David Keith is a climate scientist. And he thinks we might be able to save the planet by hacking into it. And how? Well, here's his proposal from his TED Talk.


DAVID KEITH: You could put - find particles, say sulfuric acid particles, sulfates, into the upper atmosphere, the stratosphere, where they'd reflect away sunlight and cool the planet. And I know for certain that that will work. Not that there aren't side effects, but I know for certain it will work, and the reason is, it's been done. And it was done not by us, not by me, but by nature.


UNIDENTIFIED MAN #2: A desolate and eerie landscape in the northwestern Philippines. It looks like the aftermath of a nuclear holocaust. Instead, it's the wrath Mount Pinatubo, a volcano that rained down over towns and farmlands, killing more than 300 people, leaving thousands more homeless. Casting a show over future...


KEITH: Here's Mount Pinatubo in the early '90s that put a whole bunch of sulfur in the stratosphere, with a sort of an atomic bomb-like cloud.


MAN #2: A mushroom cloud of steam, ash, and smoke rose 30 kilometers into the sky.

KEITH: Pinatubo, like many volcanoes, puts this huge cloud of ash in the air. And that's what people visually see.


MAN #2: As it settled, the debris blotted out the sun and coated hundreds of kilometers of Philippine countryside with what looked like snow.

KEITH: That ash is not the thing that changes the climate. What you can't see coming out of that eruption is sulfuric acid, or sulfate, that makes it up into the upper stratosphere, where it forms tiny little droplets, tiny fragments the size of a human hair, and those droplets become distributed around the hole of the upper stratosphere and so that reflected away some sunlight.


KEITH: Cooled the planet.

About half a degree.


KEITH: And the result of that was pretty dramatic. There's no big mystery about it. There's lots of the mystery in the details, but it clearly cools down, and one other thing, it's fast. It's really important to say. So a bunch of the other things that we 'ought to do, like slowing emissions, are intrinsically slow. So you can't step on the brakes very quickly. But if you do this, it's quick. And there are times you might like to do something quick.

RAZ: So we can do this?

KEITH: You could put sulfuric acid droplets in the stratosphere, in the upper atmosphere.

RAZ: Basically hack the stratosphere?

KEITH: Yeah. Essentially, to make a very thin cloud in the stratosphere. And these would be tiny little droplets, like a fine cloud, too small to see, that would reflect away maybe half a percentage or one percent of the sunlight coming in. It'd be pretty much invisible from the ground, but it would cool the planet.

So if you warm the climate up by adding carbon, as we've been doing for a century. And then you cool the planet back down to, say, its original temperature by adding sulfuric acid to the stratosphere, this brutally ugly technical fix of adding one balloon to offset another. If you did that you could get the globally average temperature back to be exactly what it was. Which is an amazing thing.

RAZ: It is amazing. So how would you get that sulfuric acid into the stratosphere?

KEITH: That turns out to be really easy. Suppose we want to cut global warming in half. You could start with just two aircraft, two modified fancy business jets that would operate from a single airbase and dump 20,000 or so tons of sulfur into the stratosphere every year. Now, of course, the amount of carbon in the atmosphere is increasing, so each year, if you want to cut the rate of warming in half, you have to keep adding more sulfur. So after a decade you'd be adding 200,000 tons of sulfur or more. And after 50 years, you'd be adding almost a million tons of sulfur a year into the stratosphere, and you would've cut the rate of global warming in half.


KEITH: You might argue about the sanity of it. But the leverage is real. Let's say that we don't do geoengineering, we do what we 'ought to do, which is get serious about cutting emissions. And maybe someday, like 2075, we finally reach that glorious day where concentrations have peaked and are rolling down the other side, and we have global celebrations and we've seen the worst of it.

But maybe on that day, we also find that the Greenland ice sheet is really melting unacceptably fast, fast enough to put meters of sea level on the oceans in the next 100 years, and remove some of the biggest cities from the map. That's an absolutely possible scenario. We might decide at that point that even though geoengineering was uncertain, and morally unhappy, that it's a lot better than not geoengineering.

