Coastal vegetated habitats can be important sinks of organic carbon (Corg) and mitigate global warming by sequestering significant quantities of atmospheric CO2 and storing sedimentary Corg for long periods, although their Corg burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published 210Pb-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100 years) of Corg concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and δ13C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, Corg concentrations (0.2–30%), stocks (30–465 Mg ha−1, by extrapolation to 1 m depth), and burial rates (3–378 g m−2 year−1) varied widely within and among the study areas. However, in most sites sea level rise decreased Corg concentrations and stocks in sediments, but increased Corgburial rates. Lower Corg concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of Corg than terrigenous sediments; whereas higher Corg burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. Corg accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of Corg stocks by ongoing sea level rise, the disturbance of the long-term buried Corg inventories might cause high CO2 releases, for which they must be protected as a part of climate change mitigation efforts.
Sea-level Rise, Coastal Flooding, and Storm Events
Sea-level rise is a major consequence of climate change that will continue long after emissions of greenhouse gases have stopped. The 2015 Paris Agreement aims at reducing climate-related risks by reducing greenhouse gas emissions to net zero and limiting global-mean temperature increase. Here we quantify the effect of these constraints on global sea-level rise until 2300, including Antarctic ice-sheet instabilities. We estimate median sea-level rise between 0.7 and 1.2 m, if net-zero greenhouse gas emissions are sustained until 2300, varying with the pathway of emissions during this century. Temperature stabilization below 2 °C is insufficient to hold median sea-level rise until 2300 below 1.5 m. We find that each 5-year delay in near-term peaking of CO2 emissions increases median year 2300 sea-level rise estimates by ca. 0.2 m, and extreme sea-level rise estimates at the 95th percentile by up to 1 m. Our results underline the importance of near-term mitigation action for limiting long-term sea-level rise risks.
Tidal response to sea-level rise (SLR) varies in different coastal systems. To provide a generic pattern of tidal response to SLR, a systematic investigation was conducted using numerical techniques applied to idealized and realistic estuaries, with model results cross-checked by analytical solutions. Our results reveal that the response of tidal range to SLR is nonlinear, spatially heterogeneous, and highly affected by the length and bathymetry of an estuary and weakly affected by the estuary convergence with an exception of strong convergence. Contrary to the common assumption that SLR leads to a weakened bottom friction, resulting in increased tidal amplitude, we demonstrate that tidal range is likely to decrease in short estuaries and in estuaries with a narrow channel and large low-lying shallow areas.
Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93–243 cm) and RCP 2.6 (26–98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.
Plain Language Summary
Recent ice-sheet modeling papers have introduced new physical mechanisms—specifically the hydrofracturing of ice shelves and the collapse of ice cliffs—that can rapidly increase ice-sheet mass loss from a marine-based ice-sheet, as exists in much of Antarctica. This paper links new Antarctic model results into a sea-level rise projection framework to examine their influence on global and regional sea-level rise projections and their associated uncertainties, the potential impact of projected sea-level rise on areas currently occupied by human populations, and the implications of these projections for the ability to constrain future changes from present observations. Under a high greenhouse gas emission future, these new physical processes increase median projected 21st century GMSL rise from ∼80 to ∼150 cm. Revised median RSL projections for a high-emissions future would, without protective measures, by 2100 submerge land currently home to more than 153 million people. The use of a physical model indicates that emissions matter more for 21st century sea-level change than previous projections showed. Moreover, there is little correlation between the contribution of Antarctic to sea-level rise by 2050 and its contribution in 2100 and beyond, so current sea-level observations cannot exclude future extreme outcomes.
Coastal communities around the world face challenges in planning for coastal flooding and sea-level rise related to climate change. This paper develops an approach for identifying typologies of communities on the basis of their hazard vulnerability characteristics. The approach first characterizes communities with a suite of vulnerability indicators, selected to meet criteria of breadth, relevance, and data requirements. Cluster analysis is then applied to the indicator profiles to identify groups of similar communities. The statistical centrotype of each group represents the corresponding community type. A new community from outside the original set can then be matched to the typology using a Hazard Vulnerability Similarity Index (HVSI). The approach is demonstrated with a case study of 50 communities on Canada's Pacific coast. Results yielded 10 community types, of which four were predominant. The types range from highly urbanized, wealthier, diverse central cities to remote, resource-dependent towns with semi-developed, flat coastlines. Three selected communities from a distant region, in Atlantic Canada, were then successfully matched to the most similar of these 10 types. Identifying groups of communities that share vulnerability profiles can facilitate sharing knowledge, lessons, and resources that are most relevant to local efforts to reduce natural hazard risk. This support may be especially valuable for connecting communities that are unfamiliar with one another, yet similarly vulnerable.
Rising seas will impact millions of coastal residents in coming decades. The vulnerability of coastal populations exposed to inundation will be greater for some sub-populations due to differences in their socio-demographic characteristics. Many climate risk and vulnerability assessments, however, model current populations against future environments. We advance sea-level rise risk assessments by dynamically modeling environmental change and socio-demographic change. We project three scenarios of inundation exposure due to future sea-level rise in coastal Georgia from 2010 to 2050. We align the sea-level rise projections with five population projection scenarios of socially vulnerable sub-populations via the Hamilton-Perry method and the theory of demographic metabolism. Our combined fast sea-level rise and middle population scenarios project a near doubling of the population exposed, and a more than five-fold increase for those at risk (i.e., residing in a census tract with high social vulnerability) and most at risk (i.e., high social vulnerability and high exposure) compared to the same estimate based on 2010 population data. Of vulnerable sub-populations, women had the largest absolute increase in exposure for all scenario combinations. The Hispanic/Latinx population's exposure increased the largest proportionally under the fast and medium sea-level rise projections and elderly people's (65+) under the slow sea-level rise scenario. Our findings suggest that for coastal areas experiencing rapid growth (or declines) in more socially vulnerable sub-populations, estimates based on current population data are likely to underestimate (or overestimate) the proportion of such groups' risk to inundation from future sea-level rise.
