Editing IPCC:AR6/WGII/Cross-Chapter-Paper-2 (section)

== Frequently Asked Questions ==

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=== FAQ CCP2.1 | Why are coastal cities and settlements by the sea especially at risk in a changing climate, and which cities are most at risk? ===

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''Coastal cities and settlements (C&amp;S) by the sea face a much greater risk than comparable inland C&amp;S because they concentrate a large proportion of the global population and economic activity, whilst being exposed and vulnerable to a range of climate- and ocean-compounded hazard risks driven by climate change. Coastal C&amp;S range from small settlements along waterways and estuaries, to small island states with maritime populations and/or beaches and atolls that are major tourist attractions, large cities that are major transport and financial hubs in coastal deltas, to megacities and even megaregions with several coastal megacities.''

The concentration of people, economic activity and infrastructure dynamically interacts with coast-specific hazards to magnify the exposure of these C&amp;S to climate risks. While large inland cities and coastal settlements can be exposed to climate-driven hazards, such as urban heat islands and air pollution, the latter are also subject to distinctive ocean-driven hazards, such as sea level rise (SLR), exposure to tropical cyclones and storm surges, flooding from extreme tides and land subsidence from decreased sediment deposition along coastal deltas and estuaries. With climate change increasing, the intensity and frequency of hazards under all future warming levels and thus the risks to lives, livelihoods and property are especially acute in C&amp;S by the sea.

Coastal cities are diverse in shape, size, growth patterns and trajectories, and in terms of access to cultural, financial and ecosystem resources and services. Along deltaic and estuarine archetypes, cities most vulnerable to a changing climate have relatively high levels of poverty and inequality in terms of access to resources and ecosystem services, with large populations and dense built environments translating into higher exposure to coastal climate risks.

These climate risks at the coast can also be magnified by compounding and cascading effects due to non-climate drivers directly affecting vulnerable peri- and ex-urban areas inland. These risks include disruption to transport supply chains and energy infrastructure from airports and power plants sited along the coastline, as occurred in New York City, USA, during Hurricane Sandy in 2012. The impacts can be felt around the world through globalised economic and geopolitical linkages, for example through maritime trade and port linkages.

For open coasts, settlements on low-lying small island states and the Arctic are especially vulnerable to climate change, and SLR impacts in particular, well before 2100. While the economic risks may not compare to the scale of those faced in coastal megacities with high per capita GDP, the existential risks to some nations and an array of distinctive livelihoods, cultural heritage and ways of life in these settlements are great, even with modest SLR.

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=== FAQ CCP2.2 | What actions can be taken by coastal cities and settlements to reduce climate change risk? ===

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''Sea level rise (SLR) responds to climate change over long timeframes and will continue even after successful mitigation. However, rapid global mitigation of greenhouse gases significantly reduces risks to coastal cities and settlements (C&amp;S), and, crucially, buys time for adaptation.''

Appropriate actions to reduce climate change risks in coastal C&amp;S depend on the scale and speed of coastal change interacting with unfolding local circumstances, reflecting the hazards, exposure, vulnerability and response to risks.

‘Hard’ protection, like dikes and seawalls, can reduce the risk of flooding for several metres of SLR in some coastal C&amp;S. These are most cost effective for densely populated cities and some islands, but may be unaffordable for poorer regions. Although these measures reduce the likelihood of coastal flooding, residual risk remains, and hard protection typically has negative consequences for natural systems. In low-lying protected coastal zones, draining river and excess water will increasingly be hampered, eventually requiring pumping or transferring to alternative strategies.

Whereas structures can disrupt natural beach morphology processes, sediment-based protection replenishes beaches. These have lower impact on adjacent beaches and coastal ecology and lower costs for construction and maintenance compared to hard structures. Another form of ‘soft’ protection involves establishing, rehabilitating and preserving coastal ecosystems, like marshes, mangroves, seagrass, coral reefs and dunes, providing ‘soft’ protection against storm surges, reducing coastal erosion and offering additional benefits including food, materials and carbon sequestration. However, these are less effective where there is limited space in the coastal zone, limited sediment supply and under higher rates of SLR.

