Temperature rise is the main reason behind rising sea level

Temperature rise in the Earth's atmosphere over many decades is the main reason attributed to sea level rise, therefore sea level will continue to increase between now and 2050. After that, if emissions of GHGs are deeply cut then sea level rise would slow between 2050 to 2100.

Melting of glaciers and ice sheets and natural expansion of ocean water (water expands as it warms) due to increase in temperature are prime drivers of sea level rise. Rise in sea level is a great sign of global climate change.

Excess Heat in Oceans

Due to human-activities, increasing concentrations of carbon dioxide and other greenhouse gasses causes global warming. The oceans absorb the majority of heat that greenhouse gasses traps. This excess heat warms the ocean water and as water becomes warmer, it expands. This results in a rise in ocean levels worldwide.

If global warming continues at its current rate, sea level can rise by 2 meters by the end of the century, which will lead to the displacement of around 200 million people worldwide.

Over the last two decades, Greenland and Antarctica ice sheets have become the single largest source of sea level rise.

Glaciers and ice sheets based on land are greatly affected by global warming as well. As global average temperatures are rising year-round, glaciers and ice-caps are melting at an accelerated rate.

Factors responsible for acceleration of sea level rise

Thermal expansion of ocean water due to ocean warming and glacier melt have been the dominant contributors to global mean sea-level rise in the twentieth-century.

According to World Meteorological Organization (WMO) report, the main factors contributing to global mean sea level rise are : 

1. Ocean warming
2. Loss of glaciers and ice sheets over land
3. Change in land water storage.

Ocean Warming

Thermal expansion caused by ocean warming (when water warms, it expands) and melting of glaciers and ice sheets over land are two major causes contributing to rising sea levels.

Ocean warming has the highest share and contributed 55% to the rise in sea level between 2005 to 2019 while the loss of glaciers and ice sheets has contributed 36% within the same period.

Increasing concentrations of carbon dioxide and other GHGs trap heat that the Earth radiates, around 90% of this trapped extra heat is absorbed by the oceans as heat absorbing capacity of the atmosphere is very less. This extra heat warms the ocean which leads to rise in the sea level.

Warm water in the tropical ocean will expand more than the cold Arctic Ocean water as warm water expands more than cooler one. 

The Equatorial water such as the Bay of Bengal and South China Sea are seeing the fastest sea level rise largely due to ocean dynamics.

Melting of Glaciers

Glaciers hold up around 70% of the Earth’s freshwater and cover only 10% of land surface. These glaciers are retreating at an unprecedented rate due to increasing temperature and global warming.

The Greenland and Antarctic ice sheets are the largest contributor to global sea level rise.  The Antarctic ice sheet, which is the world's largest ice sheet, has the potential to raise sea level by more than a meter by the end of the Century if it continues to melt at current rate.

 

If greenhouse gas emissions continue to rise, the melting rate of the Greenland ice sheet is expected to double by the end of the century. Greenland would raise the sea level by 20 feet, if the entire ice on it melted away.

Addition of water from melting glaciers contributes to sea level rise which in turn increases coastal erosion and intensifies storm surges (as the warm atmosphere holds more moisture and fuels the coastal storms) and flooding, posing a serious threat to coastal life.

Change in Land Water Storage 

Generally, rise in sea level is attributed to rise in ocean heat content and glacier and ice melt. However, construction of Dams on rivers and artificial lake has impounded water which reduced water flow to sea while on other hand, excessive groundwater mining, water losses from wetland and endorheic lake due to the high evaporation rate and deforestation by humans has increased river runoff which end up in adding water to sea or ocean.

Regional Variations in Sea Level Rise

Rise in sea level is not uniform around the globe but would vary regionally mainly because of internal climate variability and shifts in ocean currents. 

Role of ocean currents and internal climate variability 

Ocean currents play a role in regional variability of sea level rise as the shifts in ocean currents will probably direct more water to certain coastal areas.

Internal climate variability in certain places could cause sea level to rise by 20-30% more than what could be the result of climate change alone. For instance, coastal flooding events in Manila are expected to occur 18 times more frequently by 2100 than they did in 2006.

In a worst-case scenario, local sea levels could rise by more than 50% due to the combined effect of climate change and internal climate variability than what could be due to climate change alone. Thus posing serious risks of more severe flooding to coastal megacities and endangering millions of people. 

