for National Geographic News
In the update of its Red List of Threatened Species released today, the World Conservation Union (IUCN) says that more than 40 percent of species that have been assessed worldwide are threatened with extinction.
These include a quarter of the world's coniferous trees, an eighth of its birds, and one-third of its amphibians.
Also listed are a quarter of all the mammal species that were assessed for the survey.
For the first time, polar bears and hippopotamuses are now designated as threatened.
Polar bears, the IUCN said, are likely to become one of the most notable casualties of global warming, which is melting sea ice on which they roam in search of Arctic seals.
Without enough ice, the bears risk being trapped on land, where they face starvation. Or they may drown in attempts to swim long distances.
Earlier this year, the U.S. Fish and Wildlife Service announced that it is considering adding polar bears to the U.S. endangered species list.
Although the decline in polar bear numbers is expected to be relatively slow, other animal populations have already crashed dramatically.
The hippopotamus, for example, has declined by 95 percent in the Democratic Republic of the Congo since 1994, when 30,000 roamed wild.
Never before listed by the IUCN, hippos are now classified as "vulnerable" mainly because of unregulated hunting in the war-torn country.
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