During the last several centuries we have burned through eons worth of fossilized sunshine, changing the climate for our fellow species. We use more than half of the planet’s unfrozen land for cities, logging or food, eliminating the habitats of our fellow animals and plants. Before we even achieved civilization, we had already helped hunt the biggest, fiercest animals—woolly mammoths, giant kangaroos and giant sloths—to extinction.
Biologists and paleoecologists estimate that humans have driven roughly 1,000 species extinct in our 200,000 years on the planet. Since 1500 we have killed off at least 322 types of animals, including the passenger pigeon, the Tasmanian tiger and, most recently, the baiji, a freshwater dolphin in China. Another 20,000 or more species are now threatened with extinction according to the International Union for the Conservation of Nature, which keeps a list of all the known endangered plants and animals on the planet. The population of any given animal among the five million or so species on the planet is, on average, 28 percent smaller, thanks to humans. And as many as one third of all animals are either threatened or endangered, a new study in Science finds.
The biggest, fiercest animals still left on the planet—elephants, tigers, whales, among others—are most at risk. And we humans have shown no inclination to stop the activities—overexploitation for food, habitat destruction and others—that drive extinction.
To avoid the sixth mass extinction we will probably have to employ more aggressive conservation, such as moving species to help them cope with a changing climate. Think re-wilding: reintroducing species like wolves or beavers that were once present in a given ecosystem but have since disappeared. Aggressive conservation might also mean killing off newcomer species to preserve or make room for local flora and fauna; in New Zealand, rat extirpations have helped kakapos survive.