Better understanding the acceleration in Arctic warming
The Arctic is warming two to three times faster than the rest of the planet© Istock
EPFL professor Julia Schmale is calling on scientists to conduct detailed process studies on Arctic warming and share their data and research findings. She stresses the importance of studying how aerosols and clouds interact, as these highly complex and poorly understood mechanisms play a key role in, and are considerably affected by, climate change. In her view, scientists need to act now in this fast-changing region.
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 that’s 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 amount of solar radiation that’s reflected by the Earth’s clear surfaces like glaciers, snow packs and clouds. As the quantity of snow and ice on the planet decreases, albedo decreases as well and more radiation is absorbed by the Earth, leading to a rise in near-surface temperatures.
The other regional, yet much more complex factor that needs to be watched closely 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 and forest fires (like in Siberia) – or be produced by human activity, such as from agriculture or the combustion of fossil fuels. Without aerosols, clouds cannot form because aerosols serve as the surface on which water molecules aggregate to form droplets. Owing to this role, and more specifically to how they affect the amount of solar radiation that reaches the Earth’s surface and terrestrial radiation that escapes, aerosols are an essential element in regulating the climate – and especially the Arctic climate. What complicates the issue further is that both the Arctic climate and aerosols are changing quickly, creating a moving natural baseline.
“A lot of question marks”
In a paper published in Nature Climate Change on 8 February 2021, Julia Schmale, the head of EPFL’s Extreme Environments Research Laboratory (EERL), 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, 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 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, which would lift temperatures over the Arctic ice mass. However, the extent to which this happens would depend on the nature and quantity of the aerosols that form the clouds, which is complex and very difficult to simulate with models. “Few local observations have been made on this phenomenon because, in order to conduct research on the Arctic pack ice in the wintertime, you would need to have a crew of scientists and research equipment stationed on an icebreaker for the entire season,” says Schmale.
Improving climate models
Although many research expeditions have already been carried out in the Arctic during warmer seasons, a lot remains to be explored. One option could be to collect all the discoveries made so far on Arctic warming and use them to improve existing climate models. “A major effort is needed right away, otherwise we’ll always be one step behind in understanding what’s going on. The observations we’ve already made could be used to improve our models. A wealth of information is available, but it hasn’t been sorted through in the right way to establish links between the different processes. For instance, our models currently can’t tell us to what extent natural aerosol sources in the Arctic are impacting regional climate change,” says Schmale.
Three steps
In their paper, the research team puts forth three steps that could be taken to gain better insight into the Arctic climate and the role played by aerosols. First, they suggest creating a cross-disciplinary, interactive, open-source, virtual platform that compiles all Arctic aerosol-cloud interaction knowledge to date. This platform could be modeled after Renku, the Swiss Data Science Center’s online resource. Second, there is a need to improve existing climate models, “because what’s happening in the Arctic won’t stay in the Arctic,” says Schmale. “These processes can affect weather patterns in other parts of the northern hemisphere, and we’re well aware of the effect that melting glaciers and Greenland’s melting ice sheet are having on rising sea levels.” Finally, the authors suggest conducting cross-disciplinary process studies examining how interactions among the atmosphere, cryosphere, biosphere, oceans and land masses are affecting aerosols and cloud formation and how this is changing with a warming climate.
Julia Schmale, the Ingvar Kamprad Chair for Extreme Environment Research, sponsored by Ferring Pharmaceuticals, acknowledges funding from the Swiss National Science Foundation (projects 200021_188478 and 200021_169090). A.E. would like to acknowledge the Swedish Research Council (Vetenskapsrådet), DNR2015-05318 and the European Union’s Horizon 2020 programme, Grant Agreement no. 821205. P.Z. was supported by the Swedish Research Council (Vetenskapsrådet starting grant, project no. 2018-05045). P.Z. and A.E. also acknowledge support from the Knut and Alice Wallenberg Foundation, project Arctic Climate Across Scales (ACAS, project no. 2016.0024).
"Aerosols in current and future Arctic climate", Nature Climate Change, 8 February 2021
Julia Schmale, Paul Zieger, Annica M. L. Ekman