Global animal populations are declining, and we've got limited time to try to fix it.

That's the upshot of a new report from the World Wildlife Fund and the Zoological Society of London, which analyzed years of data on thousands of wildlife populations across the world and found a downward trend in the Earth's biodiversity.

According to the Living Planet Index, a metric that's been in existence for five decades, animal populations across the world shrunk by an average of 69% between 1970 and 2018.

Not all animal populations dwindled, and some parts of the world saw more drastic changes than others. But experts say the steep loss of biodiversity is a stark and worrying sign of what's to come for the natural world.

"The message is clear and the lights are flashing red," said WWF International Director General Marco Lambertini.

According to the report's authors, the main cause of biodiversity loss is land-use changes driven by human activity, such as infrastructure development, energy production and deforestation.

Climate change may become the leading cause of biodiversity loss

Cattle graze near a fire in Amazonas, Brazil, on Sept. 22. A new report analyzed years of data on wildlife populations across the world and found a downward trend in the Earth's biodiversity.