JOHANNESBURG, 27 October 2008 (IRIN) - "Bangladesh drowning: A reality or a myth?" read a recent headline in a national newspaper. "Would Bangladesh really disappear under water by 2100?" asked another. The questions have led to heated debates on the country's future.

The flurry of articles were spurred by a new paper by James Hansen, a leading climate change scientist and the head of NASA's Goddard Institute for Space Studies, which examined the relationship between rising carbon dioxide (CO2) levels, melting ice and rising sea levels.

Sea level rise could sound the death knell for low-lying Bangladesh, most of which is only two to 13 metres above sea level, according to various estimates. The response to Hansen's paper is therefore understandable.

The paper, Target Atmospheric CO2: Where Should Humanity Aim?, which Hansen co-authored with nine other scientists, called for greater reductions in CO2 emissions to prevent sea-level rise caused by the world's inexorably melting ice.

In email correspondence with IRIN this week, Hansen said if atmospheric CO2 concentrations were not kept below at least 350 parts per million (ppm) the results could be disastrous. The current level of atmospheric CO2 is 385ppm, and could exceed 450ppm, which the world is heading for "within decades, barring prompt policy changes".

"Business-as-usual will almost certainly cause a sea level rise of at least one to two metres by the end of the century, and quite likely five metres or more, as West Antarctica is very vulnerable," Hansen told IRIN. The European Union has set a target of 550ppm.

Hansen's projection was in sharp contrast to the most recent forecast by the Intergovernmental Panel on Climate Change (IPCC) that the global sea level would rise by between 18cm and 59cm by 2100, depending on a range of greenhouse gas emission scenarios.

In the 1980s Hansen was one of the first scientists to highlight the disastrous humanitarian impact of climate change, and was among those who had thought that keeping CO2 concentration levels at 450ppm would prevent disaster.

"If you leave us at 450ppm for long enough it will probably melt all the ice - that's a sea rise of 75 metres. What we have found is that the target we have all been aiming for is a disaster; a guaranteed disaster," he told the Guardian newspaper in the UK earlier this year.

"Business-as-usual yields an incredible climate forcing, far exceeding any natural forcings toward warming in the known paleoclimate record," Hansen told IRIN.

Most of the recent data on polar ice shows it is melting faster than previously reported, acknowledged Atiq Rahman, a leading Bangladeshi scientist and author of IPCC reports. "The accelerated melting of the Himalayan glaciers is also well documented."

Even a metre is too much

Rahman, who heads the Bangladesh Centre for Advanced Studies (BCAS), told IRIN: "In Bangladesh even a one-metre sea level rise will create serious disruption in both the socioeconomic and food-security sectors."

M. Monirul Qader Mirza, another leading author of IPCC reports, cited several studies in an article he wrote on Hansen's paper in the New Nation, a Bangladeshi daily newspaper, showing that even a one-metre rise in the sea level could be catastrophic for Bangladesh.

"IPCC's Third Assessment Report, published in 2001, projected 11 percent inundation for a 45cm sea level rise. However, the inundated area may be doubled for a one-metre rise".

Citing a study by the Institute for Water Modelling, based in Dhaka, capital of Bangladesh, Mirza wrote: "With a 32cm sea level rise, 84 percent of the Sundarbans [the world's largest mangrove swamp and a UNESCO Heritage Site] would be deeply inundated by 2050 and the entire Sundarbans [which act as a coastal bioshield against cyclones] may be lost with about a one-metre rise."

New land the answer?

Another key element in the debate has been the new land being created as a result of rising silt levels in river mouths. After studying 32 years of satellite images, Bangladeshi scientists found the landmass was increasing by 20 sq km annually as a result of silt being deposited in the Bay of Bengal by big Himalayan rivers like the Ganges and the Brahmaputra, said Mohammed Abu Syed, a research fellow at the BCAS.

Hansen acknowledged that on the time scale of a few decades "it is quite possible that rising sea level will be matched or exceeded by rising silt levels, but when we hit the point of ice sheet disintegration there is no way to keep up with rising sea level. Of course, my hope is that we will not follow business-as-usual, in which case Bangladesh could indeed be in good shape."

Rahman of the BCAS agreed that at the point of ice sheet disintegration "no amount of sedimentation will compensate Bangladesh coastal areas from rapid and drastic inundation."

Rapid cuts in emissions were urgent, he stressed. "The key question is, 'how rapidly and how deeply can we have the GHG (greenhouse gas) emission reduction?'."

On a more optimistic note, Hansen suggested that an initial target of 350ppm CO2 may be achievable if coal use were phased out by 2030, except where CO2 was captured by adopting agricultural and forestry practices that sequestered carbon.

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