| Summary: | Arctic mixed-phase clouds have been recognized as an important factor for Arctic climate change, and play an important role in polar cloud-climate feedback mechanisms. However, the importance of Arctic ice-nucleating particles (INPs) for cloud phase is still under debate, and INP concentrations in the Arctic remain poorly quantified. Here, we present a new empirical parameterization of INPs for the Arctic region, based on new INP measurements made at two Arctic sites (at approximately 70 and 80°N) in combination with active remote sensing from Space (CALIPSO/CloudSat). The parameterization yields higher INP concentrations over open ocean than over sea ice, reflecting that the Arctic sea surface is as an important source of INPs. When implementing this parameterization in the Earth System Model NorESM2, we find that Arctic cloud liquid water content is increased considerably, compared to simulations with the models’ default INP parameterization. This, in turn, increases downward infrared radiation at the surface, and thus influences Arctic surface temperatures and sea ice thickness. Furthermore, we present simulations of future warming in NorESM2 with the new parameterization, in which INP concentrations can respond to Arctic sea ice retreat, and present differences in the Arctic climate evolution due to the new INP parameterization.
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