Climate panic button: ecology scientist Ken Caldeira sheds light on some radical ideas for fighting global warming.

Among climate scientists, Ken Caldeira is a self-described troublemaker.

For instance, in a research paper delivered to the American Geophysical Union in December 2005, Caldeira annoyed tree-huggers and corporations alike by demonstrating that planting trees in most locations around the

"We like to be troublemakers and do simulations that come up with answers people don't like," Caldeira says.

Indeed, one such set of simulations produced results that Caldeira himself didn't like. Specifically, climate models developed at the Carnegie Institution's Global Ecology Department on the campus of Stanford University--where Caldeira serves as staff scientist--showed controversial "geoengineering" ideas effectively would counteract the effects of global warming, without major adverse side effects (see "Pulling the Shades on Global Warming"). Public Utilities Fortnightly caught up with Caldeira recently to discuss his perspectives on geoengineering and its possible role in strategies to address climate change.

Fortnightly: What's your perspective on geoengineering ideas such as those proposed by Edwin Teller, Freeman Dyson, and Roger Angel? Are these ideas as wacky as they seem?

Caldeira: They range from very wacky to less wacky. The wackiest ones involve putting shields in space, a million miles away, between the Earth and the sun. What's not so wacky is putting tiny particles, namely sulfates, into the stratosphere.

Fortnightly: I would've thought the space-shield idea was less risky than the idea of polluting the atmosphere with sulfur. After all, we've been trying to reduce S[O.sub.2] emissions for 30 years.

Caldeira: It's an economic issue. Carbon capture and storage technology, according to the IPCC [Intergovernmental Panel on Climate Change], might cost about $30 per ton of carbon. To achieve the equivalent cooling with spacecraft would require blocking roughly a square meter of sunlight 1 million miles out, per ton of carbon. Assuming it's even possible on the huge scale needed, the idea that you'd be able to do it for less than $30 a square yard is far fetched and wacky.

But putting about 100 cubic meters of sulfate or other tiny particles into the stratosphere would deflect enough sunlight to compensate for doubling the natural levels of C[O.sub.2], and you could keep that much stuff up there for a couple billion dollars a year.