Barrier islands and global warming
Barrier islands are narrow landforms that run parallel to the mainland, typically composed of sand and organic materials, and separated from the mainland by lagoons or bays. They have two distinct shorelines: one facing the more turbulent open ocean and the other facing the calmer mainland. These islands are primarily formed by the post-ice age rise in sea levels, which has inundated coastal areas, and they are continually shaped and maintained by processes like longshore drift, where wave action moves sand along the beach.
However, barrier islands are increasingly threatened by climate change. Rising sea levels can lead to their erosion or inundation, leading to significant habitat loss for coastal species that rely on these ecosystems. Furthermore, increased storm activity, attributed to climate change, can result in destructive wave energy impacting these islands. The potential disappearance of barrier islands could also expose the mainland to greater coastal erosion and changes in geomorphology. Additionally, many barrier islands support valuable real estate developments, which face economic risks as climatic conditions evolve. Understanding these islands is crucial for grasping the broader implications of climate change on coastal ecosystems and human communities.
Subject Terms
Barrier islands and global warming
Definition
Barrier islands are narrow strips of land that are oriented parallel to the mainland and that lie on average a few kilometers offshore. Barrier islands are largely composed of sand-sized grains of sediment plus some finer sedimentary material and organic debris. They are separated from the mainland by an intervening body of water called a lagoon or bay. Barrier islands therefore have two shorelines, one facing the open ocean and the other facing the mainland. The side facing the open ocean is typically a much more energetic shoreline, experiencing higher waves and storm surges. The ocean-facing side is typically much straighter than the mainland-facing side, which is a low-energy coastal area.
Barrier islands may have several origins, but the most common is thought to be related to the post-ice age rise in sea level that commenced about eighteen thousand years ago. Thissea-level rise inundated the world’s coastal areas, and many barrier islands probably formed from coastal sand ridges and dune fields that were surrounded by the rising sea. Once the barrier islands were established, sand that was eroded from land and washed along the shore by wave currents helped build and maintain the islands.
Barrier islands are nourished—that is, restocked with sand—by a process called longshore drift. Longshore drift is the movement of sand down the seaward coast of a barrier island, resulting from the effects of wind waves that approach the seaward coastline of the island at a slight angle. These wind waves wash up on the barrier island coast (beach face) at an angle, and their return flow is directly back to the sea but slightly displaced in the wave’s direction. As a result, the waves move sand and other material down the beach.
Significance for Climate Change
Barrier islands are significantly affected by climate change. As global sea levels rise, barrier islands are at risk of being inundated or eroded away, as seen in many areas of the world. The loss of barrier islands or a diminution in their width and continuity is a direct effect of sea-level change in many places. Increased storm activity, a result of climate change in general and of changes in sea surface temperatures in particular, affects barrier islands because they are at the front line when a sea storm comes ashore. Storm wave energy is spent on barrier islands, and the result can be dissection of the barrier islands or their complete destruction.
Barrier islands are integral parts of typically fragile coastal ecosystems, which are home to many plant and animal species. If climate change causes the loss of barrier-island habitats for coastal species, these organisms will need to adapt or perish.
Barrier islands require a continual sand supply to persist. This supply can be interrupted in many ways, including through climate change. Climatic changes that affect local runoff, for example, might reduce the flow of rivers that bring sand to the coastline and nourish the barrier islands there. There are other ways to lose sand supply, including human intervention.
A 2022 study further suggested that the rise and retreat of these islands are not always synchronous and predicted a 50 percent acceleration in the rate of barrier-island retreat within a century, even in the unlikely case of no further increase in the present rate of sea-level rise.
The potential loss of barrier islands represents the possibility that areas of mainland currently sheltered by barrier islands will become primary coastlines. This would result in many changes in coastal geomorphology and ecosystems, as the protected mainland would become the focus of wave energy, altering the shape, population, and dynamics of shorelines.
Barrier islands on some coastlines of the world contain some of the most expensive real estate developments. These developments, some of which lie upon narrow sand islands less than 3 meters above sea level, are at imminent risk of loss as climatic conditions change. Such loss could entail huge economic losses for many countries and states, which depend upon tax revenues from entities built upon the islands.
In the past, barrier islands developed along the world’s coastlines in much the same way that they had developed since the end of the last ice age. Studying ancient barrier islands, which are now part of the sedimentary rock record of the Earth, and comparing them to modern barrier islands helps scientists understand ancient climates and the history of climate change and its effects. There are lessons to be learned from the sedimentary record of barrier islands—particularly that conditions are always changing, especially at the oceanic coastline.
Barrier islands are analogous to living things in that they use energy to survive, they grow larger and smaller, they experience and recover from injuries, and they have a life cycle that ends in death. Climate change can bring on the death of a barrier island or present challenges to the continued survival of that island.
Bibliography
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Morton, Robert A. Historical Changes in the Mississippi-Alabama Barrier Islands and the Roles of Extreme Storms, Sea Level, and Human Activities. Reston: US Geological Survey, 2007. Print.
"Oceanographers Develop New Model to Better Predict Barrier Island Retreat." Science Daily, 7 July 2022, www.sciencedaily.com/releases/2022/07/220707141827.htm. Accessed 11 Dec. 2024.
Pilkey, Orrin H., and Mary Edna Fraser. A Celebration of the World’s Barrier Islands. New York: Columbia UP, 2003. Print.
Pilkey, Orrin H., Deborah Pilkey, and Craig A. Webb. The North Carolina Shore and Its Barrier Islands. Durham: Duke UP, 2000. Print.
Thomas, Jennifer, et al. "The Projected Exposure and Response of a Natural Barrier Island System to Climate-Driven Coastal Hazards." Scientific Reports, vol. 14, no. 25814, 28 Oct. 2024, doi.org/10.1038/s41598-024-76749-4. Accessed 11 Dec. 2024.