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.
To determinate 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), byhumanity’s Ecological Footprint (humanity’s demand for that year), and multiplying by 365, the number of days in a year:
(Planet’s Biocapacity / Humanity’s Ecological Footprint) x 365 = Earth Overshoot Day
If the resources are renewable because they should run out?
The essential characteristic of a renewable resource is that its quantity is not fixed and can be increased (or reduced) if the stock of this resource is allowed to regenerate.
Nevertheless, there is a maximum quantity, in the sense that no renewable resources can be replicated at levels above the subsistence capacity of the ecosystem in which they live. It is easy, therefore, easy to exhaust a renewable resource if the utilization rate continuously exceeds the natural growth rate of the resource.
Tradition has it that even resources that have continuous flows over time are called renewable: solar energy, waves or tides are examples of continuous flow resources.
Example of easy comprehension:
To better understand how a resource can run out of time, let’s take a practical example.
Consider a single species of fish, the quantity of which increases over time.
The number of fish multiplies over time (1, 2, 3), but when they start competing for food their rate of growth is reduced (3, 2, 1) up to a maximum point which is represented by the maximum livelihood capacity for that species. When the food reaches to be below the minimum threshold the species extinction takes place.
Data updated to 2018 confirm that resources of 1.7 times the annual regenerative capacity of the planet are currently consumed; we can estimate that by proceeding at this rate, by 2050, humanity will need to consume twice as much as the Earth produces.