A dramatic loss of sea ice in the Arctic Circle and its continued melting threatens indigenous people in that region, according to an international scientific study released Monday.

And the addition of all that fresh water into the world’s oceans could hamper efforts to restore Louisiana’s eroding coastline, said a key scientist involved in the federal-state restoration effort.

The Arctic sea ice has decreased by 8 percent during the past 30 years and could decline at least 10 percent by 2100, according to the Arctic Climate Impact Assessment, a four-year study by 300 scientists in the eight nations that border the Arctic region, including the United States.

The study is to be presented today at a scientific symposium in Reykjavik, Iceland.

The additional melted freshwater could add 6 inches to earlier estimates of an expected 16 to 36 inch rise in sea level in the next century, the report says.

A water rise of that magnitude could complicate the federal-state plan to rebuild Louisiana’s rapidly eroding coastline, a key scientist in that effort said Monday.

The Louisiana Coastal Area Ecosystem Restoration Study now before Congress, which includes the first $1.9 billion in proposed restoration projects, is based on an estimated sea-level rise of 2 millimeters a year, the equivalent of only 8 inches by 2100, said Robert Twilley, director of the Wetlands Biogeochemistry Institute at Louisiana State University.

The 2-millimeter estimate for annual sea-level rise was based on measurements along Louisiana’s coastline since 1978, said Twilley, who also leads a group of scientists who created computer models to predict the feasibility of restoration projects.

Twilley said the new Arctic melting estimates will require scientists working on the coastal restoration program to reconsider the effects of a more rapid sea-level rise on proposed projects. The 2-millimeter estimate already was 8 inches below the lowest estimate of sea-level rise predicted worldwide by the Intergovernmental Panel on Climate Change, a group of several thousand scientists who have issued reports on the potential effects of global warming.

The higher estimates are important, Twilley said, because individual restoration projects are designed to overcome both the effects of subsidence, the ground beneath wetlands sinking under its own weight, and future sea-level rise. Higher water levels could require more sediment to be delivered along the coastline by the Mississippi or Atchafalaya rivers or their tributaries, he said.

And if the projects aren’t built, it means vulnerable communities have less time to plan for a retreat from the coast.

“We are the canary in the coal mine, the coastal zone,” Twilley said. “It’s all a game of probabilities and risks, but what this report is telling us is that we’d better move away from the conservative number we’ve been using to some higher numbers.”

William Klein Jr., an Army Corps of Engineers official who is overseeing the preparation of an environmental impact statement for the restoration program, said the new estimate is just one issue that will have to be addressed as the program moves forward.

“We have to build around things like this,” he said. “We understood there are still major issues that must be addressed as we move forward. We’d better be dynamic, able to change.”

The study found that 386,100 square miles of sea ice, an area bigger than the nations of Sweden, Norway and Denmark combined, has disappeared during the past 30 years, and that the remaining sea ice is 10 percent to 15 percent thinner.

The average yearly temperatures rose by as much as 5.4 degrees Fahrenheit during the past 50 years over Alaska and Siberia, and by as much as 7 degrees over Canada.

The report predicts another 10 percent to 50 percent decline in the amount of Arctic sea ice by 2100, and says there’s even a chance that the entire Greenland ice cap could disappear by the end of the century.

By 2100, the report says, half of the Arctic’s summer sea ice will disappear, and the effects of climate change on the Arctic region will be dramatic long before that, the report concluded.

“Many coastal towns and facilities around the Arctic face increasing risks from erosion and flooding due to rising sea levels, decreased sea ice, and thawing coastal permafrost,” it says.

The disappearance of summer sea ice could threaten polar bears and some seal species with extinction and reduce the range of other animals important to Inuit and other native communities living in the northernmost areas.

The report’s projections were based on what it calls a moderate estimate of future carbon dioxide and other greenhouse gas emissions, and uses results from five major global climate models used by the Intergovernmental Panel on Climate Change.