The untouched wilderness on this planet is disappearing — and disappearing fast. That's bad news, and not just because trees look nice: we depend on vast swathes of pristine nature to support diverse forms of life, to keep climate change at bay, and to ensure that local economies thrive. But for all their importance, we're doing a pretty bad job ensuring wild places stay wild, new research shows.

"We started with the fairly naive assumption that we wouldn't see very big declines in wilderness areas because of the fact that they were so remote," says Oscar Venter, a professor at the University of Northern British Columbia and an author of the study. "So we were quite surprised and shocked to the levels at which these areas had been eroded since the early 1990s."

For a long time, researchers thought that wilderness takes care of itself. The thinking went that wild places are still wild because they're difficult places to live in — like parts of Siberia, or the Sahara desert, for instance. But researchers now think that those areas should be actively protected, too, because we're constantly losing wilderness. We've lost about 1.2 million square miles of wild land over the past 20 years, the researchers found, and we've made strides to protect only about 850,000 square miles of it — about the size of Alaska plus California.

In the study, a research team helmed by Venter and James Watson, director of science and research at the Wildlife Conservation Society, measured the human footprint on our planet. (That isn't the same James Watson who sold his Nobel Prize, by the way.) Using data collected by satellite and surveys over about two decades, the team was able to map where people paved roads, put down railroad tracks, navigated waterways, installed power lines, built cities, and converted land into crops and pastures. The areas without these signs of human activity was what they called wilderness. (That definition is a little different from how the US legally defines it.) The researchers found that only about 23 percent of the land across the globe can be labeled "wilderness" today — nearly a 10 percent drop from two decades ago. And those areas are concentrated mainly in North America, North Asia, North Africa, and Australia.

If this study is right, there are fewer pristine areas left in the world than conservationists thought, conservation biologist Jeremy Kerr at the University of Ottawa, who was not involved in the study, wrote in an email. "Establishing new protected areas and parks could help, but we are losing wilderness faster than new parks are being established," he says.

The study authors argue that ecosystems need as much protection as endangered species. Creating large protected areas that cross borders could help, for example. Connecting these protected areas with corridors would enable animals to move back and forth. And it's also important to empower (and fund) indigenous communities to protect the wilderness areas they depend on for subsistence and their way of life, Venter and his colleagues say.

This isn't impossible, it's just going to require some research and thought, says Jodi Hilty, president and chief scientist of the Yellowstone to Yukon conservation initiative, who was not involved in the research. "I don't think we need to protect necessarily everywhere," she says. "The job for conservation biologists is to figure out what are the most important places to connect and protect, so that over time — not just today but in future generations — these natural resources will still be flourishing for nature and for humanity."

But one thing is clear: we need to act fast. "Society needs to come to grips with this challenge: what do we want to protect and when are we going to get at it? The clock is ticking," Kerr wrote in an email. "For many of the most critical ecosystems, another couple of decades of deliberation is going to run out the clock. There just won't be any wilderness left."