In a breakout session here at Techonomy, David Keith of the University of Calgary and Margaret Leinen of the Climate Response Fund led a discussion of the prospect of geoengineering the climate—in other words, engaging in some type of deliberate intervention to alter the planet and thereby counteract global warming.

The reason scientists and policymakers are increasingly thinking about geoengineering is clear: Major climate change now looks increasingly unstoppable. As Leinen put it, even if the proposals on the table at Copenhagen had been adopted, we’d still end the century with an atmospheric carbon dioxide of 700 parts per million–more than enough to cause climate upheaval, raise seas dramatically, and so forth.

So it seems clear that if we can’t cut emissions, at some point we’ll be forced to consider a more radical alternative, at least if we want to preserve a planet anything like the one our species evolved on.

And as it happens, geoengineering does indeed appear to be on offer. According to Keith, the most popular and prominent idea for doing it—injecting sulfur particles into the stratosphere that would reflect sunlight away from the Earth, thereby causing a global cooling—could be begun almost immediately. “You could do this with current technology now,” Keith said, and he estimates that moreover, you could do so for about $ 1 billion a year. “Venice could pay to do it based solely on real estate prices,” said Keith. Read on….