TCS Daily


Resource Allocation and Sea-Level Rise

By Sallie Baliunas - January 19, 2004 12:00 AM

The Secretary-General of the United Nations, Kofi Annan, warned in late September that by the year 2100 with the "ever-increasing emission of greenhouse gases" some environmental catastrophes may be possible, including "many small islands gone..." as sea levels rise from melting glaciers.

New research bears on this possibility for the Maldives.

With an area of 300 square miles spread over 1,190 coral islands in the Indian Ocean, the Maldives is less than twice the area of Washington, DC, and lies south-southwest of India. According to the CIA's World Factbook, some 200 of the islands are inhabited, and approximately 80 more are exclusive resort destinations. Tourism is its largest industry, and around 90% of collected revenue comes from taxes on tourism and imports. Its population is around 330,000 and its population growth rate ranks first worldwide.

The Maldives was the first country to sign the Kyoto Protocol that requires developed nations to reduce greenhouse gas emissions below 1990 levels. Government officials in the Maldives strenuously argue for at least a 20% reduction in greenhouse gas emissions, apparently worldwide, by the year 2005. The reason? The altitude of the Maldives above mean sea level ranges from zero to only 2.4 m at the highest and government officials in the Maldives share the same fears as Secretary-General Annan over warming and sea level rise.

Leave aside for the moment the question of whether or not Kyoto would do anything to halt climate change and rising sea levels. Sea level rise -- no matter the cause -- would seriously impact much of the Maldives.

The Maldives has an interesting geological location. Apart from mountains, chasms, etc., the surface of the earth is nearly but not perfectly smooth -- there are subtle dimples and bulges on the scale of small continents. Part of the reason is that inside the earth, mass is not evenly distributed, so uneven gravitational pull deforms the surface upward or downward. Because the earth spins, the spinning tends to smooth out the deformations, but cannot smooth the surface entirely. The Maldives sits (Figure 1) on the deepest such depression on the earth, at about 100 m below the average surface. A bulge about 85 m high occurs to the east, near New Guinea.

Figure 1 - The surface undulations of the earth. The deepest depressions are blue and violet, with the lowest values of about 100m below the average shape of the earth. The yellow and orange and red areas are elevated above the average shape of the earth, with the highest region about 85m above the mean. The Maldives sits in the deepest depression.

http://www.ngs.noaa.gov/images/ngs/jpeg-geo/ww15mgh.jpg

The Maldives' unique geological setting is an opportunity to study sea level change through a period of extreme climate change, from the coldest period of the last glacial maximum -- about 20,000 years ago -- to present-day warmth.

During the last glacial maximum, globally-averaged sea level was approximately 120 m below today's level. The reason is that much water gets locked onto land as glaciers, especially at high latitudes, depleting sea levels. As the earth warmed, glaciers melted and returned water to the sea, thus elevating sea levels. The largest recent rate of globally-averaged sea level rise, occurring approximately 7,000 to 8,000 years ago after a period of relatively rapid warming, was 24 mm per year. In comparison, the warmed 20th century saw a globally-averaged sea level rise at a rate of approximately 1 to 2 mm per year. Should the trend in sea level rise continue, it would mean a rise of approximately 10 to 20 cm by the year 2100 averaged over the globe. How might this affect the Maldives?

The question of translating global to local sea level change is extremely complex. Because of the threat of sea level rise to the low-lying Maldives, it has become the focus of intense research by the august International Union for Quaternary Research, or INQUA, an interdisciplinary group of scientists from 35 member countries. For 75 years INQUA has studied the last 2 million years -- a period called the Quaternary -- of geologic and environmental changes. INQUA's recent Commission on Sea Level Changes and Coastal Evolution targeted the Maldives and found "a total absence of any recent sea level rise." Moreover it found "a young (last 20 years) sea level fall." The peer-reviewed paper, "New perspective for the future of the Maldives" by N.-A. Mörner et al. has just been released in the prestigious Global and Planetary Change. It describes early peoples surviving on the Maldives around 1000 years ago, when sea level was approximately 50-60 cm higher than at present.

Recall that the Maldives sits in a depression about 100 m below the average shape of the spinning earth. Because of that special location, the sea there evaporates extremely rapidly, and has contributed to the observed recent fall in sea level in the Maldives, despite recent global warming. The INQUA commission concludes:

In the region of the Maldives, a general fall of sea level occurred some 30 years ago. The origin of this sea level fall is likely to be an increased evaporation over the central Indian Ocean...there seems no longer to be any reasons to condemn the Maldives to become flooded in the near future.

The Maldives seems not to be immediately threatened by a slow sea-level rise. But because of its low altitude, it is always threatened by storm flooding. To that end, Japan is funding a sea wall around Male, the tiny island capital. Also, sand has been poured to reclaim the nearby, once-sunken island of Hulhumale to relieve the crowding on Male. Resources spent on island protection against common storminess in the Maldives are easily justified; diverting spending to costly greenhouse gas emission reductions is not. This is why science matters in saving the Maldives.


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