According to new research, sea level rise this century may disproportionately harm several Asian megacities, as well as the western Indian Ocean and the western tropical Pacific islands.

Consequences of Rising Sea Level

Coastal ecosystems, small islands, people and infrastructures are particularly in great danger due to rising sea levels. Tidal range and land subsidence will increase the severity of sea level impacts locally. The biggest impacts of sea level rise on human populations will be in low-lying islands of the Pacific and Caribbean in near future. 

Submergence of Land

Rise in sea level would lead to submergence of land, particularly in the coastal areas. The land crisis can lead to an increase in social disparities between people living in the coastal areas.

In the Sundarbans, the largest mangrove in the world, rising sea levels and coastal erosion has left more islands submerged under water. As a result, local communities have been forced to move.

Intensifying Cyclones 

Cyclones that originate in the open sea, the intensity and frequency of these cyclones would be increased due to rise in sea level and increase in ocean temperatures. This will definitely affect coastal communities and can cause displacement of them and will increase economic burden particularly on tropical countries like India and South Africa.

Coastal Ecosystem Instability

Higher global temperatures will cause sea level to rise that will lead to instability and profound changes to coastal ecosystems, including mangrove forests, coral reefs and coral islands, and tidal marshes which provide critical habitats for diverse marine species. Rising sea levels are threatening these ecosystems which means loss of biodiversity, decline in fish species and disruptions in natural balance of these ecosystems.

Endanger the socio-economic stability of coastal communities

The socio-economic stability of coastal communities will be further jeopardized by changes in the coastal ecosystem brought on by sea level rise, particularly when these changes occur more quickly than rehabilitative policies and laws can keep up. This will happen because the lives of coastal communities, including their economic activities, are closely linked to the coastal ecosystem.

Saltwater Intrusion

Saline water from seas/oceans will intrude into freshwater sources in coastal areas such as rivers and groundwater aquifers as a result of sea level rise. This will lead to freshwater contamination thus drinking water problems and affect the agriculture in the adjacent regions.

Damage to Infrastructure

Pots, airports, roads and urban conglomerations in the delta region of rivers will get damaged or even destroyed due to rising sea levels.

India's Vulnerability To Sea Level Rise

India, due to having long a coastline and rapid urbanization of coastal megacities like Chennai,  Mumbai, Kolkata and Kochi which in turn reduced their resilience to extreme weather events, is highly vulnerable to sea level rise.

Sea level rise will increase intensity and frequency of tropical storms

The coastal communities in India are vulnerable to sea level rise and tropical storms. Frequency and intensity of these storms will be increased due to rise in sea level. Warming seas will fuel tropical storms and make them more intense.

In the coming decades, even the 0.1 to 0.2 m elevation along India's coastline is predicted to frequently produce coastal flooding. 

Rapid urbanization has reduced resilience of coastal cities

According to a UN environment assessment, about 40 million Indian people will be at risk from rising sea levels by 2050, with the Mumbai and Kolkata megacities being most vulnerable to coastal flooding in the future due to their high exposure to seas and rapid urbanization and economic development of these cities.

Rapid urbanization of these coastal cities has reduced the ability of natural ecosystems to stand against extreme weather events.

Out of 20 nations, 12 are in Asia which are vulnerable to rising sea level. In the Asia Pacific Region, India with nearly 40 million people is projected to be at highest risk from rising sea levels followed by Bangladesh with 25 million and China with 15 million people.

India's coastal habitats offer a wide range of ecosystem services and support a rich biodiversity. These habitats are seriously threatened by rising sea levels and increased coastal erosion. This will result in habitat loss, decline in fish stocks, and a disruption in marine ecosystems.

Adaptations To Sea Level Rise

To reduce the risk of coastal erosion and floods, the world must invest in adaptation measures including sea walls, coastal protection, and afforestation along with strict coastal regulation.

Building Barriers 

Barriers such as sea walls should be built parallel to coast lines in order to reduce the intensity of floods and protect coastal areas against storm surge and coastal erosion.

Nature-based Solutions

Wetlands and sand dunes reduce the impacts of floodwaters and storm surge by diffusing water and decreasing its speed.

A network of protected areas is to be created that safeguards coral reefs, mangroves, seagrasses, salt marshes as well as provides ecosystem services such as food, clean water and opportunities for recreation activities.

Climate change mitigation by reducing greenhouse gas emission is the best solution as it provides long-term benefits.