The ecological footprint is a measurement of how fast humans consume resources and generate waste compared to how fast nature can absorb the waste and generate new resources. Since the late 1970s, humanity has been in ecological overshoot; i.e., the annual demands on nature exceed what the earth can generate in a year. It currently takes the earth one year and five months to regenerate what is used in one year. Mathis Wackernagel (1962–) and William Rees (1943–) developed the concept of the ecological footprint in 1990.