1. Introduction

Here, we share a summary of the recent 2024 Quantifying the Indirect Effect: From Sources to Climate Effects of Natural and Transported Aerosol in the Arctic (QuIESCENT) workshop. This workshop focused on future directions in Arctic aerosol–cloud interaction research, including Arctic aerosol–cloud interactions and their radiative impacts (Fig. 1). With this meeting summary, we aim to share workshop outcomes and discussions with those who could not join the meeting.

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QuIESCENT focuses on Arctic aerosol–cloud interactions and their radiative impacts. For example, low-level, Arctic liquid-containing clouds can be impacted by marine aerosol emissions from open ocean, melt ponds and leads, anthropogenic aerosols, and terrestrial aerosol sources like dust. However, the emissions and impacts of these aerosols on clouds are poorly quantified. Image used with permission from Matteo Ottaviani.

Citation: Bulletin of the American Meteorological Society 106, 5; 10.1175/BAMS-D-25-0051.1

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2. Context and purpose of the meeting

The workshop was set against a backdrop of significant scientific and societal challenges. The Arctic is warming nearly 4 times faster than the global average (Rantanen et al. 2022) with the warmest summer surface air temperature on record registered in 2023 (Ballinger et al. 2023) and the wettest summer on record registered in 2024 (Moon et al. 2024). Arctic warming, reinforced by polar amplification (Serreze et al. 2009), has important implications for sea level rise, weather patterns, planetary albedo feedbacks, permafrost thawing, and ecosystem disruptions (Meredith et al. 2019; Moon et al. 2024).

Mixed-phase clouds, which contain both ice and liquid water, were a key focus of this meeting. These clouds are prevalent in the Arctic and contribute significant uncertainty to predicted short- and longwave cloud radiative effects (Achtert et al. 2020). They also influence Arctic amplification but have poorly constrained, nonlinear impacts on the surface albedo feedback, leading to uncertainty in climate projections (Tan et al. 2023; Zelinka et al. 2020). Aerosol–cloud interactions in mixed-phase clouds are a major contributor to these uncertainties. For example, large radiation biases can result when models have inaccurate ice-nucleating particle concentrations (Vergara-Temprado et al. 2018; Murray et al. 2021).

On a global scale, aerosol–cloud interactions are the largest uncertainty in aerosol effective radiative forcing (Forster et al. 2021). Between the fifth and the sixth IPCC assessments, aerosol effective radiative forcing was updated from −0.9 to −1.3 W m⁻² with the range of uncertainties reduced by 0.4 W m⁻² between the two assessments (Forster et al. 2021). Aerosol–cloud interactions contribute 75%–80% to the total aerosol effect. However, it is likely that uncertainties from aerosol–cloud interactions are even greater over the poles due to fewer observations, challenges in accounting for complex mixed-phase cloud microphysics in models, and satellite limitations due to, for example, low sun angle and bright surfaces. Thus, there is great value in new field observations, satellite retrievals, and model-based contributions focused on aerosol–cloud interactions in this region to advance future climate knowledge.

Constraining aerosol effects on clouds in the Arctic is made more challenging by the rapidly changing aerosol environment. There are more frequent wildfires, more exposed ocean and land sources with the melting of land and sea ice, and policy- and economic expansion–driven changes (both positive and negative) in atmospheric pollution; at the same time, there are also potentially altered aerosol transport and loss patterns (Willis et al. 2018; Schmale et al. 2021).

Meanwhile, ideas leveraging the radiative influence of clouds and aerosols for potential climate intervention, concepts referred to as “climate engineering” or “radiation management,” are starting to gain more attention and funding. These ideas include a concept for thinning wintertime mixed-phase clouds over polar regions to enhance longwave cooling (Villanueva et al. 2022) and stratospheric aerosol injection (SAI) to reflect incoming solar radiation. Some of the candidate species being discussed for SAI (e.g., diamond nanoparticles; Vattioni et al. 2024) could be active ice-nucleating particles (INPs) (Thompson et al. 2024). However, any potential secondary effects on tropospheric clouds when these aerosols eventually settle out from the stratosphere are, as yet, poorly understood. As the potential benefits and drawbacks of these methods are still highly uncertain, it is clear that significant scientific review of any potential intervention pathways is critical.

With the most recent QuIESCENT workshop happening over 2.5 years ago, the 2024 gathering provided a platform for the international Arctic cloud and aerosol communities to collaborate, communicate, reconnect, and brainstorm collectively. Participants included experts and early career researchers across laboratory, fieldwork, satellite- and ground-based remote sensing, and modeling disciplines. Specific goals for the meeting included identification of key knowledge gaps and establishing a coordinated research plan to help inform research planning and coordination, including through the fourth International Conference on Arctic Research Planning (ICARP IV), the 2027–37 Decadal Survey for Earth Science and Applications from Space, and the International Polar Year 2032–33 (IPY32).

3. Attendance and activities

The 2024 QuIESCENT workshop included 55 participants, with 27 attending remotely and participants approximately balanced by gender, and with approximately 52% of the participants identifying as early career scientists. Most attendees (78%) participated from European entities, with the rest attending from North American, Asian, and Australian institutions. The workshop featured presentations and “World Café” style discussions to foster knowledge and share and define research priorities.

