Some Arctic warming is ‘irreversible’ even if we reduce atmospheric CO2

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

The region is also expected to retain approximately 0.1 millimeter per day of excess precipitation, whether or not we deploy large-scale carbon dioxide removal (CDR) projects.

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

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

In the new study, Xiao Dong of the Beijing Institute of Atmospheric Physics and colleagues predicted the Arctic’s potential to retain warming using 11 independent climate models. Initially, this suggests that precipitation will also remain high, says Michael Meredith of the British Antarctic Survey, who was not involved in the study.

The main reason is that the ocean, which has absorbed 90% of the heat from global warming, will continue to warm the Arctic for centuries, even as the atmosphere cools. This could be made worse by feedback loops such as loss of sea ice allowing open water to warm the air.

“Even if the atmosphere cools, the ocean will lag behind and oppose it,” says Meredith.

Because of the financial and energy costs involved, many doubt that CDR, which ranges from planting trees to sucking CO2 from the air using fans and chemical filters, is capable of significantly reducing CO2 in the atmosphere, a process that would otherwise take thousands of years.

Dong and his colleagues analyzed 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 analyzed a potential real-world climate scenario in which humanity would immediately reduce emissions, as well as a scenario in which we would continue to emit high emissions but then rapidly increase the CDR starting in 2070. In both of these scenarios, they found that the Arctic is about 1.5°C warmer and would continue to receive 0.1 millimeters of additional precipitation per day in 2100, just as in the abstract scenario.

Models predict that, unlike 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 transport less warm surface water from the tropics to this area. Research suggests that this current, driven by temperature and density differences in ocean waters, is already slowing as the global ocean warms, a trend that could eventually bring much colder winters to Europe.

Climate effects such as thawing permafrost and melting of the Greenland ice sheet would also likely continue, although the study did not model them.

“You would expect the Greenland ice sheet to behave as we observe, which is to continue to lose mass and contribute to sea level rise,” says Mark Serreze of the US National Snow and Ice Data Center.

Although this study shows that the Arctic will remain warmer for several centuries, it is likely to cool over several more centuries or millennia, he adds.