Look up conservation of energy, and solar sails in wikipedia.
It would take as much energy to keep the “shade” in place (by using a rocket engine) as you are reflecting.

Next gain for the planet = 0

If it were made from a material like liquid crystals with a more than sufficient solar power source the transparency could be adjusted. That would hurt solar here big time though so that would need to be taken into account.

Bob, you bring up a good point, but I must assume that the people from the US National Academy of Sciences have taken that into account. It would be interesting to find out what are their thoughts on the problem. Not sure if they have put any of that online...

I wouldn't count on that much forethought from the NAS, and Dr MacCracken appears to be a climatologist not a physicist. Unless you have a copy of the NAS report?

I've seen these type of schemes for ages, and they never seem to address the law of conservation of energy or the solar sail affect. One has to wonder if this is just an attempt to grab a headline.

People keep forgetting that there is nothing to push on in space, and that the only reason anything stays in orbit is that it is moving at an incredible speed (aka: it has a lot of energy).

PS: Elvis: Space is an incredibly harsh environment. Solar flares, particles traveling near the speed of light, meteors and radiation makes for a very nasty place to leave anything. Electronics have to be specially engineer to survive. Your liquid crystals would quickly degrade or just be physically destroyed.

Mike: Lets talk after World Jump Day; None of this may be necessary.

Heh, Futurama thought of this before.

I thought Global Dimming(itself a result of pollution) -was countering the Global Warming!

Nice thinking. I am under the impression that it is easier to ">turn the Earth into a giant Christo installation though. You could also sell tickets to it to recoup the investment.

what? did nobody read Arthur Herzog's book HEAT? that was their solution back in 78' in a (so so) science fiction book.. and now Brig Gen ups the ante.. he wants the sun shades to be roboticised and made on the moon. 10 billion of them, made by lunar robots and hovering between us and the sun....

..and BTW global dimming; while most people still think that chemtrails are the product of one's tinfoil hat being on too tight--- the senator from Texas says it's been done for 25 years now and might as well now do the technology transfer tango...and she's not the only one

Reminds me of Znamya which was actually launched. That was a Russian space mirror pointed AT the Earth. It was trying to produce energy. One of many space based energy plans. Does not make anyone money and someone in the shadow would sue so I don't see it happening. We just don't understand the impact. Knowing a little about Chaos Theory, I would guess the sky would turn orange. World Jump day? Wow. Remember Hands Across America? If enough did, I am sure it could be measured like an Earth quake. Would be a great symbol for the power of groups i.e able to move the world. As for the Physics, we are actually CLOSER to the sun in Winter. Weather has more to do with the tilt of the earth to the sun. That episode of the Twilight Zone was wrong. There is actually snow on Mercury because parts are in the shade all the time. Jumping could change the tilt and not break angular momentum laws I guess. If one side did it or something but it is probably a joke. I know a lot of people say that's crazy and laugh but there was a time before Michelson-Morley (Einstein really did not do much) and Wright Brothers when we thought Physics had ended and man could not fly. Now we are in the world with the H-Bomb and a rover we control on Mars. So don't laugh too hard.

None of these proponent's appear to have a background in biology or medicine. Ponder if you will prospective inpacts on photosythesis, human biorithyms, spawning and migratory cycle re-boots, vitamin D synthesis, and lots more. This is a a ghost shirt mentality that will do more harm than good.

I think that if we're ever desperate enough to try something like an orbiting solar shield, it's because global warming will do ENORMOUS damage... So while it is true that solar shield might do damange themselves, at a certain point they might be the lesser of two evils.

This is all science fiction at this point, though.

lesser of TWO evils?? who decides that one Mike? Are there any more than two? are there any climate solutions that aren't evil? or are we just going to look at the solutions that let the average person do nothing and continue to libve in a way that we know is killing the planet? cause i can think of many non-evil solutions to climate change. it seriously gets me upset to see funds and energy spent on such stupid ideas (and sorry but it is STUPID).

Got a question for you.. ever been on a submarine? they have Carbon Scrubbers there (or else the crew would die of carbon monoxide) do you think it's chaper to have massive carbon scrubbers here on planet earth or is it cheaper to launch these screens into space?? There ARE people doing stuff in the climate, geoengineering field that are WAY MORE benign than some typical male problem solving (send up rockets!)they already have close to 4,000 barges pouring salt water onto sea ice to try to keep downwelling sites. there are ideas that are way less dangerous and arent bandaides. There are the Men of The Trees in Australia and Johanna Campe and armies of people who are remineralizing the biosphere (something that we will do.. or the ice will do, take your pick, it needs to be done!)

Calling it the lesser of two evils, is a slam in the face of people who are doing ACTUAL things on the planet to try to stave off the damages that are already happening let alone the next phase of changes that will happen. If life were a science fanstasy book this would be a great band aid. but on a planet where stupid monkeys make stupid short termn decisions, if we get to teh point where that is even an option i think there is no hope left for us.

@Bob: Next to conservation of energy you'll find 'conservation of momentum'. "0.5mv^2=mgy", which is to say that the the total force exerted by the photons striking the reflector can be balanced a change in orbit. You could also take advantage of a phenomenon known as "thermal transpiration" to adjust the orbit by varying the reflectance and absorbance of the material.

