Polar bear on ice river. Iceberg melting and global warming. Climate change
Sea-level rise—largely due to melting glaciers caused largely by anthropogenic climate change—has been a hot topic for the past half century. But historically determining the baseline parameters of global sea level has never been a common exercise.
However, in a revealing new book, Sea Level: A Historyauthor Wilko Graf von Hardenberg, a senior research fellow at Germany’s Max Planck Institute for the History of Science in Berlin, eloquently describes how difficult it was to come up with a standard method of measuring mean sea level.
In the process, Hardenberg gives us a very detailed but very accessible story of how, over five centuries, the concept of measuring mean sea level was a laborious process that progressed in fits and starts.
Mean sea level is simply the average height of the ocean’s surface over time. But the boundaries between land and sea are often skewed.
The concept of sea level as an average is only one step in the long-term pursuit of a landmark in a space that is never at rest, Hardenberg writes. Sharp distinctions between land and sea are relatively new products of the modern age, he notes. Coasts are actually ecotones, spaces where different ecosystems meet and interact, porous regions that are part land, part water, he continues.
Early data
The earliest available series of land-related sea-level data began to be produced continuously almost five centuries ago in Amsterdam, Hardenberg writes in Sea Level. Elsewhere, tide gauges — the tools needed to collect sea-level measurements — were installed in a haphazard, piecemeal fashion, he notes. Such random and unbalanced development and the consequent disparity of available series has produced biases in our historical understanding of sea-level rise, Hardenberg writes.
Long before the advent of advanced geodetic systems, altimeters and satellites, our ancestors took a reliable shot at determining a global mean sea level. They weren’t entirely successful, but they tried. And it must be remembered that even with today’s global satellite technology, measuring changes in sea level from above remains a somewhat odd proposition.
Sea Level: A History
This is undoubtedly one reason why recent dire predictions about climate change have thankfully not always come true.
In a 2011 article on Central climateI emphasize that the condition of Georgia’s 100 miles of coastline have waxed and waned for thousands of years, surviving by shifting miles in the process. Sea level rise may be even more pronounced in areas such as the Georgia coastline, where the curvature of the earth already amplifies high tides of 8.2 ft, I write.
In fact, according to NOAA, global mean sea level has risen about 8-9 inches since 1880. The rise in water levels is largely due to a combination of meltwater from glaciers and ice sheets and thermal expansion of water of the sea as it warms, NOAA reports.
Getting a handle on mean sea level.
At the 1867 meeting of the American Association for the Advancement of Science, Ohio-based geologist Charles Whittlesey presented a paper on the effect of glaciation on ocean levels, Hardenberg writes. Whittlesey concluded that the melting of existing ice caps would cause catastrophic growth, the author notes.
Satellites have allowed scientists to overcome the limitations of a sparse network of tide gauges and gravimeters along coasts and on Mid-Ocean islands, finally providing continuous—and near-global—sea-level data, Hardenberg writes.
However, the accuracy of satellites is not absolute, writes Hardenberg. In fact, valid, long-term series of observations reliably collected in the field are essential for calibrating instruments on satellites, he notes.
Horrible predictions
Models predict a rise of at least 15 centimeters by 2050 and possibly more than a meter by 2100, Hardenberg writes.
like Sea Level points out, Miami has been called the “most vulnerable” major coastal city in the world. And with its deltaic geography, the country of Bangladesh is virtually vulnerable to tidal flooding and sea-level rise, Hardenberg notes.
Trial and Error
Sea Level provides a fascinating account of how science is often a partial trial-and-error enterprise. But the book also provides a sobering reminder of the inaccuracy of today’s global sea level measurements.
What about sea level rise caused by anthropogenic climate change?
Although there is no doubt that anthropogenic climate change has played a large role in the current course of global mean sea level, some of the most historic predictions about impending floods have mercifully remained so. Predictions. Not reality.
This does not mean that we should not take the subject seriously. But sea-level rise associated with anthropogenic climate change is both insidious and nuanced. Those unfamiliar with the long-term geological history of our planet are often unaware that Earth’s climate and its oceans have waxed and waned over millions and billions of years.
The conclusion?
There are no easy solutions; The climate change genie is out of the bottle, and we still have a lot to learn. But for those interested in learning how sea-level fluctuations have been historically measured, the book Sea Level worth a read.
