‘Rising sea levels threaten to drown this island nation – a sign of what’s in store for us all,’ points out UN Secretary-General Antonio Guterres referring to Tuvalu. Without a doubt, sea-level rise will have drastic effects on coastal nations and assets. Around 680 million people currently live in low-lying coastal regions, a number which is expected to surpass the one billion by 2050. Currently, coastal flooding is becoming quite common in many regions of the world like Bangladesh, India and the United States. In others, coastal agriculture is severely at risk especially in the wetlands of south-east Asia where 88% of the world’s supply of rice is grown.
Research by the Intergovernmental Panel on Climate Change (IPCC) highlights that the sea level rose from 1.4 mm yr-1 in the early 1900s to an alarming rate of 3.6 mm yr-1 in 2015. What’s more, it is very likely that 95% of the world ocean will rise by 0.29 m and 1.1 m by the end of the 21st century . Similarly, 70% of coastlines is expected to experience a sea-level change within 20% of the global mean sea-level change. Thus, coastal regions, low-lying islands and the SIDS (Small Island Developing States) will suffer tremendously from such encroaching waters.
Quite obviously, sea-level rise will lead to a retreat in coastlines, that is, coastal regions and beaches vanish. As the water level rises, it will cover more land thus decreasing the size of coasts. Throughout the history of the Earth, the coastlines receded and advanced several times due to natural processes like sea-level rise or land subsidence. The last marine transgression some 18 000 to 6 000 years ago caused the world’s coastlines to retreat as a result of climatic warming . Some 6,000 years ago this marine transgression stopped except on subsiding coasts thus forming rich estuaries and deltas. With today’s anthropogenic climate change, land is disappearing as the sea eats away expanses of land. To illustrate this, the island of Mauritius lost some 20 m of its beaches during the past decades as a result of rising sea level.
The coastal and marine environment is composed of various ecosystems like salt marshes, mangrove forests, kelp forest, sandy shores, coral reefs etc. Directly or indirectly, sea-level rise will affect them. In mangrove forests for instance, as the sea level rises, mangrove trees will not be able to cope with the increasing salinity. As such, mangrove forests may shift landwards. Yet, man-made structures like dykes may inhibit this transition. At the same time, the productivity of mangrove forests may decrease as more trees die than germinate.
What’s more, as the sea level rises, some coastal habitats within particular zones may altogether disappear. For instance, in North American bays, some 20-70% of intertidal habitats may disappear in the coming 100 years. This is associated with the steep topography of the region and the presence of artificial structures like sea walls that may restrict the inland migration of such wetlands. Additionally, if the sea level increases faster than the accretion rates of marshes and coral reefs, these biogenic habitats may decrease in size especially for the slow-growing species like coral reefs . In addition to that, some authors propound that sea-level rise may push saline water upstream rivers. As an example, a 1 m sea-level rise would push water up to 80 km upstream the Gorai River network in Bangladesh .
As it currently stands, more than 600 million people live in coastal regions that are less than 10 m above sea level. Additionally, approximately 2.4 billion people live within 100 km of the coast. Rising sea levels combined with physical conditions like waves, winds, tides and currents will inevitably lead to frequent and/or permanent flooding of coastal regions. In San Francisco Bay, for instance, research shows that a small rise of 30 cm in sea level would cause 100-year-floods to occur every 10 years.
Therefore, coastal flooding will heavily impact on settlements and infrastructure in place. At the same time, economic consequences will follow in the form of property damage, repair and maintenance. Likewise, access to essential services and transport will be limited.
One of the most serious consequences of sea-level rise is groundwater contamination as saltwater infiltrates further into the ground. This can lead to water crises in places already subject to higher temperatures and decreased rainfall. Basically, if 1% seawater contaminates freshwater, it becomes unfit for human consumption. This will thus have severe repercussions on agriculture and farming on the coasts. To illustrate this, saltwater intrusion into the ground (among other reasons) has badly affected coastal agriculture in Bangladesh. Consequently, the production of many vegetable species plummeted and one local paddy species perished.
