Three key facts about rising sea levels need to be pointed out to the world's politicians and planners: sea-level rise is now inevitable, it will happen faster than most of us thought, and it will go on for a very long time. Even if greenhouse gas emissions stopped tomorrow, the oceans will continue to swell as they warm. The climate scientists estimate that sea-level rise could well be in the region of 1 to 2 metres by 2100, with a small risk of an even greater rise. For many islands and low-lying regions, even small rises will spell disasters. Most countries, however, will only lose a tiny percentage of their land, even with a very big rise. The problem is what has been built on that land: New York, Sydney and Tokyo, to mention just a few cities. Unless something can be done, great areas of urban network will vanish beneath the waves. It will take a massive engineering effort to protect these cities—an effort that may be beyond economies that have been brought to their knees by climate change. None of this means we should despair, and stop trying to ban emissions. But alongside these efforts, we need to start acting now to rrunimise the impact of future sea-level rise. That means we must stop building in the danger zone. Countless billions are being spent on constructing homes, offices, factories and roads in vulnerable coastal areas. For instance, the skyscrapers of Shanghai are being built on land that is a mere 4 metres above sea level on average, and which is sinking under the weight of its buildings and as water is drawn from the rocks beneath them. In cities that have been around for hundreds of years, this sort of development may be understandable. But planning for new coastal developments is to go against reality. If we want to build a lasting heritage for our children, we should do so on the plentiful land that is in no danger from the sea It is one of the easiest ways to slow down climate change, and we should be acting on it now.