Rising, Risen - Sea Levels
- Scales and States Team
- Jul 13, 2020
- 6 min read
Updated: Jul 14, 2020
Rise in global sea-levels is now very well documented and recognised by everyone barring a few who think the sea-level rise as just a phenomenon of tidal waves. The Ministry of Earth Sciences titled ‘Assessment of Climate Change Over the Indian Region’ makes striking observations in this regard and gives empirical evidence for the same. However it is very important, before we analyse the observations of the report, to understand how important and significant event is sea-level rise and even before that what rise in sea-levels means.
The term sea-level rise generally designates the average long-term global rise of the ocean surface measured from the centre of the earth (or more precisely, from the earth reference ellipsoid), as derived from satellite observations. According to the National Climate Change Adaption Research Facility of Australia, a one cm rise in sea-level will lead the water one metre further landward. This is very significant for coastal states in India which has a cumulative population of over 56 crores and also for people who live on islands (4.4 lakhs). The vulnerability is further enhanced by coastal erosion, because of sediment retention behind upstream dams, hard coastal structures and/or conversion of mangrove forests to aquacultures. Sea-level rise also threatens coastal wetlands, which may not be capable to keep pace with sea level and be partly lost due to so-called coastal squeeze. Other major impacts of sea-level rise include salt intrusion, soil subsidence, loss of fertile agricultural land and unavailability of fresh drinking water.
Even though there is an unabated rise in observed global mean sea level, the spatial distribution of sea-level trends is not globally uniform. Regionally, sea-level variations can deviate considerably from the global mean and in the twenty-first century and beyond, the sea-level change will have a strong regional pattern according to the Report. The underlying causes of regional sea-level changes are associated with dynamic variations in the ocean circulation as part of climate modes of variability, changes in the wind pattern and with an isostatic adjustment of Earth’s crust to past and ongoing changes in polar ice masses and continental water storage. While on the other hand primary reasons for the rise in sea-levels on the global level are the thermal expansion of sea waters and freshwater mass exchange between oceans and land water reservoirs and groundwater storage change. Another major cause of the rise in sea-level has been melting of the continental ice storage in a warming climate has accounted for approximately 21% of the global sea-level rise since 1993.
Significant observations in the Report with regard to rise in sea-level are as follows:
There is high confidence that the rate of global mean sea level (GMSL) rise has increased. Human-caused climate change has made a substantial contribution to the rise since 1900.
The GMSL has risen by 1.7 (1.5 to 1.9) mm year since 1901 and the rate of rise has accelerated to 3.3 mm year since 1993.
Sea-level rise in the Indian Ocean is non-uniform and the rate of north Indian Ocean rise is 1.06–1.75 mm year−1 from 1874 to 2004 and is 3.3 mm year in the recent decades (1993–2015), which is comparable to the current rate of GMSL rise.
Indian Ocean sea-level rise is dominated by the ocean thermal expansion, while the addition of water mass from terrestrial ice-melting is the major contributor to the GMSL rise.
Inter-annual to decadal-scale variability in the Indian Ocean sea level is dominated by El Niño Southern Oscillation and Indian Ocean Dipole events.
Relative to 1986–2005, GMSL is very likely to rise by approximately 26 cm by 2050 and approximately 53 cm by 2100 for a mid-range, mitigation scenario.
Steric sea level along the Indian coast is likely to rise by about 20–30 cm at the end of the twenty-first century and the corresponding estimate for global mean steric sea- level rise is 18±5 cm (relative to 1986–2005), under RCP4.5 (for a mid-range emission scenario, excluding ice-melt contributions).
Extreme sea-level events are projected to occur frequently over the tropical regions (high confidence) and along the Indian coast (medium confidence) associated with an increase in the mean sea level and climate extremes.
