One species in four 'could be gone in 50 years'

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The union says that the rapid extinction rate is between 1,000 and 10,000 times higher than the expected, natural rate.

It warns that humans are to blame. Urbanisation, agriculture, deforestation and hunting all cause loss of habitat - the biggest danger to plants and animals.

Climate change is also thought to be an increasing threat.

There are already more than 16,000 species threatened with extinction, including the polar bear, hippopotamus, sharks, freshwater fish and Mediterranean flowers. The Chinese medicine trade threatens tigers and rhinos.

In the past 500 years, human activity has forced 820 species to extinction.

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