Scientists plan to use geoengineering — capturing carbon from the air, and spraying aerosols to dim sunlight — to stave off theorized global warming. Undeterred by steep cost and the interminable controversy on the very concept of global warming, scientists will again experiment with geoengineering — as a means to bolster the effect of cloud cover by seeding the atmosphere with chemicals meant to dim the light of the sun — in a concerted effort to cool the planet.