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Cryosphere

Cryosphere

Arctic heads for ‘uncharted territory’

17 Dec 2018

 

 The Arctic is continuing to warm twice as fast as the rest of the planet; air temperatures every year from 2014 to today have been warmer than all previous records since 1900.

The reasons for this trend include less snow and ice to reflect sunlight, warmer oceans releasing heat into the atmosphere later into the fall, and increasing winter cloudiness, according to the US National Oceanic and Atmospheric Administration (NOAA).

NOAA released its 13th annual Arctic Report Card, synthesizing the peer-reviewed work of 81 scientists from 12 countries, on 11 December 2018 at the American Geophysical Union (AGU) Fall Meeting in Washington, DC. The report sounded warnings about the current effects of Arctic warming in such diverse fields as caribou populations and poisoning of shellfish.

Emily Osborne, who heads NOAA’s Arctic research programme, told reporters at AGU that the higher air and water temperatures are pushing the Arctic into uncharted territory. The average temperature this past year was 1.7 °C above the long-term average, she said, and an unusually sluggish and wavy high-altitude jet stream coincided with a heat wave at the North Pole and a swarm of severe winter storms in the eastern US.

The 12 lowest extents of summer Arctic sea ice have occurred in the past 12 years, according to Donald Perovich of Dartmouth College, US, lead author of the report’s sea ice chapter. The 2018 winter extent is the second lowest on record and the minimum summer extent the sixth lowest.

“Sea ice continues to be younger, thinner, and less stable,” said Perovich, adding that “ice over four years of age makes up only 1% of the Arctic ice pack. The oldest ice has declined by 95% in the past 33 years”. The younger ice reflects back less solar radiation, contributing to further warming.

In the Bering Sea, ice reached an all-time record low for virtually the entire winter, Perovich told reporters. During two weeks in February 2018, usually the time of greatest ice growth, the Bering Sea lost around 215,000 square km of ice.

Perovich and his colleagues attribute the loss to persistent southerly circulation that brought in warm air and surface water temperatures that pushed sea ice northward. The significance, he said, was that Bering Sea ice supports one of America’s most valuable commercial fisheries and is home to a variety of seals, birds, and fish.

Howard Epstein of the University of Virginia, US, reported on land effects of warming, which can lead to either greening or browning of the tundra landscape. The trend is taking its toll on herds of caribou and wild reindeer, important species across the Arctic, he said, and their numbers are declining sharply.

Similarly, reported Karen Frey of Clark University, US, toxic algal blooms are discussed for the first time in this year’s report. Toxins are now found in Arctic birds, mammals, and fish, posing food safety issues for coastal communities where these species form a major part of the diet.

The 2018 Report Card also covers plastic pollution for the first time, especially microplastics, which are more highly concentrated in the Arctic than in other ocean basins. “We are at the beginning of understanding how this problem is affecting the Arctic,” Frey said.

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