How to Tell When the Arctic Ocean Will Be Ice Free

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Spew another trillion tons of carbon dioxide, and it’ll be smooth sailing through the Northwest Passage.

By Nathan Collins


(Photo: Harry Gerwin/Getty Images)

It was just nine years ago when, for the first time on record, an ice-free route opened through the fabled Northwest Passage. And as climate change seems to be driving Arctic sea ice extent well below historical averages, there’s a possibility of a largely ice-free Arctic Ocean in the near future—around 30 years from now, in fact, according to a new report.

“The ongoing rapid loss of Arctic sea ice has far reaching consequences for climate, ecology, and human activities alike,” Dirk Notz and Julienne Stroeve write in Science. That includes accelerated warming, effects on weather at lower latitudes, and associated impacts on plants and animals in the region.

Figuring out when those consequences will arrive is tricky, since climate models often disagree on how sea ice coverage—in particular, coverage at its September nadir—will change in years to come.

“While in the most recent Climate Model Intercomparison Project 5 some models project a near ice-free Arctic during the summer minimum already toward the beginning of this century, other models keep a substantial amount of ice well into the next century,” Notz and Stroeve write.

Fortunately, Notz and Stroeve found, there’s a robust way to predict how much sea ice we’re losing. Drawing on Hadley Centre Sea Ice and Sea Temperature data from 1953 to 1978 and the National Snow and Ice Data Center’s Sea Ice Index from 1979 to 2015, the researchers computed 30-year running averages of September sea ice coverage—that is, they computed averages for the years 1953–83, 1954–84, 1955–85, and so on.

Comparing those with estimates of the total amount of greenhouse gas emissions, they found that each additional metric ton of carbon dioxide sent into the atmosphere reduced the amount of sea ice by three square meters, or about 11 square feet.

“This number is sufficiently intuitive to allow one to grasp the contribution of personal CO2 emissions to the loss of Arctic sea ice,” Notz and Stroeve write. “For example … the average personal CO2 emissions of several metric tons per year can be directly linked to the loss of tens of [square meters] of Arctic sea ice every single year.”

The estimates also suggests, based on current sea-ice coverage, that it will take another trillion metric tons of carbon dioxide emissions before Arctic summer sea ice more or less vanishes. Given global greenhouse gas emissions of around 35 trillion metric tons per year, that suggests there won’t be any Arctic sea ice in September by mid-century.