Fast polar change and its potential impacts on weather and climate of remote regions have received a great deal of attention in recent years. In particular, the dramatic warming of the Arctic (a process referred to as Arctic Amplification) and the associated reduction in sea-ice extent/thickness may have a profound impact on the climate system in the 21st century.

Despite extensive research, the impact of observed and projected Arctic change on climate and weather (including extreme weather) in the densely populated mid-latitude Northern Hemispheric region is still uncertain.

The variety of observational and modeling studies that have tackled the problem find contradictory results, especially concerning the remote atmospheric circulation response to arctic sea-ice anomalies. This uncertainty is in large part due to inconsistency in the experimental design of model simulations, that can only be addressed through coordinated efforts such as the so-called Polar Amplification Model Intercomparison Project (PAMIP) that will be part of the Coupled Model Intercomparison Project phase 6 (CMIP6).

The proposed work will contribute to the hierarchy of coordinated model experiments represented in PAMIP using the new Energy Exascale Earth System Model (E3SM version 1). The output from the numerical experiments will be diagnosed in tandem with analysis of model output from other participants in PAMIP that run different models.

The proposed work addresses the following questions:

• What are the causes of polar amplification?
• How do changes in Arctic and Antarctic sea-ice cover affect the local and remote atmospheric circulation?
• In particular, do polar changes impact the frequency, intensity, and duration of extreme weather events in mid-latitudes?
• What is the role of the stratosphere and forcing of anomalous planetary waves in communicating the response to mid-latitudes?
• How do polar changes combine with the general response to greenhouse gas forcing at the end of the 21st century, and what is the resulting response of mid-latitude atmospheric dynamics and extreme weather events?
• What is the oceanic response to changes in sea ice, and how does it feedback onto the atmosphere?
• How can the contribution of sea-ice loss to the change in mid-latitude circulation be separated from tropical influences in the real world and in climate simulations?

The model simulations will be analyzed using diagnostic tools that have been tried and tested in the investigators’ previous work. Additional diagnostics will be derived and applied. A hierarchy of model simulations, based on the E3SM, is planned to answer specific questions that may be hard to address in the most sophisticated model setting.

The project will contribute to a deeper understanding of extreme events, modes of variability, high-latitude feedbacks, the cycling of water, and interactions in the earth system, especially between atmospheric and ocean dynamical and thermodynamic processes. This project will contribute to the national, as well as international, safety, and security during the 21st century by contributing to an understanding of the frequency and intensity of extreme weather events.