The past fifteen thousand yearsthe entire span of human civilizationhave witnessed dramatic sea level changes, which began with rapid global warming at the end of the Ice Age, when coastlines were more than seven hundred feet below modern levels. Over the next ten millennia, the oceans climbed in fits and starts. These rapid changes had little effect on those humans who experienced them, partly because there were so few people on earth, and also because those people were able to adjust readily to new coastlines.Global sea levels stabilized about six thousand years ago, except for local adjustments that caused often significant changes to places such as the Nile Delta. The curve of inexorably rising seas flattened out as urban civilizations developed in Egypt, Mesopotamia, and South Asia. The earth's population boomed, quintupling from the time of Christ to the Industrial Revolution. The threat from the oceans increased with our crowding along shores to live, fish, and trade.Since 1860, the world has warmed significantly and the ocean's climb has accelerated. The sea level changes are cumulative and gradual; no one knows when they will end. , from celebrated author Brian Fagan, tells a tale of the rising complexity of the relationship between humans and the sea at their doorsteps, a complexity created not by the oceans, which have changed little. What has changed is us, and the number of us on earth.