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The Last Ice Age shows how rising sea levels will transform coastal habitats

An international team of scientists from more than a dozen institutions, including Rutgers University, has turned to evidence from the last Ice Age to predict how rising sea levels will impact coastal ecosystems.

The study reveals that if global average temperatures rise beyond a certain threshold, the world could once again experience the rapid pace of sea level rise and coastal habitat retreat that occurred at the end of the Last Ice Age.  

Ancient coastal habitats 

In a paper published in the journal Nature, the experts describe how ancient coastal habitats adapted as the last glacial period ended more than 10,000 years ago. 

The team analyzed the ocean sediments of ancient shorelines from a time when melting ice sheets in the Northern Hemisphere drove a rapid rise across the oceans.

The goal was to gain a better understanding of how coastal ecosystems were transformed, and to more accurately predict what changes can be expected in the coming decades with projected sea level rise. 

A rising threat

“Every ton of carbon dioxide humankind emits turns up the global thermostat, which in turn increases the pace of global sea level rise,” said study co-author Professor Robert Kopp. 

“The faster the oceans rise, the greater the threat to tidal marshes, mangroves and coral reefs around the world. For example, in our analysis, most tidal marshes are likely to be able to keep up with sea level rise under 1.5 degrees Celsius [2.7 degrees Fahrenheit] of warming, but two-thirds are unlikely to be able to keep up with 2 degrees Celsius [3.6 degrees Fahrenheit] of warming.”

Paris Agreement 

According to Professor Kopp, the temperature ranges examined in the study are significant because they relate directly to the Paris Agreement, an international treaty on climate change adopted in 2015.

The Paris Agreement established a goal to limit the increase of global temperatures to 2 degrees Celsius above pre-industrial levels by substantially reducing carbon emissions worldwide. The ultimate goal of the treaty is to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius.

What the researchers learned 

The results of the study show that higher global temperatures will trigger a rise in sea levels that will lead to instability and profound changes to coastal ecosystems, including tidal marshes, mangrove forests, coral reefs and coral islands.

“Mangroves and tidal marshes act as a buffer between the ocean and the land – they absorb the impact of wave action, prevent erosion and are crucial for biodiversity of fisheries and coastal plants,” said study lead author Neil Saintilan of Macquarie University. “When the plants become water-logged due to higher sea levels, they start to flounder.”

In the worst-case scenarios, these coastal habitats, will shrink – and in some cases wash away – as they have in the distant past, according to the study.

Study implications 

“This new paper provides evidence from geological history that, without mitigation and under current projections, tidal marshes will not have the capacity to adjust,” said Professor Judith Weis, an expert on tidal marshes. 

“For many tidal marshes in New Jersey, this is not a prediction but a description of the present situation, in which sea level is rising faster than the marshes can increase their elevation. This makes it even more vital to reduce climate change as rapidly as possible.”

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