As it stands, the health impacts associated with expanding wetlands due to sea level rise is becoming alarming. In fact, until the mid-20th century, wetlands were disdained and filled for mosquito control . Though the importance of wetlands has been demonstrated over the years, the negative view of wetlands, especially by the public-health profession, still persists. For instance, research shows that the West Nile virus was transmitted along the Indian River Lagoon through mosquitoes breeding in marshes, schistosomiasis (snail fever) was transmitted to humans in South Africa by means of wetland snails or even cholera spread in Bangladesh though mangroves and estuaries.
Now with rising sea levels, larger expanses of marshes are forming with an ever increasing risk of transmission of diseases. More opportunities for transmission of diseases will thus arise in the form of mosquitoes as vectors, water borne pathogens as well as probable contamination of wastewater lines with seawater.
The world’s major economic centres such as London, Shanghai, Lagos and New York are located on the coast. These cities are densely populated and packed with facilities. In China as an example, 11 coastal provinces covering just 13.5% of the land account for 57.4% of the national GDP. Coastal regions are also heavily industrialized around the world; in the SIDS almost all of the economic centres, sea and airports are on the coasts. Thus, given their location and economic importance, analysts have examined the potential impacts of sea-level rise on coastal assets, property and building structures. For the US National Assessment of the coastal sector alone, the cumulative estimates of impacts are at roughly $20 to $200 billion for a 46 cm rise by 2100 .
Additionally, as the sea level rises, it will also affect trade and commerce. This may have repercussions further inland through migration of labourers. Sea level rise may inhibit people from moving to coastal regions due to coastal flooding, reduced waves and closed businesses. What’s more, rising sea levels may aggravate coastal storms and disasters thus decreasing the ease of export and import. This will invariably transmit to whole countries and impact heavily on nations.
Likewise, the tourism sector that relies mostly on the ‘sun, sea and sand’ image that coastal regions offer is greatly at risk. Not only will the number of coastal tourists decline, but the infrastructure that is already in place will also be greatly affected. Research into sea-level rise has shown that as much as 29% of the tourism associated assets will be flooded by a 1 m sea-level rise. Additionally, about 49% of assets will be damaged or destroyed by the cumulative effects of storm surges and extreme events . Taking Barbados as an example, 70% of the hotels are located within the 250 m high watermark level. Subsequently, a 1 m rise in sea level and associated storm surges will cause a lot of damage to hotels and assets.
One issue of international importance about global sea-level rise is related to land sovereignty. As the sea level rises and encroaches on the land, coastal jurisdictions will be displaced. Member states of the UNCLOS would hence have to re-partition and re-assess the international seas to prevent conflict of interest. Similarly, individual nations would have to reassess their high watermarks and flooding zones prior to development and implementation of adaptations structures.
Regrettably, as sea levels increase, certain regions that are subsiding will lose large expanses of land. This can be seen in the Pacific islands like Tuvalu where rising water levels are invading an already receding land. Simultaneously, storm surges and extreme sea events will worsen making habitation impossible. In such cases, people will be forced to relocate further inland adding pressure to the already saturated land space. For low-lying islands, whole nations could lose their homelands. In fact, the fifth assessment report of the IPCC states that high sea levels and recurrent swells may cause many islands like Kiribati, Marshall Islands, Micronesia and the Solomon Islands to become inhabitable within a few decades.
Thus, the negative effects of sea-level rise include the receding of coastlines, a destabilization in coastal ecosystems whereby considerable ecological changes may occur, coastal flooding will impact on settlements and infrastructure, contamination of groundwater, an increase in the transmission of diseases, threats to coastal economy and coastal tourism, the reassessment of international water and high water marks and forced relocation.
Conclusively, sea-level rise is a direct threat to many coastal nations, especially the small remote islands. Due to their small sizes, most of their settlements, infrastructure and agricultural lands are on coastal borders. For the low-lying atolls with a land area within 5 m above sea level, the impacts of sea-level rise are quite significant. Thus most coastal nations are coming up with plans and strategies to decrease the coastal impacts associated with sea level and keep the sea at bay.