
Yet today, the global level of investment[br]in these interventions

0:13:10.820,0:13:12.871
is effectively zero.

0:13:14.061,0:13:16.792
So, we need to move quickly

0:13:16.816,0:13:20.038
if we want policymakers[br]to have real information

0:13:20.062,0:13:22.029
on this kind of emergency medicine.

0:13:24.169,0:13:25.319
There is hope!

0:13:26.621,0:13:29.176
The world has solved[br]these kinds of problems before.

0:13:29.562,0:13:32.966
In the 1970s, we identified[br]an existential threat

0:13:32.990,0:13:34.760
to our protective ozone layer.

0:13:35.664,0:13:38.498
In the 1980s, scientists,[br]politicians and industry

0:13:38.522,0:13:42.497
came together in a solution to replace[br]the chemicals causing the problem.

0:13:42.937,0:13:46.450
They achieved this with the only[br]legally binding environmental agreement

0:13:46.474,0:13:48.654
signed by all countries in the world,

0:13:48.678,0:13:50.618
the Montreal Protocol.

0:13:50.642,0:13:52.652
Still in force today,

0:13:52.676,0:13:55.460
it has resulted in a recovery[br]of the ozone layer

0:13:55.484,0:13:58.426
and is the most successful[br]environmental protection effort

0:13:58.450,0:13:59.908
in human history.

0:14:01.104,0:14:03.699
We have a far greater threat now,

0:14:03.723,0:14:07.953
but we do have the ability[br]to develop and agree on solutions

0:14:07.977,0:14:09.516
to protect people

0:14:09.540,0:14:11.596
and restore our climate to health.

0:14:12.406,0:14:15.176
This could mean that to remain safe,

0:14:15.200,0:14:17.537
we reflect sunlight for a few decades,

0:14:17.561,0:14:20.723
while we green our industries[br]and remove CO2.

0:14:21.655,0:14:24.917
It definitely means we must work now

0:14:24.941,0:14:29.202
to understand our options[br]for this kind of emergency medicine.

0:14:29.901,0:14:31.052
Thank you,

0:14:31.076,0:14:35.777
(Applause)