Understanding Dynamical Linkages between the Arctic and Midlatitudes

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Over thirty years ago some of the earliest computer models of climate change successfully predicted that warming in the Arctic caused by greenhouse gas pollution would rapidly outpace warming in the rest of the world. This "Arctic amplification" (AA) of global warming is linked to melting of sea-ice, land-ice, snow, and permafrost. AA profoundly affects ecosystems, economic systems, and populations of Canada and other Northern nations. Despite this successful prediction, our understanding of the drivers, characteristics, rate, and implications of AA is unsettled. This limits our confidence in predicting future Arctic change, its causes, and its consequences. Initially, AA was thought to be caused by a positive feedback in which melting, brightly reflective sea ice and snow uncovers the darker land and sea surface, which can absorb more sunlight and drive more warming. But recent research on AA, including contributions from my research group, suggests that we need to consider a broader view on the two-way atmospheric linkages between the Arctic and the rest of the globe. In particular, we need to focus on the long-range transport of heat and moisture in the atmosphere, as well as long-range atmospheric teleconnections. We have also learned that the influence of Arctic change extends well outside the Arctic, which has practical implications for climate prediction. For example, it seems that current models are too insensitive to the influence of sea ice, snow, and the Arctic stratosphere, which limits predictability of climate on seasonal to multi-year timescales. To advance our understanding of AA and its implications, my atmospheric physics research group will analyze the latest successors to the earliest climate models: realistic Earth System Models (ESMs) that include atmosphere, land, sea ice, snow, and ocean processes and all their interactions. We will proceed on two tracks. For decadal and longer timescales, we will artificially trigger AA in ESMs by perturbing the Arctic, midlatitudes, and tropics, and from the surface to the stratosphere. Our physical analysis of these controlled experiments will help us untangle the many processes at play in linkages between the Arctic and more southern regions. To help improve climate prediction, we will design model experiments to tune the coupling between the surface, stratosphere, and the rest of the atmosphere, to help understand the simulation problems of current models. This approach promises to improve our understanding of physical drivers of predictability and potentially improve forecasts. These projects follow from my leadership of the Canadian Sea Ice and Snow Evolution Network (CanSISE, 2013-2019). The current proposal builds on observational, ESM, and forecast system work that took place within CanSISE. As we did for CanSISE, I will emphasize the education and professional promotion of the research personnel (undergraduate, graduate, and postdoctoral) supported by the requested funds.