Page last updated at 08:14 GMT, Wednesday, 8 April 2009 09:14 UK

Americas on alert for sea level rise

Beach at Cancun, south-east Mexico
Coastal areas in parts of Mexico are among those under threat

By James Painter
BBC Latin America analyst

Climate change experts in North and South America are increasingly worried by the potentially devastating implications of higher estimates for possible sea level rises.

The Americas have until now been seen as less vulnerable than other parts of the world like low-lying Pacific islands, Vietnam or Bangladesh.

But the increase in the ranges for anticipated sea level rises presented at a meeting of scientists in Copenhagen in March has alarmed observers in the region.

Parts of the Caribbean, Mexico and Ecuador are seen as most at risk. New York City and southern parts of Florida are also thought to be particularly vulnerable.

The 2007 IPCC (Intergovernmental Panel on Climate Change) report suggested that sea levels would rise by between 19cm (7.5 inches) and 59cm by the end of this century.

But several scientists at the Copenhagen meeting spoke of a rise of a metre or more, even if the world's greenhouse gas emissions were kept at a low level.

Melting of the polar ice sheets is one of the main drivers behind the new estimates.

"A rise of one metre will irreversibly change the geography of coastal areas in Latin America," Walter Vergara, the World Bank's lead engineer on climate change in the region, told the BBC.

"For example, a one-metre rise would flood an area in coastal Guyana where 70% of the population and 40% of agricultural land is located. That would imply a major reorganisation of the country's economy."

Mr Vergara and other experts are also concerned about the effect on the large coastal wetlands in the Gulf of Mexico.

Gonaives in Haiti (Sept 2008)
Rising sea levels coupled with severe storms could be devastating

"These new data on sea level rises are alarming," says Arnoldo Matus Kramer, a researcher on climate change adaptation at Oxford University.

"When combined with the exponential growth of urbanisation and tourism along the coast of the Gulf of Mexico and the Mexican Caribbean, it is extremely worrying."

A November 2008 study by UN-Habitat on the world's cities pointed out that in most Caribbean island states, 50% of the population lives within 2km (1.2 miles) of the coast. They would be directly affected by sea level rise and other climate impacts.

The Bahamas, the Guyanas, Belize and Jamaica have been pin-pointed by the World Bank as being particularly at risk from a one-metre rise.

The coastal plains around the city of Guayaquil in Ecuador, the country's main economic hub, are also known to be vulnerable to a combination of sea level rises, storms and sea surges.

A recent study by researchers at Espol, a science institute in Guayaquil, suggested that even a half-metre sea level rise would put the storm drainage system in the southern part of the city under severe strain, possibly causing it to collapse.

Fishing threatened

Ecuador's lucrative fishing industry, which is a mainstay of the economy, would also be threatened.

"A one-metre sea level rise would add another layer of threat to the shrimp and other fishing industries', says Espol's Pilar Cornejo, the author of a UN report on the issue.

According to a recent World Bank study of more than 80 developing countries, Ecuador features among the top 10 countries likely to be most affected by sea level rise when calculated as a percentage of its GDP.

Argentina, Mexico and Jamaica also appear in the top 10 when measured by the impact of a one-metre rise on agricultural lands.

Scientists stress that uncertainties remain about future sea level rises, including the behaviour of the giant polar ice sheets, the time span over which rises will take place, and their interaction with existing coastal conditions.

Cuban fishermen (Nov 2001)
Communities dependent on fishing are vulnerable to sea level changes

Another factor is the effect global warming will have on Amoc - the giant circulation of the Atlantic whereby warm sea water flows northwards in the upper ocean and cold sea water goes southwards in the deeper ocean.

New research led by Dr Jianjun Yin at Florida State University suggests that whereas South American coastal cities are not at threat this century from an extra sea level rise caused by Amoc, New York City and the state of Florida are.

New York would see an additional rise of about 20cm (7.8in) above the global mean due to Amoc by the turn of the century, according to Dr Yin's research published this year in the journal, Nature Geoscience. Florida would experience less than 10cm (3.9in).

"A one-metre rise could be a disaster for parts of Florida, particularly in the southern part of the state," Dr Yin told the BBC.

"Sea level rise superimposed on hurricane vulnerability makes for a very worrying situation."

Mr Vergara is not alone in stressing that sea level rises are "climate committed", in the sense that because of existing and projected greenhouse gas emissions, they will continue long into the future.

"The level and direction of change will destabilise extensive coastal areas in Latin America. Once flooded, there is no way back," he says.

Many scientists stress that it is not too late to mitigate the possible effects.

"We need to reduce greenhouse gas emissions and to reduce coastal developments," Dr Yin says.

"There is an urgent need for Latin American leaders to take account of these new figures on sea level rises in designing new policies," says Arnoldo Matus Kramer.

"They are not doing it at the moment."

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