The aim of this project, funded by the Villum foundation, is to establish an interdisciplinary group spanning complementing fields and expertise, in order to (i) determine the major source environments for atmospheric ice-nucleation proteins (INpro) in the Arctic;(ii) identify and quantify key microorganisms that produce INpro;(iii) provide mechanistic understanding of INpro through nucleation modelling; and (iv) ensure that ICARUS data are introduced into climate models, thereby both improving model reliability and clarifying the role of bioaerosols for cloud formation in the Arctic.