The Arctic is warming almost 4 times faster than the rest of the globe. Yet how Arctic climate change will evolve remains highly uncertain, as there are large discrepancies in the projections from different climate models. A significant contributor to this uncertainty is our poor understanding of aerosol-cloud interactions in the Arctic and thus their poor representation in the models. The cloud-aerosol puzzle is a rather complex problem, affected by several physical and chemical processes that span various scales. An important focus of the workshop will be on the relative role of anthropogenic air pollution vs the role of marine aerosols in the Arctic cloud lifecycle.