Rocky coasts, which make up more than half of the world’s coastlines, could recede more rapidly in the future due to accelerating sea level rise.
This is according to new Imperial College London research that modeled potential future rates of cliff retreat for two rocky coasts in the UK. The projections are based on sea level rise predictions of various greenhouse gas emissions and climate change scenarios.
The study finds that rocky coasts, traditionally thought of as stable compared to sandy coasts and smooth slopes, are likely to be retreating at a rate not seen in 3,000-5,000 years.
At the UK study sites in Yorkshire and Devon, this would result in rocky coast slopes retreating at least 10–22 m inland. The rate of erosion is likely between three and seven times the rate today and possibly as much as ten times.
Senior author Dr Dylan Rudd, from Imperial’s Department of Geosciences, said: “Coastal erosion is one of the greatest financial risks to society of any natural hazard. Some cliffs are already collapsing, and over the next century, rates of coastal erosion could increase ten-fold.” Even rocky coasts that were stable in the past 100 years are likely to respond to sea level rise by 2030.”
Globally, coasts are home to hundreds of millions of people and hundreds of billions of dollars of infrastructure such as homes, businesses, nuclear power plants, transportation lines, and agriculture.
The researchers are calling on policy makers, planners and insurers to take action to classify rocky coasts as high-risk areas in future climate change response planning, as well as to reduce climate change by achieving Net Zero as an immediate priority.
Dr Rudd added: “There is no turning back in rocky coast erosion: now is the time to limit future sea level rise before it is too late. Humanity can directly control the fate of our coastlines by reducing greenhouse gas emissions – the future of our coastlines is in our country.” . the hands “.
The research was published today in Nature Communications.
The new study is the first to validate models of predicted erosion of hard-rock coastlines from sea level rise using observational data over prehistoric timescales. Previous studies have mostly focused on theoretical models of soft sandy coasts. The new findings suggest that as sea levels continue to rise, the rate of coastal rock erosion will also accelerate.
To study the future rate of erosion, the researchers looked at past and current rates of cliff retreat on coasts near Scalby in Yorkshire and Bideford in Devon, and found that by 2100 they are likely to have retreated by 13-22m and 10-14m, respectively.
They collected rock samples and analyzed them for rare isotopes called cosmic radionuclides (CRNs) that accumulate in rocks exposed to cosmic rays. The concentrations of CRNs in rocks reveal how quickly and for how long the rocks were exposed, which reflects the rate of erosion and retreat.
They combined this data with the observed coastal topography to calibrate a model that tracks the evolution of these rocky coastlines over time, before comparing them to previous rates of sea level change dating back 8,000 years. They found that the rate of coastal erosion at these two locations largely matches the rate of sea level rise.
The researchers say this is clear evidence of a causal relationship between shelf retreat and sea level from which future predictions can be made, and that rocky coastlines are more sensitive to sea level rise than previously thought. They say the findings can be applied to rocky coasts around the world because the type of rock is common globally, and similar hard rocky coasts are likely to respond in a similar way to sea level rise.
Lead author Dr Jennifer Shadrick, who conducted the work in the Department of Earth Sciences and Engineering at Imperial as a member of the NERC Science & Solutions PhD Training Partnership on Changing the Planet, and now works on the marine and coastal risk management team at JBA Consulting, said: “Sea level rise is accelerating, And our results confirm that rocky coast decline will accelerate in line with this.It’s not a matter of if, but when.
“The more positive news is that, now that we have a better idea of scales and timescales, we can adapt accordingly. The more data we have on the effects of climate change on sea level rise and coastal erosion, the better prepared we can be to advocate for urgent policies that protect coastlines and their communities. “.
sea level rise
As the climate warms, sea levels are expected to rise by 1 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 over prehistoric time periods. Researchers say this erosion has been driven by waves, which will likely get larger and more powerful as sea levels rise in the future, and more land is carried out to sea.
While this study looked at the effects of sea level rise, it did not take into account the effects of powerful storms, which some studies have predicted will occur more frequently due to climate change. Next, the researchers will adapt their model to also predict the rate of cliff retreat for coasts of softer rocks, such as chalk.
Dr Rudd said: “Our study did not account for the effect of increased storm surges, which may become stronger and more frequent in the future with climate change, on wave-driven shelf erosion. However, increased storm surges will only accelerate shelf retreat more than we expected. “This is another angle of the climate crisis that we will consider in future studies to give a more complete picture of potential rates of rocky coast erosion. We are also looking to improve our models for softer rocky coasts where erosion from waves is more significant.”
“The findings are a stark warning that we must better adapt to coastal retreat or face the loss of the people, homes and infrastructure that call coastal areas home,” said Dr Shadrick.
Study co-author Dr Martin Hirst at the University of Glasgow said: “The implication is that rocky coastlines are more sensitive to sea level rise than previously thought. We need to pay more attention to how our rocky coastlines continue to erode as sea levels rise.
“The increased risk of erosion on our coasts will continue throughout this century. Even if we achieve net zero tomorrow, a significant amount of sea level rise has already been incurred as our climate, glaciers and oceans continue to respond to emissions that have already occurred.”
This study was funded by the Natural Environment Research Council (NERC), the British Geological Survey (BGS) and the Australian Nuclear Science and Technology Organization (ANSTO).