Human overpopulation and overconsumption is responsible for what scientists are calling the 'biological annihilation' of wildlife'.
The situation is so serious, it means a sixth mass extinction in Earth’s history is happening now, according to a new study published in the Proceedings of the National Academy of Sciences journal.
Scientists have claimed the crisis is a threat to human civilisation - and that we have only a 20 year window in which to act, before thousands of species are wiped out forever.
Media commentators have noted the tone of the study, which shuns the usual sombre scientific style, and uses dramatic language.
Lead scientist Prof Gerardo Ceballos, at the Universidad Nacional Autónoma de México, said: "The situation has become so bad it would not be ethical not to use strong language."
Climate change, poaching, pollution and habitat destruction are all killing off wildlife at a frightening rate.
The report says: "The resulting biological annihilation obviously will 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 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."
While previous research has highlighted the speed at which species are becoming completely extinct - faster than ever before - they still suggest that loss of biodiversity is a gradual process.
This research took what has been described as a 'broader stroke' approach - analyzing information about 7,500 species of land vertebrates, and discovering that the range of around 33 per cent of the species have shrunk. Giving an example, Ceballos said: "We used to have swallows nesting every year in my home near Mexico city – but for the last 10 years there are none."
Researchers also highlighted the lion as 'emblematic' of this trend: "The lion was historically distributed over most of Africa, southern Europe, and the Middle East, all the way to northwestern India. [Now] the vast majority of lion populations are gone."
Looking at how we can help, the review highlighted diet as a crucial part of the process.
"The time to act is very short," said Prof Cabballos. "It will, sadly, take a long time to humanely begin the population shrinkage required if civilisation is to long survive, but much could be done on the consumption front and with ‘band aids’ – wildlife reserves, diversity protection laws – in the meantime."
According to the report's authors, the commodities wealthier society's tend to spend on - meat and other animal products, sugar and starch - all require lots of resources including land and water to grow.
Eating a more plan-based diet - one heavy in fruit, vegetables, nuts and seeds - is what the study advises.
One US scientist - Prof Stuart Pimm, at Duke University - who was not involved in the study, believes the sixth mass extinction is not yet underway. He said: "It is something that hasn’t happened yet – we are on the edge of it."
He also questioned the methodology and the implications of this on the results, saying: "Should we be concerned about the loss of species across large areas – absolutely – but this is a fairly crude way of showing that.
"There are parts of the world where there are massive losses, but equally there are parts of the world where there is remarkable progress. It is pretty harsh on countries like South Africa which is doing a good job of protecting lions."
Robin Freeman, at the Zoological Society of London, UK, added: "While looking at things on aggregate is interesting, the real interesting nitty gritty comes in the details. What are the drivers that cause the declines in particular areas?"