4. Key sessions

5. Some research challenges and priorities

During the workshop, participants determined several research priorities. There is a need to better identify and quantify some of the less understood and rapidly evolving aerosol sources, including those from leads, open water, shipping, fires, and newly exposed terrestrial surfaces. The role of INP activity and aerosol aging remain an important uncertainty, and the role and sources of micro- and nanoplastics is of increasing interest as well. Improving our grasp of the surface–atmosphere exchange, cloud-phase partitioning, and atmospheric dynamics driving turbulence, entrainment, deposition, and INP recycling in the context of a changing Arctic climate would be beneficial. Participants emphasized a need to better understand how secondary ice production processes govern Arctic cloud life cycles and the relationship between cloud radiative effects and climate feedbacks. They also discussed uncertainties due to the lack of data from Russia territories. This major and undersampled sector of the Arctic is being rapidly altered with climate change, and this has related impacts on aerosol emissions.

Certain themes from previous QuIESCENT workshops recurred, such as the need for continuous long-term observations of CCN and INPs. There was also discussion on the need for improved vertical profiling of aerosol properties, especially at long-term observatories and in coordination with ground- and satellite-based lidars to help understand the combined effects of changes to aerosol concentrations in the Arctic. Additionally, a recurring theme was the necessity for enhanced chemical composition measurements, including more real-time chemical analyses.

6. Advancing methodologies and technologies

Workshop participants also discussed some new and relevant innovations in the areas of modeling, remote sensing, and field work. There is great interest in leveraging artificial intelligence and machine learning to better parameterize cloud processes, accelerate the analysis of data, and improve observational techniques. However, the remote location and harsh sampling conditions of the Arctic limit the availability of data vital for algorithm training and evaluation. As a result, more observations are essential to better train algorithms and ascertain and improve their accuracy.

Participants also discussed new advances in fieldwork, including the use of uncrewed aerial systems (UASs) and tethered balloon systems (TBSs), which can provide vertical profiles of atmospheric properties, including turbulence, aerosol properties, and cloud microphysics. Discussions highlighted the value of vertical profiles in enhancing understanding of aerosol sources and transport aloft which cannot be captured by surface-based measurements alone. Participants also considered the asset of miniaturizing instruments to facilitate easier and more regular profiling using airborne systems including UAS, TBS, and crewed aircraft systems. An additional topic of interest was how best to optimize and redesign traditional field campaigns, for example, to include sites without logistical support of a station (e.g., with UAS or extra field sites) to increase spatial sampling across the Arctic.

In the area of remote sensing, recent innovations that were discussed included Doppler radar data from the recently launched EarthCARE satellite, advancements in distinguishing aerosol effects on clouds from covarying meteorological factors in satellite-based aerosol–cloud interaction studies, new methods for tracking the temporal evolution of Arctic clouds, and new ground-based lidar estimates of CCN and INP concentrations. However, CCN and INP estimates from lidar require more in situ validation and testing in a variety of different environments that feature different particle properties. There was also a need identified to continue improving satellite product spatial resolution of surface features like leads and to evaluate lidar data against measurements to better differentiate between mineral dust and diamond dust (small ice crystals falling in clear sky).

7. Main takeaways and future directions

One key takeaway was the importance of continuing long-term measurements to understand the evolving Arctic aerosol population. Supporting long-term ground based measurements with vertical measurements aloft with improved small, lightweight sensors from platforms such as UAS, cargo aircraft, and TBS would be highly beneficial. Advancing knowledge of climate-intervention techniques, such as polar mixed-phase cloud thinning, and their potential side effects is crucial. Engaging local communities early in these discussions and increasing overall engagement with underrepresented communities were also seen as very important.

There was also discussion on the need to extend our experimental focus beyond fieldwork to include research conducted in cloud chambers and other controlled laboratory environments and to better integrate field scientists with the laboratory community. The workshop emphasized the necessity for community involvement in coordinated pre-IPY32 efforts. This includes developing facilities hosting cloud chambers capable of replicating liquid and mixed-phase cloud environments, expanding computing infrastructure, conducting ship and airborne (traditional aircraft, UAS, TBS) campaigns, and organizing coordinated, community-wide modeling experiments to identify uncertainties and support field campaign planning. One example project discussed during the meeting was the IPY-Distributed Routine Observations of Northern Environments (DRONE) effort, which highlighted an opportunity to conduct regular profiling of atmospheric properties around various Arctic sites. Favorable sites discussed for long-term measurements and coordinated deployments included Alert, Eureka, Bear Island (Canada), Pallas (Finland), Villum/Station Nord, Pituffik, Summit (Greenland), Ny-Ålesund and other Svalbard sites, Tromsø (Norway), and Oliktok Point and Utqiaġvik (U.S.). Finally, participants highlighted the strong potential benefit of additional deployment of instrumentation in, and access to data from, Russia.

Looking ahead, the potential for a fourth QuIESCENT-Arctic workshop in 2026 or 2027 was discussed, with an invitation for scientists at all career stages to join the initiative’s Steering Committee. This next QuIESCENT workshop will come at a critical time for IPY-32 planning and coordination and will be able to foster discussions stemming from enhanced application of new capabilities and techniques [e.g., artificial intelligence (AI), autonomous systems, new laboratory facilities] to help advance our collective understanding of Arctic aerosol–cloud–radiation interactions and gain insight into both naturally occurring feedbacks and those proposed as part of radiation management efforts.