So we know that humans are unintentionally altering the planet's climate by increasing the atmospheric concentration of CO2. The ideal solution to this would simply be to stop emitting so much CO2 and stabilize the atmospheric concentration at a safe level (and there is some debate what this level would be, likely in the 350-450 ppm range. Currently it's around 385 ppm and rising at a rate of around 2 ppm per year).
Another possible solution is to introduce a second human-caused effect to counteract that of CO2. For example, we could send a bunch of aerosols into the atmosphere (which block sunlight), or put some massive mirrors into orbit.
The problem with geo-engineering is that the solutions are generally very expensive, and could cause dangerous side effects that we don't anticipate.
After speaking at the AGU conference this week, James Hansen was asked “The genie is out of the bottle now — What do you think of geoengineering as a way to deal with global warming?”. He responded that it would make sense to try “soft” geoengineering first, such as no-till agricutlure and afforestation. But as a last resort, Hansen admitted, more aggressive geoengineering schemes might be necessary.
Joseph Romm's take is that as a climate-saving strategy geo-engineering is largely somewhere between a dead end and a hoax — why would you choose chemotherapy that might make you sicker if your doctors told you diet and exercise would definitely work.
John Holdren, Obama's likely new science advisor has said “The ‘geo-engineering’ approaches considered so far appear to be afflicted with some combination of high costs, low leverage, and a high likelihood of serious side effects.”
More about this on ClimateProgress.
Personally, I tend to feel similarly to Romm and Holdren. I don't like the idea of manipulating the Earth's climate because of the possibility of nasty unintended consequences. But Hansen could also be right that if we fail to sufficiently reduce CO2 emissions, geo-engineering might become a last resort.
What are your thoughts on the subject?