That the climate is changing is now “unequivocal” according to the UN’s Intergovernmental Panel on Climate Change, and even if we stopped emitting greenhouse gases tomorrow, the changes caused by our past emissions will continue for centuries. That means we have no choice but to adapt, and it is the world’s coasts that will be on the frontline of that adaptation, under threat from rising sea levels and more frequent storms and flooding. Coasts are also the most densely populated places on earth – most of the world’s major cities are on floodplains and, by 2050, they will be home to 70% of an estimated population of 9bn people. In this piece for Modus magazine, I investigated how engineers worldwide are preparing to fight the tides. I found that the response very much depends on how valuable coastal land is, and that the most valuable land is not necessarily where you’d expect. In the declining cities of the developed world, a managed retreat seems to be the only option; in Jakarta, meanwhile, demand for land is so high that the authorities are planning to build a completely new city several miles into the bay.