Since the first national parks were created in the nineteenth century, nearly 15% of the Earth’s land surface has been set aside in protected areas of one type or another.

But these protections, researchers are finding, aren’t always as permanent as people might think they are.

Since the set-asides began, 2,000,000 square kilometres of once-protected lands — an area roughly the size of Mexico — have been downgraded, downsized, or eliminated entirely, the vast bulk of them in the last two decades.

It’s a finding that comes hard on the heels of a report from a United Nations biodiversity panel, which, earlier this month, warned that as many as 1,000,000 species are at risk of extinction due to human activities.

“In light of that report, scientists are calling for protected areas to be massively scaled up,” says Rachel Golden Kroner, a social scientist at Conservation International, in Arlington, Virginia, US.

“But worldwide it is going in the opposite direction.”

Even countries such the US and Brazil, once world leaders in conservation, are now in the vanguard of the rollback. A quarter of the delisted land is in the US, and another 17% is in the Amazon Basin, where 150,000 square kilometres have been removed from protection entirely, and another 200,000 downgraded, a team led by Golden Kroner reports in the journal Science.

In the US, for example, in 2017, Congress opened Alaska’s sprawling Arctic National Wildlife Refuge to oil and gas exploration, while the Trump administration carved down two large Obama-era national monuments, Bears Ears and Grand Staircase-Escalante (both in Utah), by 85% and 51%, respectively.

There have also been rollbacks along the US-Mexico border in order to waive environmental laws and facilitate construction projects related to national security, primarily Trump’s proposed border wall.

But while the American rollbacks affected the greatest land area, the country with the largest number of alterations, the study found, was Australia, with more than 1600 changes since 1997.

Australia, Golden Kroner adds, has also reduced protections for enormous marine preserves such as the Coral Sea Marine Park — changes, which would, if counted in the total, cause Australia to rival the US in its rollbacks’ total area.

“That was the largest downgrade in the world,” Golden Kroner adds.

All told, she says, her team found more than 3700 downgrades in 73 countries, with an additional 800 protected areas potentially up for some form of future chop.

And enormous as that tally is, it’s not complete.

“We haven’t done systematic research everywhere,” she notes, partly because “access to information in some countries isn’t open.”

For the most part, she says, downgrades are linked to industrial-scale resource extraction or construction projects, such as hydroelectric dams and tourism, resorts, and casinos.

But not all are linked to commercial or industrial pressures.

In the US, for example, the National Park Service has opened the national parks to Native American tribes to harvest plants for traditional subsistence purposes, so long as their activities have “no significant ecological impact”.

And in India, a similar rule change has allowed poor, local citizens go into parks to harvest bamboo.

In a second paper in Science, Lisa Naughton-Treves, a geographer at the University of Wisconsin, Madison, notes that it’s important to distinguish changes such as these from industrial projects.

These rule changes, she says, may simply be recognitions (or reinstatements) of ancestral practices that were there long before the park or conservation area was superimposed on top of them.

For example, she notes, “I see this in Ecuador,” where a reserve was plunked down on top of indigenous territories.

“It wasn’t until 20 years later that they realised they should formally recognise that people have been living there. [The rule changes] are, in essence, correcting a situation that was existing at the time the park was established.”

It’s a controversial view, she admits, because it involves balancing the need to protect ecosystems against the need not to impose what some see as a colonial mindset on local residents.

“[We] are trying to thread the needle by looking at the trade-offs,” she says.

“Is this going to help poor people who were there all along, or some mining company that belongs to elites in the capital city to make a fortune?”

That said, Naughton-Treves thinks Golden Kroner’s team is onto something important. “[They] are right that there’s a troubling trend to shrink or eliminate some parks,” she says.

Stephen Polasky, an economist at the University of Minnesota, US, agrees.

“I found it eye-opening that there have been so many cases [of downgrading] around the world — or at least the parts of the world they could document — including the US,” he says.

“There’s so much literature out there on how many new protected areas there are [that] you get the sense that we’re increasing the amount of protection through time, and it’s only going one way, and that’s not true.”

It’s a view echoed by Margaret Walls, an economist at Resources for the Future, in Washington, DC.

“People probably think that once an area is protected, it is taken care of, and they don’t have to pay attention any more,” she says.

“This study shows that’s not the case. A lot of effort goes into designating a protected area — often years and years of work by local advocates [and] scientific studies. If these efforts are being overturned, it calls into question all that hard work.”