In the late nineteenth century, scientists started to become aware of the fact that in the past the Earth had undergone a series of much colder periods – known as ice ages (or glaciations) – separated by periods of warmer climate similar to the present – known as interglacials. Today we have a much better picture of the past oscillations of the Earth’s climate, knowing that within the past two million years or so, there have been more than twenty of these glacial-interglacial cycles.
But what is especially interesting is that these great swings of climate – they occurred every hundred thousand years or so – were accompanied by swings of sea level. It is easy to understand why. If you cool the planet to the point that large ice sheets form on the land, the water of which they are formed can only come from the ocean – the surface of which drops as a result. Conversely, when you warm the planet, this land ice melts and the water pours into the ocean, raising its level. The graph below shows the last glacial-interglacial cycle.
During the Last Interglacial (not the one we live in now) about 120,000 years ago, the sea level was actually slightly higher. Then, as temperatures fell and ice sheets started building up on the land, so the ocean surface (sea level) fell. It reached a minimum of about 120 metres lower than today 22-18,000 years ago at the coldest time of the last ice age. Shortly after this, as temperatures rose and ice started melting, sea level started rising – and this is the time from which there are many stories in some of the world’s oldest cultures about the nature and the effects of sea-level rise.
Scientists sometimes forget that things which happened in the distant past, things like the rise of post-glacial sea level, were not just processes that altered landscapes and the livelihood options for animals (and people) occupying them. These processes were experienced, they were painfully disruptive, agonizingly anxious. And it is through these ancient stories that we can glimpse such human dimensions of sea-level rise, similar to those we often hear about today.
Consider Chesapeake Bay on the eastern seaboard of the United States, a place where land has been disappearing for decades, if not centuries. Its passing is bemoaned, a very human tragedy that far outweighs its scientific explanation for the affected people. In 1922, when the last of formerly inhabited Holland Island vanished, its obituary was written –
“The paradise of the Chesapeake is no more. Today at low tide only vestiges are seen and at high tide the island is completely under water. Gone are the homes of the people. The dead remained faithful to the island of their lives and as the storms drove the tides to their work of destruction they slept on”.
The picture below shows the last house standing on Holland Island in October 2009, gone a year later.
Much further back in time, we have similar stories. One of my favourites comes from the Wati Nyiinyii people of the Nullarbor Desert along part of Australia’s south coast. Thousands of years ago, the shoreline here lay much further out to sea, tens of kilometres seawards of the massive cliffs that today mark the continental fringe here (see photo below).
Accustomed to roaming the area now seawards of these cliffs (pictured above), the Wati Nyiinyii noted the landwards movement of the shoreline. A person in their thirties might have seen a strip of land a mile (1.6 km) wide lost in their lifetime. The people became anxious, not knowing when the sea-level rise might stop, whether there was a chance it would drown all the land. So they acted.
“The Wati Nyiinyii then pour over the Eucla escarpment, rather like an army of ants … Once the Wati Nyiinyii reach the sea, they begin bundling thousands of spears to stop the encroaching water. These bundles were stacked very high and managed to contain the water at the base of what is today the cliffs” .
While today we rightly applaud science and its practitioners for the insights they have deduced about the Earth’s distant past, we might also criticize for their sidelining of others’ knowledge – ancient wisdom that was overlooked because it was deemed legendary, basically fiction. In 2020, I wrote in a piece published in the Chicago Quarterly Review that
“Science could have learned more and sooner had it treated the ‘stories’ of ancient Australians (and people of other non-western cultures) more seriously as potential sources of information about the past, had it not pejoratively dismissed such stories as entertainments rather than expository, characterized the storytellers as literati rather than true scientists communicating their wisdom along unfamiliar pathways”.
True, albeit understandable.