For a second straight year, the Arctic is warming faster than any other place in the world, and walrus populations in the area’s Pacific and Atlantic ocean regions are thinning along with the ice sheets that are critical for their survival, researchers reported Tuesday.

Overall, the outlook for the frozen top of the world is bleak, according to the annual Arctic Report Card: 2015 Update released by the federal National Oceanic and Atmospheric Administration. Since the turn of the last century, it said, the Arctic’s air temperature has increased by more than 5 degrees due to global warming.

Warmer air and sea temperatures melt ice that in turn expands oceans and causes sea-level rise, which scientists say presents a danger to cities along the entire Atlantic coast, from Miami to Washington to Boston. Walrus and other arctic mammals that give birth on ice sheets are struggling with the change, and fish such as cod and Greenland halibut are swimming north from fishermen and animals that feed on them in pursuit of colder waters.

NOAA chief scientist Richard Spinrad said changes in the Arctic portend changes that are likely to spread to the wider world — higher air temperatures, longer hot seasons, anomalous weather spikes and fish fleeing north only to be replaced by new species swimming from areas south. “The conclusion that comes to my mind is these report cards are trailing indicators of what’s happening in the Arctic. They can turn out to be leading indicators for the rest of the globe,” Spinrad said.

The annual average surface-air temperature over the period of the report, between October 2014 and September 2015, was nearly 2.5 degrees higher than the time period scientists use as a baseline to compare temperatures, 1981 to 2010. As a result, Alaska was warmer in fall 2014 and winter this year, when the snow pack that usually melts to replenish rivers and moisten the earth was extremely low.

Lightning strikes on dry land sparked that state’s second-worst wildfire season in its history. According to the NOAA report card, “the 2015 spring melt season provided evidence of earlier snow melt across the Arctic” because of the increased warmth. As of early July, the Arctic melt included more than half of the region’s ice sheet for the first time “since the exceptional melt of 2012.”  The length of the melt season was up to 4o days longer than that of the average northwestern, northeastern and western regions, the report said.

This year’s findings are largely consistent with the dire findings last year. Dozens of scientists from across the world contribute to the report card, including those from U.S. Naval Research and the Army Corps of Engineers, the Institute of Marine Research in Norway, Knipovich Polar Research Institute of Marine Fisheries and Oceanography in Russia and University of Victoria in Canada.

The report cards’ year-to-year consistency will help scientists establish whether they are watching a weather anomaly in a key part of the world or an established trend. “What you see here is stronger confirmation,” Spinrad said.

A separate study focusing on Alaska’s North Slope, which was presented late Tuesday at the fall meeting of the American Geophysical Union, estimates that the permafrost there will decline rapidly over time because of rising temperatures. Vladimir Romanovsky, head of the Permafrost Laboratory at the University of Alaska Fairbanks, said thinning permafrost is already causing roads and houses built on it to crumble.

“Under these conditions, the permafrost will become unstable beneath any infrastructure such as roads, pipelines and buildings,” Romanovsky said. “The result will be dramatic effects on infrastructure and ecosystems.”

Another researcher at the university, Santosh Panda, said permafrost that covers virtually all of five national parks as large collectively as South Carolina could decline by 10 percent within the next 35 years. “Permafrost degradation is going to touch the whole landscape through changes in water distribution, slope failures and changes in vegetation that will affect wildlife habitat and the aesthetic value of the parks,” Panda said.

In the Arctic, the age of ice generally defines the region’s health. Older ice is thicker, more resilient and resistant to atmospheric changes, and better at supporting mammals. Younger ice is thin and vulnerable to collapse.

Yet in nearly all Arctic regions, sea ice is decreasing, the report said. In 1985, 85 percent of the region’s ice qualified as old. In March, that fell to 30 percent. “This is the first year that first-year ice dominated the ice cover,” it notes. “Sea ice cover has transformed from a strong, thick pack in the 1980s to a more fragile, thin and younger pack in recent years.”

Walruses are starting to teem on land as the ice fades, exposing their young to frequent trampling events. Walruses mate on the edges of ice, and females prefer giving birth and raising pups on old ice, which they use as a base to reach feeding grounds. Now many are on land, and the long path to the feeding areas are filled with animals that prey on them, such as sharks and orcas. That is further reducing walrus numbers, the U.S. Fish and Wildlife Service concluded in its section of the report.

Ice melt “is already a pervasive threat” to walrus, the agency’s researchers said, but how much of a threat depends on the ability of animals to adapt to change, tolerate it or flee it for more suitable habitat. Scientists estimate that Pacific walrus populations have fallen by half as a result of declining sea ice and hunting. The Atlantic stock, reduced by 80 percent through unregulated hunting between 1900 and 1960, is unknown, but estimates put the population at 25,000.

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