To date, there exists considerable guidance on actions in some sectors where benefits exceed costs, though guidance is lacking in many other sectors.83 Benefit–cost information exists for adaptation responses to storms and rising seas in coastal zones, to riverine and extreme precipitation flooding, and for agriculture at the farm level.85,86 Some of the actions in these sectors, at least in some locations, appear to have large benefit–cost ratios, both in addressing current variability and in preparing for future change. A benefit–cost ratio greater than 1 suggests a promising project to undertake, because the benefits it generates are greater than its costs. For instance, while sandbags protecting individual houses can, in general, have benefit–cost ratios less than 1, in South Florida sandbags can have a benefit–cost ratio of 20 to 1,87 and along the Gulf of Mexico coastline, 3 to 1.88 Along the Gulf of Mexico coastline, levees and seawalls can have benefit–cost ratios ranging from 2.3 to 1.5 to 1 for refineries and petrochemical plants, though the ratios are lower for other assets.88
Information on the cost of actions that can achieve common goals is increasing in the water management sector, such as for operational reliability and resilience and environmental protection (Ch. 3: Water) and for responding to extreme heat events (Ch. 14: Human Health). Loss of water services or power during a high heat event, for example, can produce considerable costs that can have cascading effects on other sectors, thereby further driving up costs.89 The benefits of these adaptive actions against these threats have been studied less because they involve societal and environmental impacts that have been more difficult to quantify, study, and describe systematically.
Some studies quantify large benefits from adaptation actions involving natural systems,90 such as the decommissioning and restoration of unused forest roads, which decreases erosion and improves fish habitat and water quality; the restoration of beavers to mountain areas, whereby beaver dams improve fish habitat and improve water supply during summer months; and treatment of hazardous fuel to reduce wildland fire risks (Ch. 6: Forests). Some types of storm water management also show large benefits from green infrastructure and other nature-based responses.91,92 Coastal marsh restoration can sometimes provide benefits of protection against rising sea levels, along with added flood prevention and enhanced biodiversity. One effort involves restoring the river and surrounding lands of the Tidmarsh Wildlife Sanctuary in coastal Massachusetts, a former cranberry farm. The project includes cutting-edge environmental sensors that provide continuous data on marsh restoration, cranberry farm conversion, and climate change impacts and adaptation (see http://www.livingobservatory.org).
Extensive co-benefits may also be available from adaptation, in particular in the ecosystem services and health sectors (Ch. 7: Ecosystems; Ch. 14: Human Health). Coordinated adaptation and GHG mitigation planning may also provide defined co-benefits (Ch. 29: Mitigation, KM 4). For instance, tools are available to help decision-makers locate wind energy systems away from sensitive ecological sites, without incurring additional costs (for example, see the Nature Conservancy’s Biodiversity and Wind Siting Mapping Tool at https://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/newyork/climate-energy/working-with-wind.xml). Designs that provide green space and the use of cool and green roof technologies in cities can reduce heat-island effects, producing multiple benefits and cost reductions by helping to reduce emissions and air pollution, human health risks, and economic losses due to reduced labor productivity.93,94
Broader Measures of Well-Being
Benefit–cost analysis provides one important, but not the sole, means to evaluate alternative adaptation actions. Effective adaptation can provide a broad range of benefits that can be difficult to quantify, including improvements in economic opportunity, human health, equity, national security, education, social connectivity, and sense of place, while safeguarding cultural resources and practices and enhancing general environmental quality. Aggregating all these benefits into a single monetary value is not always the best approach,8,95 since in many cases a lack of data and uncertainty over climate projections and benefit valuations may make it impossible to give a uniform treatment to different types of benefits, thereby implicitly favoring some over others. More fundamentally, different people may value benefits differently.96 For instance, climate change can have significant impacts on equity and ecosystems, even though individuals can have strongly divergent views on distributional justice and the intrinsic value of nature and thus on how they value such impacts.
Considering various types of outcomes separately in risk management processes—termed multi-objective or multi-criteria analysis in the relevant literature97—can facilitate participatory planning processes. This also enhances the fairness of such processes by making more explicit the impacts of climate change on outcomes to different stakeholders, along with the policy tradeoffs among those outcomes. Pittsburgh’s EcoInnovation District, in the city’s Uptown and Oakland neighborhoods, employs bottom-up planning to improve the environment, support the needs of existing residents, and expand job growth. Louisiana’s Comprehensive Master Plan for a Sustainable Coast has five broad objectives: reduce economic losses from flooding, promote sustainable coastal ecosystems, provide coastal habitats that support commerce and recreation, sustain the region’s unique cultural heritage, and contribute to the regional and national economy by promoting a viable working coast.56 The plan contains actions that advance all five objectives, reflecting a set of tradeoffs broadly acceptable to diverse communities in the face of hazards, including coastal subsidence (sinking land) and sea level rise.98
Risk management approaches that consider multiple objectives can include a specific focus on equity, with important implications on the content and process of adaptation planning and action.99 Poor or marginalized populations often face a higher risk from climate change because they live in areas with higher exposure, are more sensitive to climate impacts, or lack adaptive capacity (Ch. 14: Human Health; Ch. 15: Tribes). Prioritizing adaptation actions for such populations may prove more equitable and lead, for instance, to improved infrastructure in their communities and increased focus on efforts to promote social cohesion and community resilience that can improve their capacity to prepare, respond, and recover from disasters. Equity considerations can also lead to the expanded participation of poor or marginalized populations in adaptation planning efforts. This can enhance the fairness of the process. Moreover, it can positively affect choices regarding the appropriate balance among the resources invested in reducing climate risk and those put toward other social goals, such as employment and education, and inform the most appropriate mix of adaptation actions in each community.52 Also, at the state and national level, equity considerations for climate adaptation can help allocate an appropriate distribution of resources for adaptation among different local communities.