The Washington PostDemocracy Dies in Darkness

We’ve killed off half the world’s animals since 1970

Photo by Flickr user <a href="" target="_blank">Andreas Kay</a> , used under a CC license.

The new Living Planet Index report from the World Wildlife Fund opens with a jaw-dropping statistic: we've killed roughly half of the world's non-human vertebrate animal population since 1970.

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

The WWF data show that the species declines vary by habitat and geographic area. Tropical areas saw greater declines, while temperate regions - like North America - saw lesser drops. Habitat-wise, land and saltwater species saw declines of roughly 39 percent. But freshwater animals - frogs, fish, salamanders and the like - saw 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 planet earth. "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. The only reason we're able to run above max capacity - for now - is that we're stripping away resources faster than we can replenish them.

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 per cent of our total footprint, but by 2010 (the year for which the most complete dataset is available), it comprised 53 per cent."

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 U.S. a distant second at 13.7 percent.

There are compelling reasons why we should consider the fate of the world's non-human species an urgent issue. For starters, many are economically valuable in their own right. Bees, for instance, are crucial to agriculture in the U.S.

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. Many of them will be born in poorer, more rural regions of the world, regions where people are more dependent on the land and its resources to survive.

Closer to home, we're already starting to see the effects of water shortages out West. Smarter water use will lead to less freshwater habitat degradation, which in turn will hopefully lead to a slowing of the decreases in freshwater species populations.

In short, you may be inclined to see species loss as a problem worth addressing on its own merits. Or, you may prefer to consider it as a symptom of larger environmental problems that are already starting to affect our lifestyles and our pocketbooks. Regardless, the WWF report presents a compelling case that it's something we should be paying closer attention to.