Therefore climate change, and sea level rise in particular, is a major threat for many coastal zones. Many coastal zones around the world are already lying around or even below high-water sea levels, especially coastal delta plains and small islands. Hence there is an unprecedented urgency to adopt adaption strategies with regard to climate change. A reasonable and generally preferred strategy for climate change adaptation is to start with so-called 'low-regret measures' or, even better, 'no-regret measures’. Examples of such measures are:
Choose building with nature solutions for renewing coastal infrastructural works when they have reached the end of their life span (e.g., wetland restoration, dune/beach/shore-face nourishments);
Adjust design criteria to extend the lifetime of infrastructural works by incorporating the expected sea level rise in the periodic maintenance/renovation scheme;
Make spatial reservations for nature development (or for other temporal benefits) which can eventually serve later for future reinforcement or realignment of coastal defenses;
Introduce setback lines to gradually replace settlements in future high-risk areas with nature development with a protective function (e.g., stimulating dune growth, mangrove development).
More no regret measures include early warning systems; risk communication between decision makers and local citizens; sustainable land management, including land use planning; ecosystem management and restoration; improvements to water supply, sanitation, irrigation and drainage systems; development and enforcement of building codes (considering also geotechnical aspects) and better education and awareness.
If you are willing to take steps at the individual levels, here are some measures that you can take:
Reduce your footprint: Greenhouse gasses are a major contributor to sea level rise. Calculate your “Carbon Footprint” at www.carbonfootprint.com to learn how to reduce the amount of greenhouse gases you produce each day.
Let it soak in: Hard surfaces prevent water from permeating into the ground and lead to an increase in runoff and erosion. Use stepping stones for walkways and paver blocks for patios. If you are repaving use permeable pavement which allows water to soak into the ground. Direct rain runoff to rain gardens and barrels.
Plant more plants and save trees: Plants clean the air and soak up rain. Reduce paper use to prevent trees from being cut down. Set all computers and printers to double-sided printing and reuse one-sided copies as scrap paper.
Reduce your energy use: Reducing your energy usage is good for your wallet and the environment. Turn off your lights and appliances when not in use and replace them with more energy efficient varieties. Unplug your chargers and appliances when possible because many use energy even when turned off. Adjust your thermostat to reduce AC and heat use.
Leave the car at home: Vehicles are a leading source of carbon dioxide production. Reduce the number of cars on the road by carpooling, walking, biking, or using mass transit. When driving, turn your car off if idling for more than 30 seconds. This will conserve fuel, save money, and reduce greenhouse gas emissions.
Designing and building infrastructure with future change in mind demands investment today, but it will save lives and money in the long run. We must act today. Now. This moment.
References/ Further Readings:
Syvitski, J.P., Kettner, A.J., Overeem, L., Hutton, E.W., Hannon, M.T., Brakenridge, G.R., Day, J., Vörösmarty, C., Saito, Y. and Giosan, L. 2009. Sinking deltas due to human activities. Nature Geosci. 2: 681–686
Church JA, Monselesan D, Gregory JM, Marzeion B (2013a) Evaluating the ability of process based models to project sea-level change. Environ Res Lett 8:014051
Stammer D et al (2013) Causes for contemporary regional sea level changes. Ann Rev Mar Sci 5:21–46
WCRP Global Sea Level Budget Group: Global sea-level budget 1993– present (2018) Earth Syst. Sci. Data 10:1551–1590.
IPCC, 2019. Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)]
Hallegatte, S. 2009. Strategies to adapt to an uncertain climate change. Global Environmental Change 19: 240–247
IPCC, 2011. Summary for Policymakers. In: Intergovernmental Panel on Climate Change Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. Authors: Field, C. B., Barros, V., Stocker, T.F., Qin, D., Dokken, D., Ebi, K.L., Mastrandrea, M. D., Mach, K. J., Plattner, G.-K., Allen, S. K., Tignor, M. and P. M. Midgley (eds.). Cambridge University Press
Know more:
This story is part of a four part series on the Climate Change Impact Assessment Report by the Ministry of Earth Sciences.
Do more:
Have a look at this piece about the report, or reach out to us at submissions.scalesandstates@gmail.com for feedback, queries, and sharing your thoughts.
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