Coastal settlements can ‘avoid’ new flood and erosion risks by preventing development in areas exposed to current and future coastal hazards. Where development already exists, settlements can ‘accommodate’ climate change impacts through, among other things, land-use zoning, raising ground or buildings above storm surge levels, installing flood-proofing measures within and outside properties, and early warning systems. Improving the capacity of urban drainage, incorporating nature-based solutions within urban areas and managing land upstream of settlements to reduce runoff from the hinterland reduces the risk of compound flood events. More radically, land can also be reclaimed from the sea, which offers opportunities for further development but has impacts on the natural system and wider implications for the trajectory of development.

Coastal risks and impacts such as floods, loss of fisheries or tourism, or salinization of groundwater require people to change behaviour to adapt, such as diversifying livelihoods or moving away from low-lying areas. Currently, most of these practices are reactive and help people adjust to/cope with current impacts. While a critical part of coastal adaptation, changing behaviour can be enabled by supportive policies and financial structures aligned with sociocultural values and worldviews.

Where risks are very high or resources are insufficient to manage risks, submergence or erosion of coastal C&amp;S will be inevitable, requiring ‘retreat’ from the coastline. This is the outlook for millions of people in the coming decades, including those living in river deltas, Arctic communities, small islands and low-lying small settlements in poor and wealthy nations. Whilst the impacts of retreat on communities can be devastating, the prospect of many C&amp;S and even whole nations being permanently inundated in the coming centuries underscores the imperative for urgent action.

Crucial to making choices about how to mitigate greenhouse gas emissions and adapt to climate change in coastal C&amp;S is to establish institutions and governance practices supporting climate resilient development—a mix and sequence of mitigation and adaptation actions—that are fair, just and inclusive as well as technically and economically effective across successive generations.

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=== FAQ CCP2.3 | Considering the wide-ranging and interconnected climate and development challenges coastal cities and settlements face, how can more climate resilient development pathways be enabled? ===

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''Coastal cities and settlements (C&amp;S) are on the frontline of the climate change challenge. They are the interface of three interconnected realities. First, they are critical nodes of global trade, economic activity and coast-dependent livelihoods, all of which are highly and increasingly exposed to climate- and ocean-driven hazards (FAQ CCP2.1). Second, coastal C&amp;S are also sites where some of the most pressing development challenges are at play (e.g., trade-offs between expanding critical built infrastructure while protecting coastal ecosystems, high economic growth coupled with high inequality in some coastal megacities). Third, coastal C&amp;S are also centres of innovation and creativity, thus presenting a tremendous opportunity for climate action through a range of infrastructural, nature-based, institutional and behavioural solutions (FAQ CCP2.2). Given these three realities of high climate change risks, rapid but contested and unequal development trajectories, and high potential for innovative climate action, C&amp;S are key to charting pathways for climate resilient development (CRD).''

Three key levers can enable pathways that are climate resilient and meet goals of inclusive, sustainable development. One key enabler involves flexible, proactive, and transparent governance systems, built on a bedrock of accountable local leadership, evidence-based decision-making—even under uncertainty—and inclusive institutions that consider different stakeholder voices and knowledge systems. Another key enabler is acknowledging the sociocultural and psychological barriers to climate action and incentivising people to change to lifestyles and behaviours that are pro-climate and aligned with community-oriented values and norms. In practice, coastal C&amp;S are experimenting with different strategies to change practices and behaviours, such as using subsidies and zoning policies, tax rebates and public awareness campaigns to promote individual and collective action. Finally, enabling CRD needs dedicated short- and long-term financing to reorient current trajectories of unsustainable and unequal development towards climate mitigation and adaptation action that reduces current and predicted losses and damages, especially in highly vulnerable coasts such as the small island states, the Arctic and low-lying C&amp;S. Currently, adaptation finance is concentrated in coastal megacities and tends to be deployed for risk-proofing high-value waterfront properties or key infrastructures. Addressing these financial imbalances (globally, regionally and sub-nationally) remains a critical barrier to inclusive climate resilient coastal development.

Notwithstanding the many interconnected challenges faced, from more frequent and intense extreme events to the COVID-19 pandemic, many coastal C&amp;S are experimenting with ways to pivot towards CRD. Critical enablers have been identified and lesson learned, which, if translated into practice, will enhance the prospects for advancing the SDGs and charting pathways for CRD that are appropriate to local contexts and foster human well-being and planetary health.

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