As the planet warms, the Arctic Ocean absorbs less CO2

As the Earth warms, the Arctic Ocean's ability to absorb carbon dioxide from the atmosphere is declining due to melting permafrost and worsening coastal erosion, according to new research.

A study published Monday in the journal Nature Climate Change models the ways in which Arctic areas affected by permafrost erosion are releasing more carbon than they absorb. The study concluded that by 2100, the effect could contribute to an annual increase in atmospheric carbon dioxide — a planet-warming gas — equivalent to about 10% of all European car emissions in 2021.

The findings have worrying implications for the ocean's vital ability to act as a carbon sink, or a place that removes greenhouse gases from the atmosphere, said David Nielson, lead author of the study and a researcher at the Max Planck Institute for Meteorology in Hamburg, Germany.

“For the first time, we can actually put a signal — maybe not a number, but a signal — to the change in the Arctic Ocean’s ability to absorb CO2 from the atmosphere due to coastal erosion, and that signal is negative,” Nielson said.

The study builds on previous research that found coastal permafrost erosion is accelerating and could increase by a factor of 2 to 3 by 2100. That's largely because permafrost, or once permanently frozen ground, is beginning to thaw at a faster rate and over longer periods of the year due to human-caused climate change, Nielson said.

“During the summer months along the Arctic coast, the ground is no longer frozen, so there is no ice and there is open water,” he said. “That makes the coast vulnerable to waves and storms that erode the shoreline and move this soil into the ocean.”

The researchers found that erosion could reduce the ocean's capacity to absorb more than 14 million tons of CO2 per year by the end of the century (a typical passenger car emits about 5 tons of CO2 per year).

Historically, permafrost has stored vast amounts of the planet’s carbon (by some estimates, there is 2.5 times more carbon trapped in permafrost than in the global atmosphere, according to the National Snow and Ice Data Center). Many researchers worry that permafrost loss will release that carbon and radically alter Earth’s traditional cycles.

“We ran several different simulations and in all of them, no matter how we represented this organic matter, the Arctic Ocean CO2 sink was reduced, so it’s a pretty robust result,” Nielson said.

He noted that the Arctic is already warming much faster than the rest of the planet, at a rate three to four times faster than the global average. But his model found some “hot spots” of permafrost erosion, such as Drew Point in Alaska, the Mackenzie River Delta in Canada and parts of Siberia, where local impacts include ocean acidification and adverse effects on coastal ecosystems.

Coastal communities like Shishmaref in Alaska are also facing pressure to relocate due to intensifying erosion, storms, rising sea levels and melting sea ice, which are also contributing to the loss of heritage and archaeological sites, he said.

Arctic sea ice extent has declined sharply since the 1970s, although the trend has leveled off in recent years. In July, the second warmest month on record, Arctic sea ice extent was 7% below average, according to the European Union's Copernicus Climate Change Service.

But permafrost in particular is warming at a rapid rate, and some studies show that most of the Earth's near-surface permafrost could disappear by 2100.

An iceberg floats in Scoresby Strait, Greenland, in September 2023.

(Chris Szagola/Associated Press)

As the first study to model the effects of Arctic coastal permafrost erosion on CO2 uptake, the findings help advance global understanding of the process, according to Kay McMonigal, an assistant professor of physical oceanography in the School of Fisheries and Ocean Sciences at the University of Alaska Fairbanks, who did not work on the paper.

“It’s surprising because we didn’t even know what impact signal this would have, whether it would increase or decrease the capacity of the Arctic Ocean to absorb CO2,” McMonigal said. “And they found that under a range of different sensitivity levels, it always decreases the capacity.”

Although the model focuses on one region, McMonigal said the results in the Arctic will play a major role in Earth’s future climate. The study projects that coastal permafrost erosion could exert a positive feedback loop that increases atmospheric CO2 by 1.1 to 2.2 million tons per year for every degree Celsius, or 1.8 degrees Fahrenheit, of global warming.

“It’s a fairly small area compared to the entire planet, but it still has an impact,” McMonigal said. “Arctic sea ice is melting and is expected to continue melting in the future, and I think one of the implications of this paper is that we need to better understand those processes.”

Nielson similarly said that more research and detailed modeling will be needed to better understand the mechanisms at work, and that the research still contains some uncertainties.

What's more, while the carbon contributions from this process are notable, they are tiny compared to human carbon emissions, accounting for only about 0.1% of human emissions worldwide.

But because those human emissions are warming the planet (which in turn is melting permafrost), continuing efforts to reduce fossil fuel use is critical, he said.

“As long as there is anthropogenic climate change, it will continue to accelerate,” he said of permafrost erosion. “So the solution is to stop climate change, to stop emitting carbon into the atmosphere.”