Towards a marginal Arctic sea ice cover

Recent observed changes in the Arctic have become a 'poster child' for global climatic changes, particularly because the summer sea ice extent has shrunk rapidly over the past 35 years. This retreat of the sea ice has led to growth of trans-Arctic shipping and plans to extract minerals and fossil fuels from the ocean floor.

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. 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 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.

Observations of the Arctic have improved in recent years with new satellites measuring sea ice properties from space. These satellites reveal not only that the extent and thickness of the Arctic ice cover is reducing in all seasons but that the Marginal Ice Zone (MIZ), a region of low ice area concentration consisting of a relatively disperse collection of small floes, has grown.

Model projections indicate the MIZ will grow from around 10% to 80% of the summer sea ice cover by 2050, exposing a hitherto relatively quiescent Arctic Ocean to the atmosphere. Nonlinear interactions between the air, ice, and ocean that magnify or diminish change, known as feedbacks, associated with a reduced and marginal sea ice cover will emerge or assume dominance in the coming years. Many of these feedbacks are either entirely absent or inadequately captured in current models. For example, not included is the feedback whereby the creation of smaller floes due to ice melt or breakup under ocean wave stress promotes further lateral melt and propagation of waves deeper into the pack, further enlarging the MIZ. Because existing climate models oversimplify these feedbacks, their utility for understanding and predicting variability and change in the Arctic is compromised. This leads to impairment of climate model accuracy at lower latitudes also, due to errors in meridional atmospheric and oceanic circulations as well as ice export from the Arctic.

We will investigate processes controlling evolution of the MIZ using existing and new observations. We will include physics of wave-ice interaction, ice breakup and melt, and floe collisions into ice, ocean, and climate models. We will use these models, constrained and verified with new observations, to explore feedbacks between the sea ice, ocean, and atmosphere using a series of numerical experiments. We will quantify the impact of the increase in the MIZ on the Arctic physical climate, and explore the processes responsible for the projected loss of Arctic sea ice.

Arctic sea ice reduction has become a totemic indicator of climate change with impacts on iconic species such as polar bears and the Beluga whale, as well as indigenous human populations. The reduction of Arctic sea ice extent has generated widespread interest with numerous articles in the popular press, radio, television and internet.

Reduction in the sea ice cover is already opening up shipping routes and the potential for oil exploration has generated political statements and actions including, for example, the placement of the Russian flag at the North Pole and Denmark's declaration of sea bed rights up to the North Pole. Lloyd's of London, with Chatham House, published a report called "Arctic Opening" in 2012, with business (including insurance) expansion in mind. In 2014, the PI organised a Royal Society meeting on Arctic sea ice: the evidence, models, and global impacts, which was the Royal Society's most tweeted meeting.

Understanding how and why Arctic sea ice conditions change on decadal timescales is a critical issue facing international governments and business. Improved predictions of Arctic sea ice through scientific research has economic, social and environmental implications. This research brings together broad international expertise in sea ice model development to ensure maximal benefit to sea ice research, modelling and prediction groups.

A major practical impact of this proposal is in the generation of a new sea ice module accounting for marginal ice zone physics in the sea ice component (CICE) of a Global Climate Model (GCM). The CICE sea ice component is used in several GCMs, which include the UK Earth System Model (UKESM), the HadGEM3-GC3 climate model used by the Met Office for contributions to climate projections CMIP6, and the Community Climate System Model (CCSM) at the (US) National Center for Atmospheric Research. The Met Office and Los Alamos National Laboratory are both Project Partners offering in-kind support to help deliver the improvements to sea ice models, and visits are planned for both to ensure maximal usage of the research.

The main direct beneficiaries of the knowledge generated by this project will be:

1. The Met Office and other international modelling groups who will be able to utilise an enhanced and improved sea ice component in their global climate models

2. The international climate research community, including the IPCC, through collaborative analysis of the Arctic system to understand the causes of recent changes

3. Policy makers (such as DECC, DEFRA and FCO) who will have an improved understanding of the risks and opportunities presented by a changing Arctic. This work also has the potential to be used to inform mitigation and adaptation decisions under the UNFCCC climate negotiations.

4. This project will supply part of the physical basis for future prediction systems for the Arctic and Northern Hemisphere mid-latitudes, which will have benefits to the stakeholders such as the oil, gas and mineral extraction industry, trans-Arctic shipping, tourism and indigenous communities. The general public and local communities would also benefit from improved forecasts.