Should we create a solar shade to cool the earth? | Danny Hillis

71,211 views ・ 2018-04-26

TED


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00:12
[A provocation from Danny Hillis:]
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[It's time to start talking about engineering our climate]
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What if there was a way to build a thermostat
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that allowed you to turn down the temperature of the earth
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anytime you wanted?
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Now, you would think if somebody had a plausible idea about how to do that,
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everybody would be very excited about it,
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and there would be lots of research on how to do it.
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But in fact, a lot of people do understand how to do that.
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But there's not much support for research in this area.
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And I think part of it
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is because there are some real misunderstandings about it.
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So I'm not going to try to convince you today that this is a good idea.
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But I am going to try to get your curiosity going about it
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and clear up some of the misunderstandings.
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So, the basic idea of solar geoengineering
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is that we can cool things down
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just by reflecting a little bit more sunlight
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back into space.
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And ideas about how to do this have been around literally for decades.
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Clouds are a great way to do that, 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 the same water content
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as the transparent air around it.
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And it just shows that even a little bit of a change in the flow of the air
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can cause a cloud to form.
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We make artificial clouds all the time.
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These are contrails, which are artificial water clouds
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that are made by the passing of a jet engine.
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And so, we're already changing the clouds on earth.
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By accident.
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Or, if you like to believe it, by supersecret government conspiracy.
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(Laughter)
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But we are already doing this quite a lot.
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This is a NASA picture of shipping lanes.
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Passing ships actually cause clouds to form,
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and this is a big enough effect
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that it actually helps reduce 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 about how to do this.
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People have looked at everything,
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from building giant parasols out into space
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to fizzing bubble waters in the ocean.
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And some of these are actually very plausible ideas.
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One that was published recently by David Keith at Harvard
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is to take chalk and put dust 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 common minerals on earth,
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and it's very safe -- it's so safe, we put it into baby food.
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And basically, if you throw chalk up into the stratosphere,
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it comes down in a couple of years all by itself, dissolved in rainwater.
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Now, before you start worrying about all this chalk in your rainwater,
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let me explain to you how little of it it actually takes.
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And that turns out to be very easy to calculate.
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This is a back-of-the-envelope calculation I made.
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(Laughter)
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(Applause)
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I assure you, people have done 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 at the rate of about 10 teragrams a year
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to undo the effects of the CO2 that we've already done --
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just in terms of temperature, 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 Fire Department and Taylor Milsal
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to lend me a hand.
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This is a hose pumping water at 10 teragrams a year.
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And that is how much
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you would have to pump into the stratosphere
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to cool the earth back down to pre-industrial levels.
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And it's amazingly little; it's like one hose for the entire earth.
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Now of course, you wouldn't really use a hose,
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you'd fly it up in airplanes or something like that.
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But it's so little, it would be like putting a handful of chalk
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into every Olympic swimming pool full of rain.
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It's almost nothing.
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So why don't people like this idea?
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Why isn't it taken more seriously?
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And there are some very good reasons for that.
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A lot of people really don't think we should be talking about this at all.
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And, in fact, I have some very good friends in the audience
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who I respect a lot,
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who really don't think I should be talking about this.
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And the reason is that they're concerned
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that if people imagine there's some easy way out,
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that we won't give up our addiction to fossil fuels.
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And I do worry about that.
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I think it's actually a serious problem.
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But there's also, I think, a deeper problem,
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which is: nobody likes the idea 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.
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And I don't want to mess with it.
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But we're already changing our atmosphere,
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we're already messing with it.
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And so I think it makes sense for us to look for ways
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to mitigate that impact.
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And we need to do research to do that.
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We need to understand the science behind that.
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I've noticed that there's a theme that's kind of developed at TED,
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which is kind of, "fear versus hope,"
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or "creativity versus caution."
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And of course, we need both of those.
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So there aren't any silver bullets.
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This is certainly not a silver bullet.
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But we need science to tell us what our options are;
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that informs both our creativity and our caution.
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So I am an optimist about our future selves,
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but I'm not an optimist because I think our problems are small.
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I'm an optimist because I think our capacity to deal with our problems
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is much greater than we imagine.
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Thank you very much.
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(Applause)
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This talk sparked a lot of controversy at TED2017,
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and we encourage you to look at discussions online
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to see other points of view.
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