Wildlife populations have fallen by more than two-thirds in less than 50 years, according to a major report by the conservation group WWF.
The report says this "catastrophic decline" shows no sign of slowing.
And it warns that nature is being destroyed by humans at a rate never seen before.
Wildlife is "in freefall" as we burn forests, over-fish our seas and destroy wild areas, says Tanya Steele, chief executive at WWF.
"We are wrecking our world - the one place we call home - risking our health, security and survival here on Earth. Now nature is sending us a desperate SOS and time is running out."
What do the numbers mean?
The report looked at thousands of different wildlife species monitored by conservation scientists in habitats across the world.
They recorded an average 68% fall in more than 20,000 populations of mammals, birds, amphibians, reptiles and fish since 1970.
The decline was clear evidence of the damage human activity is doing to the natural world, said Dr Andrew Terry, director of conservation at the Zoological Society of London (ZSL), which provides the data.