RAZ: What is it going to take for us to get to that point, to try it? I mean, do you think we're going to have to be at crisis point where, like the oceans are rising really fast, and I don't know, Manhattan - half of Manhattan is into the water?

KEITH: I have no idea. I think that that's objectively a stupid way to do it. So many people want to frame this as a kind of - "break glass in case of emergency" strategy.

RAZ: Yeah.

KEITH: But I think, in fact, you don't want to try an untested technique like this only in case of emergency. You're much better off if you turn it up slowly, 'cause you have more chance of figuring out how well it works. So I think we'd be much better to start earlier and do it slowly.


KEITH: Now suppose that space aliens arrived on - maybe they're going to land at the UN headquarters down the road here. Maybe they'll pick a smarter spot. But suppose they arrive and they give you a box, and the box has two knobs. One knob is the knob for controlling global temperature, maybe another knob is a knob for controlling CO2 concentrations. You might imagine that we would fight wars over that box, 'cause we have no way to agree about where to set the knobs. You have no global governance. And different people will have different places they want it set. Now, I don't think that's going to happen. That's not very likely. But we're building that box.

The scientists and engineers of the world, they're building it piece by piece in their labs. Even when they're doing it for other reasons. Even when they're thinking they're just working on protecting the environment. They have no interest in crazy ideas like engineering the whole planet. They develop science that makes it easier and easier to do. And so I guess my view on this is not that I want to do it, I do not, but that we should move this out of the shadows and talk about it seriously, because sooner or later we'll be confronted with decisions about this and it's better if we think hard about it, even if we want to think hard about reasons why we should never do it.

RAZ: Say we could do this, right, and it worked, I wonder if it would sort of give us a license or give some people a license to feel like, well, they could just continue to pollute and not really worry about it.

KEITH: Of course it will. It's absurdly naive to think otherwise. When you make cars safer by crumple zones and better seatbelts and airbags, people drive relatively faster. When you give people condoms and AIDS drugs, they engage in more risky sex. This is called risk compensation and is well-known and not necessarily a rational piece of human behavior.

RAZ: Is there a part of you that kind of feels, I don't know, that, you know, this is kind of like a surrender. That we've failed the planet so much that we have to think about things like this.

KEITH: Absolutely. And I think that whether or not we ever do this at all, it forces us to ask some big questions about humanity and nature at the scale of the planet, which sounds overblown, but those are the questions we have to answer. We're living in a world where we have powers that give us the ability to treat the planet like a garden and the question is, are we going to throw the empty cans and garbage in the back and (bleep) all over it, or are we going to treat it like a garden we love?

RAZ: Do you think that this idea of basically hacking our planet to try and save it, it's also a triumph of human ingenuity, as well, isn't it?

KEITH: Yeah. Eli Kintish, a wonderful science journalist, wrote a book called "Hack the Planet." He talked about it as a bad idea whose time has come. As if, oh, it's this awful thing that now we have to talk about, and in many ways that's true, because we're talking about it partly because of our failure to cut emissions. But that seems somehow too - it seems like we're hiding something.

We're hiding a genuine and, I think, not wrong joy in the fact that we understand something about the world that potentially gives us the ability to do these things. That understanding that nature gives us power to do great harm as well as, potentially, power to do good. But the understanding is a triumph of human ingenuity and I think it deserves some celebration. although people are afraid to do that.


KEITH: So here's one last thought that the CO2 problem - the climate problem that we've heard about is driving lots of things, innovations and energy, technologies that will reduce emissions, but also, I think inevitably, it will drive us towards thinking about climate and weather control whether we like it or not. And it's time to begin thinking about it, even if the reason we're thinking about it is to construct arguments for why we shouldn't do it. Thank you very much.


RAZ: David Keith is a professor of public policy and engineering at Harvard. And he's the author of the forthcoming book called "A Case for Climate Engineering." You can hear his full talk at Stay with us. I'm Guy Raz. More hacking in a moment, here on the TED Radio Hour from NPR.

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