Two-Thirds of Polar Bears Gone by Mid-Century

Two-thirds of the Arctic's polar bears could die off by the middle of this century as climate change, melting sea ice and other factors stress their populations, according to a new study released by the U.S. Geological Survey (USGS).

The agency has conducted a series of studies on polar bears since U.S. Secretary of the Interior Dirk Kempthorne announced plans last December to consider listing the species as "threatened" under the Endangered Species Act. Kempthorne asked the USGS to assess the polar bear's future to help the U.S. Fish and Wildlife Service to make a decision on the listing. That decision is expected in January.

In "Forecasting the Range-Wide Status of Polar Bears at Selected Times in the 21st Century," a report released this week, USGS scientists Steven C. Amstrup, Bruce G. Marcot and David C. Douglas used climate and population modeling to project likely polar bear populations in 45, 75 and 100 years.

"Our modeling suggests that realization of the sea ice future which is currently projected, would mean loss of (approximately) 2/3 of the world's current polar bear population by mid-century," they write early in the report.

However, the authors add, even that prediction could be too optimistic. Over the past two decades, sea ice has actually been melting faster than scientific models have projected, they said. In one region inhabited by polar bears, they note, "the rate of sea ice decline has been among the most profound of any in the Arctic."

Because of regional differences in polar bear habitats, some populations will likely fare worse than others, the scientists predict. For example, in an area called the Polar Basic Divergent Ecoregion, which includes the Chukchi Sea and Southern Beaufort Sea north and northwest of Alaska, the study forecasts that polar bears could disappear as early as mid-century as "very likely" by late-century.

The animal's future beyond that appears even bleaker.