This idea was never far from crazy in terms of feasability. The problem is that you're still interfering with an environmental process. Doing it just to correct another environmental process is unwise. (Note: we still can't explain climate change. We have a pretty good idea of whats going on, but ask anyone tasked with building a computer model to explain climate, and they'll tell you it's more art than science when it comes to reproducing empirical data.)

Whoa there, take a breath.

This is totally about speculative science fiction. the only way that I see that this thing could be used would be if we were working on other things (such as the things you talk about, and the things that I write about all the time) but DON'T have time to implement them fully before a catastrophe. Solar shield - if such a thing ever exist - would be just a way to buy some time temporarily before the oceans die off and there's a great disruption in food production which makes whole ecosystems collapse and a run away feedback loop accelerates everything, or some such things (*that* might be the bigger of evils).

"who decides that one Mike?"

Hopefully not me or you.

Please, relax. We're all just discussing interesting stuff here, not passing binding legislation for the future.

Actually, MGR, this isn't sci-fi at all. In 2004, Russian scientists built a solar sale with a 1kmsq surface area. It was a technology demostrator for a full size version expected to have an area of 100 kmsq. The US Air Force has been deploying parabolic reflectors much smaller for years for signals intelligence satellites. If enough people were convinced that there was dire need, such a device as the article proposes could easily be built and deployed.

The technology exists. All that is needed is the initiative. I think its right that people have informed discussion on this before some do-gooder decides to put an umbrella on the northern hemisphere. (Wasn't there an episode of GI Joe about this?)

actually we do decide. we decide to stop these insane ideas or allow them to happen through complacency. And even saying (pretty much endorsing) that they are possible last-step in-case-of-emergency options is dangerous.

if we are to seriously takle food scarcity is itsn't by hiring Mr. Burns and getting his sun blaockers in place, it's by adapting to climate change that's what we've done for 2 million years, it's how we got to even stand upright. so it's evolve or extinct. those are the options. and evolution now may be societal and not biological, but it is certainly not by taking a high-tech stab at the dark!

"it's by adapting to climate change that's what we've done for 2 million years, it's how we got to even stand upright. so it's evolve or extinct. those are the options."

I have no doubt that humans can figured out a way to do that, but what about plants and animals? They can't use technology to get through that. Biological evolution is much too slow for them to adapt to a change that is taking place that fast. That's what I was talking about.

..that's why we need more biomimicry solutions for the rest of the non-human worls. Not tech insanity. That's why we need to get into analog forestry, and remineralization, and the rest. And most likeley, it will only happen once we're left this climate regime. But Mr Burns ain't gonna help you.

menawhile ask yourself what percentage of trees and fish made it through the last few major climate changes?

..that's why we need more biomimicry solutions for the rest of the non-human worls. Not tech insanity. That's why we need to get into analog forestry, and remineralization, and the rest. And most likeley, it will only happen once we're left this climate regime. But Mr Burns ain't gonna help you.

menawhile ask yourself what percentage of trees and fish made it through the last few major climate changes?

Wouldn't we get more bang for the buck by deflecting/concentrating light at the poles, as a mechanism for managing the feedback loop in polar albedo loss/gain?

So, the idea (if it became technically feasible) would be to mitigate global warming by accelerating global dimming - an equally devastating climatological disaster. Or, could we determine where to locate it or how and when to adjust it's efficacy as to manage that issue as well? We can't even introduce or control a single species of wildlife without properly considering and managing the consequences. The likelihood that we could properly consider and address all of the consequences of something as fundamental as altering the world's supply of solar radiation is nil.

As with every great ideas mankind tends to look at the large picture and quite often fails to see the small changes that could influence the biggest. This idea of obstructing the sun has potential but lacks feasibility. Although, the idea of influencing the sun is quite possible with both materials and resources. If we look at the greatest impacts in our environment then we should be looking at our oceans and what influences weathers around the globe. Many wonderful scientist have proven that global warming is impacted mostly by oceans temperature changing and polar caps degradation. If we could conceivable shade our polar caps with a filter to reduce the negative solar rays that help to melt off ice we could conceivable slow down the cycle. So lets look at the method. Building a solar shield would be great but has it difficulties, like materials and resources. Why doesn't mankind simply do what is been doing for centuries. Let " in a fashion " pollute the space between the Sun and Earth. We have the technologies to place materials like dirt or artificial in the path between the sun and earth. We would only have to place enough material close to the sun to shield the planed for short period of time as the material could be pulled naturally into the sun . We could select the best material to reduce certain type or ray wile letting other types pass true.

every notice those pesky "persistent contrails" we seem to be seeing more and more of?

Ever notice those 'persistent contrails' we seem to be seeing more and more of?>

Wouldn't it be cheaper and more environmentally benign to lauch hundreds of thousand of huge disk shaped silver balloons? They would float on the upper edge of the atmosphere providing similar reflectivity with a launch cost of next to nothing. Would perhaps make the undersides black so they didn't reflect heat radiating upwards.

Global wamring can be reduced and slowed by solar shields untill your giant carbon scubbers can be put on line. As to the fear of Global Dimming make you solar Screen retrackable so it can be opened and closed at will and when needed to keep things in balance. in addition why not add collectors to the back side of the shield and generate useble power supply that is unlimited we have the tech. As to Cost make the project world united becasue after all what we are trying to fight effects the entire world all have the same things to loose. Tax big Buiness not just the little poeple cause Industry is what put us in this possition to begin with. Get more trees planted produce and reseed algee in the seas. Make saving the earth a world project