The global sea level history and projections from 1800 to 2100 under the RCP 2.6, RCP 4.5, and RCP 8.5 scenarios.

The water level in the oceans is rising around the globe. The sea-level rise refers to the upsurge in the particular level of the oceans resulting from the impact of global warming. The Global Mean Sea Level (GMSL) has risen by an estimated 8-9 inches since 1880.[1] The problem is affecting the lives of millions of people living in coastal areas and negatively affecting ecosystems.[2] There will be a 2.3 meters rise in sea levels per 1°C rise in temperature within the next 2000 years.[3] The sea-level rise is a significant problem since it is happening rapidly; even a small increase may have a negative impact on various coastal habitats, including through wetland flooding and erosion. Consequently, it may cause agricultural and aquifer soil contamination and loss of habitat for the plants, birds, and fishes.[4] The major cause of rising sea levels is global warming. The two main factors that influence global warming are the expansion of sea waters and the melting of ice glaciers. The increase in reliance on fossil fuel-powered machinery increases greenhouse gases (GHGs) emissions and results in higher atmospheric temperature.[1] The increasing atmospheric temperature has led to heating and expansion of the ocean by 2°C to 4°C since the previous glacier period.[5] The consistency of the high temperatures caused by global warming has increased average summer melting and diminished snowfall, leading to glaciers' continuous melting.[4]

The Upsala Glacier in Argentina has been thinning and retreating rapidly from 2006 to 2010; it receded 40 meters per year. During summer 2012, significant calving events prevented boat access to the glacier.

Some of the areas that have experienced adverse climatic conditions due to sea-level rise include Indonesia, Greenland, Yemen, China, India, Thailand, Bangladesh, and Haiti.[6] The sea level in Indonesia is rising at a rate of 1cm per year in southern Jakarta, up to 15 cm in the West, and up to 25 cm in North Jakarta.[7] In the USA, the sea level is expected to rise up to 4.3 feet by 2100.[8]

The problem of sea-level rise is very extensive and has intensive consequences for the marine ecosystem.[9] It has caused an increase in precipitation in coastal regions. For example, Superstorm Sandy in 2012 caused flooding in the low altitude regions in Long Island, New York City, and New Jersey.[5] The increase in water deposition into the ocean increases deposits of agricultural fertilizers into the ocean contributing to an algae bloom.[10] As the algae sinks, it decomposes and depletes oxygen in the water during the process. The shortage in water supply threatens marine life and interferes with currents and tide cycles of the ocean water. Furthermore, the light required for photosynthesis is also reduced. Studies have also shown that the population-level shifts due to intolerance to new environments caused by the sea-level rise. Changes in the interaction among species, alteration in community structure and diversity, and extinction have also been observed.[11]

Impact of Sea Level Rise on Marine Ecosystems and Organisms

Areas of Impact

Since the recent sea level rise is a primarily global issue, there are many ecosystems that are impacted by it. Examples of such ecosystems include:

This graph depicts an overall decrease (black line) of accumulated ice coverage in the Gulf of St. Lawrence from the years 1971 to 2005. Though annual ice coverage varies greatly, there is a general trend of reduced duration and extent of ice cover.[12]

Some major ways that these ecosystems are affected by sea level rise are by coastal retreat and habitat loss as well as frequent storms and sea ice loss.

