ocean and air temperatures. The melting was made worse by a cloudless summer in the Arctic, the researchers said.

“The Arctic sea ice is the first signal, and the biggest signal, of the effects of rising global temperatures,” said Walt Meier, a research scientist at the center.

Data show the sea ice also is thinner. It’s breaking up earlier in the spring and is freezing over later in the fall. There are more days with greater expanses of open water.

That changes centuries-old patterns for Alaskans and others living in the Arctic Circle. They’re having to alter their land travel routes and how they store food. Traditional hunting is changing, and buildings are collapsing as the permafrost melts. Storm patterns are unpredictable - waves are eroding coastlines.

Some see benefits. The Northwest Passage stays open longer to vessel traffic between Europe and Asia, cutting the voyage from London to Tokyo to 9,950 miles. That voyage via the Suez Canal is 13,000 miles; the Panama Canal route is 14,300 miles. Also, less ice over the Arctic land means more space exposed for oil and gas extraction.

In other effects, Arctic wildlife such as the polar bear, the walrus, the ring seal and seabird species are finding it harder to find food and habitat, pushing them closer to extinction, scientists say.

Two weeks ago, U.S. Geological Survey scientists predicted that two-thirds of the world’s polar bears would be gone by 2050, including all of the Alaskan bears. The animals don’t do well when they are forced to come to land, and some bears appear to have drowned trying to make the long swim between the shrinking ice and the land. The federal government is considering listing the bears as threatened under the Endangered Species Act.

Walruses feed in near-shore shallow ocean water but keep calves on the sea ice. As the pack ice shrinks, the females face the choice of finding food or abandoning their young, according to Defender of Wildlife scientists who are monitoring the animals’ behavior.

Marine mammal researchers say that the Pacific gray whale also could be affected by a changing food supply in the Bering Sea as the climate warms.

Arctic temperatures are rising faster than the global average. The summer sea ice has shrunk about 8 percent each decade since the late 1970s, but that percentage is likely to be higher when the latest data are considered, Meier said.

On Thursday, after hearing about the new low in sea ice, Kassie Siegel, staff attorney for the Center for Biological Diversity, which petitioned the federal government to protect the polar bear under the Endangered Species Act, said, “the stunning thing is that there’s less sea ice in the Arctic now than most climate models project for 2050.”

The USGS scientists who predicted the loss of polar bears also cautioned that they might be underestimating the animals’ decline because the models seem to be underestimating the ice loss, Siegel added.

NASA has been providing satellite images of the Arctic floating pack ice since 1979.

Scientists use a baseline average between 1979 and 2000 to compare with current sizes. There are usable data going back to the 1950s from vessel navigational reports. Sporadic satellite data started in the 1960s.

Melting sea ice doesn’t raise ocean levels as do melting glaciers and other land-based ice. But what happens in the Arctic affects the globe as a whole, according to the Intergovernmental Panel on Climate Change, an international body of experts preparing studies of Earth’s physical functions as well as effects on humans and the economy.

The Arctic melt is expected to amplify the Earth’s warming, as there is less sea ice to reflect sunlight back into space and more dark ocean to absorb solar energy. Warmer water flowing from the Pacific Ocean through the Bering Strait into the Arctic Ocean and fresher water flowing into the North Atlantic from the Arctic also will change ocean temperatures and currents.

According to the National Snow and Ice Data Center, the local weather conditions in the Arctic this summer played into establishing the record low. A persistent high-pressure condition in June and July and into August meant fewer clouds to reflect energy into space. Instead, that energy gets absorbed in Earth’s surface and helps melt the ice.

The sea ice hit its annual low Sept. 16. After that date, the pack ice started to reform, and will reach its largest size in January or February.

“We have this long-term trend, but there is a lot of variability,” Meier said. “Some years it goes up. Some years it goes down.”