Supply and demand are most often thought of in the study of markets and economics. The concept is relevant to the environment as well, however. Each year, a mathematical calculation is made concerning the resources the earth has in comparison to the demand humans place on those resources. The equation is essentially the earth's biocapacity divided by the ecological footprint that humans create. The ecological footprint is the total amount of resources consumed. Multiply that by 365, and the answer is Earth Overshoot Day, the day in which the planet begins to run on credit.
Resources like grazing lands and crops, forest land to absorb emissions, land on which to build homes and infrastructure and oceans for more food sources. Environmentalists have only been calculating Earth Overshoot Day for about the last decade. Initially, it fell in October, but as resources have been depleted and the population has grown, the day gets earlier in the calendar each year, now falling at the beginning of August. It varies by location as well. The United Kingdom hit their overshoot in May of 2017, and smaller, less developed countries like Cuba will likely not come up against it until nearer to the end of the year. Experts estimate that the equivalent of 1.5 earths are used each year and that math just doesn't work for the long term.