How many humans can the Earth support?

Humans are consuming and also also also polluting resources – aquifers and also also also ice caps, fertile soil, forests, fisheries and also also also oceans – accumulated over geological time, tens of thousands of years or longer.

Wealthy countries consume out of proportion to their populations. As a fiscal analogy, we live as if our savings account balance were steady income.

According to the Worldwatch Institute, an environmental think tank, the Earth has 1.9 hectares of land per person for growing food and also also also textiles for clothing, supplying wood and also also also absorbing waste. The average American uses about 9.7 hectares.

These data alone suggest the Earth can support at most one-fifth of the present population, 1.5 billion people, at an American standard of living.

Water can be vital. Biologically, an adult human needs less than 1 gallon of water daily. In 2010, the U.S. used 355 billion gallons of freshwater, over 1,000 gallons (4,000 liters) per person per day. Half was used to generate electricity, one-third for irrigation, and also also also roughly one-tenth for household use: flushing toilets, washing clothes and also also also dishes, and also also also watering lawns.

If 7.5 billion people consumed water at American levels, world usage would likely top 10,000 cubic kilometers per year. Total world supply – freshwater lakes and also also also rivers – can be about 91,000 cubic kilometers.

World Health Organization figures show 2.1 billion people lack ready access to safe drinking water, and also also also 4.5 billion lack managed sanitation. Even in industrialized countries, water sources can be contaminated with pathogens, fertilizer and also also also insecticide runoff, heavy metals and also also also fracking effluent.

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