Sunshades for Global Warming

by Paul Gilster on April 5, 2007

Could a cloud of two-foot wide sunshades 60,000 miles long save the Earth from a global warming emergency? Roger Angel (Steward Observatory, University of Arizona) has been studying the idea of making the spacecraft out of micron-thick glass weighing one gram per sunshade. That’s the weight of a butterfly for each unit, but we’re talking about trillions of them out at the L1 Lagrangian point, an almost fixed zone in relation to Earth whose mild orbital instability can be overcome by onboard intelligence. Total sunshade mass: 20 million tons.

This article in the Arizona Daily Wildcat has more on the improbable concept and what Angel is doing today:

One of the big problems for the project is getting the total mass of all the sunshades into space…so Angel came up with using electromagnetic force to propel the spacecraft up a two-kilometer launch tube.

The launch tube would have a series of electrical coils that propel the rocket until it accelerates to escape velocity, about 25,000 mph, the speed needed to escape Earth’s gravity.

Hmmm… A two-kilometer tall launch tube would be an architectural marvel but prohibitive in cost, and the electromagnetic liftoff would likely shred the sunshades on the way up. With NASA funding terminated, Angel may not have time to work out these problems; he’s now looking for ways to keep us from having to use sunshades in the first place by tackling global warming here on Earth. If the shades are ever launched, though, don’t expect immediate results. One to two centuries seems to be a realistic figure for dropping carbon dioxide levels and lowering the heat.

ADDENDUM: A better way to put that last sentence would be: “One to two centuries seems to be a realistic figure for lowering the heat to compensate for greenhouse effects.” See Paul Dietz’ comment below.

And note this: Dr. Angel developed this concept as a potential solution to a planetary emergency, not as a final fix. He’s quoted on this in a Steward Observatory news release: “The sunshade is no substitute [for] developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out.”

Paul Dietz April 5, 2007 at 10:32

If the shades are ever launched, though, don’t expect immediate results. One to two centuries seems to be a realistic figure for dropping carbon dioxide levels and lowering the heat.

Huh? The shades would lower temperature by reducing sunlight hitting earth, not by reducing CO2 levels. The effect would be almost immediate once they were in place.

This class of concepts is related to solar sails, with an important difference: a shade, if placed near the Earth-Sun L1 point, doesn’t need to reflect light, it just needs to deflect it slightly (a degree or so). This could be done by small-angle scattering off scatterers much less than a wavelength wide, which could potentially require much less mass than a mirror or opaque absorber. The light pressure would also be much less (since little momentum is transfered) allowing a lighter system to remain in place. In theory, the mass could low enough to be affordably launched with conventional rockets (details of design and deployment left as unsolved problems.)

david April 5, 2007 at 11:04

Unless we use orion style vehicles putting 20 million tons into orbit
is way beyond anything we could hope to do. Even if it were the
trillions of dollars such a project would require might be better used
building a space based industry that once it is finished with the
sunshade could be used to build other interesting things. Such as
a human crewed vehicle that could study europa to see if there is
life there or not. Such a craft could actually be the seed for an
asteroid colony that …. (which is off topic)

It is possible for a 100 ton spacecraft to bring back 10,000 tons of
payload from an asteroid. (
That would mean 2,000 trips, or 200,000 tons lifted from the earth
into orbit. Less if such vehicles were reusable. Less since after
the first trip the fuel for such vehicles, which would be most of the
mass, could come from the asteroid. Though that would also mean
more trips.

The possibilities are endless. 20 million tons would be enough material
to provide shielding for 10 million square meters of habitat for a space

Sadly humanity seems to have other less constructive interests as its
main focus.

Paul Dietz April 5, 2007 at 11:14

A small angle scattering system could have a mass measured in thousands, not millions, of tons. Something innovative like magnetically confined charged dust particles might be workable (make the particles self-charging by photoelectric absorption, perhaps).

ljk April 5, 2007 at 12:26

How about sending up clouds of nanobots?

ljk April 5, 2007 at 12:29

One trillion nanosats to stop global warming?

To quote:

Researchers have proposed various alternatives for cooling the planet, including aerosol scatterers in the Earth’s atmosphere. The idea for a space shade at L1 to deflect sunlight from Earth was first proposed by James Early of the Lawrence Livermore National Laboratory in 1989.

“The earlier ideas were for bigger, heavier structures that would have needed manufacture and launch from the moon, which is pretty futuristic,” Angel said. “I wanted to make the sunshade from small ‘flyers,’ small, light and extremely thin spacecraft that could be completely assembled and launched from Earth, in stacks of a million at a time. When they reached L1, they would be dealt off the stack into a cloud. There’s nothing to assemble in space.”

