I think Nathan Myhrvold [1] proposed something like this. There's a summary of it on one of the Freakonomics podcasts, but the summary is basically that it acts like an erupting volcano to cool the earth slightly.

"MYHRVOLD: So, climate change is a 1-percent effect. Now all we have to do is make the sun 1 percent dimmer. Now I don’t literally mean changing the sun. But there are a variety of things that bounce sunlight back into space. Clouds are one of those things: white clouds bounce white light back up into space. It turns out that volcanoes throw ash and particles, if it’s a big volcano, very high in the atmosphere. That reflects some of that light. And in fact this happened in 1991 when Mount Pinatubo went off. It cooled worldwide temperatures by a degree, degree-and-a-half-Fahrenheit for 12 to 18 months. Well, my company has come up with some very practical and cost-effective ways of deliberately putting particles into the upper atmosphere. And on paper, it works out that you could nullify all of global warming that way." [2]

[1] http://www.nathanmyhrvold.com/ [2] http://freakonomics.com/podcast/save-the-planet/