India, March 3 -- Halting the loss of biodiversity is one of the greatest conservation challenges of the 21st century. Despite decades of effort, the pace of decline shows little sign of slowing. Since the 1990s, ecologists have warned of an impending mass extinction. It would be the Earth's sixth-but unlike any that has come before. Today's crisis is driven by a potent mix of pressures: climate change, pollution and the relentless exploitation of land, sea, plants and animals. What makes this crisis unprecedented is that every major ecological upheaval can be traced back to a single species: Home sapiens.

So far, the damage has been stark: at least 680 vertebrate species have been driven to extinction since 1500. Losses are accelerating...