Half of the world's beaches threatened with extinction

France could lose a quarter of its sandy beaches and coastlines. In other parts of the world, thousands of kilometres of sandy coastline will be drowned under water, causing shores to recede, wiping out buildings, villages, ports and cities. According to new research, nearly half of the world's beaches will have been considerably reduced by the end of the century, with effects that will be strongly felt in the coming years. Coastal flooding, the two main causes of which are climate and human intervention.

Climate change and rising sea levels could wipe out half of the world's sandy beaches by 2100, according to a study published on 2 March in Nature Climate Change. Even though humanity is sharply reducing the greenhouse gas emissions responsible for global warming, more than a third of sandy coastlines are threatened, according to this study.

 "We must prepare ourselves"Their disappearance would have an impact on tourist activities, but not only. « Apart from tourism, sandy beaches often provide the primary mechanism for protection against storms and flooding, and without them, the impacts of extreme weather events are likely to be greater. "said Michalis Vousdoukas, who led the study and is a researcher at the European Commission's Joint Research Centre.

Heavy tribute

Sand erosion will endanger wildlife and could take a heavy toll on coastal settlements that will no longer have buffer zones to protect them from sea-level rise and storm surges. In addition, government measures to mitigate damage are expected to become increasingly costly and, in some cases, unsustainable.

Some countries, such as the United States, are already planning large-scale defence systems, but in most other states such massive engineering projects will be impractical, unaffordable or both. Australia could be the hardest hit, according to the study's findings, with nearly 15,000 kilometres of white sand coastline washed away over the next 80 years, followed by Canada, Chile and the United States. The 10 countries most likely to lose sandy coastline are also Mexico, China, Russia, Argentina, India and Brazil.

Sandy beaches occupy more than a third of the world's coastlines and are often located in densely populated areas. But they are threatened by erosion due to new construction, rising sea levels, storms, threatening infrastructure and lives.

In 30 years' time, erosion will have destroyed 36 097 km, or 13.6 % of sandy coastlines identified on satellite images by scientists from the European Commission's Joint Research Centre (JRC). They predict that the situation will worsen in the second half of the century, washing away an additional 95 061 km, or 25.7 % of the world's beaches.

These estimates are far from being the most catastrophic; they are based on an optimistic prediction of international action to combat climate degradation, a scenario known as RCP4.5. In this scenario of reduced ice sheet melting and reduced thermal expansion of water, the oceans will have increased by only 50 cm by 2100.

However, if the world continues to emit carbon at the current rate, sea levels will rise by about 80 cm, according to the Intergovernmental Panel on Climate Change. If this happens, a total of 131,745 km of beaches, or 13 % of the world's ice-free coastline, will be under water.

Worldwide, the average coastal retreat will be 86.4 metres in the RCP4.5 scenario or 128.1 metres in the high-carbon scenario, but the amounts will vary considerably from place to place. Flatter or wilder coastlines will be more affected than those with steeper waterfronts, or those that are artificially maintained as part of coastal development.

" The length of shoreline at risk includes areas that will be submerged by more than 100 metres, assuming there are no physical limits to potential setback. ", says Michalis Vousdoukas. « Our 100-metre threshold is conservative because most beaches are less than 50 metres wide, especially near human settlements and in small islands, such as the Caribbean and the Mediterranean. ".

Coastal retreat

Large beaches will shrink by 100 to 200 metres on the Atlantic and Pacific coasts and on the Australian part of the Indian Ocean, removing more than 60 % from sand deposits in a number of economically fragile developing countries heavily dependent on coastal tourism.

• READ IN UP' : Six out of ten French people live in a risky environment

But early action to limit emissions and combat climate degradation could, according to experts, help reduce the impact. Moderate mitigation of emissions could prevent the loss of 17 % of coastline by 2050 and 40 % by 2100, which would preserve an average of 42 metres of sand between land and sea, the authors of the study project.

Rising sea levels exacerbate the problems caused by construction and barriers on the coast, such as buildings, roads or dams, which have altered the natural cycle of replenishment of sandy beaches. In some areas, such as the Baltic, marine erosion is compensated for by rising land levels. Sediments can also be brought in by rivers, either naturally, as in the Amazon, or as a result of artificial activities, as in the Chinese deltas that accumulate residues from upstream industrial sites.

• READ IN UP' : The sand slipped through our fingers. Soon there won't be any more.

A third erosion factor is the intensification of storms, which is associated with climate degradation. These can further erode the most vulnerable beaches. By the end of this century, up to 63 % of the world's low-lying coastal areas will have been eroded by tides. In these areas, population density and development are generally higher than inland.

" Human expansion towards the sea will continue, mainly on intact coasts, which are particularly extensive in Asia and Africa. ", observes Mr. Vousdoukas. « Adaptation measures are urgently needed ".

With AFP

This interactive map shows the beaches that will lose or gain ground