Global-scale changes in the area of atoll islands

Global warming has resulted in a continuous rise in sea levels, posing significant challenges to coastal and island ecosystems. While atoll islands have largely avoided widespread erosion in recent decades, the majority of existing studies has concentrated on atolls within the Pacific and Indian Oceans, leaving the broader study of global islands insufficiently addressed. Notably, the melting of glaciers and snow in boreal regions is a major contributor to sea level rise, heightening erosion risks for islands in northern latitudes.

To bridge this research gap, the study adopted a comprehensive approach by encompassing islands across all five climatic zones. Its primary objective is to assess the Changes in morphology and ecological structure and of small and medium-sized islands over the past 40 years. Leveraging data from Landsat 5, 7, 8 and 9 satellites, the study employed image normalization techniques to enhance the identification of smaller islands and applied support vector machines (SVM) to classify normalized difference spectral vector (NDSV) images. This methodology enabled the detailed analysis of shifts in area, shape and ecological community composition, while also investigating the underlying factors driving these changes.

Recognizing the diverse climatic dynamics across temperate zones, the study also incorporated a region- and size-specific evaluation framework to improve the accuracy of erosion pattern predictions for atoll islands. The findings reveal that islands with larger populations and close to the mainland demonstrate greater resilience to erosion, largely due to the benefits associated with artificial reinforcement. The study highlights that land area changes are predominantly influenced by human activities, particularly in the Maldives and the South China Sea. Furthermore, alterations in shallow reef ecosystems emerge as a critical driver of island size variability.

Finally, the research explored the relationship between island size and erosion, emphasizing the significant proportion of smaller islands among those experiencing changes in area and shape. These insights provide a nuanced understanding of the interplay between anthropogenic and ecological factors shaping island dynamics in the context of rising sea levels.