The decline in the world's wildlife populations is much worse than was previously thought, much of it down to human pressures on nature, a global environmental group says.

There has been a 52 percent decline in populations of wildlife from 1970 to 2010, about twice the figure a previous study reported in 2012, the World Wildlife Fund reports.

The new figure was the result of better methods of surveying populations of mammals, fish, birds, reptiles and amphibians than were available to the earlier study, the group says in its latest "Living Planet" study.

The 2012 study, which reported a 28 percent population loss, was based on data mostly from North America and Europe, whereas the new study included developing countries where species loss has been much more prevalent, the WWF says.

The study examined data on around 10,000 populations of more than 3,000 vertebrate species, using a database created by the Zoological Society of London in 1970 and updated periodically since.

Most of the increases in species losses were seen in tropical regions, the WWF reported, mainly in Latin America but also in the Asia-Pacific region

Species loss was greatest among freshwater species, at 76 percent, followed by marine and terrestrial populations, which both declined 39 percent, the WWF says.

Species in land-based protected areas fared better, it says, but still declined by 18 percent.

The study, in attempting to identify the main threats to global wildlife populations, singled out ongoing loss and deterioration of wildlife habitats, climate change, and hunting and fishing.

"This damage is not inevitable but a consequence of the way we choose to live," says Ken Norris, science director for the London society. "There is still hope. Protecting nature needs focused conservation action, political will and support from industry."

It would take 1.5 Earths to regenerate the natural resources we are consuming, the WWF says, as the current rate of deforestation, overfishing and carbon emissions point to an unsustainable future as humans pursue economic development at the expense of the environment.

In less than two human generations, populations of the world's vertebrate species have declined by half, says WWF International Director General Marco Lambertini.

"There is no room for complacency," he says.

Norris says he agrees, and that the new numbers should be a strong warning of the need for global action.

"If half the animals died in London zoo next week it would be front page news," he says. "But that is happening in the great outdoors."

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