Additional info from The Climate Reality ProjectSome people recognize that climate change is manmade, but are a bit confused about the main cause. “It’s methane from livestock,” they say. Or: “It’s waste heat from our appliances.” “It’s soot” is another. It’s true that each of these factors contribute to warming. But they are not the main cause of the global warming we’re seeing today. That prize goes to carbon dioxide, which we send into the atmosphere when we burn fossil fuels and cut down trees. Let’s take a step back and define the term “soot.” Soot is emitted when we burn wood, fossil fuels and other plant-based fuels. (Remember that coal, oil and natural gas are the remains of fossilized plants.) Soot is what coats the inside of a fireplace chimney, for example, or the tailpipe of a diesel truck. Soot is made of several kinds of particles, including something called “black carbon.” Black carbon is a solid form of carbon that absorbs incoming sunlight and outgoing heat (PDF). So as you might imagine, black carbon is pretty effective at warming the atmosphere. Black carbon is also good at warming the Earth’s surface. When black carbon falls on snow and ice, it absorbs sunlight and accelerates melting. Think about how quickly a dirty slush pile melts, compared to a fresh pile of snow. The problem is that ice-covered areas of the world help cool the planet by reflecting sunlight. The more ice that melts because of black carbon, the faster the world warms. Here’s where things get more complicated: Black carbon can also have a slight cooling effect! For example, black carbon can interact with clouds to reduce the amount of sunlight reaching the surface of the Earth. So while experts think black carbon has an overall warming effect, the exact amount of warming is not yet clear. Regardless of whether black carbon causes a lot of warming or just a little, it makes good sense to keep this pollution out of the air we breathe. We don’t need to go back to the Industrial Revolution to find examples of cities choked with soot and smog — just check out modern-day China. Thankfully, the fixes to the black carbon problem can help the climate and our health. For example, pollution controls on diesel trucks in the U.S. will make a big difference to the nearly 26 million Americans with asthma. And clean cookstoves can provide relief to the 3 billion people around the world who cook their daily meals with wood, coal or dung.