Tom, Ron, Bob and Gary,
Sometimes an idea grows on you. I know I'm no expert in the areas I am going to address, so it's very likely any one of you will explain quickly how wrong this is. Nevertheless, the idea has not gone away, so I'm writing.
1. Some Assumptions
a. Global climate change is real, and significantly caused by burning of fossil fuels. This is the scientific assumption. There are zillions of details involved, which I am glossing over. People can debate furiously which predictions are most likely right.
b. Global climate change will produce significant changes that will cause difficulty for people. In other words, people would be better off if climate change could be slowed or stopped.
c. Lots of opinion leaders, both scientific and political, have called for action to stop or slow climate change by burning less fossil fuels.
d. The current global system of governance (several major, independent, mutually suspicious actors: the US, China, the EU, Russia, Japan, India--along with lots of lesser, but important nations) does not allow for coordinated political action necessary to significantly reduce burning of fossil fuels.
2. A Conclusion
The policy changes called for by scientific and political leaders will not be enacted in time to prevent very damaging climate changes. The details that I glossed over in 1a become important here. Maybe climate change won't be so severe. Maybe it won't be damaging. So my conclusion should be restated: Probably the policy changes advocated by the loudest voices, scientific and political, to combat climate change will fail to prevent very damaging climate changes.
3. Comments on assumption 1d. The key factor here is that China, and to a lesser extent India, will not cooperate with a carbon emissions scheme that gets in the way of rapid economic expansion. The global "haves" (the US and the EU) are beginning to slow or reduce carbon emissions. But Russia has no motivation to slow oil & gas production, since that is their main export. China argues, with some justice, that the "haves" used fossil fuels to build their economies and it is unfair to keep China from doing so as well.
It's possible that UN leadership will bring China and India into line, that the "have" nations will pay to help China and India develop without fossil fuel dependency. (How??) But I am skeptical. I don't think the current political situation in the world will succeed in meeting the challenge of global climate change. It's unfortunate that world leaders must simultaneously face the challenge of Muslim extremism; fighting terrorism naturally takes much of their attention.
If the current proposal won't work, we need some other way to attack the problem of global climate change. It would be nice if a new proposal had the advantage of not asking the Chinese to slow their economic growth so that the rich countries can enjoy what they've already got. It would also be nice if the new proposal didn't require huge changes in the global political system. (Huge changes in the global political system will come someday, but I don't think addressing climate change should hang on that.)
5. The proposal: build a million umbrellas.
Look at the problem from a solar system perspective. The earth is the target of the sun's radiation. The diameter of the earth is roughly 8,000 miles. That means light from the sun strikes a target of approximately 50,000,000 square miles (radius squared times pi). Solar radiation is by far the greatest source of energy on the planet. Solar radiation is either reflected back into space or absorbed by the atmosphere and surface of the planet. As I understand it, global warming is caused by changes in the chemical make-up of the atmosphere which causes a small increase in the energy trapped into the planetary system. (Small, that is, when compared with the enormous amount of energy striking the earth. This "small" increase in trapped energy is enough to play havoc with the climate.)
The current policy proposal is to stop polluting the atmosphere with heat trapping emissions. What if we tried to block some of the solar radiation?
Imagine a solar umbrella. It is carried into orbit by an unmanned rocket, just like most of our satellites. Once in orbit, the package unfolds an extremely thin material on an extremely light frame. The umbrella has a diameter of a little more than a mile; its total surface area is 1 square mile. The umbrella reflects solar radiation that would have hit the earth back into space.
A million such umbrellas would represent 2% of the target area of solar radiation hitting earth. Of course, if the umbrellas were larger, we wouldn't need so many. If the umbrellas were more sophisticated, they could be controlled from earth in some way to allow more radiation at some times and less at others. The umbrellas would not need to be in low earth orbit. There should be an internationally agreed "umbrella zone" for the umbrellas to fly in. 1000-2000 miles up? Half of the time, the umbrellas would be on the night side of the planet, so we might need to double my numbers.
a. China and India could burn coal and publicize all their umbrella launches as compensatory behavior. It would give the Chinese space program something useful to do.
b. In general, the umbrella program gives the rich and powerful something to do as opposed to changing something they are comfortable doing. Producing, installing, and monitoring space umbrellas will be big business.
c. Air pollution is still air pollution. Space umbrellas don't make air breathable. We still would need governmental programs to discourage pollution.
d. Someone will object: but now you're playing God with the climate! Answer: of course we are, and we have been since we discovered that coal will burn. The current policy proposal (somehow change fossil fuel usage worldwide) is merely a different way of playing God with the climate.
e. If visible from earth, space umbrellas will change the night sky forever. Poets should be consulted.
7. Questions I thought of. I'm sure there are others.
a. Is it possible and realistic to build space umbrellas? This is an engineering question, Gary.
b. Am I too pessimistic about international cooperation in regard to carbon emissions? Tom and Ron, this is for you.
c. Would blocking 2% of solar radiation be enough to prevent and/or slow climate change? Bob, we're looking at you.
The biggest question is: what obvious errors am I making?