The Earth’s climate is strongly affected by the partitioning of carbon between its mobile reservoirs, primarily between the atmosphere and the ocean. The distribution between the reservoirs is being massively perturbed by human activities, primarily due to fossil fuel emissions, with a range of consequences, including ocean warming and acidification, sea-level rise and coastal erosion, and changes in ocean productivity. These changes directly impact valuable habitats in many coastal regions and threaten the important services the habitats provide to mankind. Among the most productive and diverse systems are coral reefs and vegetated habitats, including saltmarshes, seagrass meadows, and mangroves. Coral reefs are particularly vulnerable to ocean warming and acidification. Vegetated habitats are receiving heightened attention for their ability to sequester carbon, but they are being impacted by land-use change, sea-level rise, and climate change. Overall, coasts play an important, but poorly quantified, role in the global cycling of carbon. Carbon reservoirs on land and in the ocean are connected through the so-called land–ocean aquatic continuum, which includes rivers, estuaries, and the coastal ocean. Terrestrial carbon from soils and rocks enters this continuum via inland water networks and is subject to transformations and exchanges with the atmosphere and sediments during its journey along the aquatic continuum. The expansive permafrost regions, comprised of ground on land and in the seabed that has been frozen for many years, are of increasing concern because they store vast amounts of carbon that is being mobilized due to warming. Quantitative estimates of these transformations and exchanges are relatively uncertain, in large part because the systems are diverse and the fluxes are highly variable in space and time, making observation at the necessary spatial and temporal coverage challenging. But despite their uncertainty, existing estimates point to an important role of these systems in global carbon cycling.
Katja Fennel, Tyler Cyronak, Michael DeGrandpre, David T. Ho, Goulven G. Laruelle, Damien Maher, and Julia Moriarty
Hans von Storch, Katja Fennel, Jürgen Jensen, Kristy A. Lewis, Beate Ratter, Torsten Schlurmann, Thomas Wahl, and Wenyan Zhang
Coasts are those regions of the world where the land has an impact on the state of the sea, and that part of the land is in turn affected by the sea. This land–sea interaction may take various forms—geophysical, biological, chemical, sociocultural, and economic. Coasts are conditioned by specific regional conditions. These unique characteristics result, in heavily fragmented regional and disciplinary research agendas, among them geographers, meteorologists, oceanographers, coastal engineers, and a variety of social and cultural sciences. Coasts are regions where the effects and risks of climate impact societal and ecological life. Such occurrences as coastal flooding, storms, saltwater intrusion, invasive species, declining fish stocks, and coastal retreat and morphological change are challenging natural resource managers and local governments to mitigate these impacts. Societies are confronted with the challenge of dealing with these changes and hazards by developing appropriate cultural practices and technical measures. Key aspects and concepts of these dimensions are presented here and will be examined in more detail in the future to expand on their characteristics and significance.
Wenyan Zhang and Peter Arlinghaus
Coastal morphology refers to the morphology and morphological development of the coast in response to a combined influence of atmospheric, oceanic and anthropogenic forcing. Coastal morphology comprises a wide variety of landforms (exposed to air) and bedforms (submerged in water) manifested in a large spectrum of spatial scales (10−2–105 m scale) and shapes ranging from mildly sloping lower shoreface to steep cliffs, from small ripples to large river deltas. Coastal zones are cradles for life. About 40% of the global human population and 50% of marine life are living in low-lying coastal zones with elevation less than 10 m above the mean sea level. Coasts contain the highest biodiversity in the surface earth system yet are highly vulnerable to environmental stressors associated with human activities and climate change. Climate impacts coastal morphology in multiple ways, including ice cover/melting, precipitation, temperature, and wind. In response to a changing climate, adaptation of coastal morphology can be categorized into three basic states: erosional, stable, and accretionary. Each state may persist or iterate at any given part of a coast, even in the context of a persistently warming or cooling climate. Anthropogenic protection has been globally implemented to ease erosion and protect human property. However, it remains largely unknown whether the existing measures would be able to counteract the effects of climate change in the upcoming decades.
