Better understanding the reasons behind Arctic amplified warming

It’s clear that rising greenhouse gas emissions are the main driver of global warming. But on a regional level, several other factors are at play. That’s especially true in the Arctic – a massive oceanic region around the North Pole which is warming two to three times faster than the rest of the planet. One consequence of the melting of the Arctic ice cap is a reduction in albedo, which is the capacity of surfaces to reflect a certain amount of solar radiation. Earth’s bright surfaces like glaciers, snow and clouds have a high reflectivity. As snow and ice decrease, albedo decreases and more radiation is absorbed by the Earth, leading to a rise in near-surface temperature. 

The other regional, yet much more complex factor that scientists need to pay detailed attention to relates to how clouds and aerosols interact. Aerosols are tiny particles suspended in the air; they come in a wide range of sizes and compositions and can occur naturally – such as from sea spray, marine microbial emissions or forest fires (like in Siberia) – or be produced by human activity, for exemple from the combustion of fossil fuels or agriculture. Without aerosols, clouds cannot form because they serve as the surface on which water molecules form droplets. Owing to this role, and more specifically to how they affect the amount of solar radiation that reaches the Earth surface, and the terrestrial radiation that leaves the Earth, aerosols are an essential element in regulating the climate and Arctic climate in particular.

“A lot of question marks”

What complicates the matter is that Arctic climate is changing rapidly which means that sources and processes of aerosols in the Arctic also change rapidly, hence creating a "moving natural aerosol baseline".

In a paper published in Nature Climate Changeon 8 February, Julia Schmale, the head of EPFL’s Extreme Environments Research Laboratory, alerts the scientific community to the need for a better understanding of aerosol-related processes. “How albedo is affected by ice is fairly well understood” says Schmale. “But when it comes to aerosols, there are many variables to consider: will they reflect or absorb light, will they form a cloud or not, are they natural or anthropogenic, will they stay local or travel long distances, and so on. There are a lot of question marks out there, and we need to find the answers quickly because the Arctic is changing so rapidly.” She worked on the paper with two coauthors: Paul Zieger and Annica M. L. Ekman, both from the Bolin Centre for Climate Research at Stockholm University.

The Arctic climate tends to warm fastest in the winter – despite there being no albedo effect during this period of 24-hour darkness. Scientists still don’t know exactly why. One reason could be that clouds present in winter are reflecting the Earth’s heat back down to the ground; That would lift temperatures above the Arctic ice mass, however, cloud formation is complex and very difficult to simulate with models. “Few observations have been made on this phenomenon because, in order to conduct research over the Arctic pack ice in the wintertime, you have to freeze in an icebreaker with scientists and research equipment for the entire season,” says Schmale.