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US scientists say the world is heading towards a "seasonally ice-free Arctic Ocean." Germany's research ship Polarstern is on its way home after even reaching the North Pole through open water patches.
The Arctic's sea ice had shrunk last week to 3.74 million square kilometers (1.44 million square miles), US snow and ice monitors said Monday.
The ice extent is the second-lowest measured via satellite since records began in 1979.
The melt illustrated that "we are headed towards a seasonally ice-free Arctic Ocean," said Mark Serreze of the Colorado-based National Snow & Ice Center (NSIDC).
Serreze said a Siberian heat wave last spring and a natural Arctic climate phenomenon were at play as well as the warming from the burning of coal, oil and natural gas.
"This year is another nail in the coffin," said Serreze. "It's been a crazy year up north."
Hamburg-based Greenpeace marine biologist Christian Bussau said the NSIDC ice dissipation data showed "how massive climate warming is advancing."
Last April, Hamburg university scientists calculated that by 2050 the North Pole would be ice-free in some Arctic summers.
Every ton of carbon dioxide emitted worldwide led to 3 square meters of ice melt in the highly sensitive Arctic, said the study's lead earth scientist Dirk Notz.
As Arctic sea ice vanishes, climatologists say, it leaves dark, open water that absorbs solar radiation, a process that has amplified Arctic temperatures twice as fast.
Last month, large openings melted in the sea ice above Greenland enabled the ice breaker to reach the geographic North Pole, previously too difficult for shipping.
"At times we had open water as far as the eye could see," expedition leader Markus Rex said, referring to the area usually covered in thick sea ice.
"I'd never experienced that before so far north," added Polarstern captain Thomas Wunderlich.
The project called Mosaic involved scientists from 17 nations, including Russia, France, the USA and China. It delivered findings to 80 research institutes.
The Polarstern is due in its Alfred-Wegener-Institute home port, Bremerhaven, on October 12.
In a study published last month, the institute said Greenland had lost a record 532 billion metric tons of ice during the Arctic summer of 2019.
Melted, that equated to California being 1.25 meters (four feet) deep in water.
"Not only is the Greenland ice sheet melting, but it's melting at a faster and faster pace, said Ingo Sasgen, lead author and Alfred-Wegner-Institute geoscientist.
That translated, worldwide, into slowly rising sea levels, added NASA ice scientist and co-author Alex Gardner.
In late July, according to the Canadian Ice Service, the Milne Ice Shelf at the fringe of Ellesmere Island in Canada's remote Nunavut territory had collapsed.
The 80 square kilometer chunk had been Canada's largest remaining intact ice shelf, said Ottawa-based glaciologist — larger than New York's Manhattan island.
The Milne shelf had "disintegrated, basically," said Copland, highlighting that the 2020 Canadian Arctic summer was 5 degrees Celsius above the 30-year average.