Reviewed by John Clay Bruner, (University of Alberta)

Von Hardenberg, W. G. 2024. Sea Level: A History. Oceans in Depth Series. K. Anderson and H. M. Rozwadowski, eds. University of Chicago Press, Chicago, IL. 200 pp. SBN-13:978-0-226-83183-1. ($16.50 cloth, $16.19 e-book with 40% PS discount.)

There is probably no one better qualified to write a book on the history of sea level than Wilko Graf von Hardenberg. In the acknowledgments, you will find the idea for the book was first funded by the Deutsches Museum in Munich. Later Wilko spent two years teaching at the University of Wisconsin, Madison, where the feedback of the students helped refine his work. Finally, at the Max Planck Institute for the History of Science, his colleagues helped hone his ideas, read, and commented on early chapter drafts. At all institutions, Wilko benefitted from the library staff in obtaining obscure references. 

This book includes a table of contents followed by a Foreword by the series editors (ix-x), an Introduction: From Heights to Muds (1-14 pp.), six chapters entitled: Finding Sea Level (15-34 pp.); Infrastructures of Measure (35-58 pp.); Standards of Height (59-81 pp.); Theories of Change (83-102 pp.); Going Global (103-121 pp.); and The Rising Tide (123-136 pp.). This is followed by three pages of acknowledgments (137-139 pp.), 17 pages of Notes on the introduction and chapters (141-158 pp.), 26 pages of References (159-185 pp.) and finally a 12-page Index (187-199 pp.). 

In the introduction and the first chapter, we learn 300 years ago it was thought sea level was declining from Noah’s Biblical flood. In 1743, Andreas Celsius produced evidence using centuries of seal hunters’ wills to document the lowering of the Baltic Sea. He did not realize the land was rising from glacial rebound causing the seal rocks to rise, rather than the sea level declining. Charles Lyell in 1830 discussed local land uplift in Scandinavia and stated the Baltic’s sea level was relatively stable. The first data on sea level relative to land began in Amsterdam 500 years ago. Reliable data on sea level was rather hit or miss until the first automated tide gauges were invented in the early 1800’s. William Whewell in 1836 was put in charge of a British Association for the Advancement of Science committee to determine relative sea level around the U.K. coast. Building on the work of many others, Whewell determined sea level was relatively stable. This led to using sea level as a stable reference for measuring altitude on land. 

Engineers wanted a universal standard for measuring altitude, especially when canals, roads, and railroads crossed state lines. European countries had dissimilar methods for determining altitude. In Chapter Two (“Infrastructures of Measure”), we learn the invention of mareographs helped establish sea level as a standard for measuring altitude. Not having accurate sea level measurements stalled the construction of the Suez Canal by 50 years. During the French invasion of Egypt, Napoleon’s chief surveyor, Jacques-Marie Le Pere, in a 25-day survey across the Suez isthmus, determined the Red Sea was 10 meters higher than the Mediterranean. In 1847, Paul-Adrien Bourdaloue, with the support of Egypt’s ruler, undertook a new survey of the isthmus and determined the Mediterranean and Red Sea were essentially the same height. Another potential canal across Panama was stalled by the belief that the Pacific was thousands of feet higher than the Atlantic. John Augustus Lloyd, using a trigonometric survey, in 1828 determined a discrepancy of only 3.5 feet between the two oceans which was within the standard error of measurement. 

In Chapter Three (“Standards of Heights”), mean sea level, measured at various points along Europe’s coasts, became the standard reference point. Between 1885 and 1895, France used the mean sea level at Marseille, Austria-Hungary used the mean sea level at Trieste, Italy the level at Genoa, Spain used the level at Alicante, and Portugal used Cascais’ sea level. The German Reich in 1879 used the Normalnull as its universal vertical datum which was based on leveling of the Amsterdam ordnance datum. Europe often did not follow their own country’s vertical datum standard in their respective colonies. Eventually, attempts to determine a European vertical point zero faded away. 

In Chapter Four (“Theories of Change”), Hardenberg recounts how the Austrian geologist Edward Suess in the 1860’s theorized that eustasy, widespread global sea level changes, were responsible for sea deposits in Austria and in Hungary 250 miles away. In 1840, Louis Agassiz proposed glaciation was important in the formation of landscapes. In 1842, Charles Maclaren proposed Agassiz’ ice age would produce major changes in sea level. Discovery of alternate layers of marine sand and land debris 100 meters above sea level along a Scottish railroad being built in 1849 led Robert Chambers to theorize significant multiple rises and falls of sea level as a method of land formation along the British coast. Chambers also cited Charles Darwin’s theory of coral formation to register changes in sea level. Later geologists such as Reginald Daly, Albrecht Penck, Henri Baulig expanded on Maclaren’s early insights, and glacio-eustatism, the theory explaining repeated changes in sea level through the ice ages, was born. 

In Chapter Five (“Going Global”), von Hardenberg documents that sea level is rising because of anthropogenic climate change. New technologies, such as using carbon-dated Dutch shells and peat compared with data collected from Texas and Louisiana ruled out local tectonic shifts in favor of eustatism. Satellite oceanography has improved the accuracy of measuring sea level rise and computing a global mean sea level.

In Chapter Six (“The Rising Tide”), von Hardenberg points out the impact of a rising sea level. Severity of storms will increase and flooding from sea surges is being augmented. In the twentieth century, average annual increase of global mean sea level was 1.7 millimeters. In the twenty-first century, the rate has more than doubled to 3.6 millimeters. In the next decades, models predict an even higher rate of increase. Interactive maps on the internet predict potential changes to coastlines, such as Alex Tingle’s Flood Maps website, Climate Central, and NOAA Sea Level Rise Viewer. Rising sea level will affect the territorial waters of many nations.

If you are interested on the effect of climate change and its impact on sea level change, you should buy this book.