The world has a poop problem. In the U.S., the challenge is biggest on farms: livestock produces more than a billion tons of solid waste a year, or roughly 87,000 pounds of shit a second. That’s more than 130 times greater than the amount of human waste that goes into sewers. Farm waste—especially on large industrial feedlots—often ends up polluting nearby drinking water and contributes to a significant chunk of greenhouse gas emissions. Researchers at the University of California are working on turning piles of poo into something useful—fuel that can run in ordinary cars instead of gas. It’s carbon-neutral and renewable.