Climate change is about big things: melting ice sheets, rising seas, the feverish temperature of the planet. But scientists say it’s also about little things — namely, microbes. Everywhere you look on Earth, you’ll find these single-celled organisms making a living. And in the process, they produce and consume greenhouse gases including carbon dioxide, methane and nitrous oxide, helping to control the concentration of these planet-warming substances in the atmosphere. Collectively, they play an enormous role in regulating the climate.