A Sea Change in Understanding: The Long and Winding History of Measuring Sea Level
The specter of rising sea levels, largely attributed to human-induced climate change and glacial melt, looms large in the 21st century. While the urgency of the issue is undeniable, the historical process of establishing a standardized method for measuring mean sea level has been a complex and often overlooked endeavor. Wilko Graf von Hardenberg, a senior research scholar at the Max Planck Institute for the History of Science in Berlin, tackles this intricate story in his new book, "Sea Level: A History." Hardenberg’s meticulous research reveals a five-century-long journey, marked by fits and starts, towards quantifying the average height of the ocean’s surface.
Defining mean sea level seems deceptively simple. However, as Hardenberg highlights, the dynamic interplay between land and sea complicates this seemingly straightforward task. Coastal regions, he argues, are not clearly demarcated lines but rather porous ecotones, where terrestrial and aquatic ecosystems intertwine. This inherent ambiguity presented a significant challenge for early attempts to establish a consistent measurement of sea level. The book underscores that the concept of an average sea level is a relatively recent human construct developed to understand a constantly shifting and restless environment.
Hardenberg traces the first systematic efforts to measure sea level relative to land back to 16th-century Amsterdam. These early attempts, however, were constrained by the limitations of the time. The subsequent introduction of tide gauges, crucial instruments for collecting sea-level data, was a disorganized and uneven process. This haphazard development, explains Hardenberg, has introduced biases into our understanding of historical sea-level trends. The sparse and uneven distribution of early data collection efforts meant that a truly global picture of sea level change remained elusive.
Long before the advent of sophisticated satellite technology, our ancestors grappled with the concept of a global mean sea level. Their efforts, while not entirely successful, demonstrate a remarkable early understanding of this complex issue. It’s important to note that even with today’s advanced satellite systems, accurately measuring sea-level changes from space remains a challenging undertaking. This inherent uncertainty is partly why some of the more extreme climate change predictions have thankfully not materialized. The Earth’s climate and oceans have fluctuated dramatically over millennia, adding another layer of complexity to understanding current trends.
Hardenberg cites Charles Whittlesey, a 19th-century geologist and surveyor, who presented a paper at the 1867 meeting of the American Association for the Advancement of Science on the potential impact of glacial melt on sea levels. Whittlesey’s work foreshadowed contemporary concerns, predicting a catastrophic rise in sea levels should existing ice caps melt. The evolution of scientific understanding, as documented by Hardenberg, reveals a growing awareness of the interconnectedness of climate, glaciers, and sea levels. The historical context provided in "Sea Level" allows readers to appreciate the long trajectory of scientific inquiry into this phenomenon.
The advent of satellite technology has revolutionized sea-level monitoring. Satellites have enabled scientists to overcome the limitations of sparsely distributed tide gauges and gravimeters, providing continuous and near-global coverage. However, Hardenberg cautions against overreliance on satellite data. Their precision, he emphasizes, is not absolute. Ground-based observations remain crucial for calibrating satellite instruments and validating their measurements. The book advocates for a balanced approach, integrating data from various sources to gain a more comprehensive and accurate picture of sea-level changes. Hardenberg highlights the ongoing challenge of accurately measuring and predicting future sea-level rise, despite advancements in technology. He cites current models that predict a minimum rise of 15 centimeters by 2050 and potentially over a meter by 2100, highlighting vulnerable coastal regions like Miami and Bangladesh. The book stresses the importance of acknowledging the inherent uncertainty in these predictions while also emphasizing the need for proactive measures to mitigate potential risks.
