A warning sign in Greenland about tsunamis caused by icebergsODD ANDERSEN/AFP via Getty ImagesRising temperatures in the Arctic are causing glaciers to retreat onto land, exposing thousands of kilometres of coastline in Greenland and other areas with potential geopolitical consequences.Jan Kavan at the University of South Bohemia in the Czech Republic and his colleagues used satellite imagery taken in 2000 and 2020 to track changes in marine-terminating glaciers across the northern hemisphere. They found that almost 2500 kilometres of new coastline had emerged over this period due to glaciers retreating onto land, with two-thirds of this