Gregory Benford's proposal for climate re-engineering is discussed at future pundit The Benford proposal possesses the advantages of being both one of the simplest planet-cooling technologies so far suggested and being initially testable in a local context. He suggests suspension of tiny, harmless particles (sized at one-third of a micron) at about 80,000 feet up in the stratosphere. These particles could be composed of diatomaceous earth.
Benford says treating the Arctic would cost only $100 million per year. You could do the whole planet for a couple of billion.