The meaning of sea level rise – a comparison between an ancient Scottish village and the Queensland coast
Nothing we do at C&R Consulting can be separated from “climate”, or its offsider “weather”, and nor should it be. In some way, shape or form, the “climate” dictates how the oldest natural phenomena, the “geology”, ends up as sand fragments along our coastline and in our oceans. Every tree, every coastline, every desert, every river, is where it is because of “climate”. Australia is still demographically young enough to expose the location of our towns and cities to the human reliance on water. Settled from around 1778 onwards, our need for access to easy transport dictated that our first settlements would be along the coastline. The survival of that colonisation depended on access to non-saline water. Now the argument has come full circle and we are told our coastal cities are threatened by rising sea levels. And more: Those rising waters are considered anthropogenically driven.
As geomorphologists, geologists, hydrologists, biologists, climatologists, we follow the arguments. We listen. And we think. Many of the arguments make sense. Nobody in the C&R office follows a single stream of science. Every stream mingles and argues every point until a common (or sometimes relatively) common goal is reached.
Recently, the two directors of C&R Consulting were in Great Britain on work-related issues. The archaeological remnants of the stone-built Neolithic settlement of Skara Brae in the Orkney Archipelago had been making headlines in Australia. Fears the historical treasure would end up in the cold waters of the North Atlantic were horrendous. The finger was pointed at sea level rise and funds were needed to rebuild an earlier protective seawall undermined by fierce wave action driven by the almost constant gale force winds.
The geology, principally Devonian flagstones (age 412 to 359 million years ago), which facilitated the building of the Neolithic villages of the Orkney Archipelago, is superb. The geomorphology, after the relatively recent glaciation (possibly as recently as 10,000 years ago), is even better. The engineering ability of a small group of people with limited resources (Skara Brae was constructed using the local Devonian flagstone around 5000 years ago) is incredible. Anthropologically induced climate change and its offspring sea level rise (around 100 years old), is the relatively new kid on the block. The archaeology is the tie that binds. The two C&R directors decided to “take a look”.
As predicted, the site is spellbinding. To stand in a village where other humans have cooked and slept and laughed and argued 5000 years earlier is a feeling that can never be explained in words. Skara Brae must be saved, and we all need to help save it.
BUT: There is evidence along the Queensland coast that around 5000 years ago – the same period when Neolithic man was living in the village now known as Skara Brae – the sea level was around two metres higher than it is today. Some scientists argue higher, some argue slightly less. However, two metres is a reasonable approximation. It would seem safe to presume that if the sea level was two metres higher in the western Pacific Ocean 5000 years ago, it would have been two metres higher in the Atlantic Ocean as well. If that was the case, the Neolithic villagers must have built their stone village very close to the shore line. Would they have chosen to build so close to a shoreline exposed to the fierce waves of the North Atlantic Ocean? If so, why?
How do we interpret this? Certainly, the coastline adjacent to Skara Brae is being eroded. And yes, it certainly puts the Neolithic village under threat. But is it sea level rise? Could it be tectonic movement? Has there been buckling and warping along the western coastline of the Orkney Archipelago? The whole landscape itself is likely to have risen a little over the last 10,000 years as a tectonic (isostatic) response to relief from the weight of ice during the last period of glaciation. Has the base geology of the coastline beneath the Neolithic village gradually eroded backwards in response to constant chemical dissolution and physical attack by the never-ending pounding of the North Atlantic Ocean? Or is it a combination of a mish-mash of geomorphological, geological, mineralogical, climatological and oceanographic factors?
Does it matter? Academically yes! Scientifically, yes! Historically, yes! Regardless of the cause, the bottom line remains the same. Skara Brae is threatened by an eroding coastline. Skara Brae has earned its UNESCO World Heritage Site status. Every attempt must be made to save it. The rest is academic.