Scientists have warned that humans and animals on Earth may face mass extinction sooner than predicted if necessary measures to protect the planet are not taken.
The Earth is being pushed to its limit quicker than ever before, over-population and over-consumption by the wealthiest in society are to blame, researchers said.
This warning has been published in the Proceedings of the National Academy of Sciences journal and the study involves scientists at both Stanford and Mexico City universities. Species are being wiped out from Earth 100 times faster than during the last millennium, it said.
Experts claim that Earth is several stages further forward than predicted in terms of extinction. "Earth's sixth mass extinction episode has proceeded further than most assume," experts believe.
The current rate of vertebrate extinction during the last century was two species a year, the report found. And this was compared with two species every 100 years over the last two million years.
The scientists warned that the estimates were likely to be "conservative", with "several" species of mammal now endangered despite being at "relatively safe" levels at the turn of the millennium.
The report said: "As much as 50 per cent of the number of animal individuals that once shared Earth with us are already gone, as are billions of populations.”
"We emphasise that the sixth mass extinction is already here and the window for effective action is very short, probably two or three decades at most.
"All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life."
“Scientists said the loss of animals from the planet would "promote cascading catastrophic effects on ecosystems", including plants and other wildlife.
The report added: "The resulting biological annihilation obviously will also have serious ecological, economic, and social consequences.
"Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe."
The report was based on analysis of 27,600 mammals, reptiles and amphibians. It cited double-digit decreases in the populations of species such as African lion, which has witnessed a 43% drop since 1993.