PRE-MELT: Preconditioning the trigger for rapid Arctic ice melt

The oldest, thickest sea ice in the 'last ice area' of the Arctic - a region thought to be most resilient to climate warming - unexpectedly broke up twice in the past year. Our current theories assume that the end-of-summer ice-covered area will steadily retreat into the Central Arctic Basin as global warming accelerates over coming decades. However, the dynamic break-up events witnessed in 2018 challenge this prevailing view. Here we hypothesise that a weaker, increasingly mobile Central Arctic ice pack is now susceptible to dynamic episodes of fragmentation which can precondition the ice for rapid summer melt. This mechanism of dynamic seasonal preconditioning is unaccounted for in global climate models, so our best current projections are overlooking the possibility for rapid disintegration of the Arctic's last ice area.

Our team has demonstrated that seasonal preconditioning is already responsible for the neighbouring Beaufort Sea becoming ice-free twice in the past five years. Even ten years ago this region contained thick perennial sea ice, mirroring the Central Arctic Ocean, but it has now transitioned to a marginal Arctic sea. Could the processes responsible for the decline of the Beaufort Sea ice pack start to manifest themselves in the Central Arctic? Currently, a shortfall in satellite observations of the Arctic pack ice in summer prevents us from testing our hypothesis. We desperately require pan-Arctic observations of ice melting rates, but so far satellite observations of sea ice thickness are only available during winter months. Our project will therefore deliver the first measurements of Arctic sea ice thickness during summer months, from twin satellites: ESA's Cryosat-2 & NASA's ICESat-2. We have designed a new classification algorithm for separating ice and ocean radar altimeter echoes, regardless of surface melting state, providing the breakthrough required to fill the existing summer observation 'gap'. Exploiting the recent launch of multiple SAR missions for polar reconnaissance, our project will integrate information on ice-pack ablation, motion and deformation to generate a unique year-round sea ice volume budget in the High Arctic.

This record will inform high-resolution ice dynamics simulations, performed with a suite of state-of-the-art sea ice models from stand alone (CICE), ocean-sea ice (NEMO/CICE), to fully coupled regional high resolution (RASM), and global coarser resolution (HadGEM) models, all now equipped with the anisotropic (EAP) sea ice rheology developed by our team. Using the regional and stand-alone models we will analyse the role of mechanics in this keystone region north of Greenland to scrutinise the coupling and preconditioning of winter breakup events - such as those witnessed in 2018 - to summer melting rates. Using the coupled models, we will quantify the likelihood of the Arctic's last ice area breaking up much sooner than expected due to oceanic and atmospheric feedbacks and how this will affect the flushing of ice and freshwater into the North Atlantic.

We anticipate that four broad categories of user group will benefit from the results and activities of the project, in addition to scientists working directly on Arctic sea ice, climate and oceanography. We aim to particularly engage with UK and Canadian stakeholders based on the locations and experience of the project team.

(i) Climate change policy community
Our novel sea ice thickness budget analysis combining model and observation sea ice thickness budget in the Central Arctic Ocean will provide an objective diagnose of the errors in climate models contributing to IPCC reports. The conclusions of this project will therefore be of critical importance to bodies charged with summarizing (IPCC, Met Office) and directing (NERC, European Space Agency) climate science. Our team's research has previously been represented in NGO climate change reviews (such as the recent AMAP: SWIPA assessment, but also IPCC AR5 reports and ArcticNet Hudson Bay IRIS), and in Davos at the Arctic Science Forum.

(ii) Marine transportation industry
The Northeast and Northwest Arctic passages have been sea ice-free for a longer summer season in many recent years, providing a quicker cheaper alternative to traditional shipping routes between Europe and Asia. Tourist cruise ships, such as the Crystal Serenity in 2016, are also beginning to navigate Arctic waterways during summer, and ship traffic through the Canadian Arctic has more than doubled over the past 40 years. We anticipate that our sea ice thickness intialised forecasts could be used to predict least-cost (i.e. viable, lowest risk) routes for both ice-reinforced and non-reinforced ships through Arctic passages, helping to identify zones of high vulnerability to ice hazards. Moreover, these data would be valuable for marine insurance risk & exposure management and for international shipping regulatory authorities, e.g. the International Maritime Organization (IMO), to support polar transportation conventions. In recent years, private industry stakeholders such as this have been an active participant in SIPN and will be able to easily access our data through this platform.

(iii) Oil and gas industry
Anticipated decline in output from existing oil and LPG resources will potentially require the development of nearly 50% new worldwide energy production capacity by 2035. Incidentally, the Arctic is thought to hold 30% of the world's undiscovered gas and 13% of its undiscovered oil (including 84% offshore). Oil and gas companies have begun to perform initial prospecting and drilling tests, for example by Shell in the Chukchi Sea in 2015. However, it is crucial that these operations are only executed in a sustainable way, with particular attention paid to the risk of sea and glacial ice hazards on infrastructure. Our project will inform forecasts of the probability and timing of ice-free zones over oil and gas leasing areas, such as those in the Chukchi Sea, as well as over active British leases in the Norwegian Arctic. Results will be communicated to private sector firms in marine transportation and O&G industries through a dedicated user workshop towards the end of the project.

(iv) General public
In addition to a large media exposure by our team members (radio, TV, newspapers, YouTube), we intend to develop sea ice products that are accessible to beneficiaries at a variety of levels, including primary and secondary school students via our UCL @GeoBus and through SIPN. We will also host with NASA colleagues and IASC fellows a Hackathon on Arctic risks and extremes. The forthcoming upgraded SIPN-2 platform and our CPOM website will be capable of providing straightforward and visually appealing maps of our products, along with links to non-technical web pages explaining how the satellite data are acquired and processed. In addition, we will produce a set of free public-outreach posters, for use in secondary schools, museums, outreach events in the UK, Germany, Canada etc.