Editing IPCC:AR6/SR15/TS (section)

=== Mitigation and Adaptation Options and Other Measures ===

'''A mix of mitigation and adaptation options implemented in a participatory and integrated manner can enable rapid, systemic transitions – in urban and rural areas – that are necessary elements of an accelerated transition consistent with limiting warming to 1.5°C. Such options and changes are most effective when aligned with economic and sustainable development, and when local and regional governments are supported by national governments {4.3.3, 4.4.1, 4.4.3}.''' Various mitigation options are expanding rapidly across many geographies. Although many have development synergies, not all income groups have so far benefited from them. Electrification, end-use energy efficiency and increased share of renewables, amongst other options, are lowering energy use and decarbonizing energy supply in the built environment, especially in buildings. Other rapid changes needed in urban environments include demotorization and decarbonization of transport, including the expansion of electric vehicles, and greater use of energy-efficient appliances (''medium evidence, high agreement''). Technological and social innovations can contribute to limiting warming to 1.5°C, for example, by enabling the use of smart grids, energy storage technologies and general-purpose technologies, such as information and communication technology (ICT) that can be deployed to help reduce emissions. Feasible adaptation options include green infrastructure, resilient water and urban ecosystem services, urban and peri-urban agriculture, and adapting buildings and land use through regulation and planning (''medium evidence, medium to high agreement''). {4.3.3, 4.4.3, 4.4.4}

'''Synergies can be achieved across systemic transitions through several overarching adaptation options in rural and urban areas.''' Investments in health, social security and risk sharing and spreading are cost-effective adaptation measures with high potential for scaling up (''medium evidence, medium to high agreement''). Disaster risk management and education-based adaptation have lower prospects of scalability and cost-effectiveness (''medium evidence, high agreement'') but are critical for building adaptive capacity. {4.3.5, 4.5.3}

'''Converging adaptation and mitigation options can lead to synergies and potentially increase cost-effectiveness, but multiple trade-offs can limit the speed of and potential for scaling up.''' Many examples of synergies and trade-offs exist in all sectors and system transitions. For instance, sustainable water management (''high evidence, medium agreement'') and investment in green infrastructure (''medium evidence, high agreement'') to deliver sustainable water and environmental services and to support urban agriculture are less cost-effective than other adaptation options but can help build climate resilience. Achieving the governance, finance and social support required to enable these synergies and to avoid trade-offs is often challenging, especially when addressing multiple objectives, and attempting appropriate sequencing and timing of interventions. {4.3.2, 4.3.4, 4.4.1, 4.5.2, 4.5.3, 4.5.4}

'''Though CO<sub>2</sub> dominates long-term warming, the reduction of warming short-lived climate forcers (SLCFs), such as methane and black carbon, can in the short term contribute significantly to limiting warming to 1.5°C above pre-industrial levels. Reductions of black carbon and methane would have substantial co-benefits (''high confidence''), including improved health due to reduced air pollution. This, in turn, enhances the institutional and socio-cultural feasibility of such actions.''' Reductions of several warming SLCFs are constrained by economic and social feasibility (''low evidence, high agreement''). As they are often co-emitted with CO<sub>2</sub>, achieving the energy, land and urban transitions necessary to limit warming to 1.5°C would see emissions of warming SLCFs greatly reduced.  {2.3.3.2, 4.3.6}

'''Most CDR options face multiple feasibility constraints, which differ between options, limiting the potential for any single option to sustainably achieve the large-scale deployment required in the 1.5°C-consistent pathways described in Chapter 2 (''high confidence'').''' Those 1.5°C pathways typically rely on bioenergy with carbon capture and storage (BECCS), afforestation and reforestation (AR), or both, to neutralize emissions that are expensive to avoid, or to draw down CO<sub>2</sub> emissions in excess of the carbon budget {Chapter 2}. Though BECCS and AR may be technically and geophysically feasible, they face partially overlapping yet different constraints related to land use. The land footprint per tonne of CO<sub>2</sub> removed is higher for AR than for BECCS, but given the low levels of current deployment, the speed and scales required for limiting warming to 1.5°C pose a considerable implementation challenge, even if the issues of public acceptance and absence of economic incentives were to be resolved (''high agreement, medium evidence''). The large potential of afforestation and the co-benefits if implemented appropriately (e.g., on biodiversity and soil quality) will diminish over time, as forests saturate (''high confidence''). The energy requirements and economic costs of direct air carbon capture and storage (DACCS) and enhanced weathering remain high (''medium evidence, medium agreement''). At the local scale, soil carbon sequestration has co-benefits with agriculture and is cost-effective even without climate policy (''high confidence''). Its potential feasibility and cost-effectiveness at the global scale appears to be more limited. {4.3.7}

'''Uncertainties surrounding solar radiation modification (SRM) measures constrain their potential deployment.''' These uncertainties include: technological immaturity; limited physical understanding about their effectiveness to limit global warming; and a weak capacity to govern, legitimize, and scale such measures. Some recent model-based analysis suggests SRM would be effective but that it is too early to evaluate its feasibility. Even in the uncertain case that the most adverse side-effects of SRM can be avoided, public resistance, ethical concerns and potential impacts on sustainable development could render SRM economically, socially and institutionally undesirable (''low agreement, medium evidence''). {4.3.8, Cross-Chapter Box 10 in this chapter}