Full article plus graphic here:

Administrator April 5, 2007 at 12:57

What I’d really like to do is get into Angel’s NIAC report to see what he says about the time needed for the sunshades to be effective, but the NIAC site again seems down. I hope this doesn’t presage the site — and all research reports — disappearing, but I have no confirmation yet either way.

Paul D. is right about my clumsy phrasing. I’m going to re-phrase the original post on that.

andy April 5, 2007 at 14:06

So, we send up a bunch of starshades and then we can go happily belching out greenhouse gases since we’ve got the planet temperature under control? Let’s just forget about OTHER effects of releasing pollutants, e.g. ocean acidification, which get far less media hype. I hate to think about the amount of pollution produced by launching these kind of systems into space.

Administrator April 5, 2007 at 14:29

I agree, Andy. And it’s got to be cheaper — and far better for the long haul — to fix these problems here on Earth once and for all. But I have no doubt Dr. Angel would agree with that — see the addendum to today’s post.

Paul Dietz April 5, 2007 at 14:44

What I’d really like to do is get into Angel’s NIAC report to see what he says about the time needed for the sunshades to be effective, but the NIAC site again seems down.

Well, you need to think about natural situations where temperature varies in response to changes in the amount of solar energy hitting the local environment, and how fast the temperature changes.

Maybe you can think of an example of such a situation this evening. :)

Administrator April 5, 2007 at 14:52

Point taken and enjoyed — yep, it’s getting cooler right now (almost 4 PM), and the Sun hasn’t even set yet! ;-)

Paul Dietz April 5, 2007 at 14:55

I agree, Andy. And it’s got to be cheaper — and far better for the long haul — to fix these problems here on Earth once and for all.

Perhaps better (shades don’t address ocean acidification, for example, nor the lessening of the equatorial/polar temperature gradient). Cheaper? Not necessarily. And easier? Not clear at all. Geoengineering solutions have the huge advantage of not requiring global cooperation, and could work even if warming-induced ‘natural’ CO2 and methane emissions make limiting direct anthropogenic emissions ineffective.

Eric S. April 5, 2007 at 16:44

Actually, the direction of the linkage between CO2 and temperature is at the center of the global warming discussion. Your original statement is correct if rising temperatures act to increase CO2, rather than the other way around.

– Eric.

Administrator April 5, 2007 at 16:53

Eric, thanks for that clarification. I’m out of my depth on the global warming issue, but take some solace from the fact that there are so many uncertainties involved.

Brian Wang April 5, 2007 at 17:12

Gregory Benford’s cooling plan seems to be the best so far.

“The political impossibility of what I call the prohibitionist agenda–that is, carbon prohibitionism–brings a kind of hallucinogenic quality to the global-warming discussion,” says Benford. “No economist I know believes that global carbon emissions can be restrained within a century to even the level we have now. Every economist knows that the timescale for changing energy infrastructure is at least half a century to a century, just because of replacement costs. Economists are scientists too, and ignoring them isn’t just blind: it’s perverse.”

Benford has a proposal that possesses the advantages of being both one of the simplest planet-cooling technologies so far suggested and being initially testable in a local context. He suggests suspension of tiny, harmless particles (sized at one-third of a micron) at about 80,000 feet up in the stratosphere. These particles could be composed of diatomaceous earth. “That’s silicon dioxide, which is chemically inert, cheap as earth, and readily crushable to the size we want,” Benford says. This could initially be tested, he says, over the Arctic, where warming is already considerable and where few human beings live. Arctic atmospheric circulation patterns would mostly confine the deployed particles around the North Pole. An initial experiment could occur north of 70 degrees latitude, over the Arctic Sea and outside national boundaries. “The fact that such an experiment is reversible is just as important as the fact that it’s regional,” says Benford.

Is Benford’s proposal realistic? According to Ken Caldeira, a leading climate scientist at Stanford University and the Carnegie Institution’s Department of Global Ecology, “It appears as if any small particle would do the trick in the necessary quantities. I’ve done a number of computer simulations of what the climate response would be of reflecting sunlight, and all of them indicate that it would work quite well.” He adds, “I wouldn’t look to these geoengineering schemes as part of normal policy response, but if bad things start to happen quickly, then people will demand something be done quickly.”

