Climate Central: Nobody wants to be a defeatist, but considering the rate at which nations are reducing emissions of heat-trapping greenhouse gases — which is to say very slowly, if at all — it’s not unreasonable to begin thinking of what else the world might do to avoid major climate disruptions. One idea that’s gotten increasing attention lately is geoengineering, a grab-bag of technologies that include doping the ocean with iron to fertilize carbon-eating algae. Most geoengineering schemes, …