How Earth Overshoot Day Is Calculated
Every year Global Footprint Network calculates the number of days of that year that Earth’s biocapacity suffices to provide for humanity’s Ecological Footprint. The remainder of the year corresponds to global overshoot. Earth Overshoot Day is computed by dividing the planet’s biocapacity (the amount of ecological resources Earth is able to generate that year) by humanity’s Ecological Footprint (humanity’s demand for that year). This ratio is multiplied by 365 to get the date when Earth Overshoot Day is reached:
(Planet’s Biocapacity / Humanity’s Ecological Footprint) x 365 = Earth Overshoot Day
The estimated level of resources and ecosystem services required to support human activities today is just over 1.7 Earths. Since 1961, the first year consistent United Nations statistics were available, humanity’s demand on resources has gone from being within the means of what nature could support to significantly over budget. Our planet went into global overshoot in the early 1970s.
On a positive note, the rate Earth Overshoot Day has moved up on the calendar has slowed to less than one day a year on average in the past five years, compared to an average of three days a year since overshoot began in the early 1970s.