They already knew climate change was changing their lives for the worse.

The ice the Iñupiat people used for centuries to hunt bowhead whales on a fragile barrier island on the Chukchi Sea had thinned so much that hunting was too risky. Ice melted by high temperatures from climate change made flooding part of their way of life. State and federal officials have seriously considered moving their entire village inland. But no one had a full assessment of the threat.

Now the U.S. Geological Survey has confirmed everyone’s worse fears. Alaska’s remote northern coast where several native communities live “has some of the highest shoreline erosion rates in the world,” a USGS study released Wednesday said. Results varied along the shore, but more than a yard is being washed off most of the coast each year. In extreme cases, the study said, nearly 30 yards of coast disappeared from some beaches.

[The remote island village that needs to be relocated due to climate change]

“Coastal erosion along the Arctic coast of Alaska is threatening Native Alaskan villages, sensitive ecosystems, energy and defense related infrastructure, and large tracts of Native Alaskan, State, and Federally managed land,” said Suzette Kimball, acting director of the USGS.

Federal officials have talked about the need to move native villages for at least eight years. Eighty-six percent of 213 Alaska-native villages are suffering from flooding and erosion to some degree, a Government Accountability Office report said in 2009.

At the time, at least four communities were making arrangements to relocate because of erosion and flooding caused partly by rising temperatures — Newtok, Koyukuk, Shishmaref and Kivalina.

“The extent to which additional villages may need to relocate as the impacts of climate change increase and of how federal agencies in collaboration with state agencies can assist the villages in their relocation efforts was discussed in an October 11, 2007,” the GAO report said.

But assessments of the problem were poor, so officials didn’t know its full extent. The frightening USGS report sharpened the view.

[As ice melts, hungry polar bears are slowly migrating north]

The report is called the “National Assessment of Shoreline Change: Historical Shoreline Change Along the North Coast of Alaska, U.S.-Canadian Border to Icy,” and is the 8th in a series of USGS reports on coastal impacts.

“This report provides invaluable objective data to help native communities, scientists and land managers understand the natural changes and human impacts on the Alaskan coast,” said Ann Gibbs, a USGS geologist who led the research.

The causes of Alaska coastal erosion can include warmer and higher seas, and also the loss of Arctic sea ice. With less ice off the coast, storms can hurl higher waves at coastlines, and large waves may also occur during longer seasons of the year.