Actors can be (i) individuals and households whose personal decisions and actions (as consumers, prosumers, citizens) impact products/services/energy and resources; (ii) civil society, non-governmental organizations (NGOs), and social movements; and (iii) business firms, the financial sector, and professional organizations, who shape and incentivize technological and social innovation and the behavior of professional actors (Roy et al., 2012; Creutzig et al., 2022b). Transformation to climate-resilient cities requires a massive effort by all agents, from individuals to social entities.

Individual differences in climate risk perception and motivation to change behavior suggest the need for segmentation in the way different individuals or groups are targeted in information or climate action campaigns, with age, education, political values, and personal experience being important segmentation variables. Collective action by individuals as part of formal social movements or informal lifestyle change can significantly impact climate mitigation and adaptation. Movements that shift social norms can produce tipping points toward new lifestyles (Niamir et al., 2020; Otto et al., 2020). Community initiatives involve collective action by civil society, typically local residents and community groups. Such initiatives can help with climate mitigation to improve energy efficiency, shifts to renewable energy and to reduce fuel poverty through collective ownership, benefit and control over decision-making. They are also important for climate adaptation to create opportunities for expanding existing skills among participants, e.g., leadership, finance, management as well as knowledge. In addition, communities of building managers, landlords, energy advisers, technology installers and car dealers influence patterns of mobility and shelter and the associated energy consumption by acting as middle actors in the provision of services. Business firms, financial markets, insurance agencies, and professionals and their organizations also have a role to play in climate change mitigation and adaptation and enhancing resilience. To achieve climate-resilient cities equitably, social change, addressing social practices and ways of organizing and challenging dominant norms and beliefs, is needed. Social innovation, whereby new combinations of social practices, which cope with human needs and problems better than existing practices, offers novel approaches to ecological crises that differ from traditional technology-based solutions and demonstrates the relevance of sustainable behavioral and lifestyle changes (Mont et al., 2014; Pel et al., 2020; Haskell et al., 2021).

Examples in the literature that explore the role such actors have played in a transition to more climate-resilient coastal cities include an empirical investigation of variations in factors shaping households' adaptations to flooding, the costliest hazard worldwide (Noll et al., 2022). The authors of this work discuss how social influence, worry, climate change beliefs, self-efficacy, and perceived costs exhibit universal effects on household adaptations, despite contextual differences. Thus, they argue that to see prompt household adaptation behavior, personalized narratives should complement the communication of climate-driven risks. Other work has explored the potential of social innovation and its relation to individual behavioral change and governance to transform urban green spaces in Groningen and London (Spijker and Parra, 2018). This study concluded that social innovations can have various positive impacts on the urban landscape and human wellbeing, empower people in their quest for new values in urban space, turn neglected spots into places with meaning, and connect the individual with the urban. Thus a transition to climate-resilient coastal cities requires a focus on multi-actor governance and collaboration, often with a focus on citizens and inclusion of grassroots initiatives, both through bottom-up and top-down processes and their combinations (see also the section on institutions).

Climate change discloses fault lines of poverty, inequality, weak governance, and inadequate infrastructure. Conversely, studies show that inclusive governance and institutional capacity are key enablers for cities to adapt to and mitigate climate change. Policy contributes to shaping demand for services, travel and mobility, and given the range of activities, the policy agenda involves reaching out to a wide range of actors that includes practitioners and the general public. Therefore, a systematic deployment of effective regulatory and enforcement frameworks is required, which consists of regulations, market-based instruments, information-based instruments, and voluntary agreements at various governance levels to address a wide range of stakeholders and their concerns.

A growing literature recognizes the importance of aligning adaptation planning with overall city development and the significant potential co-benefits with climate mitigation actions (Thornbush et al., 2013; Lee et al., 2020; Boyd et al., 2022). Yet, this research also reveals the considerable barriers to mainstreaming a focus on climate mitigation co-benefits in city adaptation, development, and resilience planning. There are, however, significant benefits to redesigning policies to harness synergies across actions adaptive to support current needs, that mitigate to avoid future adaptation needs, and build resilience by taking a proactive human-centered, longer time-horizon, and iterative learning systems perspective. Recent literature highlights successful coastal city cases, e.g., Durban, Cape Town, London, and Vancouver, where synergistic and strategic adaptation and mitigation planning could deliver near-term benefits (Boyd et al., 2022). In addition, examples from research presented in the previous section (e.g., cooperative projects in Vienna, Helsinki, Amsterdam, and Copenhagen) showcase important ways in which this is being achieved and suggest that efforts to enhance such initiatives more widely would be worthwhile. In particular, to secure liveable and climate-resilient coastal cities, inclusive, equitable and actor-orientation in policies is needed. This includes individual and collective behavioral and lifestyle changes, political commitment, inclusive governance and integration across actors and sectors. Strengthening adaptation measures benefits vulnerable coastal cities and can reduce -but not eliminate all- losses and damages. At the same time, mitigation actions benefit from avoiding future damages and reduce future adaptation costs but entail higher up-front investment costs. Resilience planning strives to transform coastal cities and raise their ability to respond systemically and dynamically to present and future shocks and global challenges including unsustainable development patterns, rapid and ad hoc urbanization, climate change, and inequalities (Brunetta and Caldarice, 2020). Forging synergies among adaptation, mitigation and resilience planning can benefit from actor-oriented approaches in addition to the traditional focus on infrastructures and technologies.

Much of the research discussed here emphasizes the critical role of the governance context for coastal cities. Addressing climate change and improving human wellbeing requires an inclusive, equitable and all-of-society approach. Studies show that national policies together with solid institutions—which empower multi-scalar governance and local-level initiatives—enable coastal cities to take action. Several governments have been investing in this system and strongly rely on their recommendation, namely, the London Climate Change Committee and the Trusted Advocates project in Seattle. The choices and actions we take now will have impacts for thousands of years. Multi-level governance and effective institutions can enable mitigation and adaptation strategies by prioritizing inclusive decision-making, enhancing equitable access to finance, infrastructure and technology, setting targets and priorities, and mainstreaming climate actions across sectors and actors. Immediate transitions across all sectors and systems that prioritize equity, social justice, and inclusion are needed to achieve mitigation and adaptation outcomes that shift pathways toward climate-resilient cities. While climate policy support is influenced by actors in civil society, business, youth, women, indigenous people, and local communities, policy effectiveness is enhanced by and requires political commitments, national and international partnerships, and cooperation.