This Scientist Wants to Block the Sun to Cool the Earth

David Keith was a graduate student in 1991 when a volcano erupted in the Philippines, sending a cloud of ash toward the edge of space.Seventeen million tons of sulfur dioxide released from Mount Pinatubo spread across the stratosphere, reflecting some of the sun’s energy away from Earth. The result was a drop in average temperatures in the Northern Hemisphere by roughly one degree Fahrenheit in the year that…