concept

Planetary boundaries

A scientific framework (Rockström et al., 2009) identifying nine biogeochemical systems that regulate Earth's stability, each with a threshold inside which humanity has a "safe operating space." To cross a boundary - too much carbon in the air, too high a rate of extinctions, too much fixed nitrogen flooding in - is to shove the system out of the stable equilibrium that defined the Holocene, the 12,000-year calm in which all of human civilisation was built. The framework turns the abstract notion of a self-regulating planet into something measurable: the dial has walls, and we have already pushed several of them.