Earth Overshoot Day marks the date when humanity’s demand for ecological resources and services in a given year exceeds what Earth can regenerate in that year. We maintain this deficit by liquidating stocks of ecological resources and accumulating waste, primarily carbon dioxide in the atmosphere. Earth Overshoot Day is hosted and calculated by Global Footprint Network, an international think tank that coordinates research, develops methodological standards and provides decision-makers with a menu of tools to help the human economy operate within Earth’s ecological limits.
To determine the date of Earth Overshoot Day for each 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), and multiplying by 365, the number of days in 2015:
(Planet’s Biocapacity / Humanity’s Ecological Footprint) x 365 = Earth Overshoot Day
Measuring Ecological Wealth
Just as a bank statement tracks income against expenditures, Global Footprint Network measures a population’s demand for and ecosystems’ supply of resources and services. These calculations then serve as the foundation for calculating Earth Overshoot Day.
On the supply side, a city, state, or nation’s biocapacity represents its biologically productive land and sea area, including forest lands, grazing lands, cropland, fishing grounds, and built-up land.
On the demand side, the Ecological Footprint measures a population’s demand for plant-based food and fiber products, livestock and fish products, timber and other forest products, space for urban infrastructure, and forest to absorb its carbon dioxide emissions from fossil fuels.
Both measures are expressed in global hectares—globally comparable, standardized hectares with world average productivity. A hectare is equivalent to 10,000 square meters or 2.47 acres
Each city, state or nation’s Ecological Footprint can be compared to its biocapacity. If a population’s demand for ecological assets exceeds the supply, that region runs an ecological deficit. A region in ecological deficit meets demand by importing, liquidating its own ecological assets (such as overfishing), and/or emitting carbon dioxide into the atmosphere.
At the global level, ecological deficit and overshoot are the same, since there is no net import of resources to the planet.
The concept of Earth Overshoot Day was first conceived by Andrew Simms of the UK think tank New Economics Foundation, which partnered with Global Footprint Network in 2006 to launch the first global Earth Overshoot Day campaign. At that time, Earth Overshoot Day fell in October. WWF, the world’s largest conservation organization, has participated in Earth Overshoot Day since 2007.