Sea Level and Us

If you are any kind of sentient being, a reader of literature, especially as a resident of western Pennsylvania, you know about Rachel Carson and her “The Sea Around Us” (1950). The New York Herald Tribune said of its publication: “It is a work of science; it is stamped with authority. It is a work of art; it is saturated with the excitement of mystery. It is literature.”

And you also know of Ernest Hemmingway’s “The Old Man and the Sea” (1952), a novel about a man’s struggle to catch a giant marlin. Books, if you do not live on the sea, or near it, or depend on it, are how you know the sea. And you, like me, have probably taken the apparently simple term “sea level” for granted, whether reading fiction or listening to the climate scientists on record since the latter 20th century.

In respect to the last, simple Physics 101 tells you that climate change is real and that sea level, whatever its absolute mean, must therefore be on the rise. That’s all mathematics though and maybe too abstract. Until you read in the news that the residents of the South Pacific island nation of Tuvalu and Australia have agreed to a pact allowing Tuvalu’s 11,000 climate-change-threatened residents an annually controlled rate of migration to safer, meaning higher, ground in Australia, in anticipation. That’s real, even if you are a science denier.

But now the deeper question: What is sea level, or its mean value? How is it measured and averaged considering solar and lunar gravitational tugs and tides, the effect of wind, effects from the earth’s own land shifts, and glacial ups and downs that contribute to sea volume and even those land shifts. Does it vary across oceans? It does. How must this be quantified for those who do have the sense to seek the science, including port navigators, builders of canals, and, of course, climate scientists? How, in respect to the latter, to combat illiteracy, fantasies, or even just ennui?

Wilko Graf von Hardenberg has taken up the subject in his “Sea Level: A History” (2024). He is an historian of science at Humboldt University in Berlin and leads the project “The Sound of Nature: Soundscapes and Environmental Awareness, 1750-1950.” He is also coauthor, with Marco Armiero and Roberta Biasillo, of “Mussolini’s Nature: An Environmental History of Italian Fascism” (2022), a title translated from the Italian that is screaming for access to my bedside pile.

While the historical account is written as somewhat of a scientific scrum through the 19th century, without tidy enough landmark points of view for most readers, there are key takeaways. And then, the fog begins to clear in the 20th century with the evolution and use of automated tidal measuring instruments, and then, especially, instrument-equipped space satellites. Satellite observations have eliminated sole dependence on locally averaged littoral measurements, each with its own national and commercial purposes in mind.