Where, how fast, and why arctic permafrost coasts undergo coastal erosion?

Permafrost coasts represent 34 % of the global coastline and are likely to become one of the most impacted environments of the Earth under changing climate conditions. The lengthening of the open-water season and the increasing open-water area, the warming of permafrost, the increasing occurrence of coastal thermokarst, and the increase in sea surface temperatures are all thought to impact the pace of coastal erosion. In particular, storms are predicted to hit the coasts later in the fall season. These storms are thought to bear staggering threats to the coasts in the form of destruction of community and industry infrastructure as well as dramatic changes in sedi-ment and nutrient pathways in the nearshore zone. Alas, there is little data available to provide a cir-cumarctic picture of coastal erosion and to indicate erosion trends. Indeed, arctic coasts remain largely unknown and unexplored, which puts current adap-tation and mitigation strategies in northern commu-nities into jeopardy.In this presentation, we present the latest results from the Arctic Coastal Dynamics project, initiated by the International Permafrost Association and the International Arctic Science Committee in 1999. A classification, built to consistently describe the geo-morphological characteristics and processes ob-served at the coast along the arctic rim, indicates that the geomorphological setting of arctic coasts is highly spatially variable. This dataset highlights the major influence of this setting on the erosion rates observed and the in fine difficulty in providing sta-tistics at the global level. It shows, however that some striking regional traits can be deduced from the dataset. Alaskan and Canadian coasts in the Beaufort Sea are characterized by larger ground ice contents but also by much smaller cliff heights than other arctic coasts. Overall it shows that circumpolar coastal erosion is on average 0.5 m/yr, but again with strong differences between arctic regions, with rates close to 10 m/yr in some areas and stable coasts in others. A second outcome of the ACD project is a recent as-sessment of erosion rates and their evolution throughout the second half of the twentieth century and the beginning of the twenty-first century. Despite the recent media attention to coastal erosion, reliable long-term datasets asserting an increase in coastal erosion are scarce in the Arctic. This presen-tation will present the latest datasets published in the literature and compare their spatial coverage to the extent of permafrost coasts at the arctic scale.

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