Coastal Retreat and Habitat Loss

There is a 1.0-1.5 metre coastal retreat rate for every centimetre of sea level rise.[12] Sea level rise will change the areas where estuaries can grow and will inflict higher rates of erosion for salt marshes.[16] Wetlands such as marshes will be overtaken if they fail to migrate.[15] The rocky intertidal will undergo altered vertical zonation, and coral reefs, shelf sea benthos, and seagrass meadows will experience habitat loss.[16]

Frequent Storms and Sea Ice Loss

Sea ice is a major source of protection for coasts from storms. Due to sea level rise, thaw-frost cycles are increasing in frequency, leading to higher coastal erosion rates due to winter storm activity, and sea ice cover is generally experiencing reductions in duration and volume.[12]

Factors Resulting in Increased Vulnerability

A variety of factors cause certain ecosystems to be particularly vulnerable to the sea-level rise. Delicate shores such as cliffs made out of glacial tills are susceptible to the changes in winter conditions.[12] Ecosystems such as mangroves along micro-tidal coastlines or in areas adjacent to significant river input are particularly vulnerable to the impact of sea level rise due to their proximity to saltwater and low rates of upland space.[13] Freshwater-dependent ecosystems in general are at risk of dramatic change when rising sea levels allow saltwater to enter the habitat.[14]

Impacted Organisms

Organisms that are particularly vulnerable to rising sea levels consist mainly of those that reside on the coast; however, those inland are affected as well. Notable impacted organism groups include:

Sea level rise causes coastal erosion, leaving a road in Richibucto Head abandoned.[12]

Organisms are affected in a number of different ways by sea level rise, including structural damage and salinity changes resulting in osmotic stress. There can be consequences for organisms who lack mobility and are prone to changes in temperature.

Structural Damage

Receding coastlines can affect humans by increasing the probability of flooding during storms in addition to causing damage to house foundations, roads, and railways.[12]

Salinity and Osmotic Stress

Salinity changes in mangroves could result in significant changes to various plant structures,[16] and may also result in the arrival of invasive species.[13]

Osmotic stress occurs when there is a drastic change in solute concentrations outside of the cell, leading to rapid water movement across the cell membrane.[18] If sufficient saltwater is introduced into a system, mature terrestrial trees could potentially die from osmotic stress;[14] if enough forest recedes, a “ghost forest” of dead trees would remain, severely impacting the ecosystem in which they reside.[19]

Lack of Mobility and Temperature Resistance

Sedentary organisms, especially those with low thermal tolerance such as corals, will not be able to shift appropriately to the rising sea level.[16] Organisms must adapt to the changes in oxygen, temperature, and salinity levels, otherwise they will not be able to survive.[16]

What is the extent of the problem?

Changes in Ecosystems

The rise of sea level affects global coastal areas, from the most desolate areas of the Antarctic to the megacities like New York and Los Angeles. These coastal areas, no matter the latitude, are crucial for protection, biodiversity, nurseries for animals, and for humans, enhancing tourism and fisheries.[20] However, the biggest impacts can be seen from the shorelines themselves: the rise of sea levels contributes to high tide and critical coastal erosion, impacting the highly sensitive and vulnerable coastal communities.[21]

Global sea level rise projected to 2200 by different representative concentration pathways. RCP 8.5 has continuously increasing GHG emissions, leading to high GHG concentration. RCP 4.5 shows emissions balanced at 2100, leading to a lower GHG concentration. RCP 2.6 is a ‘peak and decline’ model, as GHG concentration peaks around 2050 and returns to much lower values by 2100.[22]

Continued erosion of coastlines cause these ecosystems, such as wetlands, to migrate landwards. However, much of the inner-continental land is now urbanized and unsuitable for these ecosystems to settle in, making it extremely difficult for crucial shoreline habitats to combat the rising sea levels and continued loss of space at the coasts.[23] One significant example is Malaysia, in which 2327 km of the 4809 km coastline has been determined as vulnerable to coastal erosion in 2000.[20] Melting glaciers and loss of ice sheets, while contributing to the sea levels, are also habitats themselves. The accelerating melt of Arctic and Antarctic ice poses a threat to the coldest areas and the resilient organisms residing there as well.

