Local factors of magnified Arctic warming

Long-term observations of surface temperatures show increased surface warming in Canada, Siberia, Alaska and the Arctic Ocean relative to the rise in global average temperature. This warming pattern, commonly referred to as amplification in the Arctic, is consistent with computer models, simulating the response to increasing greenhouse gas concentrations. However, the physical processes underlying intensive warming are still elusive.

A new international study on the cause of amplification in the Arctic published this week in the journal Nature Climate change shows that local concentrations of greenhouse gases and Arctic climate responses outweigh other processes. Using complex computer simulations, scientists were able to refute the previously suggested hypotheses, which emphasized the role played by heat transport from the tropics to the poles as a key factor of amplified warming in the tropics. Arctic.

"Our study clearly shows that local forcing of carbon dioxide and polar reactions are the most effective for amplification in the Arctic compared to other processes," said L & # 39; Corresponding author, Malta Stuecker, Project Manager at the IBS Climatology Center (ICCP) in Busan, South Korea.

Increased anthropogenic carbon dioxide (CO₂) the concentrations retain heat in the atmosphere, resulting in a warming of the surface. Regional processes can then amplify or mitigate this effect, thus creating the typical pattern of global warming. In the Arctic region, warming of the surface reduces the extent of snow and pack ice, decreasing reflectivity of the surface. As a result, a greater amount of sunlight can reach the top of the soil and ocean layers, resulting in accelerated warming. In addition, changes in Arctic clouds and in the vertical atmospheric temperature profile can improve warming in the polar regions.

In addition to these factors, the heat can be transported in the Arctic by the winds. "We are observing this process, for example during El Niño events." "Tropical warming, caused either by El Niño or by anthropogenic greenhouse emissions, can lead to an overall change in atmospheric weather patterns that may change surface temperatures in remote areas such as the Arctic., "said Kyle Armor, co-author of the study and professor of atmospheric science and oceanography at the University of Ottawa. University of Washington.

In addition, global warming outside the Arctic region will also lead to increased temperatures in the Atlantic Ocean. Ocean currents, such as the Gulf Stream and the North Atlantic Drift, can then transport the warmer waters to the Arctic Ocean, where they could melt sea ice and undergo further amplification due to local processes.

To determine whether tropical warming, atmospheric winds, and changes in ocean currents are contributing to the future amplification of the Arctic, the team has designed a series of computer model simulations. "Comparing simulations with only Arctic CO₂ changes with simulations that apply CO₂ on a global scale, we find similar warming patterns in the Arctic. These results demonstrate that remote physical processes outside the polar regions do not play a major role, contrary to previous suggestions, "said co-author Cecilia Bitz, professor of atmospheric science at the University of California. University of Washington.

In the tropics, powered by high temperatures and high humidity, the air can easily move in high altitude, which means that the atmosphere is unstable. On the other hand, the Arctic atmosphere is much more stable with respect to the vertical movement of the air. This condition improves CO₂– induced warming in the Arctic near the surface. In the tropics – because of the unstable atmosphere – CO₂ Warms the upper atmosphere mainly and the energy is easily lost in the space. This is the reverse of what is happening in the Arctic: less outgoing infrared radiation escapes from the atmosphere, further amplifying surface-trapped warming.

"Our computer simulations show that these changes in the vertical atmospheric temperature profile in the Arctic region outweigh the other regional feedback factors, such as ice albedo feedback, often cited," states Malta Stuecker.

The new findings of this study underscore the importance of Arctic processes in controlling the rate at which sea ice will retreat into the Arctic Ocean. The results are also important for understanding how sensitive polar ecosystems, Arctic permafrost and Greenland ice sheet will respond to global warming.

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More information:
Malta F. Stuecker et al., Polar amplification dominated by local forcing and returns, Nature Climate change (2018). DOI: 10.1038 / s41558-018-0339-y