The ice sheets of Greenland and Antarctica will contribute more to sea-level rise this century than any other source. By mid-century, a 2 °C increase is predicted1 to swell the global oceans by around 20 centimetres, on average. By 2100, most large coastal cities will face sea levels that are more than a metre higher than currently.
If nothing is done, 0.5–5% of the world’s population will be flooded each year after 21002. For example, a 0.5-metre rise in Guangzhou, China, would displace more than 1 million people; a 2-metre rise would affect more than 2 million1. Without coastal protection, the global cost of damages could reach US$50 trillion a year. Sea walls and flood defences cost tens of billions of dollars a year to construct and maintain2.