Human dimensions of sea level change

Sea level rise threatens coastal societies with a large range of socio-economic consequences, such as the reduction or loss of vital coastal ecosystem services (e.g. storm protection through mangroves), or loss of biodiversity; damage of critical infrastructure (e.g. transport and communication networks, power plants and grids, military facilities, etc) and resources along the coast; loss of human life and health impacts; forced displacement due to land-loss and storm surge risk.

Therefore, the vulnerability of coastal societies and their potential adaptive capacity to changes in sea level depends both on the magnitude of local sea level changes and on the human responses to those changes, in addition to other drivers such as socio-economic development.

Most of future climate-related, socio-economic impacts of sea level change are expected to interact with and to aggravate already existing coastal issues (Nicholls et al., 2007;Wong et al., 2014;Brown et al., 2014). Sea level change will further exacerbate coastal erosion and inundation hazards in many regions of the world (Hinkel et al., 2013), especially deltaic and low-lying coastal areas as well as small islands (e.g.Nicholls and Cazenave, 2010). Densely populated and heavily farmed delta plains and coastal low-lands will become even more vulnerable to sea level change if combined with various environmental and anthropogenically altered hydrological patterns, soil erosion, agriculture, industrial development, and urbanization, e.g. alterations in the corresponding river systems.

Socio-economically, the areas most threatened are rapidly growing coastal megacities in delta plains, such as the Asian cities of Shanghai, Hong Kong, Bangkok, Manila and Jakarta (McGranahan et al., 2007; Hallegatte et al., 2013;Yang et al., 2014). The extent of the impact will depend on the rate of sea level change and the natural response of the coastal systems, but also on the technical, economic, and political pathways which societies choose to adapt, and the interaction patterns between social agents, including conflict and cooperation.

In addition, water withdrawal, oil/gas extraction, land use change, or coastal developments directly affect relative sea level change. For small island states, the most evident problems of sea level change are coastal land inundation, submergence, and saltwater intrusion (Ratter, 2008; Fenoglio-Marc et al., 2012), calling for an integrated coastal protection against multiple risks (Link, 2014).

To address the human dimension of sea level change and to promote adequate responses, it is necessary to better understand human-environment interactions in the context of sea level rise, existing coastal issues, socio-economic and other stressors. This involves researching how coastal societies have been able to adapt to past sea level changes, e.g. in coastal cities which have subsided by several meters during the last century (Nicholls, 1995) as well as improving integrated coastal impact models to simulate future impacts under a range of adaption strategies and sea level rise scenarios.

Regional to global sea level change information need to be provided at the coastlines, including the full range of uncertainty across multiple models and assessment methods. Equally important, governments, stakeholders, and local inhabitants need to be provided with this information and tailored decision-analytical frameworks, in order to make informed decisions for future development. Largest uncertainties in coastal sea level rise projections presently originate from uncertainties in polar ice sheet dynamics, glaciers and the related mass input into the ocean, the future heat uptake and the regional response of sea level on basin to coastal scales to climate forcing.

For quantitative coastal zone management studies, respective signal and uncertainty measures have to be propagated from the large spatial scale down to coastal locations and targeted at the specific kind of decision a coastal manager is facing. Coastal sea level projection studies are truly global and interconnected problems, and require investigating sea level on multiple space and time scales in conjunction with an analysis of the requirements from local coastal risk management. When talking about local sea level change, we must take into account that even human interventions may dramatically change the sea level locally, with severe impacts for coastal communities. This has to be taken into account when planning for future.