Climate change is undoubtedly the biggest challenge of this century, with consequences for our global ecosystems, fauna and flora species, human settlements, and economies. Effects of climate change can already be observed worldwide and are likely to increase, with more droughts, wildfires, heatwaves, storms, floods, ice melting, sea level rise, ocean acidification, loss of biodiversity and habitats [1; 2; 3].
Rising sea levels and associated flooding are risks most commonly associated with global warming. Studies have proven a strong link between the concentration of greenhouse gases in the atmosphere, the global mean temperature and the global mean sea level, with evidence dating back circa 800 thousand years before present (Fig. 1.a and 1.b) [4; 5; 6].
The sharp increase in greenhouse gases concentration in the atmosphere since the industrial revolution has been proven to be the main cause of the recent rise in the global mean temperature and, consequently, in rising sea levels [1; 4; 6; 7]. Human activities are estimated to have already caused approximately 1.0°C of global warming above pre-industrial levels, and global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate .
There is a scientific consensus of the need to limit the global mean temperature below 2.0°C above pre-industrial levels (the baseline scenario) to avoid the worst climate change scenario, and this target can only be achieved if the human civilisation reaches a net zero emissions by 2100 or earlier . However, according to the recently published Emissions Gap Report 2020 , the world is still heading for a temperature rise in excess of 3°C this century — far beyond the Paris Agreement goals of limiting global warming to well below 2°C and pursuing 1.5°C .
If the most optimistic target is achieved, there is an expectation that sea level will rise around 0.5 metres above the current level by 2100 and between 1 and 2 metres by 2300. Otherwise, if the business-as-usual scenario of emissions continues, the global mean temperature could exceed the baseline scenario in 4.0°C by 2100 leading to a rise of more than 1 metre in sea level by 2100 and more than 5 metres by 2300  — Fig. 2.
The global mean sea level rise is a consequence of both combined land-based ice melting and the thermal expansion of seawater as it warms [10; 11]. Global mean sea level has risen about 21–24 centimetres since 1880, with about a third of that occurring in just the last 25 years . From 2006–2015, global mean sea level rose by 3.6 millimetres per year, i.e., 2.5 times the average rate of 1.4 millimetres per year observed throughout most of the twentieth century . Sea level rise leads to coastal erosion, inundations, storm floods, tidal waters encroachment into estuaries and river systems, contamination of freshwater reserves and food crops, loss of nesting beaches, as well as displacement of coastal lowlands and wetlands .
Ocean warming has been linked to extreme weather events as increasing seawater temperatures provide more energy for storms that develop at sea, leading to fewer but more intense tropical cyclones globally . The gradual sea level rise added to the increased frequency of severe storms are the main causes of coastal erosion and flooding [10; 13; 14]. Considering that more than 600 million people (around 10% of the world’s population) lives in coastal areas that are less than 10 meters above sea level [12; 15], these threats will bring critical social and economic consequences for vulnerable coastal communities. Based on sea level projections for 2050, land currently home to 300 million people will fall below the elevation of an average annual coastal flood and by 2100, and 200 million people could sit permanently below the high tide line . If an instability of the Antarctic ice sheet is assumed, circa 300 million people are considered as currently living on land that is at risk .
Climate change effects can be expected along the coast of Ireland, a country with more than 7,000 km of shoreline and in which more than 50% of the country’s population lives within 15 km of the coastline , concentrated mainly in the coastal cities of Dublin, Cork, Limerick and Galway . Changes in Ireland’s climate are in line with global trends where temperatures have increased by 0.8°C between 1900 and 2011, an average of 0.07°C per decade over this period [14; 17].
Sea level rise, coastal storms and flooding represent the most immediate risks on a national basis . Rising sea levels, when combined with potential increases in levels of storminess and the increased risk of storm surges, will result in increased coastal inundation and erosion of beaches and cliffs, and degradation of coastal ecosystems [14; 17; 18].
Satellite observations indicate that the sea level around Ireland has risen by approximately 0.04–0.06 metre since the early 1990s [18; 19], with studies indicating a mean sea level rise of approximately 1.7 mm per annum (from 1916 to 2012) . Estimates indicate that approximately 350 km2 of land along the Irish coast is vulnerable to a sea level rise of 1 metre, increasing to 600 km2 to a sea level rise of 3 metres [13; 14].
A slower rate of sea level rise will enable greater opportunities for adaptation in the human and ecological systems of small islands, low-lying coastal areas and deltas . However, even if emissions decline in line with the Paris Agreement objectives , sea levels will still rise between 30 and 60 centimetres by 2100 , for this reason it is important to act immediately both in terms of mitigation and adaptation .
The Intergovernmental Panel on Climate Change (IPCC) defines adaptation as “the process of adjustment to actual or expected climate and its effects, in order to moderate harm or exploit beneficial opportunities” . Rising seas and greater storm surges will certainly impact urban economies and force hundreds of millions of people in coastal cities from their homes, with an estimated cost of more than $1 trillion each year by 2050 . The Global Commission on Adaptation states that investing $1.8 trillion globally in climate adaptation schemes over the next decade could generate $7.1 trillion in total net benefits. The World Bank estimates that an extra three per cent of adaptation investment upfront in resilient infrastructure would be offset by savings of up to four times the cost of the loss and damage that would have occurred without said investment [21; 22].
Considering the facts above mentioned, it becomes clear that adaptation measures are urgently needed and delaying such measures will only exacerbate the risks imposed by climate change. Nature-based solutions (such as the conservation and restoration of natural ecosystems) should be considered as a fundamental adaptation option once it connects adaptation and mitigation purposes. The participation of coastal communities is essential in supporting governments to find the best adaptation option accordingly to the local reality in places affected by climate change.
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