December 6, 2021

Sea levels will rise and affect small islands in the Caribbean

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rising-sea-level1The Organization of Eastern Caribbean States (OECS)1: Expected sea level rise and ocean acidification in a 4°C warmer world

1. Background

Like most Small Island Developing States (SIDS)2, the impacts of climate change will have serious deleterious environmental, social and economic consequences. Apart from their small physical size, the characteristics3 of these islands that make them so vulnerable to climate change include the fact that they are surrounded by large expanses of ocean, have limited natural resources, are in areas that are subject to frequent natural disasters and extreme events, are relatively isolated, possess extremely open economies highly sensitive to external shocks, have large populations with high growth rates, contain poorly developed infrastructure, and are constrained by limited funds, human resources and skills.

2.         Impacts of Climate Change: Sea Level Rise and Ocean Acidification

Given the location of the infrastructure, most of which is based along the coastlines, and the sensitivity of coastal ecosystems, in particular coral reefs, the livelihood of 40 million people is extremely vulnerable to the threats of climate change and has actually already experienced the toll of a different climate system following an increase of global mean temperature of about 0.8°C above preindustrial levels4.

OECSAmong the most dangerous threats, sea level rise and ocean acidification represent unprecedented challenges to the economies, if not the very existence, of these small and exposed countries.

The Copenhagen Accord5, agreed by the Conference of the Parties (COP) in 2009, states that “The Parties agree that deep cuts in global emissions are required according to science, and as documented by the IPCC Fourth Assessment Report with a view to reduce global emissions so as to hold the increase in global temperature below 2 degrees Celsius….” as the same agreement considers such target6 enough to “…..prevent dangerous anthropogenic interference with the climate system7”

According to the World Bank “Turn Down the Heat8” report, however, even if the current commitments and policies on CO2 emission reductions were implemented, there would still be 20% chance to exceed a 4o C increase by 2100. A business as usual scenario9 would generate a 4o C increase within the end of this century.

The consequences of a 4o C increase, in terms of sea level rise and ocean acidification would be calamitous for SIDS.

a.         Sea level rise10

Sea level rise is a straightforward consequence of global warming for two main reasons: ocean water expands as it heats up and extra water from melting land ice ends up in the oceans. Updated estimates and reconstructions of sea-level rise, based on tidal gauges and more recently, satellite observations, confirm the findings of the AR4 and indicate a sea-level rise of more than 20 cm since preindustrial times to 2009. The rate of sea-level rise was close to 1.7 mm/year (equivalent to 1.7 cm/decade) during the 20th century, accelerating to about 3.2 mm/year (equivalent to 3.2 cm/decade) on average since the beginning of the 1990s11.

In the event of a 4o C increase, an estimated sea-level rise12 of 0.5 to 1 meter is projected by 2100. Under this scenario, we can expect:

•          significant loss of current total beach; •     reduction of freshwater lenses; •    saline intrusion into freshwater lenses; •  accelerated coastal erosion;

•          increased flooding. b.            Oceans Acidification13

Recent_Sea_Level_RiseThe oceans have absorbed up to 25% of anthropogenic CO2 emissions during the period 2000- 0614. The CO2 reacts with sea water generating a weak acid which reduces the water’s pH, which eventually results in the acidification of the oceans. The rate of changes in overall ocean biogeochemistry currently observed and projected appears to be unparalleled in Earth history.

The current atmospheric concentration of 390 ppm of CO2 represents a 0.1 pH reduction compared to pre-industrial times. A reduction of 0.1 pH is equivalent to a 30% increase of ocean acidity. In a 4o C increase scenario, we can expect an atmospheric concentration of 880 ppm of CO2, which would lead to a further 0.3 pH decrease and therefore a 150% increase of ocean acidity compared to preindustrial levels.

Such process will inevitably affect the wellbeing of coral reefs, various species of marine calcifying organisms, and ocean ecosystems generally. If atmospheric CO2 concentration reaches 450 ppm, coral reef growth around the world is expected to slow down considerably and at 550 ppm reefs are expected to start to dissolve.

One palpable consequence of ocean acidification is coral bleaching15. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white.

3.         Way forward

Tourism is the main economic driver in the Caribbean. Climate change impacts on this sector must be considered seriously. Planned adaptation should be an absolute priority. New science and observations should be incorporated into existing sustainable development efforts. Climate change adaptation will come at a cost but the financial and human costs of inaction will be much greater.


1 Anguilla (associate member), Antigua & Barbuda, British Virgin Islands (associate member), Dominica, Grenada, Montserrat, St. Kitts and Nevis, St. Lucia, and St. Vincent & the Grenadines 2

3 IPCC 4AR 4 Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided http://www- 2749/Rendered/PDF/NonAsciiFileName0.pdf 5 6 Other schools of thought believe 1o C increase is “dangerous” enough to generate deleterious consequences. 7 Art. 2 of UNFCCC

8 See f.n. 5 9 Predicted temperature increases are based on estimates of the amount of greenhouse gases in the atmosphere in the years to come. The IPCC AR4 referred to the Special Report on Emissions Scenarios (SRES) while the IPCC AR5 refers to Representative Concentration Pathways (RCP). 10 See f.n. 5. 11 See f.n. 5 12 13 14 See f.n. 5


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