How can we slow down global warming? Reduce carbon emissions? How about dimming (使暗淡) the sun? Bill Gates, the former CEO of Microsoft, wants to spray (喷) millions of tons of chalk (白垩粉) into the stratosphere (平流层) to reflect sunlight and slow global warming, the Daily Mail reported. American scientists will test the system by sending a large balloon 12 miles (about 19.3 km) above the Earth and have it drop two kilograms of chalk dust into the stratosphere. The idea is to have the chalk deflect (使转移) a portion of the sun’s radiation (辐射) to cool the planet.