Our global climate is changing. There are many contributing factors to this change. One factor that is often ignored is soot: black and brown particles emitted by the burning of fossil fuels—diesel, coal, gasoline, and jet fuel—and the burning of solid biofuels—wood, manure, and dung (used for heating homes and cooking in many locations). Just like a black shirt worn on a sunny day, soot in the atmosphere absorbs solar radiation, heating the surrounding air. It also absorbs light reflecting off Earth’s surface—a double whammy for further warming. Unlike CO₂, which lingers in the atmosphere for decades, soot lingers for only a few weeks before being washed out. Thus, reducing soot emissions can be very helpful in slowing the trend toward global warming. How can soot emission be reduced?