Dismissing any hopes of new species evolving at the same pace as animals and plants are driven to extinction, a new study has said that the human destruction of natural habitats and loss of diversity of life is much faster.

Conservation experts have already signalled that the world is in the grip of the "sixth great extinction" of species, driven by the destruction of natural habitats, hunting, the spread of alien predators and disease, and climate change.

Simon Stuart, chair of the Species Survival Commission for the International Union for the Conservation of Nature – the body which officially declares species threatened and extinct – said that point had now "almost certainly" been crossed. "Measuring the rate at which new species evolve is difficult, but there's no question that the current extinction rates are faster than that; I think it's inevitable," he said.

The IUCN had earlier in 2004 calculated that the rate of extinction had reached 100-1,000 times that suggested by the fossil records before humans.

No formal calculations have been published since, but conservationists agree the rate of loss has increased since then, and Stuart said it was possible that the dramatic predictions of experts like the renowned Harvard biologist E O Wilson, that the rate of loss could reach 10,000 times the background rate in two decades, could be correct.

" Extinction is part of the constant evolution of life, and only 2-4% of the species that have ever lived on Earth are thought to be alive today. However fossil records suggest that for most of the planet's 3.5bn year history the steady rate of loss of species is thought to be about one in every million species each year.

However Stuart said that the IUCN figure was likely to be an underestimate of the problem, because scientists are very reluctant to declare species extinct even when they have sometimes not been seen for decades, and because few of the world's plants, fungi and invertebrates have yet been formally recorded and assessed.

The calculated increase in the extinction rate should also be compared to another study of thresholds of resilience for the natural world by Swedish scientists, who warned that anything over 10 times the background rate of extinction – 10 species in every million per year – was above the limit that could be tolerated if the world was to be safe for humans, said Stuart.

"No one's claiming it's as small as 10 times," he said. "There are uncertainties all the way down; the only thing we're certain about is the extent is way beyond what's natural and it's getting worse."

Many more species are "discovered" every year around the world, than are recorded extinct, but these "new" plants and animals are existing species found by humans for the first time, not newly evolved species.

In addition to extinctions, the IUCN has listed 208 species as "possibly extinct", some of which have not been seen for decades. Nearly 17,300 species are considered under threat, some in such small populations that only successful conservation action can stop them from becoming extinct in future. This includes one-in- ive mammals assessed, one-in-eight birds, one-in-three amphibians, and one-in-four corals.

This year has been declared the International Year of Biodiversity and it is also hoped that a UN report on the economics of ecosystems and biodiversity will encourage governments to devote more funds to conservation.