WASHINGTON, Sept 7 (Reuters) - Two-thirds of the world's current polar bear population could be gone by midcentury if predictions of melting sea ice hold true, the U.S. Geological Survey reported on Friday.

The fate of polar bears might be even more imperiled than that estimate, because sea ice in the Arctic might be vanishing faster than the available computer models predict, the geological survey said in a report aimed at determining whether the arctic bear should be classified as a threatened species.

"Projected changes in future sea ice conditions, if realized, will result in loss of approximately two-thirds of the world's current polar bear population by the mid 21st century," the report's executive summary said.

"Because the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models, this assessment of future polar bear status may be conservative."

In January, the U.S. Fish and Wildlife Service proposed listing the polar bear as a threatened species under the Endangered Species Act, noting polar bears depended on sea ice as a platform to hunt seals. Projected sea ice loss due to global climate change was believed to jeopardize the bears' range.

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