Estimates of changes in the frequency or height of contemporary extreme sea levels (ESLs) under various climate change scenarios are often used by climate and sea level scientists to help communicate the physical basis for societal concern regarding sea-level rise. Changes in ESLs (i.e., the hazard) are often represented using various metrics and indicators that, when anchored to salient impacts on human systems and the natural environment, provide useful information to policy makers, stakeholders, and the general public. While changes in hazards are often anchored to impacts at local scales, aggregate global summary metrics generally lack the context of local exposure and vulnerability that facilitates translating hazards into impacts. Contextualizing changes in hazards is also needed when communicating the timing of when projected ESL frequencies cross critical thresholds, such as the year in which ESLs higher than the design height benchmark of protective infrastructure (e.g., the 100-yr water level) are expected to occur within the lifetime of that infrastructure. We present specific examples demonstrating the need for such contextualization using a simple flood exposure model, local sea-level rise projections, and population exposure estimates for 414 global cities. We suggest regional and global climate assessment reports integrate global, regional, and local perspectives on coastal risk to address hazard, vulnerability and exposure simultaneously.

Coastal climate adaptation public works, such as storm surge barriers and levees, are central elements of many strategies to limit damages from coastal storms and sea-level rise. Academic analysis of such public works projects is dominated by technocratic and engineering-driven frameworks. However, social conflict and politics have been crucial in the conception, design, and implementation of other public infrastructure and natural hazard preparedness projects. In this review, we highlight the role of interest mobilization, political motivations, siting opposition, and flexible/adaptive decision-making in both creating and overcoming political obstacles. Better understanding the social and political factors that enable or hinder the implementation of adaptation works could encourage strategies and policies that are less likely to result in deadlocks, delays, or failure, thus saving valuable time and planning resources.

Storm surge barriers, levees, and other coastal flood defense megaprojects are currently being proposed as strategies to protect several U.S. cities against coastal storms and rising sea levels. However, social conflict and other political factors add a layer of complexity that casts doubt on their status as practical climate adaptation options. The specific mechanisms for why some projects do not progress beyond initial planning stages has remained unclear. Here we study the outcome of two U.S. Army Corps of Engineer (USACE) storm surge barrier proposals to explore the political reasons why some coastal flood protection megaprojects break ground in the U.S., while others do not. Using original archive research, we conclude that storm surge barriers are politically challenging climate adaptation options because of 1) modern environmental laws that provide avenues for expression of oppositional views within the decision process and 2) the allure of alternative options that are more aesthetically pleasing and cheaper and faster to implement. To better allocate public resources and the expertise of the USACE, future flood protection megaprojects should first achieve broad support from the public, NGOs, and elected officials before beginning serious planning. This support could be achieved through new innovative designs that simultaneously address adverse environmental impacts and provide co-benefits (e.g., recreation). New designs should be studied to better understand the level of protection offered and associated reliability so that the USACE has confidence in their use.