A landfill on fire doesn't only emit a horrid stench — it has devastating consequences for the environment, too. The culprit is methane, an often underestimated greenhouse gas produced in large part by food systems, organic waste and yes, cow burps. Biochemical engineer Marcelo Mena explains the source of this sneaky pollutant, why its emissions need to be cut in half by 2050 — and what you can do to help.