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The impacts of sea-level rise are too complex to predict

Sea-level rise will impact humans and coastlines in complicated and unpredictable ways, according to research from the University of Exeter. The experts found that in the past, there were variable rates of changes across societies and landscapes that did not match the pace of rising sea levels.

“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,” said study lead author Dr. Robert Barnett.

“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 localized. For example, communities may have powerful reasons for refusing to abandon a particular place.”

The study was focused on the Isles of Scilly off the southwest coast of the UK. Less than 1,000 years ago, this chain of 140 islands existed as one single island.

The researchers reconstructed sea-level rise to produce maps of coastal changes over the last 12,000 years across the Isles of Scilly. The maps were compared to reconstructions of the region’s landscape, vegetation, and human population. Much of the data had been collected by the Lyonesse Project, 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, the land was rapidly becoming submerged. As the coastline shifted, people did not abandon the new landscape, but rather stayed put and adapted to it. 

The study suggests that land was being lost at a rate of 10,000 square meters per year. About half of this land was transforming into intertidal habitats, which may have been able to support the coastal communities.

“This new research confirms that the period immediately before 4,000 years ago saw some of the most significant loss of land at any time in the history of Scilly – equivalent to losing two-thirds of the entire modern area of the islands,” said Charlie Johns, who is the co-director of the Lyonesse Project.

The islands continued to be submerged, even when the rate of sea-level rise was as low as one millimeter per year.

“It is clear that rapid coastal change can happen even during relatively small and gradual sea-level rise,” said Dr. Barnett. “The current rate of mean global sea-level rise (around 3.6 mm per year) is already far greater than the local rate at the Isles of Scilly (1 to 2 mm per year) that caused widespread coastal reorganization between 5,000 and 4,000 years ago.”

“It is even more important to consider the human responses to these physical changes, which may be unpredictable. As can be seen today across island nations, cultural practices define the response of coastal communities, which can result in polarised agenda, such as the planned relocation programmes in Fiji versus the climate-migration resistance seen in Tavalu.”

Dr. Barnett pointed out that the coastal reorganization at the Isles of Scilly led to the availability of new resources for coastal communities. “It is perhaps unlikely that future coastal reorganization will lead to new resource availability on scales capable of supporting entire communities.”

“More certain though, is that societal and cultural perspectives from coastal populations will be critical for responding successfully to future climate change.”

The study is published in the journal Science Advances.

By Chrissy Sexton, Staff Writer

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