Low Islands

“Shouldn’t people who live on islands in the Pacific be worried about . . . rising sea level . . .?”

Scientists believe that global warming causes the sea to rise in two ways — through the thermal expansion of ocean water, and through the melting of ice caps and mountain glaciers. And it’s true that even a small rise in sea level could flood low-lying coastal areas. These might be places now used for settlements, agriculture and tourism.

Sea level has been rising since the end of the last ice age — but it’s only in the past century that it’s become more obvious. Oceanographers now use tide gauge records that show a sea level rise in the last 100 years of one to two millimeters — a fraction of an inch — every year. Sea level is now rising even faster, and it’ll rise faster still if scientists are correct about global warming in this century.

And that’s why a number of international organizations have formed to address global warming and lessen its impacts. And it’s the small island states — as well as countries with long stretches of coastline — that are most active in these organizations.

Studies show that a one meter sea level rise would result in the following land losses: 0.05% in Uruguay, 1.0% in Egypt, 6% in the Netherlands, 17.5% in Bangladesh and about 80% in the Marshall Islands. The Intergovernmental Panel on Climate Change (IPCC) estimates that if nothing is done to curb greenhouse gas emissions, the sea level will rise by around 65 cm (25 inches) by the year 2100. Many of islands and atolls are already now quite vulnerable to flooding caused by tsunamis (tidal waves) and storm surges.

Global climate change is expected to lead to increased storm activity, especially in the monsoon climates. Most small island nations are located in these climates. People in the Pacific and Indian Oceans are very definitely concerned. Islanders listen to the radio for news about issues of global warming and sea level rise. There’s also an issue here about how people would adapt to a sea level rise vs. how the islands themselves would adapt.

As sea level rises, living corals at the edges of many islands grow. The corals have been keeping pace with rising sea level for many thousands of years already. The question may be whether they can continue to keep pace, if sea level rises as rapidly as some scientists predict in the coming century. On the one hand, it seems very likely that they can. Atoll reefs can grow upward rapidly, so the reefs themselves may not be threatened by rising sea level.

Some scientists have suggested that a rapid rise in sea level might even be good for the reefs. On the other hand, if the world gets warmer in the coming century, it’s possible that the islands might not grow fast enough to stay above water. There have been signs of occasional diseases in coral reefs that might weaken them and make them more susceptible to drowning during rapid sea level rise. There’s also the possibility that elevated water temperatures associated with greenhouse warming might create conditions deleterious to corals. No one knows yet whether all the diseases that are now being found in corals are something old and previously unnoticed or whether they may be related to the discharge of nutrient rich, pesticide-rich, and warmer waters. There is a tendency among scientists to suspect that the corals are being weakened by environmental disturbances that allow various diseases to get a foothold on reefs. But there have not been enough studies to know whether the atolls themselves disappear, in the event of a rapid sea level rise. They might be able to adjust to rising sea level, although it seems certain the adjustment process would lag behind rapidly rising sea level.

People do not live directly on coral reefs, but they do live on land made of coral debris on atolls and many low coral coasts. It’s also possible for this land area to “grow” upward, in compensation for rising sea level. But, for this to happen, material must be washed onshore and cover the existing land, usually during storms. This will happen more often if sea level is rising and the “freeboard” of an island is continually reduced. If sea level is stable, then the washing of material onto the land happens much less often. However, the process of building up the land area in response to rising sea level may not be at all pleasant. People would no doubt be happier if sea level remained stable, so that the atolls and low coasts did not have to build themselves up to stay ahead of sea level rise. Thus it seems that a rapid rise in sea level is an issue of more concern for people than for the atolls themselves.

If you enjoyed this show, the following article may be of further interest to you:

David Scheider “The Rising Seas” Scientific American, March, 1997, p. 112

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