Sea level rise and decrease are ancient phenomena related to the geologic glacial/interglacial cycles. But since the 19th century and the industrial revolution, an acceleration of sea level rise has been observed through tide gauge measurements and satellite altimetry.

Thus, whereas the sea level rose at an average rate of 1 to 2 mm/year since 1900, it has risen at nearly 3 mm/year in the last decade. It is estimated that the global rise in the 20th century is of 0.17 meter.

Even if scientists do not agree on prediction models it seems that sea level rise does not affect all the regions similarly. Some will show a rise twice superior to the global average rise whether some will observe a sea level drop. The most affected areas are Indonesia, Thailand and Bangladesh that are experiencing above-average sea level rise and most of the Pacific and Atlantic basins that are experiencing average to above-average sea level rise. It is still a debate whether small islands are condemned to progressively vanish from the landscape because of sea level rise. However it is a fact that Pacific islands for example have experienced stronger erosion and cyclones in the last decade.

This significant acceleration of sea level rise is imputable to the thermal expansion of the oceans due to warmer temperatures and the melting of land ice (mountain glaciers, small ice caps, and, in a lesser proportion, ice sheets in Greenland and Antarctica).

The cases of Greenland and Antarctica are subject to controversy. It is estimated that the melting of entire Greenland ice sheet would induce a sea level rise of 7.2 meters. Similarly, the melting of Antarctic ice sheet would lead to a sea level rise of 61.1 meters. However, such total melting is not expected to spread over less than several millennia and there is still uncertainty on how far it has contributed to the global sea-level rise till now.

Other factors that could be accountable for sea level rise (still not determined to what extent) are, groundwater pumping, wetland drainage, and deforestation making the soil unable to retain the water.

Impact on nature and human societies

Coastal areas and systems are projected to be the most affected by sea level rise. Even if a rise of 3 mm/year doesn't seem much it is sufficient to have dramatic impacts on coastal areas and to noticeably diminish emerged land surface in low-lying regions, which are often characterized by rapid economic development and a high population density.

Sea level rise is expected to increase flooding from the sea in large deltas and low-lying areas, more particularly in Africa, Asia (Bangladesh) and Europe (the Netherlands). Coastal inundation, typhoons, storm-surges, floods, erosion are also expected to increase.

These natural phenomena induced by global warming will keep big pressure on coastal areas' infrastructures: housings, roads, administrative and business buildings. Different measures to protect the coast and the existing infrastructures will have to be implemented such as construction and reinforcement of seawalls, dykes and dunes.

Millions of people living in small islands and in or near coastal areas will be severely affected through loss of habitat and properties. Displacement of populations living in low lying areas represents a big challenge. This concerns especially developing countries which will have to bear a huge financial burden to relocate economic activities (agriculture, industry) and housings.

Another major consequence of sea level rise concerns water quality. Flooding by seawater will lead to salinization of groundwater that will have negative impacts on irrigation, aquaculture and fresh water availability. In some regions it will be necessary to invest in expensive desalinization techniques and to develop rainwater-harvesting systems.

It will accelerate the erosion of coastal lands and the destruction of coastal ecosystem and bio-diversity (coral bleaching, mangroves' submersion, extinction of plants and animal species). This negative impact on itself will also affect local economies based on the exploitation of natural milieu, like tourism.

The detrimental effects of sea level rise are projected to be global but some differences and inequalities are likely to appear between regions and countries.

The first kind of differentiation relates to the natural environment and its degree of vulnerability and ability to adapt to new conditions. The second relates to human and economic capabilities in areas like technology, research and development that could enable a society to innovate, mitigate and face the challenge successfully.

Developing countries, that have contributed a minor part to the human induced climate change, are paradoxically expected to be the most threatened by its negative effects and less financially and technologically capable to cope with them.

What can climate change and sea level rise do to a country?: The case of Bangladesh

Bangladesh has the highest population density of the world (1000 inhabitants/sq. km). According to the World Bank sea level rise is presently of 4 to 8 mm/year in the Bay of Bengal. Ninety percent of Bangladesh territory is composed of flood plains and nearly 20% of the land is within one meter of sea level

Cyclones and floods from the rivers, which are also increasing due to the melting of Himalayan glaciers and increased monsoon rainfalls, are expected to reinforce the devastating effects of floods from the sea.

In such a situation the dramatic sea level rise is expected to affect not less than 13 to 30 million of people and their means of livelihood: crops, mainly rice production which could show a decrease of 30% because of floods and excessive salt in the soil, and livestock.

Chittagong, Bangladesh’s main export port, could badly suffer. It is estimated that if sea level rises by 1 metre, the economic losses could reach 10% of Bangladesh Gross Domestic Product. Because of poor sanitation, diseases like Cholera and Malaria are likely to spread as well.

The consequences for the wild life will be severe. In the Sundarbans, the world's largest mangrove forest, Bengal tigers will be endangered as well as marine turtles, fresh water dolphins, crocodiles and many bird species. And submerged Sundarbans would no more be able to act as a natural protection against storms.

There do not exist many solutions to cope with sea level rise in Bangladesh as there is no free land where the inhabitants could be relocated. Building of dykes is also very controversial as it could affect agricultural system. Construction of shelters on concrete pillars can save people’s life but not crops, livestock and infrastructure.

References

1.Wikipedia article on sea level rise - Click here

2.IPCC, Fourth Assessment Report,2007 - Read more

3.Bruce C. Douglas (NOAA, National Oceanographic Data Center, Washington, D.C), Global sea level change: Determination and interpretation - Click here

This study presents a view of where the field of sea level research stands today and how further progress can be made, from the already available literature. This paper serves as a resource for the non-specialist. This last goal reflects the fact that the study of sea level is interdisciplinary, involving oceanography, geophysics, meteorology, geology, geodesy, coastal geomorphology, and other related and specialized fields.

4. A photographic documentation of Climate Change - Click here
This link provides a photographic documentation of Climate Change, maintained by Gary Braasch. He is also the author of the book, 'Earth under Fire'. He has done a study on Sea level rise in some of the most vulnerable regions where sea level rise is taking place.

The one meter sea level rise generally predicted, if no action is taken about global warming will inundate more than 15 percent of Bangladesh, displacing more than 13 million people and cut into the crucial rice crop. Intruding water will damage the Sundarbans mangrove forest, a world heritage site.

5.Germanwatch,Sea-Level Rise in Bangladesh and the Netherlands. One Phenomenon, Many Consequences - Read more

Regional consequences do not only depend on the environmental conditions in a specific region, but also on the economic and social situation as well as the available options to respond to the new challenges. This means that especially developing countries, which until now have hardly contributed to the anthropogenic climate change, will usually be the most affected by the consequences. A comparison between Bangladesh and the Netherlands, which are both seriously affected by rising sea levels, illustrates this fact.

6.World Bank, Bangladesh: Climate change and sustainable development, 2000