In particular, these satellites now provide estimates of the sea ice thickness across the Arctic during the winter months. This development allows better monitoring of the state of the sea ice and a new way to test and assess our physical understanding and the latest climate model simulations. The latest assessment of the Intergovernmental Panel on Climate Change (IPCC) concluded that it was likely that the Arctic would become reliably ice-free by 2050 assuming greenhouse gas emissions continue to increase. This change would provide both enormous risks and opportunities. However, the climate simulations used by the IPCC often fail to realistically capture large scale properties of the Arctic sea ice, such as the extent, variability and recent trends. Therefore, there is a key need to improve simulations of Arctic sea ice to provide better understanding of the recent observed changes and credible projections of the future to help assess risks and opportunities and inform important policy decisions about adaptation and mitigation. In addition, there is a growing need for shorter-term sea ice forecasts, such as a few weeks or months ahead, to help inform local communities and industry stakeholders, such as shipping companies. This project will seek to better understand the role of natural weather and climate fluctuations in producing recent Arctic sea ice changes on annual to decadal timescales. One essential ingredient for improving the climate model simulations is to better represent the missing relevant physical processes in the latest sea ice models. This proposal will develop and implement improved physics for the sea ice model, which is used by many international groups, including the Met Office. The enhanced sea ice model will be further developed to improve its simulation of Arctic climate, and its ability to provide more reliable sea ice predictions will also be tested.