Current Status and Future Projections

Global Changes

Sea levels on Earth have changed in the evolution of the planet, but the rate at which it rises has been accelerating since the late 19th century. The estimated average sea level rise during the 20th century is about 1.7 mm per year, but since 1993, this rate has increased to 3 mm per year—almost twice the rate it was in the previous century.[24] Global sea levels are estimated to rise 0.3 m at the minimum and at the maximum, 1.2 m depending on the different pathways of Representative Concentration Pathways (RCP).[22] RCP is a set of four different projections by the IPCC of different atmospheric greenhouse gas (GHG) concentrations.[24] The rise of global sea level by 2200 is estimated up to 2.8 m under RCP 8.5, which is the highest projected atmospheric GHG concentration. and even the lowest estimates at RCP 2.6 is a sea level rise of 0.5 m.[22]

Local Changes

Although a global phenomenon, the amount of sea level rise and its effects differ substantially at the local level. In 2004, over 20% of the human population lived within 30 km of the coast, and 37% within 100 km.[21] While not all coastal communities will be irreparably damaged due to sea levels, the effects of higher sea levels on natural disasters such as floods and storms will be significantly worse for all, even for those away from the coasts. Shoreline ecosystems also serve as protection and habitats for not humans and non-human species alike, an example being marshes around New England, protecting shores from storms and floods.[25] Physical impacts from sea level rise also includes salinization, where the salt water intrudes into freshwater rivers and land areas.[26] These physical changes to coastlines also result in economic damage, such as the loss of agricultural land and forced migration of highly populated coastal cities. To mitigate these impacts, adaptations to protect such vulnerable coasts have a steep economic price or are unreliable for the accelerating rise of sea levels in recent years.[26]

Possible Solutions to Sea Level Rise

A satellite image of the Great Barrier Reef. Coral reefs and other coastal habitats provide a barrier from waves and storm surges.

Global solutions

In order to limit the amount of sea level rise that happens on a global scale, global greenhouse gas emissions need to be greatly reduced. However, the even the very best-case scenario for greenhouse gas emissions predicted in 2017 still had the global mean sea level rising by 0.3 meters by 2100. This prediction is based on net-zero emissions by 2075 and net removal of carbon dioxide from the atmosphere afterwards.[27] Therefore, local measures such as seawalls, migration, and habitat protection will still be needed to mitigate the effect of sea level rise on people and ecosystems, even with massive greenhouse gas reductions.

Local Solutions

In many cases, man-made structures such as seawalls or breakwaters, barriers built into the water to prevent the sea from damaging the land, are the best protection from sea level rise.   For example, the Vancouver Seawall protects the land in Stanley Park from erosion, and seawalls are common in coastal urban areas such as in Florida. However, these can be detrimental to the natural environment, and they can have high construction and maintenance costs. [28] On small islands that would be completely consumed by sea level rise, artificially raising the land to allow people to survive there can be an option. [29]

Providing healthy coastal habitats may be a more sustainable way to protect against sea level rise. Ecosystems such as coral reefs and mangroves can provide a significant buffer against waves and large storm surges, the biggest problem with high sea levels. When a coral reef or a mangrove forest is near the coast, the waves are suppressed and the hazards of sea level rise can be reduced by half.[30]

New technologies can also be developed to help mitigate the damage from sea level rise. The Tidal Replicate method is a gate system that helps improve conditions in coastal wetlands by replicating the past tides. The system is meant for a type of saltmarsh with a single, narrow entrance/exit for water. In testing, it improved the vegetation cover in the saltmarsh significantly.[31]

In a scenario where barriers and other measures will no longer be effective against sea level rise, other options may include accepting sea level rise and adopting 'aquatic architecture,' in which cities accept water as part of the overall city makeup and adopt floating houses as a norm.[32]

However, for human survival, sometimes the only safe option is migration. In Louisiana, there is a government program to relocate the entire community of the Isle of Jean Charles, as the low-lying island is under severe threat from sea level rise.[33] Protecting upland habitat is also a priority, as endangered wildlife species threatened by sea level rise have a place to live once their habitat is reduced by the rising sea.[30]


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