I will post the following to www.conocophillips.com if I can get some more good ideas. Obviously the space elevator would be a big help with the 800 metric tons. Some experts are of the opinion that L1 = almost two million kilometers sunward from Earth is the best place for a solar shade. Others of us think LEO = low Earth orbit = about 500 kilometers above Earth's surface is best. Typical LEO satellites are shaded by  Earth 45% of the time. An approximation of a polar orbit, however is solar synchonous = The orbiting sun shade will stay over two PM or other time continiously as the Earth turns. This means the satellite is shaded only briefly over the North pole for a few minutes in November, December and January, and similarly over the South Pole in May, June and July. A thousand kilometer = 600 mile diameter sun shade would reduce Earth's average temperature by at least 0.9 degrees f = 0.5 degrees c, which may be more cooling than is desirable, assuming that 1/2 percent of Earth's sunlit surface is completely shaded by the satellite on the average = total eclipse. An L1 sun shade this size would appear as a tiny speck on the Sun and produce negligible cooling of Earth. I believe we can instal the shade satellite in solar sychronous orbit 500 kilometers above the surface by 2012, with lots of funding.
More details: A = 3.24 times radius squared = 3.14 times 250,000 square kilometers. At one kilogram per square kilometer, that is 800 metric tons of thin film in orbit. Spinning at one turn per day the disk of film will remain approximately flat, in spite of occasional holes made by space junk and micrometeorites. One kilogram per square kilometer is one milligram per square meter of film = 100 picograms per square centimeter. This is an average thickness of 10 nano meters, if my arithmetic is correct and the density of the film is 1. The disk will face the distant stars continiously unless we cause the axis of rotation to tilt 360 degrees per year to face the Sun, so that it can be an effectve sun shade. How do we turn this increadibly flimsy disk?   Neil

I am one of the people who propose putting the Sun shield at L1, but I must admit I do not understand how the polar orbit would work.  I have a few questions which maybe someone could answer
1) How far out is it if the orbit takes one year ?
2) Would this be cheaper to reach than L1 ?
3) Is the orbit eay to maintain in the correct orientation ?
4) What percentage of the time is the shield providing  useful cooling ?

A sun shade at L1 would appear as a tiny dot I agree but there is no problem with this and it would stop complaints from people on the ground that they are living in darkness. The cooling on Earth is still approximately the same as in LEO as the partial shadow almost perfectly covers the whole Earth side facing the Sun.

It is better to be prepared for a disaster that does not happen than be hit by a disaster that you predictred may not happen.
The best solution would probably be to reduce the growth in the worlds population so that we have a chance to handle all these disasters and oil shortages that are predicted.
At somepoint nature will not give us a choice in this matter and millions are going to die