Everyone knows that too much carbon dioxide is bad. It warms our planet, raises sea levels, and generally wreaks havoc on our environment (why leaders all over the world have gathered in Paris this week to talk about carbon emissions). Now, scientists have discovered a different way that CO2 harms us: if we’re exposed to too much of it indoors—like in an office—it hurts our ability to think, which may ultimately affect both our well-being and our job performance.