On June 15, 1991, Mount Pinatubo erupted in the Philippines, sending around 5 cubic kilometers (1 cubic mile) of mountaintop into the atmosphere. Some of that material, mostly sulfuric acid and ash, rose 20 kilometers (12 miles) into the stratosphere and repeatedly circled the globe. The result: the volcanic eruption reflected sunlight and cooled the Earth by 0.5° Celsius (0.9° Fahrenheit) for several years. Some scientists for a couple of decades now have been considering whether or not humans could — orshould — attempt to artificially replicate the effects of volcanic eruptions like Pinatubo…