August 20 is Earth Overshoot Day 2013, marking the date when humanity exhausted nature’s budget for the year.

It is the annual marker of when we begin living beyond our means in a given year. Ecological Debt Day is calculated by dividing the world biocapacity (the amount of natural resources generated by Earth that year), by the world Ecological Footprint (humanity’s consumption of Earth’s natural resources for that year), and multiplying by 365, the number of days in one Gregorian calendar year:

（World Biocapacity/World Ecological Footprint）× 365 = Ecological Debt Day

When viewed through an economic perspective, Ecological Debt Day represents the day in which humanity enters deficit spending, scientifically termed “overshoot”. While only a rough estimate of time and resource trends, Ecological Debt Day is as close as science can be to measuring the gap between human demand for ecological resources and services, and how much Earth can provide.