If everyone in the world lived like an American, we would need 3.9 planets

Humans are wiping out animals so fast that populations of mammals, birds, reptiles, amphibians, and fish are roughly half what they were in 1970, according to the World Wildlife Fund’s Living Planet Index (LPI), in its latest report (pdf). The index, which was compiled in partnership with the Zoological Society of London and the Global Footprint Network, tracks more than 10,000 populations of 3,000 different vertebrate species, bundling them the way you might with stocks to compose the S&P 500 or a basket of goods to calculate consumer price inflation.

The decline in animal populations since 1970 (WWF)

“Put another way, in less than two human generations, population sizes of vertebrate species have dropped by half,” said Marco Lambertini, the director-general of WWF International. “These are the living forms that constitute the fabric of the ecosystems which sustain life on Earth. We ignore their decline at our peril.”

Of all the animal in the LPI, those that live in freshwater—including everything from fish and frogs to otters and geese—have suffered the most. Their populations have fallen more than three-quarters since 1970—a rate that’s nearly double that of land and marine species, which have dropped by 39% apiece. The WWF blamed the dwindling of freshwater species on habitat loss resulting from hydropower dam construction, industrial pollution, and other human activity.

But to evaluate mankind’s broader impact, the report constructed something called the “ecological footprint,” which tracks how much land and water—which the report terms “biocapacity”—a single person requires to both produce the resources he consumes and absorb the waste he creates.

It turns out that climate change is also a big factor behind the decline in species, according to this analysis. In 1961 only 36% of humanity’s ecological footprint came from burning fossil fuels; by 2010, that share had soared to more than half.

“While biocapacity has increased globally, there is now less of it to go around,” the WWF said. For instance, that if every person on Earth had the lifestyle of the average resident of Qatar, we would need 4.8 planets. If everyone adopted American habits, we would need 3.9 planets.

But the blame doesn’t fall only on rich countries. Growing populations and wealth mean that even poorer countries are not living sustainably. If each human had the footprint of a South African, we would still need 1.4 planets. “Low-income countries have the smallest footprint,” the WWF notes, “but suffer the greatest ecosystem losses.”

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