The experts warn that if we don’t get carbon dioxide emissions under control and soon we could would face an catastrophic global warming event that could lead to a runaway green house effect. Once carbon dioxide is emitted it can stay in the atmosphere for a thousand years or more. International efforts to create a climate treaty have failed. It takes a lot of convincing to get people to give up the cheap energy source that is in fossil fuels and the wealth that they can generate. All indications are that the world intends to gamble on continuing to increase, not decrease the burning of fossil fuels.
Planetary scale engineering
Geo–engineering may be the only way that can reduce the effects of increasing green house gases and prevent a runaway green house effect. One idea that has been put forward is solar radiation management. You find some way to reflect solar radiation before it can get to the surface. Some have said that the cheapest way to do this would be to spray large quantities of aerosol particles into the stratosphere in order to reflect sunlight. This might work to manage solar radiation but it could have a lot of other undesirable effects like interacting in unexpected ways with chemistry of the atmosphere. It would be difficult to get international support for this method. Another method for solar management that was put forward is to build a massive solar shield to reflect sunlight into space. So far no one has taken this seriously since the rough estimates of size and cost of such a project seem out of reach.
The method that I have thought of to build a solar shield should be significantly cheaper and easier to build. The main components of this shield would be satellites and a thin reflective material. What you would do would be to build pairs of satellites. Each one would take a large roll of light-weight, but strong reflective material. This would be attached to a long bar like structure on the satellites. After the satellites reach their desired position they would then pull apart and unroll the reflective material so that it stretches-out between them. You should be able to have each pair covering a large area with this material, maybe a thousand km2 or more. They would also need to be smart enough to always be in a good position to block sunlight but also be able to avoid collisions. Small collisions by asteroids to the reflective material would only result in tearing a hole through it that could be repaired. Large collisions would be detected and avoided. You would want to position them in orbit over a polar region to have the most effect because the polar regions heat up faster and receive more solar radiation. You also wouldn’t want to block sunlight getting to solar energy locations.
Even with this cheap method of building a solar shield it would still have to cover a huge surface area. I have roughly estimated it to be somewhere from 3-5 million km2. At first glance then that makes the task seem impractical because it would require too much material to be launched into space and thus would be cost prohibitive. I believe that this problem could be overcome by gathering materials and fuel from near-earth asteroids and possibly the moon. We should probably use smart robotic craft like those sent on previous missions to asteroids.
Time to build
Do we have time? The carbon dioxide we emit today takes about 40 years to turn into future warming. We have currently warmed the planet about 1 degree C and are already seeing some changes to weather patterns and sea level rise. Some experts think that we have until about 2100 before we would get to a highly undesirable 2.5-3.5 C warming. So we have approximately 40-70 years to build the solar shield to manage solar radiation. I think that with enough effort it could be done over a 50 year span of time. Improvements in efficiently building could increase the surface area exponentially.
Since most of the work and materials gathering would be done in space or on the moon, it should have a negligible impact on the Earth’s environment. It would not take the place of reducing carbon dioxide emissions or reducing pollution in general. That is still extremely important to accomplish for many reasons other than warming. What this does is buy more time to reach the desired goal of zero carbon emission by replacing fossil fuels with alternative clean energy sources.
IPCC 5th assessment
NASA New Imagery of Asteroid Missions
If you use this idea I just ask that you give me some credit for originating it.