It’s a common joke among travellers that soon there will be nowhere on the planet left undiscovered, but a new study has shown that wild places really have drastically declined in the last two decades.

Researchers reporting in the Current Biology journal show huge declines in the world’s wilderness areas over the last 20 years – losses of around a tenth. That’s a total area equivalent to half the size of the Amazon rainforest.

The startling findings have sparked renewed calls for international policies to recognise the value of wilderness areas, and to fight back against the threats facing them.

Wilderness in danger

“Without any policies to protect these areas, they are falling victim to widespread development,” said Dr James Watson of the University of Queensland, Australia. “We probably have one to two decades to turn this around.”

Although much has been done globally to protect endangered species, less attention has been paid to protecting wilderness areas that might make up entire ecosystems.

Around 20% of the world’s land area (30.1 million km2) remains as wilderness, primarily in North America, North Africa, North Asia, and Australia. The study found that since the 1990s 3.3 million km2 of wilderness area has been lost. Worst affected is South America, which showed a 30% decline.

“If we don't act soon, there will only be tiny remnants of wilderness around the planet, and this is a disaster for conservation, for climate change, and for some of the most vulnerable human communities on the planet,” Watson said. “We have a duty to act for our children and their children.”