Some Arctic warming ‘irreversible’ even if we cut atmospheric CO2

The Arctic will retain about 1.5°C of warming even if the carbon dioxide in the atmosphere returns to pre-industrial levels and the planet as a whole cools.

The region is also predicted to retain about 0.1 millimetres per day of excess precipitation, regardless of whether we deploy large-scale carbon dioxide removal (CDR) projects.

“These findings highlight the irreversible nature of Arctic climate change even under aggressive CDR scenarios,” the researchers wrote in the study.

Atmospheric CO2 levels are currently about 1.5 times as high as they were in the pre-industrial era, and the Arctic has warmed by more than 3°C. A study published in March found that average sea ice extent would remain 1 million square kilometres smaller even if excess CO2 was removed.

In the new study, Xiao Dong at the Institute of Atmospheric Physics in Beijing and his colleagues predicted the Arctic’s potential to retain warming using 11 independent climate models. In a first, it suggests that precipitation will also stay elevated, says Michael Meredith at the British Antarctic Survey, who wasn’t involved in the study.

The main reason is because the ocean, which has absorbed 90 per cent of the heat from global warming, will continue heating the Arctic for centuries even if the atmosphere cools down. This could be compounded by feedback loops like the loss of sea ice allowing open water to heat the air.

“Even if you get the atmosphere cooling, the ocean will be lagging behind that and pushing against that,” says Meredith.

Because of the financial and energy costs involved, many are sceptical that CDR, which ranges from planting trees to sucking CO2 out of the air with fans and chemical filters, will be able to significantly reduce CO2 in the atmosphere, a process that would otherwise take thousands of years.

Dong and his colleagues analysed an abstract scenario in which atmospheric CO2 quadruples from pre-industrial levels over 140 years, declines for 140 years and remains at pre-industrial levels for another 60 years.

They also analysed a potential real-world climate scenario in which humanity immediately slashes emissions, as well as one in which we continue high emissions but then quickly ramp up CDR starting in 2070. In these two scenarios, they found the Arctic is about 1.5°C warmer and would continue to receive an additional 0.1 millimetres of precipitation per day in 2100, just as in the abstract scenario.

The models predict that, unlike in the rest of the far north, temperature and precipitation will decrease over a swath of ocean just south of Greenland and Iceland. This suggests that the Atlantic Meridional Overturning Circulation (AMOC) will be transporting less warm surface water from the tropics to this area. Research suggests this current, which is driven by temperature and density differences in ocean waters, is already slowing down as the global ocean warms, a trend that could eventually bring much colder winters to Europe.

Climate effects like thawing of permafrost and melting of the Greenland ice sheet would also probably continue, although the study didn’t model them.

“You’re going to expect that the Greenland ice sheet will behave as we observe it to, which is that it will be continuing to lose mass and contributing to sea level rise,” says Mark Serreze at the US National Snow and Ice Data Center.

While this study shows the Arctic will remain warmer for several centuries, over many additional centuries or millennia it should eventually cool, he adds.