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The first summer on record that melts practically all of the Arctic’s sea ice, an ominous milestone for the planet, could occur as early as 2027.

For the first time, an international research team, including CU Boulder climatologist Alexandra Jahn and  from the University of Gothenburg in Sweden, used computer models to predict when the first ice-free day could occur in the northernmost ocean. An ice-free Arctic could significantly impact the ecosystem and Earth’s climate by changing weather patterns. 

“The first ice-free day in the Arctic won’t change things dramatically,” said Jahn, associate professor in the Department of Atmospheric and Oceanic Sciences and fellow at CU Boulder’s Institute of Arctic and Alpine Research. “But it will show that we've fundamentally altered one of the defining characteristics of the natural environment in the Arctic Ocean, which is that it is covered by sea ice and snow year-round, through greenhouse gas emissions.”  

Alexandra Jahn

The findings were Dec. 3 in the journal Nature Communications. Jahn will also the results Dec. 9 at the American Geophysical Union annual meeting in ���Ĺ���ý D.C.

A Blue Arctic

As the climate warms from increasing greenhouse gas emissions, sea ice in the Arctic has disappeared at an unprecedented speed of more than 12% each decade.

In September, the National Snow and Ice Data Center reported that this year’s Arctic sea ice minimum—the day with the least amount of frozen seawater in the Arctic—was one of the lowest on record since 1978.

At , or 4.28 million square kilometers, this year’s minimum was above the all-time low observed in September 2012. But it still represents a stark decline compared to the average coverage of 6.85 million square kilometers between 1979 and 1992.

When the Arctic Ocean has less than 1 million square kilometers of ice, scientists say the Arctic is ice free.

Previous projections of Arctic sea ice change have focused on predicting when the ocean will become ice free for a full month. Jahn’s prior research suggested that the first ice-free month would occur almost inevitably and might happen by the 2030s.

As the tipping point approaches, Jahn wondered when the first summer day that melts virtually all of the Arctic sea ice will occur.

“Because the first ice-free day is likely to happen earlier than the first ice-free month, we want to be prepared. It’s also important to know what events could lead to the melting of all sea ice in the Arctic Ocean,” Heuzé said.

Non-zero possibility

Arctic sea ice is melting as a result of climate change. (Credit: Céline Heuzé/University of Gothenburg)

Jahn and Heuzé projected/estimated the first ice-free Arctic day using output from over 300 computer simulations. They found that most models predicted that the first ice-free day could happen within nine to 20 years after 2023 regardless of how humans alter their greenhouse gas emissions. The earliest ice-free day in the Arctic Ocean could occur within three years. 

It’s an extreme scenario but a possibility based on the models. In total, nine simulations suggested that an ice-free day could occur in three to six years.

The researchers found that a series of extreme weather events could melt two million square kilometers or more of sea ice in a short period of time: A unusually warm fall first weakens the sea ice, followed by a warm Arctic winter and spring that prevents sea ice from forming. When the Arctic experiences such extreme warming for three or more years in a row, the first ice-free day could happen in late summer.

Those kinds of warm years have already happened. For example, in March 2022, areas of the Arctic were , and areas around the North Pole were nearly melting. With climate change, the frequency and intensity of these weather events will only increase, according to Heuzé.

Sea ice protects the Arctic from warming by reflecting incoming sunlight back into space. With less reflective ice, darker ocean waters will absorb more heat from the Sun, further increasing temperatures in the Arctic and globally. In addition, warming in the Arctic could change wind and ocean current patterns, leading to more extreme weather events around the world.

But there’s also good news: A drastic cut in emissions could delay the timeline for an ice-free Arctic and reduce the time the ocean stays ice-free, according to the study. 

“Any reductions in emissions would help preserve sea ice,” Jahn said.