Given that our social systems would crash without the economic growth that depends on the existing energy infrastructure that we have, Benford personally believes that governments can’t be counted on to develop and deploy alternatives: “Anybody who thinks governments are suddenly going to leap into action is dreaming.” Benford says that one of the advantages of his scheme is that it could be implemented unilaterally by private parties. “Applying these technologies in the Arctic zone or even over the whole planet would be so cheap that many private parties could do it on their own. That’s really a dangerous idea because it suggests the primary actor in this drama will not be the nation-state anymore. You could do this for a hundred million bucks a year. You could do the whole planet for a couple of billion. That’s amazingly cheap.”

There are plenty of other plans

Administrator April 6, 2007 at 8:27

I dropped a note to Roger Angel about the time needed for cooling after deployment of his sunshade. Here’s his response:

“Not my area of expertise – you should ask a modeling expert. But I expect
both answers are right. The atmosphere has not much thermal inertia and
would respond (as it did to Pinatubo aerosol cooling) in less than a year.

“The oceans have a time constant more like a century, and just as they
will take a long time to heat up with greenhouse warming, the will take a
long time to cool off. Incidentally, I estimate it would take 10 years
minimum to launch all of the 20 million ton shield, and without
replacements, it would last around 50 years. It could be removed quickly
though. The cloud of spacecraft would dissipate in a few months if the
radio location beacons were switched off, or the individual elements could
be commanded to move off the Earth-sun line.”

Paul Dietz April 6, 2007 at 11:13

Eric S. wrote:

statement is correct if rising temperatures act to increase CO2,

The current rise in CO2 is clearly mostly not being caused by increasing temperature. It is being caused by combustion of fossil fuels (and, to a lesser extent, human destruction of biomass).

If rising temperatures in the future prompt additional CO2 release, this will only make the problem worse.

Administrator April 6, 2007 at 15:04

Brian, that Benford idea is fascinating — I hadn’t run into it before. Thanks for the tip! And I agree that the regional and reversible nature of this scheme makes it quite attractive in the event of a sudden climatic emergency.

Eric James April 6, 2007 at 22:21

Those are really neat and exotic sounding ideas, but how about a few low tech suggestions:

Grow trees, lots and lots of fast growing trees and vegetation.

Paint as many surfaces as possible, white.

Spread white sand, dust, and any other safe white groundcover materials, everywhwere.

Seed the clouds, regularly.

Build industrial sized CO2 scrubbers.

Use less energy.

Chris Wren April 8, 2007 at 0:30

Paul Dietz said: “If rising temperatures in the future prompt additional CO2 release, this will only make the problem worse.”

Actually one of the more ominous consequences of global warming is already looking to be the massive release of stored methane as northern permafrost thaws – and methane is a MUCH more powerful greenhouse gas than carbon.

pfdietz April 8, 2007 at 17:33

Large methane releases will also insert large amounts of water into the stratosphere, where a significant fraction of the emitted methane is oxidized. Ice crystals there are potent sites of ozone destruction. Increased GH gases also *cool* the stratosphere (a signal already being seen, and one not consistent with changes in the solar constant as the cause of warming) making it easier for ice to form there.

Stephen April 11, 2007 at 9:54

A two-kilometer tall launch tube would be an architectural marvel but prohibitive in cost,

You don’t have to build a 2 km tower. There are lots of mountains that tall. What angle do you want to toss it at? There’s probably a mountain just that angle. Need a mountain at the equator? Not a real problem.

ljk April 25, 2008 at 9:51

‘Planetary sunshade’ could strip ozone layer by 76%

New Scientist Environment April 24, 2008

Planetary engineering projects to
cool the planet could backfire quite
spectacularly: a new model shows
that a “sulphate sunshade” would
punch huge holes through the ozone
layer above the Arctic. To make
matters worse, it would also delay
the full recovery of the Antarctic
ozone hole by up to 70…

ljk October 5, 2010 at 21:35

Chronicle Online e-News

Geoengineering solutions could prevent irreversible climate crisis, study finds

Oct. 5, 2010
By Krishna Ramanujan

Geoengineering could prevent the potentially catastrophic climate-change tipping points that loom just ahead, reports a new Cornell study.

Cornell earth system scientist Charles Greene, the lead author of the study published in the September-October issue of Solutions magazine (Vol. 1, No. 5), says time is running out, yet governments have done little to reverse rising carbon dioxide (CO2) levels.

Many scientists warn that to avoid excessive warming, sea level rise and extreme weather, CO2 in the atmosphere needs to be reduced to 350 parts-per-million (ppm) by the end of this century from the current level of around 390 ppm.

If actions aren’t taken soon, ocean acidification and greenhouse warming in the atmosphere will reach a tipping point this century that will take more than 1,000 years to reverse, the paper warns.

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