Rising sea level does not mean the end of sandy beaches: paper

An international team of coastal scientists has dismissed suggestions that half the world’s beaches could become extinct over the course of the 21^st century and that Australia was one of the highest at-risk countries with 40 percent of its beaches threatened with extinction.

The claim had been made by European researchers in a paper published in Nature Climate Change in March 2020 (Sandy coastlines under threat of erosion by Vousdoukas et al). However, academics from Australia, the United Kingdom, France, South Africa, New Zealand and the United States have re-examined the data and methodology that underpinned the original study, and say they strongly disagree with its conclusion.

They have now published a rebuttal to the article in the same journal, and concluded that with the global data and numerical methods available today, it is impossible to make such global and wide-reaching predictions.

Critical to their disagreement with the original paper’s conclusions is the fact that they say there is potential for beaches to migrate landwards as sea levels rise and shorelines retreat.

The key notion behind that is that if beaches have space to move into under the influence of rising sea levels – referred to as accommodation space – they will retain their overall shape and form but in a more landward position.

The new research says that beaches backed by hard coastal cliffs and engineering structures, such as seawalls, are indeed likely to disappear in the future due to sea-level rise because these beaches are unable to migrate landward. They will first experience ‘coastal squeeze’ resulting in a decrease in width, and will eventually drown. This will occur on beaches like Collaroy and Wamberal in NSW.

However, beaches backed by low-lying coastal plains, shallow lagoons, salt marshes and dunes, which is the case with most Australian beaches, will migrate landward as a result of rising sea level. In these cases, the shoreline will retreat, but the beaches are still likely to remain, albeit a little raised in elevation and located landward, and will certainly not go ‘extinct’.

While beaches might not commonly be threatened in Australia, the same cannot be said for coastal dwellings. “In NSW hazard lines have been mapped for 2020, 2050 and 2100 on all beaches, so we know what to expect during extreme storm events as sea level rises,” Professor Short added.

“These are reviewed every five years as more data becomes available, and submitted for review to the State government.”

Co-author Honorary Professor Andrew Short from the School of Geosciences at the University of Sydney’s Faculty of Science, who has investigated all 12,000 Australian beaches, said: “I have found no evidence of widespread erosion, let alone accelerated erosion of Australian beaches.” 

He explained: “As most have ‘space to move’, the vast majority should be able to slowly adjust and accommodate the rising sea level, definitely until 2100 and most beyond.”

Coastal structures such as seawalls prevent beaches from naturally adjusting to rising sea level by migrating landward, and in those settings, removal of the structures (managed realignment) or nature-based solutions (for example, sand replenishment) may be the only methods to safeguard the future of these beaches. This is the case at Australian beaches like Collaroy and Wamberal.

Andrew Cooper, Professor of Coastal Studies at Ulster University and the new paper’s lead author, said new methods were needed for predicting impacts of sea-level rise on the coast: “This will require better datasets of coastal morphology and improved understanding of the mechanisms of shoreline response in given settings,” he said. 

“As sea level rises, shoreline retreat must, and will, happen but beaches will survive. The biggest threat to the continued existence of beaches is coastal defence structures that limit their ability to migrate.”