Air temperatures over the Arctic landscape were higher over the past year than at any other time since 1900, and the circumpolar north continues to change rapidly as the climate warms, according to an annual report released Tuesday by government and academic scientists.

The 2015 Arctic Report Card, a project sponsored by the National Oceanic and Atmospheric Administration, details the state of weather, sea ice, snow cover and marine and wildlife habitat in the Arctic and subarctic, and how those have changed as the region continues to warm at about twice the global pace.

"We know this is due to climate change. And its impacts are creating major challenges for Arctic communities who depend on the region for sustenance and cultural identity. We also know what happens in the Arctic doesn't stay in the Arctic," Rick Spinrad, NOAA's chief scientist, said at a news conference at the annual meeting of the American Geophysical Union in San Francisco, where the report card was unveiled.

Arctic change affects the global climate and international security, he said. "One could argue that the trailing indicators of the Arctic are in fact the leading indicators for the rest of the planet."

This year's Arctic Report Card, the 10th such annual report, was authored by 72 scientists from 11 nations. It comes days after governments of 196 nations reached an agreement in Paris to curb carbon dioxide emissions. The governments committed to limit global warming to 2 degrees Celsius (3.6 degrees Fahrenheit) and set a more ambitious goal of achieving a 1.5-degree limit.

Would accomplishing that arrest or reverse Arctic climate change? Not in the short term, said a coauthor of the Arctic Report Card.

"Unfortunately, we passed some critical points on that," Jim Overland, a NOAA oceanographer, said at the news conference. "If the globe goes to 2-degree warming, we're looking at a 4- or 5-degree warming for the winter in the Arctic by 2040, 2050. That's based upon the CO2 that we've already put into the atmosphere and will be putting in for the next 20 years."

However, actions taken now to curb emissions will likely pay off later, Overland said. "We do know that with a reasonable mitigation scenario, that will slow down and have a big effect in the second half of the century," he said. "The next generation may see an ice-free summer but, hopefully, their descendants will see a return of more sea ice later in the century."

For now, sea ice is continuing its trend toward seasonal disappearance, according to the report card. In February, Arctic sea ice extent hit its annual maximum -- the lowest maximum since satellite records began in 1979. The melt season began 15 days earlier than average and was the second-earliest start in the 38-year satellite record. In February and March, the time of peak freeze, 70 percent was new and fragile first-year ice and only 3 percent was thick multiyear ice more than 4 years old. That compares to the situation in 1985, when 20 percent of the ice was more than 4 years old and only 35 percent was first-year ice, the report said.

The good news about sea ice, Overland said, is that it appears that there will not be a "tipping point" that scientists had feared. In 2007, after sea ice had hit what was a record low at the time, the concern was that future melt would be so severe that it would send the Arctic into one-way warming spiral, he said. But that seems not to be the case, he said.

Over the past year, the increase in Arctic air temperature was dramatic.

For lands north of 60 degrees latitude, average annual surface air temperatures were 1.3 degrees C (2.3 F) warmer than the long-term average measured from 1981 to 2010 -- and 2.9-degrees C (5.2 F) warmer since the beginning of the 20th century, the report said. That means air temperatures over land in the circumpolar north were higher during the course of the past year than at any other time since detailed records first began being kept, the report said.

"Strong connections" between the usual warmth in the Arctic and conditions in more temperate latitudes were documented, the report said. That was particularly evident in the North Pacific, where warm air flowed across Alaska from November 2014 to June 2015, creating conditions that contributed to the state's second-biggest wildfire season on record, the report said.

Warming was evident in the waters of the circumpolar north as well, according to the Arctic Report Card.

Sea-surface temperatures in all seas of the Arctic Ocean are increasing, and the most dramatic warming over the past year was found in the Chukchi Sea off Alaska and eastern Baffin Bay off Greenland, where surface water temperatures have risen 0.5 degrees C (0.9 F) per decade since 1982, the report said. Melting sea ice is allowing much more sunlight to penetrate the upper levels of the ocean, causing widespread and "exceptional" phytoplankton blooms, the report said.

The warming trend is also putting more fresh water into the Arctic Ocean. Flow from the eight biggest Arctic rivers, including the Yukon and Mackenzie in North America, has increased 10 percent from the annual average recorded in the 1980s, the report said. Those changes, which include earlier peak discharge than in the past, are attributed to increased Arctic precipitation that is linked to warming.

Spring snowmelt continues to occur earlier, a trend previously observed, and June snowpack in the North American and Eurasian Arctic was the second lowest in a satellite record that goes back to 1967, the report card said.

One puzzling finding highlighted in the report is a trend to tundra "browning" -- the disappearance of plants in the Arctic. Until recently, high-latitude vegetation was blooming and spreading, but that process has reversed. Tundra greenness in 2014, the most recent year of measurement, was below the 33-year average, the report said.

What is the explanation? "It's an excellent question. And we don't have the answer to the question yet," said Howard Epstein, a University of Virginia environmental scientist and coauthor of the report card. A drop in Arctic greenness lasting a year or two doesn't attract much attention, but this trend has gone on for four years in some spots, so it has "actually just gotten on our radar," he said at the news conference.

Other changes noted in the Arctic Report Card include:

• The past year's unusual surface melt in Greenland, which was the most extensive since the record-low sea ice year of 2012;

• Threats to walruses, especially disappearing summer and fall sea ice, but also overhunting, ship traffic and offshore industrialization, including oil development;

• The northward migration of boreal fish, like cod, to higher latitudes, a trend most noticed in the Barents Sea; and

• The emerging work of local observer networks, such as the program established by the Alaska Native Tribal Health Consortium, and their role in supplying data to the world scientific community.

Some of the changes highlighted in the report card were predicted through modeling, but that is not always the case, Overland said.