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  • [A provocation from Danny Hillis:]

  • [It's time to start talking about engineering our climate]

  • What if there was a way to build a thermostat

  • that allowed you to turn down the temperature of the earth

  • anytime you wanted?

  • Now, you would think if somebody had a plausible idea about how to do that,

  • everybody would be very excited about it,

  • and there would be lots of research on how to do it.

  • But in fact, a lot of people do understand how to do that.

  • But there's not much support for research in this area.

  • And I think part of it

  • is because there are some real misunderstandings about it.

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

  • But I am going to try to get your curiosity going about it

  • and clear up some of the misunderstandings.

  • So, the basic idea of solar geoengineering

  • is that we can cool things down

  • just by reflecting a little bit more sunlight

  • back into space.

  • And ideas about how to do this have been around literally for decades.

  • Clouds are a great way to do that, these low-lying clouds.

  • Everybody knows it's cooler under a cloud.

  • I like this cloud because it has exactly the same water content

  • as the transparent air around it.

  • And it just shows that even a little bit of a change in the flow of the air

  • can cause a cloud to form.

  • We make artificial clouds all the time.

  • These are contrails, which are artificial water clouds

  • that are made by the passing of a jet engine.

  • And so, we're already changing the clouds on earth.

  • By accident.

  • Or, if you like to believe it, by supersecret government conspiracy.

  • (Laughter)

  • But we are already doing this quite a lot.

  • This is a NASA picture of shipping lanes.

  • Passing ships actually cause clouds to form,

  • and this is a big enough effect

  • that it actually helps reduce global warming already by about a degree.

  • So we already are doing solar engineering.

  • There's lots of ideas about how to do this.

  • People have looked at everything,

  • from building giant parasols out into space

  • to fizzing bubble waters in the ocean.

  • And some of these are actually very plausible ideas.

  • One that was published recently by David Keith at Harvard

  • is to take chalk and put dust up into the stratosphere,

  • where it reflects off sunlight.

  • And that's a really neat idea,

  • because chalk is one of the most common minerals on earth,

  • and it's very safe -- it's so safe, we put it into baby food.

  • And basically, if you throw chalk up into the stratosphere,

  • it comes down in a couple of years all by itself, dissolved in rainwater.

  • Now, before you start worrying about all this chalk in your rainwater,

  • let me explain to you how little of it it actually takes.

  • And that turns out to be very easy to calculate.

  • This is a back-of-the-envelope calculation I made.

  • (Laughter)

  • (Applause)

  • I assure you, people have done much more careful calculations,

  • and it comes out with the same answer,

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

  • to undo the effects of the CO2 that we've already done --

  • just in terms of temperature, not all the effects, but the temperature.

  • So what does that look like?

  • I can't visualize 10 teragrams per year.

  • So I asked the Cambridge Fire Department and Taylor Milsal

  • to lend me a hand.

  • This is a hose pumping water at 10 teragrams a year.

  • And that is how much

  • you would have to pump into the stratosphere

  • to cool the earth back down to pre-industrial levels.

  • And it's amazingly little; it's like one hose for the entire earth.

  • Now of course, you wouldn't really use a hose,

  • you'd fly it up in airplanes or something like that.

  • But it's so little, it would be like putting a handful of chalk

  • into every Olympic swimming pool full of rain.

  • It's almost nothing.

  • So why don't people like this idea?

  • Why isn't it taken more seriously?

  • And there are some very good reasons for that.

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

  • And, in fact, I have some very good friends in the audience

  • who I respect a lot,

  • who really don't think I should be talking about this.

  • And the reason is that they're concerned

  • that if people imagine there's some easy way out,

  • that we won't give up our addiction to fossil fuels.

  • And I do worry about that.

  • I think it's actually a serious problem.

  • But there's also, I think, a deeper problem,

  • which is: nobody likes the idea of messing with the entire earth --

  • I certainly don't.

  • I love this planet, I really do.

  • And I don't want to mess with it.

  • But we're already changing our atmosphere,

  • we're already messing with it.

  • And so I think it makes sense for us to look for ways

  • to mitigate that impact.

  • And we need to do research to do that.

  • We need to understand the science behind that.

  • I've noticed that there's a theme that's kind of developed at TED,

  • which is kind of, "fear versus hope,"

  • or "creativity versus caution."

  • And of course, we need both of those.

  • So there aren't any silver bullets.

  • This is certainly not a silver bullet.

  • But we need science to tell us what our options are;

  • that informs both our creativity and our caution.

  • So I am an optimist about our future selves,

  • but I'm not an optimist because I think our problems are small.

  • I'm an optimist because I think our capacity to deal with our problems

  • is much greater than we imagine.

  • Thank you very much.

  • (Applause)

  • This talk sparked a lot of controversy at TED2017,

  • and we encourage you to look at discussions online

  • to see other points of view.

[A provocation from Danny Hillis:]

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B1 US TED chalk earth stratosphere hose optimist

【TED】Danny Hillis: Should we create a solar shade to cool the earth? (Should we create a solar shade to cool the earth? | Danny Hillis)

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    Zenn posted on 2018/05/01
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