Sea-level rise will have complex consequences for coasts and communities

Crab's Ledge on the Isles of Scilly (Credit: Cornwall Council)

Rising sea levels will affect coasts and human societies in complex and unpredictable ways, according to a new study involving the University of Plymouth.

Researchers reconstructed 12,000 years of sea-level rises to produce maps of coastal changes at thousand-year intervals.

They found that today’s Isles of Scilly, off the coast of Cornwall, emerged from a single island that only became the current configuration of more than 140 islands less than 1,000 years ago.

The study, published in Science Advances, found that changes in both land area and human cultures happened at variable rates and often out of step with the prevailing rate of sea-level rise.

With climate change now driving rapid sea-level rise, the team says the effects will not always be as simple as a forced human retreat from coasts.

Co-authored by Professor of Geospatial Information Ralph Fyfe, the study was led by the University of Exeter, in partnership with Cornwall Council and 15 other institutes. Its other authors included Dan Charman, former Professor of Physical Geography in Plymouth, as well as former PhD students Dr Robert Barnett and Dr Marta Perez.

Professor Fyfe contributed long-term ecological data to the project, and said:

“The major strength of this work is that it links together archaeologists, modellers and geographers to address a significant global environmental challenge. It uses empirical date from the Isles of Scilly to tell a story around sustainability and human response to environmental change, via the interactions between people, environment, climate and sea-level rise. That is a story that continues to develop, but charting past change can help us understand the potential effects of future predicted climate change.”

Dr Barnett, the study’s lead author now based at Exeter, added:

“When we’re thinking about future sea-level rise, we need to consider the complexity of the systems involved, in terms of both the physical geography and the human response. The speed at which land disappears is not only a function of sea-level rise, it depends on specific local geography, landforms and geology. Human responses are likely to be equally localised. For example, communities may have powerful reasons for refusing to abandon a particular place.”

The researchers developed a new 12,000-year sea-level curve for the Isles of Scilly, and looked at this alongside new landscape, vegetation and human population reconstructions created from pollen and charcoal data and archaeological evidence. The new research extends and enhances data collected by the Lyonesse Project (2009 to 2013), a study of the historic coastal and marine environment of the Isles of Scilly.

The findings suggest that during a period between 5,000 and 4,000 years ago land was rapidly becoming submerged. In response to this period of coastline reorganisation, people appeared to adapt to, rather than abandon, the new landscape.

By the Bronze Age (after 4500 years ago), the archaeological record suggests the area had a permanent population – and instead of leaving the islands, it appears that there may have been a “significant acceleration of activity”.

The reasons for this are unclear, but one possibility is that new shallow seas and tidal zones provided opportunities for fishing, shellfish collection and hunting wildfowl.

This period of rapid land loss happened at a time of relatively slow sea-level rise – because lots of Scilly’s land at that point was relatively flat and close to sea level.

The study found that between 5000 and 4,000 years ago, land was being lost at a rate of 10,000m2 per year, which is equivalent to a large international rugby stadium. However, about half of this land was turning into intertidal habitats, which may have been able to support the coastal communities.

After 4,000 years ago, the island group continued to be submerged by rising sea levels, even during modest (e.g. 1 mm per year) rates of sea-level rise.

The fully study – Barnett et al: Non-linear landscape and cultural response to sea-level rise – is published in Science Advances, doi: 10.1126/sciadv.abb6376.


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