Spatial planning is expected to facilitate climate change adaptation by directing future spatial and infrastructure developments away from zones that are exposed to climate-related hazards. This study attempts to confirm this understanding by mapping the effects of the various spatial plans on the northern coast of Java, Indonesia. First, the study maps the extent of coastal hazards for the baseline year of 2010 using a GIS-based inundation model. An overlay in GIS demonstrates the influence of spatial plans for the projection year of 2030. This allows for calculating the economic losses of the planned developments. The case study shows that the current provincial spatial plans direct land use conversions along the northern coast of Java to continue to occur in the future. This could significantly decrease the regional capacity in dealing with the exposure to coastal inundation. The analysis also demonstrates that a total area of 55,220 ha of land prone to inundation, consisting of protected area (1488 ha), fishponds (32,916 ha) and agricultural land (20,814 ha), is planned to be converted into industry (13,399 ha) and settlements (41,821 ha). Thus, these areas will be also prone to inundation in 2030. This change would potentially lead to an economic loss of 246.6 billion USD. The spatial plans issued by the national and provincial governments for regulating the future land use on the northern coast of Java have not integrated measures against hazards related to global sea level rise. Meanwhile, many existing developments have already been affected by coastal inundation. Rather than reducing the exposure towards coastal flood hazards, the case study shows that spatial plans could even increase the risk of climate-related hazards and cause higher economic losses. These findings provide a different perspective on the role of spatial planning for climate change adaptation than what is stated in the literature.
This chapter includes an assessment of physical vulnerability of the coast, including a coastal vulnerability index composed of 9 physical variables—elevation, distance to shore, tide amplitude, significant wave weight, erosion/accretion rates, geology, geomorphology, ground cover vegetation, and anthropogenic actions—followed by a quantification of coastal recession and the data of special report on emissions scenarios (SRES) developed by the Intergovernmental Panel on Climate Change (IPCC) on the rise in average sea level. It includes an estimate of the economic value of an area of recreation based on the travel cost method. Finally, a bibliographic review is made to assess strategies and responses to the impacts of sea level rise in order to make comparisons and to develop a road map of interventions for shoreline protection. The proposed methodology was applied to a case study on the Portuguese coast corresponding to the beaches of Costa de Caparica, Almada.
The impact of changing climate on terrestrial and underwater archaeological sites, historic buildings, and cultural landscapes can be examined through quantitatively-based analyses encompassing large data samples and broad geographic and temporal scales. The Digital Index of North American Archaeology (DINAA) is a multi-institutional collaboration that allows researchers online access to linked heritage data from multiple sources and data sets. The effects of sea-level rise and concomitant human population relocation is examined using a sample from nine states encompassing much of the Gulf and Atlantic coasts of the southeastern United States. A 1 m rise in sea-level will result in the loss of over >13,000 recorded historic and prehistoric archaeological sites, as well as over 1000 locations currently eligible for inclusion on the National Register of Historic Places (NRHP), encompassing archaeological sites, standing structures, and other cultural properties. These numbers increase substantially with each additional 1 m rise in sea level, with >32,000 archaeological sites and >2400 NRHP properties lost should a 5 m rise occur. Many more unrecorded archaeological and historic sites will also be lost as large areas of the landscape are flooded. The displacement of millions of people due to rising seas will cause additional impacts where these populations resettle. Sea level rise will thus result in the loss of much of the record of human habitation of the coastal margin in the Southeast within the next one to two centuries, and the numbers indicate the magnitude of the impact on the archaeological record globally. Construction of large linked data sets is essential to developing procedures for sampling, triage, and mitigation of these impacts.
Feedbacks among inundation, sediment trapping, and vegetation productivity help maintain coastal wetlands facing sea-level rise (SLR). However, when the SLR rate exceeds a threshold, coastal wetlands can collapse. Understanding the threshold helps address key challenges in ecology—nonlinear response of ecosystems to environmental change, promotes communication between ecologists and resource managers, and facilitates decision-making in climate change policies. We studied the threshold of SLR rate and developed a new threshold of SLR acceleration rate on sustainability of coastal wetlands as SLR is likely to accelerate due to enhanced anthropogenic forces. Deriving these two thresholds depends on the temporal scale, the interaction of SLR with other environmental factors, and landscape metrics, which have not been fully accounted for before this study. We chose a representative marine-dominated estuary in the northern Gulf of Mexico, Grand Bay in Mississippi, to test the concept of SLR thresholds. We developed a mechanistic model to simulate wetland change and then derived the SLR thresholds for Grand Bay. The model results show that the threshold of SLR rate in Grand Bay is 11.9 mm/year for 2050, and it drops to 8.4 mm/year for 2100 using total wetland area as a landscape metric. The corresponding SLR acceleration rate thresholds are 3.02 × 10−4 m/year2and 9.62 × 10−5 m/year2 for 2050 and 2100, respectively. The newly developed SLR acceleration rate threshold can help quantify the temporal lag before the rapid decline in wetland area becomes evident after the SLR rate threshold is exceeded, and cumulative SLR a wetland can adapt to under the SLR acceleration scenarios. Based on the thresholds, SLR that will adversely impact the coastal wetlands in Grand Bay by 2100 will fall within the likely range of SLR under a high warming scenario (RCP8.5), highlighting the need to avoid RCP8.5 to preserve these marshes.