Better understanding the reasons behind Arctic amplified warming
EPFL professor Julia Schmale is calling on scientists to conduct dedicated process studies and to share their data and research findings on Arctic warming. She stresses the importance of studying how aerosols and clouds interact, as these highly complex and poorly understood mechanisms play a key role in climate change, but are also strongly affected by it. According to her, the region is in rapid transition and scientists need to act to not run behind.
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.
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 how important natural local Arctic aerosol sources are for regional climate change,” says Schmale.
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. They suggest creating an interactive, open-source, virtual platform that compiles all Arctic aerosol-cloud interaction knowledge to date, for example following the model of the Swiss data science centercollaborative platform Renku. “We need to improve our climate models because what’s happening in the Arctic will not stay in the Arctic. It can affect weather patterns in other parts of the northern hemisphere, and we are well aware of the impact on sea level rise from melting glaciers and the ice sheet in Greenland,” says Schmale. Another step, which the authors suggest, in addition to collaboratively explore data and develop Arctic system models, is to conduct interdisciplinary process studies. Those should unveil how interactions between the atmosphere, cryosphere, the ocean, land and the biosphere affect aerosols and cloud formation and this changes 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