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Sea level rise dramatically, rock coastline retreats 10-22 meters

Sea level rise dramatically, rock coastline retreats 10-22 meters

Rising sea levels could push Britain’s coastline back by up to 72 feet (22 meters) by 2100, according to a new study. Researchers from Imperial College London modelled the consequences that different future climate change scenarios will have on the country’s cliffs.

The study found that rocky shorelines, traditionally considered stable compared to sandy shorelines and soft cliffs, are likely receding at a rate not seen in 3,000 to 5,000 years.

Rock coastline retreats

At the UK study sites in Yorkshire and Devon, this will cause the rocky cliffs on the coast to recede at least 10 to 22 meters inland. This erosion rate is likely to be three to seven times the current rate, and potentially up to ten times higher.

A study published today in Nature Communications found that rocky shorelines, traditionally considered stable compared to sandy shorelines and soft cliffs, are likely receding at a rate not seen for 3,000-5,000 years.

The study sites. A) Map of Great Britain with sites located. B) Bideford sample site location. C) Scalby sample site location. D) Bideford topography and sample locations. E) Scalby topography and sample locations. F) Bideford field photo. G) Scalby field photo. Credit: Shadrick et al.

ANSTO’s role in the research was to quantify cosmogenic radionuclides, 10Be and 26Al concentrations in rock samples using accelerated mass spectrometry at the Sirius accelerator at the ANSTO Accelerator Science Center.

Lead author Dr Dylan Rood, from Imperial’s Department of Earth Sciences, said: “Coastal erosion is one of the biggest financial risks to society of any natural hazard. Some rocky cliffs are already crumbling, and Within the next century, rocky shoreline erosion rates could increase tenfold. Even rocky shorelines that have been stable over the past hundred years will likely respond to sea level rise by 2030.”

Globally, coastlines are home to hundreds of millions of people and hundreds of billions of dollars in infrastructures such as homes, businesses, nuclear power plants, transportation links, and agriculture.

A rocky road

The new study is the first to validate models of the expected erosion of hard-rock shorelines due to sea level rise using observational data on prehistoric time scales. Previous studies have mainly focused on theoretical models of soft-sand shorelines. The new results suggest that as sea levels continue to rise, the rate of rocky coastal erosion will also accelerate.

To study the future rate of erosion, the researchers looked at past and present rates of cliff retreat on the coasts near Scalby in Yorkshire and Bideford in Devon, and found that by 2100 they are likely to recede by between 13-22m and 10-14m. m, respectively.

The upper end of those ranges is believed to be the result if the current trajectory of our greenhouse gas emissions remains unchanged.

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The rate of erosion is likely to be between three and ten times the current rate, one that has not been seen for 3,000 to 5,000 years, and is much faster than previously thought.

This is because erosion in the past was driven by waves, and they are likely to become more powerful as sea levels rise and storms become more frequent due to climate change.

They collected rock samples and analyzed them for rare isotopes called cosmogenic radionuclides (CRNs) that accumulate in rocks exposed to cosmic rays. CRN concentrations in the rock reveal how quickly and for how long the rock has been exposed, reflecting the rate of erosion and retreat.

Rising sea levels

As the climate warms, sea levels are projected to rise one meter by 2100 unless greenhouse gas emissions are reduced.

This study is the first to confirm with observational data that the rate of past coastal erosion followed the rate of sea level rise on prehistoric time scales. The researchers say this erosion was driven by waves, which are likely to become larger and more powerful as sea levels rise in the future and more land is delivered to the sea.

While this study looked at the effects of sea level rise, it did not take into account the effects of stronger storms, which some studies predict will occur more frequently due to climate change. Next, the researchers will adapt their model to also predict the rate of retreat of cliffs on softer rocky shores, such as chalk.

Study co-author Dr Martin Hurst from the University of Glasgow said: “The implication is that rocky shorelines are more sensitive to sea level rise than previously thought. We need to pay more attention to how our rocky shorelines continue to erode as sea levels rise.

“The greatest risks of erosion on our coasts will continue throughout this century. Even if we achieve Net Zero tomorrow, a substantial amount of sea level rise is already accumulating as our climate, glaciers, and oceans continue to respond to emissions that have already taken place.”

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