One fifth of animal and plant species are under the threat of extinction, a global conservation study has warned.
Scientists who compiled the Red List of Threatened Species say the proportion of species facing wipeout is rising.
But they say intensive conservation work has already pulled some species back from the brink of oblivion.
The report is being launched at the UN Biodiversity Summit in Japan, where governments are discussing how to better protect the natural world.
Launched at the UN Convention on Biological Diversity (CBD) meeting, the report says that amphibians remain the most threatened category of animals, with 41% of species at risk, while only 13% of birds qualify for Red-Listing.
The highest losses were seen in Southeast Asia, where loss of habitat as forests are cleared for agriculture, including biofuel crops, is fastest.
"The 'backbone' of biodiversity is being eroded," said the eminent ecologist, Professor Edward O Wilson of Harvard University.
"One small step up the Red List is one giant leap forward towards extinction. This is just a small window on the global losses currently taking place."
However, the scientists behind the assessment - who publish their findings formally in the journal Science - say there is new evidence this time that conservation projects are having a noticeable global impact.
"Really focused conservation efforts work when we do them - many island birds are recovering, lots of examples like this," said Simon Stuart, chair of the Species Survival Commission with the International Union for the Conservation of Nature (IUCN).
"We can show for sure that when we focus conservation efforts and really address the threats and put enough money into it, then you see positive results."
Species that have benefited from such action include three bred in captivity and returned to the wild - the California condor and black-footed ferret of the US, and Przewalski's horse in Mongolia.
The ban on commercial whaling has led to such a swiftly increasing population of humpback whales that they have come off the Red List entirely.
Meanwhile, a parallel study, also published in Science, asks where trends of increased risk, but also increased conservation effort, will lead the natural world in future.
Researchers analysed a range of scientific studies and global assessments. Although projections varied, all found that fundamental changes are needed in order to avoid declining populations across many types of plant and animal species.
"There is no question that business-as-usual development pathways will lead to catastrophic biodiversity loss," said research leader Paul Leadley from the Universite Paris-Sud.
"Even optimistic scenarios for this century consistently predict extinctions and shrinking populations of many species."
This picture is, in large part, what the CBD meeting is supposed to prevent.
One of the many debates currently ongoing at the meeting here is what the global target for 2020 should be - to completely halt the loss of biodiversity, or something less ambitious.
Dr Leadley's analysis backs up the view of many that a complete halt is not feasible.
But governments do at least appear united in their desire to do something, according to Dr Stuart, one of a large IUCN team monitoring developments here.
"They've said that they want to see improvements in status, especially in those species that are most at risk," he told BBC News.
"That to us is a very good target - we think it's achievable with a lot of effort.
"There doesn't seem to be much disagreement between countries on that issue - on other issues, yes, but on the species issue they're pretty solid."
However, on financing for species protection there is a lot of disagreement.
Some developing countries want a 100-fold increase in current rates of spending by the West. Other nations are arguing for a 10-fold rise.
But given the economic problems facing the world, that climate change is also supposed to see a huge and rapid increase in spending, and that no-one knows what the current spend on biodiversity actually is, all bets are currently off on what wording delegates will eventually arrive at.