Editing IPCC:AR6/WGII/Chapter-16 (section)

==== 16.5.3.3 Climate Adaptation Scenarios ====

<div id="h3-38-siblings" class="h3-siblings"></div>

One approach to understand adaptation benefits for risk reduction is to contrast projected impacts for the same climate and development conditions but different levels of adaptation. For example, global-scale coastal protection studies considering both RCPs and SSPs suggest that, under a given RCP, the total flooded area may be reduced by 40% by using 1-m height dykes, compared with a no-adaptation baseline ( [[#Tamura--2019|Tamura et al., 2019]] ). The global cost of SLR over the 21st century can be lowered by factor of two to four if local cost–benefit decisions consider migration an adaptation option, in addition to hard protection ( [[#Lincke--2021|Lincke and Hinkel, 2021]] ). Under a low-warming scenario, it is estimated that adaptation (i.e., changes in crop variety and planting dates) could reduce the total number of people at risk of hunger globally by about 4%, and by about 10% in a high-warming scenario ( [[#Hasegawa--2014|Hasegawa et al., 2014]] ). Impacts on heat-related mortality would be cut from 10 to 7 deaths per 10,000 people yr –1 in 2100 by adaptation actions beyond those assumed to be driven by income growth ( [[#Carleton--2020|Carleton et al., 2020]] ). In a regional example, proactive adaptation efforts on infrastructure (especially roads, runways, buildings and airports) in Alaska, USA, could reduce damage-related expenditure by 45% under medium or high warming ( [[#Melvin--2017|Melvin et al., 2017]] ).

Another approach infers the potential future effectiveness of adaptation based on current sensitivity of impacts to interventions. For example, the future disease burden of malaria is likely to be highly dependent on the future development of health services, deployment of malaria programs and adaptation. Investments in water and sanitation infrastructure are also recognised to have the potential to reduce severe risks of waterborne disease, although these improvements likely need to provide transformative change ( [[#Cumming--2019|Cumming et al., 2019]] ). The potential for severe risks may also be substantially reduced through the development of vaccines for specific enteric diseases ( [[#Riddle--2018|Riddle et al., 2018]] ), although most current vaccines target viral pathogens, incidence for which tends to be inversely correlated with ambient temperature ( [[#Carlton--2016|Carlton et al., 2016]] ). In addition, international migration as well as forced movement of people across borders will be influenced by developments in legal and political conditions ( [[#McLeman--2019|McLeman, 2019]] ; [[#Wrathall--2019|Wrathall et al., 2019]] ), but the fact that these developments are unknown strongly limits any forecasts on the magnitude of adaptation benefits ( [[#16.5.2.3.8|Section 16.5.2.3.8]] ).

Last, there is growing concern that even ambitious adaptation efforts will not eliminate residual risks from climate change ( [[#16.4.2|Section 16.4.2]] ). A synthesis of risk assessments in the recent IPCC Special Reports ( [[#Magnan--2021|Magnan et al., 2021]] ) concludes that high societal adaptation is expected to reduce the aggregated score—the proxy used in the study—of global risk from anthropogenic climate change by about 40% under all RCPs by the end of the century, compared with risk levels projected without adaptation. It, however, also shows that, even for the lowest warming scenario, a residual risk one-third greater than today’s risk level would still remain (with a doubling of today’s aggregated score under the high-emissions scenario).

<div id="16.5.3.4" class="h3-container"></div>

<span id="illustration-risk-and-adaptation-pathways-in-densely-populated-and-agricultural-deltas"></span>