After a year of extreme melt, Arctic sea ice ended up dropping to its second-lowest level on record — a mark only surpassed by melting in 2012.

The National Snow and Ice Data Center (NSIDC) announced Monday that the Arctic's minimum sea ice extent for 2019 — meaning the smallest area of Arctic ocean covered in sea ice before cooler fall temperatures begin to rebuild the ice — was the second-lowest in the 40-year satellite era. This sea ice extent, a clear indication of a rapidly warming planet, was over 2 million square kilometers (811,000 square miles) below the average minimum extent measured in previous decades.

"The overall take-home message is that the long-term negative trend of sea-ice decline continues," said Lars Kaleschke, a physicist and sea ice expert at the Alfred Wegener Institute for Polar and Marine Research who had no role in the NSIDC report. "There is no sign of a pause or reversal of the Arctic warming trend."

"The rapid changes in the Arctic are some of the clearest indicators of anthropogenic climate change," added Zack Labe, a climate scientist and Ph.D. candidate at the University of California, Irvine who also had no involvement in the NSIDC announcement. "2019 is consistent with the long-term declining trends of Arctic sea ice area and its thickness."

The long-term trend is certainly clear. "The 13 lowest extents in the satellite era have all occurred in the last 13 years," the NSIDC noted in their announcement.

2019's minimum sea ice extent was well below the 1980 to 2010 average (depicted by the yellow line). Image: nsidc

Arctic sea ice trends. Image: nsidc

2019's sea ice extent "effectively" tied the years 2007 and 2016 for the second-lowest minimum on record, the NSIDC said, though it's still possible for some more late-season melt to occur.

Critically, it's not just young, thin sea ice that's melting. Much of the sea ice most resistant to melting is vanishing, or has already disappeared. "The amount of older and thicker sea ice is rapidly dwindling," said Labe.

How rapidly? In 1985, the oldest ice (which is ice greater than four years old) comprised 16 percent of Arctic's total sea ice, a National Oceanic and Atmospheric Administration report concluded in 2018. But by March 2018, the old ice made up just 0.9 percent of the Arctic's ice — a 95 percent reduction.

Arctic sea ice is particularly vulnerable to something called the albedo effect, wherein bright white sea ice melts (often due to warmer air temperatures). This leaves large swathes of dark ocean exposed to absorb more heat from the sun, which warms the ocean and in turn melts more ice. It's a vicious, relentless feedback loop of melting. Labe noted that the albedo effect has enhanced the warmth of surface waters in the Arctic, but by just how much is an active question in science, and vital to grasping the fate of the Arctic.

Fortunately, Arctic scientists are intensively researching the question of how such feedbacks are amplifying Arctic warming, including an exceptional project beginning this very month. Specifically, the seafaring MOSAiC experiment — in which a hardy German icebreaking vessel will intentionally get trapped in a floating mass of ice and drift through the Arctic for a year — intends to gather data about the air, ice, and ocean.

"The MOSAiC experiment will provide year-round measurements in the highest northern latitude which will be used to investigate this question of the "Arctic amplification," explained Kaleschke.

#Arctic melt season in review... (daily evolution since April 1)



————— 2019 Monthly Statistics (NSIDC) —————

April - *lowest on record*

May - 2nd lowest on record

June - 2nd lowest on record

July - *lowest on record*

August - 2nd lowest on record pic.twitter.com/LYsN0Z8Dt8 — Zack Labe (@ZLabe) September 22, 2019

Amplified warming in the Arctic is solid evidence that the climate is changing, and changing rapidly — similar to increases in wildfires, "off-the-charts" melting in Greenland, historic, prolonged drought in the Southwest, the smashing of temperature records, retreating (or newly dead) glaciers around the globe, a relentlessly warming ocean, skyrocketing atmospheric carbon dioxide levels, a dramatic boost in extreme deluges, and so on.

Welcome to climate change. "This isn't something far off into the future," said Labe. "It's happening right now."