NOAA Arctic Report Card: Update for 2018, Effects of persistent Arctic warming continue to mount

In its 13th year, NOAA's Arctic Report Card (www.arctic.noaa.gov/Report-Card/) reflects on a range of land, ice, and ocean observations made throughout the Arctic during the 2018 calendar year. A series of 14 essays written by more than 80 scientists from 12 countries are included in the 2018 Arctic Report Card. As in previous years, this update highlights the changes that continue to occur in, and among, the physical and biological components of the Arctic environmental system.

In 2018, surface air temperatures in the Arctic continued to warm at roughly twice the rate relative to the rest of the globe, a phenomenon that has been termed "Arctic Amplification." The year 2018 was the second warmest year on record in the Arctic since 1900 (after 2016), at +1.7° C relative to the long-term average (1981-2010). Arctic air temperatures for the past five years (2014-18) have exceeded all previous records since 1900. Growing atmospheric warmth in the Arctic results in a sluggish and unusually wavy jet-stream that coincided with abnormal weather events in both the Arctic and mid-latitudes. Notable extreme weather events coincident with deep waves in the jet-stream include the heat wave at the North Pole in autumn 2017, a swarm of severe winter storms in the eastern United States in 2018, and the extreme cold outbreak in Europe in March 2018 known as "the Beast from the East."

Continued warming of Arctic atmospheric temperatures in 2018 is an indicator of both regional and global climate change and a driver of broad Arctic environmental change. In the terrestrial system, atmospheric warming continued to drive broad, long-term trends in declining terrestrial snow cover, melting of the Greenland Ice Sheet and lake ice, increasing summertime Arctic river discharge, and the expansion and greening of Arctic tundra vegetation. Despite the growth of vegetation available for grazing land animals, herd populations of caribou and wild reindeer across the Arctic tundra have declined by nearly 50% over the last two decades.

As a result of atmosphere and ocean warming, the Arctic is no longer returning to the extensively frozen region of recent past decades. In 2018 Arctic sea ice remained younger, thinner, and covered less area than in the past. The wintertime maximum sea ice extent measured in March of 2018 was the second lowest in the 39-year record, following only 2017. For the satellite record (1979-present), the 12 lowest sea ice extents have occurred in the last 12 years. The disappearance of the older and thicker classes of sea ice are leaving an ice pack that is more vulnerable to melting in the summer, and liable to move unpredictably. When scientists began measuring Arctic ice thickness in 1985, 16% of the ice pack was very old (i.e., multiyear) ice. In 2018, old ice constituted less than 1% of the ice pack, meaning that very old Arctic ice has declined by 95% in the last 33 years. The pace and extent of the changes to summer sea ice cover, along with regional air temperatures and advection of waters from the Pacific and Atlantic oceans, are linked to the spatial patterns of late summer sea surface temperature. August mean sea surface temperatures in 2018 show statistically significant warming trends for 1982-2018 in most regions of the Arctic Ocean that are ice-free in August.

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