People have clustered at the water's edge throughout civilization for the most fundamental of reasons: without water there is no life. Every major city in the world has a body of water or aquifer nearby, since rivers and lakes predetermined where people would gather and dwell, groundwater...

Some 200 million people lived on Planet Earth at the start of the modern era. That number rose to 2.5 billion by 1950. At mid-2008, the population is now 7.0 billion and is expected to reach 9.0 billion by 2040. It thus took 1,950 years for the global population to grow ten-fold but only an...