A recent feature in National Geographic magazine posed a provocative question: What would today’s world look like without ice? Earth was last ice-free during the Eocene (56 million years ago) and didn’t start cooling down until 40 million years ago. If all of that frozen water was melted into Earth’s oceans now, sea level would be about 216 feet higher than it is now, flooding Florida, the Eastern seaboard and California’s Central valley.
The global meltdown isn’t anticipated for millennia, but within the next century we can reasonably expect to see the waters rise about 1-2 meters. For the residents of low-lying oceanic islands, this could be a bit of a problem. Islands often harbor plants and animals found nowhere else in the world and these ‘endemic’ species are prime candidates for the big so-long if their homes become submerged. Just how many species are at risk of extinction simply because their island paradises are soon to be flooded?
This summer, researchers at the University of Paris-Sud published an analysis of how the loss of area to 4447 islands in biodiversity hotspots would affect endemic species. If the sea-level rises 1m, 267 islands will be completely sunk and 489 islands will lose more than half of their area, with islands in the Caribbean being the most endangered. Most islands (2,579), will make out without any area lost. However, the researchers also ran the numbers for more extreme estimates of sea-level rise (up to 6m) and found that such inundation could lead to the sinking of 826 islands with 1,423 losing more than half of their area.
How do these areal losses convert to species extinctions? One of biogeography’s few ‘laws’ is that islands with larger areas have more species following a fairly precise mathematical relationship (SAR). Calculations based on this relationship can be used to find the area that needs to be lost in order to remove the last individual of a species and, with a little more calculation, how many extinctions are probable when a given amount of area disappears.
Using these rules, the researchers estimated that 26 plant species, 1 bird and 1 reptile species are likely to go extinct. Under more extreme conditions (i.e. 6m sea level rise) these numbers rise to 300 plants, 8 birds, 18 reptiles, and an additional 8 amphibians, 3 fish, and 2 mammals. Considering that this is out of 58,195 endemic species, this is good news, at least in the compounding drama that is Earth’s climate change woes. Unfortunately, a shrinking island may be the least of most of these species concerns. Human activities, like farming and city-ing, can shrink island habitat much faster than a melting ice-cap can raise the waters.
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