Unexpected Consequences of Climate Change: How Human Relocation from Rising Sea Levels Harms Island Biodiversity

Many policymakers have accepted the “inconvenient truth” of global warming that sea levels across the globe will rise, causing humans living on the coast to relocate and numerous species to lose their habitats. While scientists have previously investigated how drastically sea levels will rise, none until now have examined the secondary effects of human relocation on existing island habitats. A pioneering study by scientists Florian Wetzel, W. Daniel Kissling, Helmut Beissman, and Dustin Penn explores the problems society will face even after rising oceans. An international team of professors from the University of Veterinary Medicine in Vienna and Aarthus University in Denmark, the researchers found that human migration due to rising seas would significantly reduce species biodiversity in island mainlands.

Many believe that rising sea levels are the biggest conservation threat we must face. However, according to this research, it may be time to take a second look at the domino effect of climate change. Secondary effects from human migration can be an added burden to already destroyed or now-underwater island habitats. As the team argues, secondary effects of human displacement on island species should be included in conservation efforts and risk assessment.

Wetzel and Kissling’s team focused on approximately 1,200 islands in the Southeast Asian and Pacific region, a known hotspot of biodiversity with numerous endemic and short-range species. Several recent studies suggest that this area is highly susceptible to rising ocean levels, as the Phillipines have already experienced a rise in sea levels. The scientists selected individual islands known to have growing urban settlements along coastal areas as well as agricultural lands to measure the effects of human migration inland.

Next, the team chose three scenarios of rising sea levels, 1m, 3m, and 6m, to determine the amount of land lost. Wetzel and Kissling’s research is truly groundbreaking, as few existing models for rising seas or predicted human displacement from climate change exist currently. Nevertheless, for each specific island they estimated the amount of land that would become underwater through NASA’s Digital Elevation Model and an erosion rate given that erosion increases with rising sea levels. When calculating threatened habitats, the scientists assumed that inhabitants forced to move would occupy an equal area in the middle of the island. The Wetzel and Kissling group then utilized datasets such as the IUCN Red List on species distribution in the islands to determine how rising seas affect species biodiversity, choosing 54 mammals on 106 of the islands. Using data from the Gridded Population of the World dataset, they predicted the future distribution of inhabitants in the islands. Researchers investigated the secondary as well as primary effects on species extinctions given human resettlement through conservative models.

The study’s grim results demonstrate the importance of considering secondary effects of human resettlement in island conservation. In islands with the highest amount of urban settlement and agriculture along the coasts, secondary habitat loss from human resettlement ranged from 6-24%. This is in addition to the already 13-44% habitat destruction from the primary effect of higher seas. The scientists discovered that for nearly all of the 54 species studied in the islands, secondary effects worsened their loss of habitat. For species with ranges completely falling in likely migration areas, the risk of extinction from habitat destruction rises even higher. Potential consequences for biodiversity include negative impacts on species that require large ranges and are vulnerable to secondary habitat destruction, such as the smoky brown squirrel. The researchers discovered the squirrel was not as much at risk for initial effects, but would suffer a 2-60% range loss after humans forcibly relocate.

Given that a 1m loss of land is predicted at the end of the decade, implementing policies to protect biodiversity from effects of human migration inland seems necessary. It may not be enough to only investigate immediate problems of rising sea levels. If we want to ensure the survival of unique island species in the future, these findings suggest that it is necessary to consider negative outcomes of human migration in conservation policies as well.

Article: Wetzel, F. T., Kissling, W. D., Beissmann, H. and Penn, D. J. (2012), Future climate change driven sea-level rise: secondary consequences from human displacement for island biodiversity. Global Change Biology, 18: 2707–2719. doi: 10.1111/j.1365-2486.2012.02736.x

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