On land and at sea, the Arctic is under a relentless global warming siege.

Rising temperatures, melting ice and thawing permafrost threaten ecosystems and communities across the far north with direct impacts like toxic algae outbreaks, harm to fisheries and caribou herds, and coastal erosion.

There are also indirect climate impacts that affect the rest of the world. Emerging research shows the warming Arctic drives changes to the jet stream that can result in extreme weather in North America and Eurasia, and more atmospheric moisture can fuel heavy rain storms.

The National Oceanic and Atmospheric Administration and partnering research organizations explain the impacts in the 2018 Arctic Report Card, highlighting issues like record-low sea ice in the Bering Sea and heat waves across the central Arctic.

Overall, 2018 was the second-warmest year for the Arctic since record-keeping for the region began in 1900, and the Arctic continued to warm at about twice the rate of the global average, to 3.06 degrees Fahrenheit above the 1981-2010 average. Arctic air temperatures for the past five years (2014-2018) exceeded all previous records, and Arctic sea ice extent was the second-lowest overall, with the lowest-recorded winter ice in the Bering Sea.

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As they announced the report card findings, the authors also said research has documented a disturbing increase in microplastic pollution in the Arctic Ocean, which isn't directly related to global warming but may show how warmer ocean currents are spreading farther into the once-frozen region.

"All roads in the global ocean circulation system lead to the Arctic," said Clark University Arctic climate researcher Karen Frey.

The most visible sign of the vast changes in the Arctic is the continued decline of sea ice, which acts as a global cooling system by reflecting solar radiation back into space. But Earth's cooling shield is shrinking — the 12 lowest sea ice levels on record have all occurred in the last 12 years.

And the disappearance of older, thicker sea ice leaves the Arctic's ice cover vulnerable to melting in the summer and prone to unpredictable movement, which threatens shipping. Since scientists started measuring sea ice thickness with satellites in 1985, thick multiyear ice has declined by 95 percent.

Is the Arctic Ice Machine Shutting Down?

In 2018, according to the Arctic Report Card, old ice constituted less than 1 percent of the ice pack, down from 16 percent just 33 years ago, and German researchers who contributed data to the report card are trying to figure out why by looking at some of the Arctic sea ice nurseries.

In those formation zones, like the Barents Sea and the Laptev Sea, icy autumn and winter winds blow from land out over the ocean. The wind freezes the surface, including the fresh water from rivers, pushes the ice away from the shore and compacts it to thicker floes that don't all melt in summer — that's how the multiyear ice that's so critical to overall sea ice extent is formed.

One very distinct trend is visible in the Barents Sea, north of Norway and Western Russia. That part of the Arctic Ocean is in the process of "Atlantification," says ice researcher Lars Kaleschke, with the Max Planck Institute for Meteorology in Hamburg.

"The Barents Sea is one of the fastest-changing regions of the Arctic, with a strong decline of winter-time sea ice cover, which is clearly linked to the increasing heat content of the ocean," Kaleschke said.

Signs of Tipping Points?

Julienne Stroeve, a researcher with the National Snow and Ice Data Center, said transformation of the Barents Sea could represent a tipping point in Arctic systems, with data already suggesting that the adjacent Kara Sea could be the next to experience a big decline in sea ice.

"We are now witnessing transformation of Arctic waters in that region to Atlantic waters, and this warm/salty water is not allowing the winter ice to form," said Stroeve, who didn't work on this Arctic Report Card but did work on a previous edition. "If this entire region becomes an extension of the Atlantic, this may start to pose an irreversible change."

Stroeve said the cumulative Arctic changes affect ocean circulation, fisheries, and add moisture to the atmosphere, perhaps increasing the likelihood of winter rain-on-snow events that put caribou, reindeer and musk oxen at risk.

"And of course this region of the Arctic has been implicated in many mid-latitude weather changes, such as breakdown of the polar vortex and cold air outbreaks in winter," she added.

For the world, Arctic warming is like leaving the freezer door open, said National Snow and Ice Data Center Director Mark Serezze. More and more of the frozen area will be exposed to above-freezing temperatures, and the ice will melt.

"The way I've always viewed it is, the critical tipping point in the Arctic is very tangible, it's the melting point, 32 degrees Fahrenheit. When you start reaching that, if affects everything else," he said. "The melting season is longer and more intense and it doesn't get as cold as it used to. If you warm the Arctic by a few degrees, it has big, big impacts," he said.

Extreme Arctic Heat Waves

Along with the ongoing changes in the Barents Sea, Kaleschke said an extreme Arctic heat wave in 2018 was especially noteworthy as a sign of rapid Arctic change.

In February, temperatures across parts of the Arctic were up to 40 degrees Fwarmer than average for that time of year.

In the summer, extreme heat generated record temperatures over land, contributing to the dry conditions that fueled forest fires north of the Arctic Circle in Scandinavia.

Kaleschke noted that open water formed near the northern coast of Greenland several times during the year, suggesting fundamental changes in a part of the Arctic that is supposed to be the final stronghold for the oldest and thickest sea ice, and perhaps a last refuge for ice-dependent animals like polar bears and some species of seals.

Impact on Humans & Ecosystems

Humans in the Arctic region have lived in rhythm with ice-dependent wildlife for thousands of years, but global warming is disrupting the balance.

The report card says pan-Arctic data suggest a long-term decline of coastal ice that's frozen to the land. Decline of this landfast ice is making it more difficult, and in some cases almost impossible, for indigenous people to hunt and fish, and the loss of the ice buffer is also making coastal communities more vulnerable to erosion from destructive ocean waves.

The Arctic Report Card also explains how rapid warming is linked to serious impacts to plants and animals on land and in the ocean.

Bering Sea ice was at a record low extent for virtually the entire 2017-2018 season, which increased plankton and algae reproduction by up to 500 percent. Changes in the quantity and timing of algae growth and plankton blooms can affect the rest of the food chain.

On land, some caribou herds have already declined by as much as 90 percent, affecting traditional native subsistence hunting in parts of Canada, said Yukon College caribou researcher Don Russell, who studies the roles of climate change and other factors affecting caribou herds, such as disease, loss of habitat and spreading human activity.

Global warming directly affects caribou by changing their habitat and the availability of food, and it may be enabling the spread of disease northward.

"Caribou populations have always cycled every 40 to 70 years, but the numbers now are as low as we've ever seen them, and that's a caution for us," said Russell, who authored a section on the decline in the Arctic Report Card. "What concerns us this time, is that there are unprecedented factors, including climate change, hunting and development coming together that could really slow down recovery."

In Canada, east of the Mackenzie River, most of the development disturbing wildlife comes from hardrock mining, while in Alaska, there's a continuing threat of more oil and gas development along the North Slope.

'Alaska Fisheries Will Change Dramatically'

Subsistence and commercial fisheries are also threatened by warming Arctic waters. The report links increasing temperatures with outbreaks of dangerous toxin-producing algae that lead to paralytic shellfish poisoning (PSP), which can affect wildlife and humans.

"Paralytic shellfish poisoning events in the North Pacific appears to be primarily driven by warmer ocean temperatures. My studies have looked at ocean acidity, marine nutrients, currents, but warmer waters primarily explains the locations and intensity of the PSP events," said Bruce Wright, a researcher with the Aleutian Pribilof Islands Association.

Warming is also coinciding with an expansion of harmful algae species responsible for toxic algal blooms in the Arctic Ocean. Considerable concentrations of algal toxins have been found in the tissues of Arctic clams, seals, walrus and whales.

"The future looks bleak," Wright said. "I expect that in the decades to come Alaska fisheries will change dramatically."