Permafrost coasts make up to 34 per cent of the world's coastlines. Erosion of these coasts currently averages 0.5 m a-1, which is similar to or greater than rates observed in temperate regions. The erosion rate has risen on the Arctic coast of Alaska during the first decade of the 21st century as the minimum sea ice extent has declined. Increasing erosion leads to higher engineering and relocation costs for coastal villages (US$140 million for Kivalina alone to adapt and eventually relocate), and to greater quantities of organic carbon contained in permafrost being released to the near-shore zone (up to 46.5 Tg a-1). Modelling of coastal erosion has begun to include permafrost-specific components such as block failure. The absence of basic information on Arctic coasts that would be provided by a dedicated observing network, especially on lithified coasts, has hindered the development of a system model with predictive capability.