By adding up all of those withdrawals, we can calculate the human footprint on the planet—a measure of how much we are using the Earth’s natural resources. The withdrawals come in six categories:
- Carbon: A measure of carbon emissions, represented by the amount of forest land that would be needed to sequester carbon dioxide emissions, not including the fraction that is absorbed by the oceans and leads to acidification.
- Cropland: The amount of cropland used to grow plants for food, fiber, animal feed, and commodities including oil, soy and rubber.
- Grazing land: The amount of grazing land used to raise livestock for meat, dairy products, hide and wool.
- Forests: The extent of forests required to supply timber, pulp and fuel wood.
- Fishing grounds: The estimated primary production required to support the fish and seafood caught in freshwater and marine environments.
- Built-up land: The amount of land covered by human structures, including transportation, housing, industrial structures and reservoirs created by dams.
At the same time, we calculate the planet’s total biocapacity—Earth’s ability to produce natural resources, provide land for humans to build on, and absorb waste such as carbon emissions.
Put the two numbers together and the problem becomes increasingly clear. It takes a year and a half to generate the resources that the human population uses in only a year. Simply put, this is not a sustainable path for our planet’s future.
Another way to look at this is to say that it would take 1.6 Earths to produce all the renewable resources we use. And worse, the human population is expected to use the equivalent of 2 Earths of renewable resources per year by 2050. The effect of this overuse is a growing scarcity of resources—2.7 billion people, for example, already face water scarcity at least one month out of the year.