Report: Humans have killed half of all vertebrates since 1970

The new Living Planet Index report from the World Wildlife Fund opens with a jaw-dropping statistic: We’ve killed about half the world’s nonhuman vertebrate animal population since 1970.

The main culprits? Exploitation (i.e., overfishing and overhunting) and habitat degradation.

The WWF data show that species population declines vary by habitat and geographic area. Tropical areas had greater declines, while temperate regions — such as North America — had lesser drops. Habitat-wise, land and saltwater species had declines of roughly 39 percent. But for freshwater animals — frogs, fish, salamanders and the like — there was a considerably sharper 76 percent drop. Habitat fragmentation and pollution (think algae blooms) were the main killers of freshwater species.

The declines are almost exclusively caused by humans’ ever-increasing footprint on the planet. “Humanity currently needs the regenerative capacity of 1.5 Earths to provide the ecological goods and services we use each year,” according to the report.

Carbon consumption — the burning of fossil fuels — represents a huge and growing chunk of the demand we put on the Earth. “In 1961, carbon was 36 percent of our total footprint, but by 2010 (the year for which the most complete data set is available), it comprised 53 percent,” the report says.

At the country level, China is now the leading drain on the earth’s resources. China accounts for nearly 20 percent of the overall demand, with the United States a distant second at 13.7 percent.

There are compelling reasons why we should consider the fate of the world’s nonhuman species an urgent issue. For starters, many are economically valuable in their own right. Bees, for instance, are crucial to agriculture in the United States.

We’re also set to add another 2.4 billion humans to the world’s population by 2050. Those people are all going to need water to drink, places to live and food to eat.