While cosmic accident or climate change used to be the cause of such biological cataclysms, humans alone are responsible for nearly every loss of species in the past few thousand years. Since the advent of Homo sapiens, Wilson says, extinctions have occurred 100 to 100,000 times faster than before, principally because we have degraded and destroyed forests, spread agriculture, introduced animals into new environments, and polluted the air, water, and soil. There are at least 10 million species on Earth, and experts estimate we're killing 30,000 of them each year, a pace that appears to be increasing. Some scenarios predict that nearly 50 percent of all living species could be lost in the next 50 years. Think of an Earth without elephants, orangutans, giant pandas, rhinoceroses, dolphins, macaws, frogs, frankincense.
Habitat loss is the single biggest problem.
In Hawaii, two thirds of the original forest cover has been destroyed, half of the islands' 140 native bird species are extinct, and 30 more are endangered. Birds of wider range are dying too. The Spix's macaw, native to Brazil, is down to a single individual in the wild, and the ivory-billed woodpecker, which once ranged over the southeastern United States, is probably gone altogether. Twelve percent of all surviving bird species worldwide are endangered, reports a BirdLife International study. Roughly a quarter of the world's plant species will be threatened over the next few decades, says Peter Wyse Jackson, of Botanic Gardens Conservation International.