Closely connected to the twentieth century's changes in science, technology, economics, and politics have been those to the environment. One historian wrote that “the human race, without intending anything of the sort, has undertaken a gigantic uncontrolled experiment on the earth. In time, I think, this will appear as the most important aspect of twentieth-century history, more so than World War II, the communist enterprise, the rise of mass literacy, the spread of democracy, or the growing emancipation of women.”

In his book The Coming Anarchy (2000), Robert Kaplan declared that “it is time to understand ‘the environment’ for what it is: the national-security issue of the early twenty-first century. The political and strategic impact of surging populations, spreading disease, deforestation and soil erosion, water depletion, air pollution, and, possibly, rising sea levels in critical, overcrowded regions like the Nile Delta and Bangladesh—developments that will prompt mass migrations and, in turn, incite group conflicts—will be the core foreignpolicy challenge from which most others will ultimately emanate.”

Two major and interconnected factors, both fuelled by scientific and technological developments, were responsible for the twentieth century's unprecedented environmental changes and their importance by century's end: population growth and economic activities, especially industrialization and increased consumption. The explosion of twentieth century consumption (see Chapter 3) not only placed increasing demands on scare resources to produce more goods, but also increased pollution in the process of producing and disposing of worn out or obsolescent products.