Local and Remote Moisture Sources Both Increase Late Twenty-First Century Arctic Precipitation

Abstract Arctic precipitation increases in a warmer world as more moisture is available to condense. These increases in precipitation and moisture result from both local surface evaporation and remote transport. Despite ongoing efforts, the relative contribution of each moisture source to future Arctic precipitation change remains unknown. Here, new atmospheric model experiments are used to isolate the contributions of these two moisture sources to Arctic precipitation. During the preindustrial era, remote transport controls Arctic precipitation in all months. By the late twenty-first century, local surface evaporation becomes increasingly important due to local surface ocean warming and sea ice loss. In fact, late twenty-first century fall and winter precipitation increases are driven by these local surface ocean changes. In contrast, late twenty-first century moisture transport driven by nonlocal surface ocean warming entirely explains late twenty-first century summer precipitation increases. Furthermore, these new experiments show that late twenty-first century Arctic precipitation increases are directly driven by surface ocean warming and sea ice loss, indicating that surface ocean evaporation directly drives these increases rather than land-sourced moisture. Additionally, our experimental design enables an understanding and quantification of the coinfluence between local surface evaporation and remote moisture transport. This coinfluence acts to reduce late twenty-first century Arctic precipitation during the fall and early winter. Overall, these results show when and where surface ocean warming and sea ice loss affect future Arctic precipitation increases. Significance Statement Late twenty-first century Arctic precipitation increases result from changes in two moisture sources: local surface evaporation over the Arctic and remote transport of moisture into the Arctic from lower latitudes. Here, we analyze new atmospheric model experiments to isolate the contributions of these two moisture sources on late twenty-first century Arctic precipitation increases. We show that wintertime Arctic precipitation increases are due mainly to local surface evaporation, while summertime Arctic precipitation increases are due entirely to remote moisture transport. Furthermore, we quantify the coinfluence between these two moisture sources and show that the coinfluence reduces Arctic precipitation during fall and winter. This work demonstrates the importance of isolating moisture sources to understand the mechanisms underlying Arctic precipitation change.