By 2050 Bangladesh's population is expected to reach about 220 million, while a large part of its territory will be under the sea. This could force ten to thirty million people from the southern coast to move, a mass of 'climate refugees' fleeing their homes; by mid-century the world may count 250 million climate refugees. Seen globally, it would be the largest migration in human history. How many more people can Dhaka absorb? When the city is overwhelmed and on the verge of collapse, where will the climate refugees go, and who will take them in? We are sitting on a giant time bomb.