To Cool the Earth, Plan Would Pull a Shade

A recently announced plan to reduce the effects of global warming would send a huge glass shield into space, lining it up to deflect 2 percent of the sunlight bound for the Earth. Robert Siegel talks with Roger Angel, professor of Astronomy and Optical Sciences at the University of Arizona, where he started the Steward Observatory Mirror Lab.

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ROBERT SIEGEL, host:

Roger Angel has an idea, and as ideas go, this is a pretty big one. Roger Angel is professor of Astronomy and Optical Sciences at the University of Arizona, where he started the Steward Observatory Mirror Lab, and his plan is to send a huge glass shield into space and line it up so that it deflects 2 percent of the sun's rays bound for the earth.

Professor Angel presented his idea yesterday to members of the National Academy of Sciences at their annual meeting.

Welcome to the program, and we should say the point about all this is to, in some way, arrest global warming and your idea, admittedly, is not something that's just going to be practical tomorrow.

Mr. ROGER ANGEL (University of Arizona): That's right. In fact, the idea is not so new, but what I have been doing recently is taking it seriously, just enough to understand if we ever did get to the point where we wanted to cool the earth because things were bad, then maybe we should have some tricks that we've looked at and understood about how to do it.

SIEGEL: So I'm trying to imagine an enormous shield of glass somewhere between earth and the sun. How far away would it have to be for it to stay put?

Mr. ANGEL: Well, it has to be at a very precise distance, which is about a million miles from earth, and there is a point there where you can orbit a spacecraft and it will stay permanently in line between the earth and the sun.

SIEGEL: It would not be opaque, I gather, or a mirror that would send the light back to the sun?

Mr. ANGEL: That's right. You could try making something like a mirror, which is what you might first think of, but it turns out if you make it very lightweight, the pressure of light from the sun upsets the orbit and it no longer will work there, so the idea of a glass screen is instead of blocking the light, we let it through, but we just bend it a little bit so it misses the earth.

SIEGEL: So that the light is diffused and much of it does not come straight at us.

Mr. ANGEL: It's a diffuse screen, yes.

SIEGEL: How big would such a screen have to be, in theory, for it to have any measurable effect on the earth?

Mr. ANGEL: A bit less than 2,000 miles across, so it's pretty big.

SIEGEL: So something on the order of the United States from the Appalachians to the Rockies would have to get it there, and how on earth could people someday put such a piece of glass up in space?

Mr. ANGEL: If we designed the glass to be as thin as possible, but still do its job, this thing would have to weigh about 20 million tons, and launch by rockets is precluded, both by the cost, but also by the environmental impact of making the fuel. You would actually make the problem worse instead of better. So you need some new way to launch the thing and there is a way for launching that's never been used because it requires a lot of upfront capital costs that, normally, you wouldn't justify it.

But if we have a million tons to launch, then this cost becomes okay. And so a magnetic launch, where you basically have a magnetic field that rises up a tube and pushes a piece of metal up, that looks as though it could, in this huge volume, be the cost that might be affordable.

SIEGEL: And you have brought for us an electromagnetic launcher here. It's straight out of WATCH MR. WIZARD, what you've brought us, and you're going to flip the switch in a moment, and is it a steel ring that's around it?

Mr. ANGEL: It's an aluminum ring.

SIEGEL: And aluminum ring?

Mr. ANGEL: And this is something that every physics student at the university sees, but if we turn on the magnet, then the current induced in the ring shoots it up in the air, and if I turn on the switch --

(Soundbite of electromagnet gadget)

SIEGEL: All right. Now, if I just imagine that aluminum ring being a few million times larger than it in fact is, I might imagine it, well, what could happen for us to launch the construction components of a glass shield into space.

Mr. ANGEL: Well, yeah, the ring that we would actually use for launching would be three or four feet in diameter and not a couple inches like this one and the tube to launch it would be a mile or so long, aiming straight up, and so we would be shooting out a couple of tons every five minutes for ten years, and if we do that with ten launches, then we get about 20 million tons.

SIEGEL: Now, when we reach the point of thinking it's worth it to put a multi-trillion-dollar glass band aid up into space between us and the sun, is that also a message that, for less money, we might be able to do things to produce less global warming right now?

Mr. ANGEL: Exactly, I would hope that if we start to take this idea seriously, then maybe cleverer people with other techniques will think of a way to do the job efficiently for less money. Certainly, it would seem that at least studying these ideas and understanding them is something we should be doing now.

SIEGEL: Well, Professor Angel, thank you very much for talking with us.

Mr. ANGEL: Thank you.

SIEGEL: And also for bringing the electromagnetic launcher with you.

Roger Angel, who is professor of Astronomy and Optical Sciences at the University of Arizona.

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