Low-lying reef islands like the Pacific Ocean’s Marshall Islands could become unstable by midcentury if measures to adapt to rising sea levels are not implemented, according to new research.
Coral reef atoll islands are home to thousands of people around the world, but researchers still don’t agree on how sea level rise will impact these islands and their communities. Conflicting messages can slow or hinder the abilities of local communities to develop effective plans to protect their islands’ livability in the coming century.
In a new study, Kane and Fletcher used an integrated model that incorporates the 5,000-year geological history of the Marshall Islands with updated emissions and sea level rise projections to understand what will happen to atoll islands in the coming decades. The results suggest higher tides and more destructive waves will inundate the Marshall Islands and deteriorate their freshwater sources and forests as soon as midcentury.
Islanders can proactively bolster their islands’ natural ability to adapt and change, however, by preserving and restoring reef ecosystems that protect coasts and provide new sediment to the structure of the island. Without such measures, the islands could be permanently lost as soon as 2080.
Young, Dynamic Islands
Reef atolls are low-lying islands made up of sand and coral that support lush forests and narrow bands of rain-fed freshwater aquifers. Researchers have debated how these islands will be affected by climate change–driven sea level rise because they have been subjected to rising seas before. Most of these islands formed less than 5,500 years ago, but even in that short time, they have been subjected to sea levels 1 to 2 meters higher than current levels.
Some scientists argue that this means reef islands could be resilient to human-caused sea level rise, but most such studies consider islands and their people to be separate entities, said Haunani Kane, a coastal geologist with the University of Hawai‘i at Hilo and lead author of the new study.
“I found that as really being disconnected from the way that we live on islands,” she said. “This study eliminates some of the confusion and the gaps in knowledge related to how sea level rise will impact low-lying islands because it considers the impacts upon and resilience of both the place and the people.”
Modeling Future Change
To address this disconnect, Kane developed a model that treats islands and their people as inseparable components. The model uses a mixture of fossil data, historical photographs, and modern observations of tide and wave events to understand the geological processes of the Marshall Islands over 5,000 years. Using this information about how the islands have grown and responded to past changes over time, she projected each island’s ability to adapt to the next century’s increasing rate of sea level rise.
Kane found that individual islands will respond slightly differently depending on their shape and location. “Even within one nation, there are differences in how islands will respond,” she said.
Broadly, however, she found that the rate of sea level rise will be at least 10 times faster than what the islands were exposed to in the geologic past, and by 2080, sea levels will be higher than anything the islands have experienced in their lifetimes. Through analysis of fossil reef cores and sediment, Kane realized the island’s structure was largely made up of just one species of foraminifera, single-celled organisms with a hard shell. Currently, no new foraminifera are being deposited on the islands. As sea levels rise, waves could wash more of these island-building organisms ashore, but the processes that encourage such growth involve big waves and a dynamic coastline.
“That can be a good thing for the islands, but it could make it difficult to live on an island,” Kane said. Encouraging the islands’ natural ability to grow and change could save them, but living on such a dynamic landmass comes with trade-offs. Kane stresses that she does not seek to tell islanders what to do with her study, only to arm them with information based on the latest science. “The people of that place have the ultimate authority over the decisions that they think are best,” she said. (Earth’s Future, https://doi.org/10.1029/2020EF001525, 2020)
—Rachel Fritts (@rachel_fritts), Science Writer