The overarching goal of the project is to advance understanding of Arctic climate system operation and variability to improve model prediction of Arctic climate change at decadal to centennial scales. A set of specific objectives is proposed centered on the following main science hypothesis: Given the projections of continued global warming and its northern high-latitude amplification, the Arctic will become nearly ice-free during summer in the near future, resulting in altered physical state of and interconnections within the Arctic climate system. To confirm or disprove the above hypothesis, our approach is to use subsets of model components and fully coupled RACM to address the following specific objectives: - Identify potential improvements in the simulated sea ice thickness distribution and deformation due to increasing model resolution and representation of fine-scale ice-ocean interactions - Investigate effects of shrinking and thinning sea ice on ice kinematics and its consequences on changing air-ice and ice-ocean interactions - Examine and quantify consequences of melting sea ice on the increased upper ocean heat content and its potential for increased ice melt due to a positive ice-ocean feedback loop - Assess the influence of excess oceanic heat release, especially in fall and winter, on potentially enhancing cyclonic tendency in the atmosphere - Explore the importance of increased sea ice melt and runoff to the Arctic hydrological cycle and its acceleration in the context of first-year ice growth and survival - Integrate positive and negative feedback processes into model simulations of warming climate scenario to determine their net impact on the long-term state of Arctic ice cover - Identify physical and numerical requirements of future GCMs to significantly improve model skill in representing past and present and in predicting future Arctic climate change. A hierarchy of well designed one-way and fully coupled regional climate system model experiments will focus on the above objectives. Such experiments will provide advanced insight into the behavior of the Arctic climate system that is not currently attainable using either individual regional component models or GCMs. The proposed project helps to lay the foundation for a community regional Arctic System Model as recommended in the recently published report to NSF. This research will also address or facilitate other studies related to potential implications of Arctic sea ice melt and warming climate, including consequences for the global ocean thermohaline circulation, Greenland ice sheet, ecosystem, shipping, natural resource development, policymaking and defense. Output from the baseline simulations will be made available to the community through either the ARCSS Data Coordination Center or a Live Access Server at the Naval Postgraduate School, to be developed in support of this project.