How to cool the planet

Most scientists agree that global warming is real, but disagreement abounds about what to do about it.

The idea of taking carbon out of the atmosphere and storing it so that it can't warm the planet has been pretty widely discussed. Here are some techniques you might not know about; they involve large-scale geoengineering.

Basically, scientists are trying to figure out how to cool the planet by reflecting some of the sunlight back.

One idea is shooting sulfur particles into the stratosphere, which could decrease the temperature of the planet by about 2 degrees Celsius, said experts today at the American Association of the Advancement of Science meeting. Ken Caldeira of the Carnegie Institution says cooling methods like this are a little like chemotherapy for cancer patients - they solve problems, but have their own side effects.

A critic of this proposal, Martin Bunzl of Rutgers University, cautions that this approach could disrupt the monsoon cycle and potentially lead to famines. The dynamics of this on precipitation are also poorly understood, he said. In other words, it's like a doctor telling a patient "here’s something we can try" without knowing how it works.

"There’s a substantial risk of ecological effect," he said. "We don’t really know how long particles we put into the stratosphere remain in the stratosphere."

Another alternative is lightening clouds with sea salt. Philip Rasch of Pacific Northwest National Laboratory says the trade-off here is that you're getting brightening in local regions, whereas the sulfur method brightens the entire globe a little bit.

Right now a lot of what we know about these methods comes from computer modeling. Will they be feasible for the planet? More is yet to be learned.