There were once nearly a million caribou in Canada's famous George River herd. Now, there are less than 6,000.

That dramatic loss is just one sign of a vast global crisis. On average, wildlife species on Earth have lost more than half their populations since 1970, according to a new report from the World Wildlife Fund.

This is as much a crisis as climate change. - Justina Ray, president of Wildlife Conservation Society Canada

In Canada, half of all monitored species are on the decline. Some have lost more than 83 per cent of their populations.

If that trend continues, the consequences will extend far beyond individual species like the caribou.

Earlier this year, an international consortium of scientists warned that human activities are propelling the planet toward a sixth mass extinction event from which we may not be able to recover.

"Biodiversity loss is a huge threat to the planet. It's a huge threat to humans," World Wildlife Fund Canada president Megan Leslie told Day 6.

"I don't think we fully understand how big it is — or how urgent it is that we act."

Twenty years ago, 800,000 caribou from the George River herd roamed this land. There are now less than 6,000. (Marika Wheeler/CBC)

The twin crises

Justina Ray, president and senior scientist with Wildlife Conservation Society Canada, says biodiversity loss represents a fundamental threat to humankind.

"This is as much a crisis as climate change," she told Day 6 host Brent Bambury.

She and her colleagues have long referred to biodiversity loss and climate change as "the twin crises."

This week, Ray penned an op-ed for Canadian Geographic warning that Canada's caribou are headed for extinction.

But she emphasized that the consequences of biodiversity loss extend much further.

We do not know what the tipping point is. - Justina Ray, president of Wildlife Conservation Society Canada

"Biodiversity is life on Earth, both land and water," she said. "It's not just species, it's the genetic diversity within species [and] also ecosystems. In a word, you could define it as nature."

As wildlife populations dwindle, the environmental stresses are felt long before a species goes extinct, Ray says.

In some parts of Canada, caribou herds have declined by 90 per cent in recent decades, leaving some herds with fewer than 25 animals. With numbers so low, they are unable to fulfill their role within the broader ecosystem.

All of Canada's caribou populations are now at risk of extinction because of climate change and habitat destruction, according to Justina Ray. (Facebook)

Those populations are already functionally extinct.

"You know, [the species] often only get attention … when there's only a handful of them, when you can name them," Ray said. "But it's a good deal beforehand that we should be worried."

"Often we don't understand their value until they're gone."

Only a small fraction of the species on the planet are being diligently monitored, according to Ray. Even scientists do not fully understand how the decline of so many individual species will transform the habitats they live in.

"We do not know what the tipping point is," she said.

Sockeye salmon swim the Adams River north of Kamloops, B.C. Wildlife populations in rivers and lakes have fallen 83 per cent globally since 1970, according to the World Wildlife Fund. (Briar Stewart/CBC)

'We have to have time'

According to the World Wildlife Fund report, only one quarter of the land on Earth remains unaffected by human activity. Habitat loss, largely caused by agriculture, is the number one threat to global biodiversity.

Climate change, chemical pollution and over-exploitation are also wreaking havoc on the planet's wildlife.

People … will have to make societal choices. And they may be very difficult ones." - Justina Ray, president of Wildlife Conservation Society Canada

In 2016, a study published in Science found that 71 per cent of humans live in regions where the loss of biodiversity could threaten ecosystems' ability to support human societies.

The Canadian government has taken some action to address these issues in recent years, Ray says, including a public commitment to meet the protected area requirements laid out in the international Convention on Biological Diversity.

On Oct. 31, the Canadian government announced new measures to protect British Columbia's southern resident killer whale population.

Southern resident killer whales have struggled since they were listed as an endangered species in 2005. Indigenous communities want a seat at the decision-making table to ensure that protection of the rivers, streams and the Salish Sea, especially of the salmon and the whales, is paramount. (Dave Ellifrit/Centre for Whale Research)

Individual Canadians can also do their part, Leslie says — even simple actions like planting milkweed and other native species on balconies or in backyard gardens can help restore habitat.

But Ray said governments and individuals alike need to be more proactive when it comes to protecting the planet's remaining wilderness.

"I am concerned every day by the people who surround me who are not aware and not concerned because they can't see it," she said.

"Particularly in urban environments, the average person is very far removed from nature. But I'm convinced that when things really start to fall apart — if that happens — then people … will have to make societal choices. And they may be very difficult ones."

Still, when asked if there is still time to turn things around, Ray did not hesitate.

"We have to have time," she said. "I can think no other way."