Estimates of Coastal Populations

The excellent article by Peter M. Vitousek et al . ([25 July, p. 495][1]) states: “The human population is concentrated near coasts—about 60% within 100 km [kilometers]… .” This assertion comes from a recent World Resources Institute report ([1][2], p. 254): “An estimated 60 percent of the global population lives within roughly 100 kilometers of the shore.” This statement comes from a 1990 book ([2][3], p. 7): “Probably 60 percent of humanity, or nearly 3 billion people, live on or within 100 km of a sea coast.” The author of the latter book, Don Hinrichsen, an environmental journalist, informed one of us (J.E.C.) ([3][4]) that this statement was his “own assessment based on extensive back-of-the-envelope estimates using the best available data at the time.” More recently, Hinrichsen reported ([4][5], p. 39): “Nearly two-thirds of the world's people make their homes within 150 kilometers of the shore.” To our knowledge, the first public digital map of the world's human population appeared in 1995 ([5][6]). The data are freely available on the World Wide Web ([6][7]). These data make it possible to obtain more precise estimates of coastal populations as of 1994. As part of larger research programs, two groups with interests in the interactions between the earth sciences and the social sciences have independently co-registered the global digital population map on digital maps of coastlines. Using the digital World Vector Shoreline ([7][8]), two of us (C.S. and J.E.C.) estimate that approximately 37% (2.07 billion) of the 1994 population (5.62 billion) lived within 100 km of a coastline, and approximately 44% (2.45 billion) within 150 km of a coastline. These percentages are lower than those of Hinrichsen. In addition, C.S. and J.E.C. estimate that 49% of the 1994 population lived within 200 km of a coastline, and 66% within 400 km. Using the boundaries (compounded from various sources) provided by the gridded population of the world ([6][7]) and a different algorithm for computing distance to coastline, three of us (A.M., J.G., and J.S.) estimate that 37% lived within 100 km of a coastline. This estimate agrees with that of C.S. and J.E.C. Both groups anticipate that these estimates could be refined by the use of better data and methods. While our estimates of coastal population size are considerably smaller than Hinrichsen's, we agree that very large numbers of people affect and are affected by coastal zones. 1. [↵][9]World Resources Institute, World Bank, World Resources 1996-97 (Oxford Univ. Press, New York, 1996). 2. [↵][10]D. Hinrichsen, Our Common Seas: Coasts in Crisis (Earthscan, London, and Nairobi, Kenya, 1990). 3. [↵][11]\___|, personal communication. 4. [↵][12]\___|, Issues Sci. Technol. 12 (no. 4), 39 (1996). 5. [↵][13]W. Tobler, U. Deichmann, J. Gottsegen, K. Maloy, “The global demography project” (Technical Report 95-6, National Center for Geographic Information and Analysis, University of California, Santa Barbara, CA, 1995). 6. [↵][14]CIESIN, “Gridded population of the world,” 7. [↵][15]National Imagery and Mapping Agency, “World Vector Shoreline,” # {#article-title-2} Response: We thank Cohen et al . for their analysis, which should become the standard statement on coastal populations. [1]: /lookup/doi/10.1126/science.277.5325.494 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #ref-4 [6]: #ref-5 [7]: #ref-6 [8]: #ref-7 [9]: #xref-ref-1-1 View reference 1 in text [10]: #xref-ref-2-1 View reference 2 in text [11]: #xref-ref-3-1 View reference 3 in text [12]: #xref-ref-4-1 View reference 4 in text [13]: #xref-ref-5-1 View reference 5 in text [14]: #xref-ref-6-1 View reference 6 in text [15]: #xref-ref-7-1 View reference 7 in text