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Coastal wetlands are inching closer to extinction as the world heats up

A recent study published in the journal Nature has raised alarming concerns about the survival of the world’s coastal wetlands and coral reef islands in the face of rising sea levels caused by climate change. 

An international team of researchers found that the ability of marshes and other low-lying coastal areas to survive depends significantly on whether global warming can be limited to less than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels, as outlined by the Paris Agreement.

Moving towards a tipping point

“Coastal ecosystems exist where our oceans meet the land, including mangroves, coastal marshes and the fringes of sandy coral islands – the low-lying areas flooded and drained by tidal salt water,” said study lead author Professor Neil Saintilan from Sydney’s Macquarie University.

“Our research shows these coastal habitats can likely adapt to some degree of rising sea levels but will reach a tipping point beyond sea-level rises triggered by more than 1.5 to 2°C of global warming.”

“Without mitigation, relative sea-level rises under current climate change projections will exceed the capacity of coastal habitats such as mangroves and tidal marshes to adjust, leading to instability and profound changes to coastal ecosystems.”

Sea-level rise 

The experts found that coastal marshes, mangroves, and reef islands are unlikely to keep up with sea-level rise rates that exceed 7 millimeters (about one quarter of an inch) per year. 

Unfortunately, such rates are anticipated by the year 2100 in most parts of the world if there are no substantial efforts to decrease greenhouse gas emissions. 

Regions along the Gulf Coast are already experiencing higher sea-level rise rates. Earlier research from Tulane University indicated that the existing rate of sea-level rise could submerge marshlands in Louisiana and potentially other Gulf Coast areas within the next 50 years.

No way to escape

“Mangroves and other tidal plants have to get oxygen down to their roots to survive, and so that phase of the tide when water drains right out is really important,” said Professor Saintilan.

“When the plants become water-logged due to higher sea levels, they start to flounder. At Sydney Olympic Park, we’ve seen whole patches of mangroves die when water can’t drain out properly.”

“This sort of death would be devastating for many natural mangrove forests across Asia which are restricted in their capacity to retreat from rising seas due to land development and human habitation.”

Some of the world’s most valuable ecosystems 

Study co-author Torbjörn Törnqvist, a professor in Tulane’s Department of Earth and Environmental Sciences, emphasized the global significance of these ecosystems. 

“Collectively, these are among the most valuable ecosystems on the planet. For example, the world’s fisheries depend to a significant extent on the health of coastal wetlands and coral reefs,” said Professor Törnqvist.

The findings of the study are closely aligned with the most recent sea-level projections of the Intergovernmental Panel on Climate Change (IPCC), published in 2021. 

Potential for widespread collapse 

The researchers discovered that if global warming stays below 2 °C compared to pre-industrial temperatures, many of the world’s coastal ecosystems will likely survive along the shorelines by 2100. 

However, higher levels of warming will probably result in widespread collapse. Professor Törnqvist highlighted the critical role of the Paris Agreement in this context. 

“This shows the importance of the Paris Agreement that aims to keep warming within 2 °C and ideally 1.5 °C,” he said. “Clearly, this would make a huge difference for coastal ecosystems. However, right now we are on track for 2.4 to 3.5 °C of warming by the end of this century, so a change of course is desperately needed. And this would have to happen very quickly.”

Study implications 

Even if global warming is limited to 1.5 °C, some coastal regions will lose the majority of their wetlands by the end of the century. The coastlines of Louisiana and Texas are particularly vulnerable. 

The recent surge of record-breaking heat across much of the world indicates that this level of warming could be achieved in just a few years.

The study included contributions from researchers at other Australian universities and co-authors from Singapore, Hong Kong, the United Kingdom, and the United States.

Professor Törnqvist’s role in the research primarily involved developing innovative methods to assess wetland vulnerability to sea-level rise in the geologic past. His work was supported by the U.S. National Science Foundation.

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