Surging Oceans: The Acceleration of Global Sea Level Rise

By Dennis Mombauer

After 3.000 years of largely unchanged global mean sea levels (GMSL), the oceans have begun to rise from the 20th century onward, encroaching higher and higher onto the coastlines of continents and islands and threating the livelihoods of millions (if not billions) of people. The reason for this is twofold and directly connected to the global warming caused by increasing greenhouse gas concentration in the atmosphere: the water warms up and expands (thermal expansion), and the higher temperatures cause glaciers and ice shelves (primarily in Greenland and Antarctica) to melt.

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Acceleration of Sea Level Rise

A study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on February 12th, 2018, confirms the long-held apprehensions of climate change models: the speed of GMSL rise has been accelerating and will lead to much larger increases than originally projected. The research findings are based on data collected over a period of 25 years.

In 25 years, the GMSL has risen by around 7,5 cm (3 inches), which equates to around 3 mm per year. However, the data shows that this rate is not constant, but accelerating by 0,084 mm per year, leading to an acceleration of around 65 cm (2 feet) higher than the current prediction for the end of the century. The research scenario assumes a “business as usual” scenario without a significant reduction of greenhouse gas emissions, and aligns with the projections of the Intergovernmental Panel on Climate Change (IPCC), which assumed 52 to 98 cm by 2100 in their 2013 Assessment Report.

Adapting to Rising Sea Levels

A GMSL rise of 2 feet over a hundred years might not sound insurmountable. One third of the Netherlands lies up to 22 feet below the current sea level, and their system of dams and dikes seems to be well capable of preventing flooding – what are two additional feet going to change? And if the Netherlands can protect themselves, why not other countries? This perspective, however, overlooks several critical factors.

First, not every area in the world will be equally affected, and not every country has the resources of the Netherlands, one of the world’s richest countries. Second, the mean sea level rising by just inches or feet makes extreme water levels (high tides, storm surges etc.) exponentially more catastrophic, as can increasingly be seen around the world. Third, flooding is not the only risk associated by rising sea levels: just one further example would be the intrusion of salt water into the drinking water supply of coastal cities, many of whom are already in a constant state of water stress (one in four of the world’s largest cities according to a 2014 study published in Global Environmental Change), as dramatically illustrated by Cape Town, South Africa, at the time of writing.

The sea levels will not stop rising by 2100, and the estimate of 2 feet till then is still a conservative one: both the PNAS study and the IPCC models place very high probability on the further acceleration of sea level rise and a significant increase of sea level extremes in some regions of the globe.

South Asia’s Challenge

Among the most seriously affected regions will be South Asia, which has large areas of low elevation land in the coastal zone (LECZ) and is especially vulnerable to the effects of climate change to the GMSL. Many densely populated coastal areas with tens of millions of inhabitants (for example Chennai and Kolkata in India or Dhaka in Bangladesh) will be at a high risk of increased storm surges and floods, while adjacent river deltas are simultaneously sinking due to groundwater extraction and sediment-catching dams.

As island countries, Sri Lanka and the Maldives especially have long coastlines with low elevations; in the Maldives, the highest natural island is only 2,5 m above the current sea level, so the entire country is threatened with inundation as the oceans rise further. Sri Lanka has a lot of coastal cities as well, for example Negombo, which lies only 2 m above the current sea level and is criss-crossed by canals and lagoons; with the projected sea level rise, it would in large parts become inundated if there are no expensive measures being taken. GMSL rise will put Negombo and many other coastal cities in Sri Lanka at risk, with huge repercussions for their population, infrastructure, freshwater supplies, agriculture, tourism, biodiversity, and wetlands.

Addressing Sea Level Rise

The existing vulnerabilities of developing countries are aggravated by the increasing impacts of climate change. The risks and vulnerabilities of these countries and communities need to be addressed and support provided to ensure that their needs are met against climate change impacts such as sea level rise. While diverse support mechanisms exist, it is important to identify whether the transfer of finance and technology reaches the vulnerable communities, which will lead to more accountable, effective, and impact driven climate action.

 

References

“Climate-change–driven accelerated sea-level rise detected in the altimeter era” in Proceedings of the National Academy of Sciences of the United States of America, 2018. (http://www.pnas.org/content/early/2018/02/06/1717312115)

“Climate Change 2014: Impacts, Adaptation, and Vulnerability.”, IPCC, 2014.

“Climate-Focus-Paper: Regional Sea Level Rise South Asia”, Climate Service Center Germany (GERICS), 2015 (https://www.kfw-entwicklungsbank.de/PDF/Entwicklungsfinanzierung/Themen-NEU/Regional-Sea-Level-Change-South-Asia.pdf)

“Sea Level Change” in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, 2013. (https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter13_FINAL.pdf)

“Sea Level Rise: Hazard Profiles of Sri Lanka”, Disaster Management Center, Ministry of Disaster Management (http://www.dmc.gov.lk/hazard/hazard/Report/UNDP%20BOOK%20CHAP%2007_%20SEA%20LEVEL%20RISE.pdf)

“Water on an Urban Planet: Urbanization and the Reach of Urban Water Infrastructure” in Global Environmental Change, Vol. 27, 2014.

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