Crutzen's plan is to inject about 1 million of sulphur a year into the stratosphere. The added layer of sulphates located 10 miles above the surface would increase the reflectivity of the Earth and add a "positive cooling effect".
One million tons is a small fraction of our emissions of sulphates into the lower atmosphere today: sulphur is a common pollutant that has been a major cause of acid rains, among other things. Crutzen's recent paper about these artificial volcanos has made the debate about this old idea much more serious: his Nobel prize helps, too. Even some environmentalist organizations offered their measured support.
I personally think that only insane people can promote the very expensive "solutions" of the "problems" today when the climate is actually cooling on the annual basis, no climate problem exists, and the proposed solutions don't solve anything except for crippling the economic growth. A wiser attitude to these matters would be to wait at least for 10 more years. In these 10 years, some people would be competing in developing the best possible technologies to control the climate.
After the 10 years, we would see whether we really need such a thing. My guess is that everyone will agree in 2016 that we don't need anything like that because the recent irrational hysteria will have faded away. But if the opinion will be different, there will exist realistic technologies to do whatever the civilization needs and the best technology may be realized in practice.
Helium 3 on the Moon
Incidentally, many sources recently discussed the existence of helium-3 on the Moon. Once we're capable to use the element for fusion, we could obtain some of it from the Moon. The Chinese space agency thinks that it is a good idea to become the first country to be able to do such things. NASA apparently discusses similar issues, too.