Tropical nations to see above average sea-level rises


Source: SciDev.Net

BUENOS AIRES -- Coastal areas in the tropics may see some of the largest sea-level rises due to take place this century because of climate change, according to a study.

This would particularly affect the Indian Ocean and Western Pacific, which include many small island states, such as the Maldives, and vulnerable coastal deltas, including the Bay of Bengal.

The findings may help analyse the impacts of climate change and plan infrastructure for adaptation, says the study, published in Earth System Dynamics.

At low latitudes, 'this generally represent a 10-20 per cent higher sea-level rise compared with the global average and many vulnerable developing nations — especially small island states — are located in these areas,' says lead author Mahé Perrette, a researcher at the Potsdam Institute for Climate Impact Research in Germany.

One reason for this above-average rise is that polar ice caps exert less gravitational pull on surrounding seas as they melt, causing water levels to fall, which, in turn, pushes up tropical seas. In addition, seawater expands as it warms, and different warming patterns make it expand more in certain regions such as the tropics, than it does in others.

'The main conclusion we draw is that tropical regions are likely to experience relatively higher sea-level rise than polar zones due to the reduced gravitational pull of melting ice sheets located near the poles,' Perrette says.

'Nevertheless, the bigger danger, which carries most uncertainties in the projections, is Greenland and Antarctica's future contribution to sea-level rise [because of ice-sheet melting], with a range of about 0.5-1 metre by 2100 for a scenario leading to four degrees Celsius warming above pre-industrial temperatures,' he adds.

Yet, actual sea-level rises in any one place can differ widely from the global mean because of changes in wind and ocean currents, and the gravitational adjustments that cause seawater redistribution away from ice masses, says Perrette.

'In Argentina, the melting of Patagonian glaciers and the Antarctic ice sheet [will] tend to produce lower-than-average sea-level rise south of about 40 degrees South. This means that in the region of Buenos Aires, which is further north, our projections indicate slightly above-average sea-level rise,' he says.

Angel Menéndez, head of the Computational Hydraulics Program at the National Institute for Water in Argentina, says: 'The uncertainties in the projections of sea-level rise due to climate change are relatively high'.

He adds: 'Depending on the assumed scenarios for ice-sheet melting, the global sea-level rise may vary from about 40 to 80 centimetres by the end of the century. However, local phenomena produce deviations from that global average.'

Menéndez says that for Buenos Aires, the study indicates the sea level would only rise a few centimetres above the average global rise. 'That is not necessarily good news, but at least one feels that we are not in the worst situation,' he concludes.

Link to full study

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