With warming came rising sea levels well documented by scientific measurements.Both warming and climbing oceans are, of course, phenomena that humans have encountered before, but today there’s a new element to this familiar experience—rising coastal population. We live in the era of the megacity, of uncontrolled migration from rural hinterlands into ever-expanding urban landscapes. Many of today’s cities are chaotic and confrontational. They bristle with seemingly intractable problems of poverty, sanitation, and water shortages, just like the issues faced by our forebears two thousand years ago—but with a difference. Today cities with more than a million inhabitants located close to sea level are now routine. In the next five chapters, I journey repeatedly between past and present, for, in each area we visit, the experience of ancient societies, often our direct ancestors, form a continuity between earlier times and today. We cannot understand the dilemmas of the present without placing them in a deeper historical context.
