How many Earths do we need?

 

It has been suggested that if everyone on the planet consumed as much as the average US citizen, four Earths would be needed to sustain them. But where does this claim originate, and how is it calculated?

The world's seven billion people consume varying amounts of the planet's resources. Compare the lifestyle of a subsistence farmer with that of a wealthy city-dweller in a developed country. More land is required to grow the city dweller's food, more materials are used to build the city dweller's home and workplace, more energy is required for transport, heating and cooling.
So it's obvious that Americans consume more, on average, than the people of less developed countries. But the claim that four Earths would be needed if everyone lived like Americans is still a striking one.
It has been recurring on social media at least since 2012, when science writer Tim De Chant produced this infographic illustrating how much land would be required if seven billion people lived like the populations of nine selected countries from Bangladesh to the United Arab Emirates.