Beate Ratter and Catherine Leyshon
Coasts are dynamic places operated on by powerful natural and human forces. They are also historically attractive places for human settlement and use, with a still constantly growing concentration of people due to increased population growth and migration toward the coast. Coastal societies historically have evolved and developed culturally embedded relationships with their environment, which have resulted in different cultural settings, influencing the way they experience and react toward climate change impacts in their lifeworld. Coastal risks are specific to different regional, natural, and societal settings and can be distinguished between slow-onset (e.g., sea level rise or ocean acidification) and sudden extreme events (e.g., tropical cyclones or storm surges). Coastal climate risks come from flooding, storms, storm surges, saltwater intrusion, invasive species, declining fish stocks or shifting species’ regimes, coral bleaching, coastal erosion, and morphological change. For centuries, coastal societies have learned to defend the coast against threats from the sea with a broad range of technical measures based on a long history of trial and error, with successes and failures. Further, for centuries, littoral societies have constructed coasts and infrastructure according to their interests and needs (e.g., engineering the coastline, installing coastal defenses, constructing harbor and landing infrastructures, and even claiming land from the sea). Risks at the coast have always been there—but are exacerbated by climate change. A more integrated and transdisciplinary approach to understanding coastal climate risks is required, in keeping with the characterization of climate change as a wicked problem. The ways in which individuals, societies, and politics respond to climate change are in many cases contingent on perceptions of its causes, consequences, and wider implications. To study climate change impacts, therefore, an improved understand is required of the place-specific perception of coast and of coastal climate risks. These perceptions, along with other influencing factors, such as economic interests and politics, will inform the societal resilience and response of a coastal community. Resilience—understood as people’s ability to respond adequately to shocks and stressors—is place-dependent and closely connected to historic experiences and learning processes in dealing with hazards as well as the existing political and institutional arrangements that underpin governance structures. Resilience does not simply reflect the expected effects of quantifiable factors such as level of assets, or even less quantifiable social processes such as people’s experience, but is also determined by more subjective dimensions related to people’s perceptions of their ability to cope, adapt, or transform in the face of adverse events. Based on the existing place-specific experience of the littoral society, with its liminal environment and development, adaptation strategies and policies for the future need to be developed between the extremes of “living with” and “making way for” coastal and climate changes. Against this background, climate change adaptation (CCA) strategies have to be integrated and merged with disaster risk reduction (DRR) challenges, based on the integration of multiple interests in a transdisciplinary way. Societal risk construction and negotiation are crucial elements of integrative risk management, requiring participative, transparent, and flexible processes for the implementation of discursive practices and—in extreme situations—the transformation of governance structures. To understand and evaluate climate change adaptation strategies and measures along the coastline, climate change impacts threatening coastal livelihoods have to be understood alongside the societal frames of CCA policies. The capacity to adapt to changing conditions is based on the ability to develop new risk cultures and the flexibility to transition by (a) developing new norms, practices, and material culture; (b) resisting the lock-ins from routines and habits; and (c) guiding changes through scrutinizing new options or creating technocultural niches that favor certain technologies over others. Adaptive capacity in coastal societies plays an important role in dealing with coastal climate risks. The focal questions are the following: Which societal frames of climate change perception precondition adaptation? Which risks are perceived? Which cultural and political barriers hinder successful adaptation? How can DRR be integrated in CCA endeavors and future climate-resilient and sustainable pathways?
Thomas Wahl and Sönke Dangendorf
Sea level rise leads to an increase in coastal flooding risk for coastal communities throughout the world. Changes in mean sea level are caused by a combination of human-induced global warming and natural variability and are not uniform throughout the world. The key processes leading to mean sea level rise and its variability in space and time are the melting of land-based ice and changes in the hydrological cycle; thermal expansion due to warming oceans; changes in winds, ocean currents, and atmospheric pressure; and, when focusing on the relative changes between the land and the ocean, any vertical motion of the land itself (subsidence or uplift). In addition to the change in mean sea level, which is the main climatic driver for changes in coastal flooding risk in most regions, additional changes in tides, storm surges, or waves can further exacerbate, or offset, the negative effects of mean sea level rise. Hence, it is important to analyze, understand, and ultimately project the changes in all of these sea level components individually and combined, including the complex interactions between them. Advances in sea level science in the 21st century along with new and extended observational records including in situ and remote sensing measurements have paved the path to being able to provide better and more localized information to stakeholders, particularly in the context of making decisions about coastal adaptation to protect the prosperity of coastal communities and ecosystems.