0:00:01.929,0:00:04.873
[It's time to start talking[br]about engineering our climate]

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What if there was a way[br]to build a thermostat

0:00:08.390,0:00:11.133
that allowed you to turn down[br]the temperature of the earth

0:00:11.157,0:00:12.424
anytime you wanted?

0:00:13.695,0:00:18.085
Now, you would think if somebody[br]had a plausible idea about how to do that,

0:00:18.109,0:00:20.363
everybody would be very excited about it,

0:00:20.387,0:00:22.982
and there would be lots[br]of research on how to do it.

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But in fact, a lot of people[br]do understand how to do that.

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But there's not much support[br]for research in this area.

0:00:33.444,0:00:35.631
And I think part of it

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is because there are some real[br]misunderstandings about it.

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So I'm not going to try to convince you[br]today that this is a good idea.

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But I am going to try to get[br]your curiosity going about it

0:00:48.570,0:00:51.736
and clear up some[br]of the misunderstandings.

0:00:52.266,0:00:56.387
So, the basic idea of solar geoengineering

0:00:56.411,0:00:59.038
is that we can cool things down

0:00:59.062,0:01:01.800
just by reflecting[br]a little bit more sunlight

0:01:01.824,0:01:02.978
back into space.

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And ideas about how to do this[br]have been around literally for decades.

0:01:10.023,0:01:14.482
Clouds are a great way to do that,[br]these low-lying clouds.

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Everybody knows it's cooler under a cloud.

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I like this cloud because it has exactly[br]the same water content

0:01:21.800,0:01:23.678
as the transparent air around it.

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And it just shows that even a little bit[br]of a change in the flow of the air

0:01:28.363,0:01:29.780
can cause a cloud to form.

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We make artificial clouds all the time.

0:01:33.823,0:01:37.180
These are contrails,[br]which are artificial water clouds

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that are made by the passing[br]of a jet engine.

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And so, we're already changing[br]the clouds on earth.

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By accident.

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Or, if you like to believe it,[br]by supersecret government conspiracy.

0:01:51.559,0:01:53.634
(Laughter)

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But we are already doing this quite a lot.

0:01:56.807,0:02:00.379
This is a NASA picture of shipping lanes.

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Passing ships actually cause[br]clouds to form,

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and this is a big enough effect

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that it actually helps reduce[br]global warming already by about a degree.

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So we already are doing solar engineering.

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There's lots of ideas[br]about how to do this.

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People have looked at everything,

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from building giant parasols[br]out into space

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to fizzing bubble waters in the ocean.

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And some of these are actually[br]very plausible ideas.

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One that was published recently[br]by David Keith at Harvard

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is to take chalk and put dust[br]up into the stratosphere,

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where it reflects off sunlight.

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And that's a really neat idea,

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because chalk is one of the most[br]common minerals on earth,

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and it's very safe -- it's so safe,[br]we put it into baby food.

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And basically, if you throw chalk[br]up into the stratosphere,

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it comes down in a couple of years[br]all by itself, dissolved in rainwater.

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Now, before you start worrying[br]about all this chalk in your rainwater,

0:03:04.738,0:03:08.949
let me explain to you[br]how little of it it actually takes.

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And that turns out to be[br]very easy to calculate.

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This is a back-of-the-envelope[br]calculation I made.

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(Laughter)

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(Applause)

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I assure you, people have done[br]much more careful calculations,

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and it comes out with the same answer,

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which is that you have to put chalk up[br]at the rate of about 10 teragrams a year

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to undo the effects of the CO2[br]that we've already done --

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just in terms of temperature,[br]not all the effects, but the temperature.

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So what does that look like?

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I can't visualize 10 teragrams per year.

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So I asked the Cambridge[br]Fire Department and Taylor Milsal

0:03:51.823,0:03:53.315
to lend me a hand.

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This is a hose pumping water[br]at 10 teragrams a year.

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And that is how much

0:04:03.284,0:04:06.863
you would have to pump[br]into the stratosphere

0:04:06.887,0:04:10.728
to cool the earth back down[br]to pre-industrial levels.

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And it's amazingly little;[br]it's like one hose for the entire earth.

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Now of course, you wouldn't[br]really use a hose,

0:04:19.513,0:04:22.021
you'd fly it up in airplanes[br]or something like that.

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But it's so little, it would be like[br]putting a handful of chalk

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into every Olympic[br]swimming pool full of rain.

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It's almost nothing.

0:04:33.192,0:04:37.545
So why don't people like this idea?

0:04:37.569,0:04:39.291
Why isn't it taken more seriously?

0:04:39.315,0:04:42.109
And there are some[br]very good reasons for that.

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A lot of people really don't think[br]we should be talking about this at all.

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And, in fact, I have some[br]very good friends in the audience

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who I respect a lot,

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who really don't think[br]I should be talking about this.

0:04:59.056,0:05:01.898
And the reason is that they're concerned

0:05:01.922,0:05:05.374
that if people imagine[br]there's some easy way out,

0:05:05.398,0:05:08.985
that we won't give up[br]our addiction to fossil fuels.

0:05:09.553,0:05:11.287
And I do worry about that.

0:05:11.871,0:05:14.101
I think it's actually a serious problem.

0:05:14.927,0:05:19.914
But there's also, I think,[br]a deeper problem,

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which is: nobody likes the idea[br]of messing with the entire earth --

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I certainly don't.

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I love this planet, I really do.

0:05:30.175,0:05:32.214
And I don't want to mess with it.

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But we're already changing our atmosphere,

0:05:36.494,0:05:38.049
we're already messing with it.

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And so I think it makes sense[br]for us to look for ways

0:05:45.285,0:05:47.130
to mitigate that impact.

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And we need to do research to do that.

0:05:49.456,0:05:51.980
We need to understand[br]the science behind that.

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I've noticed that there's a theme[br]that's kind of developed at TED,

0:05:58.212,0:06:02.552
which is kind of, "fear versus hope,"

0:06:02.576,0:06:05.971
or "creativity versus caution."

0:06:07.026,0:06:09.045
And of course, we need both of those.

0:06:09.747,0:06:12.231
So there aren't any silver bullets.

0:06:12.255,0:06:14.533
This is certainly not a silver bullet.

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But we need science to tell us[br]what our options are;

0:06:20.159,0:06:24.474
that informs both[br]our creativity and our caution.

0:06:25.293,0:06:29.807
So I am an optimist[br]about our future selves,

0:06:30.426,0:06:34.426
but I'm not an optimist[br]because I think our problems are small.

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I'm an optimist because I think[br]our capacity to deal with our problems

0:06:41.220,0:06:43.353
is much greater than we imagine.

0:06:43.859,0:06:45.158
Thank you very much.

0:06:45.182,0:06:46.199
(Applause)

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This talk sparked[br]a lot of controversy at TED2017,

0:06:48.403,0:06:50.453
and we encourage you[br]to look at discussions online

0:06:50.483,0:06:51.783
to see other points of view.

0:00:00.261,0:00:01.905
[A provocation from Danny Hillis:]