Overpopulation of urban areas has led to numerous problems. The document discusses two major problems caused by rising sea levels: flooding of coastal residences, displacing millions of people from their homes and possessions, and provides the example of devastation from the 2011 Japan tsunami. It then suggests that building flood barriers like dikes, dams and floodgates could help solve the problem by stopping flood waters from reaching populated coastal areas, citing the Netherlands' successful flood defense systems. The document provides guidance on discussing problems and solutions by suggesting how to structure paragraphs and includes sample language to introduce problems and solutions.