Between 100 B.C. and about A.D. 1600, global populations doubled from around 300 million to more than 600 million people. The second doubling in world population was very much faster. It occurred between 1600 and 1800, when improvements in medicine and living conditions resulted in a dramatic reduction in mortality rates. The third doubling in world population, from 1.2 billion to 2.5 billion was faster still, in the 150 years following 1800—in spite of the occurrence of two world wars. The fourth doubling occurred in less than 40 years, bringing global population in 1990 to more than 5 billion. Although the rate of population increase has slowed, a fifth, and perhaps final, doubling of population in the next 50 years is projected by the United Nations, bringing projected world populations in 2050 to somewhere between 7.6 and 10.6 billion. In the past 200 years, then, we have increased the number of people on our planet by a factor of 10. We might conclude from this that whatever the impact of earthquakes on human history, it may be very different from what we may expect in our future. Neither the rates nor the distributions of large earthquakes have changed appreciably in millions of years, but the risk has grown simply because the sizes of the targets are now so much greater than ever before. Of particular note for the present discussion, the recent tenfold increase in human populations has occurred largely in cities. During the Middle Ages the rural population outnumbered the urban population by about 100 to 1, a ratio that reflected the high risk of communicable disease in cities. Cities were essentially places for the excess rural population to move to, and to die young. Advances in medicine upset the natural mortality of cities that had checked their growth, and urban populations have grown steadily since 1600.
Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.
If you think you should have access to this title, please contact your librarian.