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Last fall, scientist and provocateur David Keith offered one of the most conversation-provoking TEDTalks ever — calmly discussing ideas for geo-engineering our climate that border on shocking (like shooting a cloud of sulphurous particles into the stratosphere to simulate the cooling effects of a major volcanic eruption). It’s a scary subject, but as Keith pointed out, someone, someday, is going to think that major geo-engineering is a very good idea. (As a commenter said just this morning: “/sigh.”)

Now Philip Boyd of the National Institute of Water and Atmospheric Research in Dunedin, New Zealand, takes the next step in the New Scientist, and ranks the major ideas in geo-engineering by risk, cost, speed of implementation, and how well they would work. The chart above comes from Nature Geoscience, which is behind a paywall, but the kind bloggers at The Great Beyond share it.