Climate change and sea level – More beaches or fewer islands?

Don’t hold your breath; climate change is here to stay, says Nirmal Shah, in this article in today’s Seychelles Nation.

Sea-level rise will submerge most of our low-lying areas, including entire coral islands – this is the conventional wisdom.

But a new study by 13 scientists at the University of Colorado and the National Centre for Atmospheric Research in the United States, published on June 11 in the online Nature Geoscience journal, says the opposite.

The paper – entitled Patterns of Indian Ocean sea-level change in a warming climate – states that since the 1960s there has been a substantial fall in sea levels around Seychelles and the south tropical region of the Indian Ocean including Zanzibar – a surprising conclusion.

The paper says that sea-level rise is not uniform across the world and is affected by changes in atmospheric or oceanic currents. The study combined actual sea surface measurements and satellite observations of the Indian Ocean sea level since the 1960s with climate-model simulations.

Sea-level rises have been much higher along the coastlines of East Africa, the Mascarene islands, the Bay of Bengal, the Arabian Sea, Sri Lanka and the Indonesian islands of Sumatra and Java, the paper says.

The major instigator is the Indo-Pacific warm pool, a very large bathtub-shaped area of the tropical oceans stretching from East Africa to the International Date Line in the Pacific. It is known that the warm pool has heated up by about 0.5 degrees Celsius in the past 50 years.

But the two major atmospheric wind patterns in the Indian Ocean, known as the Hadley circulation and the Walker circulation, cause an uneven distribution of water levels across this huge “bathtub”, which explains the drop in sea level in some areas and the increase in others.

However, another group of scientists studying the same phenomenon have reacted to the paper this week and are claiming just the opposite.

Axel Timmermann, Shayne McGregor and Fei-Fei Jin of the University of Hawaii – who have a paper in press in the Journal of Climate published by the American Meteorological Society – have said they are astonished by these conclusions.

Their paper – entitled Wind effects on past and future regional sea-level trends in the southern Indo-Pacific – says Seychelles could see up to 10% more sea-level rise than the global average.

The main difference between the two studies is in their estimation of how wind patterns will change due to climate change.

The computer-generated climate models of Timmermann, McGregor and Jin, as well as those of  the Intergovernmental Panel on Climate Change, predict more warming near the equator and on the western side of the ocean basin. But in reality the observed warming has been on the eastern side.

There could be two reasons for this difference. Timmermann says the actual changes in sea surface temperature are due to natural variability in the ocean that cancelled out the human-caused changes predicted by the models.

The second possibility, says Weiqing Han, lead author of the Nature Geoscience paper, is that climate models are not very good for this part of the ocean, and we should expect the future to be more in line with the real changes we have seen so far – a pragmatic point of view, others say.

Whatever the case may be, don’t hold your breath. Climate change is here to stay; we just do not know what to expect – more beaches or fewer islands.

Climate change and sea level – do we gain beaches or lose islands? – 26.07.2010 Source: Seychelles Nation

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