Editing IPCC:AR6/SRCCL/Chapter-6 (section)

=== 6.4.2 Sensitivity of the integrated response options to climate change impacts ===

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With continued increases in warming, there are risks to the efficacy of some of the response options due to future climate change impacts, such as increased climate variability and extreme events. While many of the response options can help increase capacity to deliver adaptation benefits (Section 6.3.2), beyond certain thresholds of climate impacts they may be less effective or increasingly risky options. This requires that some response options need to anticipate these climate impacts in their implementation. We outline some of these impacts below.

Agriculture response options: Increased food productivity as a response option is highly sensitive to climate change impacts. Chapter 5 (Section 5.2.3.1) notes that global mean yields of some crops (maize and soybean) decrease with warming, while others (rice and wheat) increase with warming, up to a threshold of 3°C. Similarly, improved cropland management response options that rely on crop diversification or improved varieties may face challenges in efficacy from production declines. Improved grazing land management may continue to be feasible as a response option in the future under climate change in northern regions, but will likely become more difficult in tropical regions and Australia as temperature rises will reduce the carrying capacity of lands (Nardone et al. 2010 <sup>[[#fn:r979|979]]</sup> ) (Section 5.2.3.2). Improved livestock management also faces numerous challenges, particularly related to stresses on animals from temperatures, water, and diseases; overall, livestock numbers are projected to decline 7.5–9.6% by 2050 (Rivera- Ferre et al. 2016 <sup>[[#fn:r980|980]]</sup> ; Boone et al. 2018 <sup>[[#fn:r881|881]]</sup> ) (Section 5.2.3.2). Pastoralists may also be less likely to implement improved measures due to other risks and vulnerabilities under climate change (Thornton et al. 2009 <sup>[[#fn:r982|982]]</sup> ).

The impact of climate change on agroforestry is more difficult to model than single crops in process-based crop models, as agroforestry systems are far more complex (Luedeling et al. 2014 <sup>[[#fn:r983|983]]</sup> ); thus, it is unknown how the efficacy of this response option might be impacted. Agricultural diversification has been promoted as an adaptive strategy to climate impacts, given that diversity is known to increase resiliency of agricultural and natural systems, such as in resistance to increased pests or diseases; it can also provide diversified income portfolios when some crops may become sensitive to climate events (Bradshaw et al. 2004 <sup>[[#fn:r984|984]]</sup> ; Lin 2011 <sup>[[#fn:r985|985]]</sup> ). Diversified farms are expected to increase in Africa by 2060 as specialised farms with single crops face challenges under climate change (Seo 2010 <sup>[[#fn:r986|986]]</sup> ). However, it is not known if these options and advantages of diversification have a temperature threshold beyond which they are less effective.

Reduced grassland conversion is not likely to be affected as a response option per se since it is directed at conserving natural grassland areas, but these areas may face increased pressures for conversion if farmers experience crop failures under climate change and need to expand the cultivated area holdings to make up for losses. Lobell et al. (2013) <sup>[[#fn:r997|997]]</sup> have estimated the impacts of investment decisions to adapt to the effects of climate change on crop yields to 2050 and find that cropland will expand over 23% more land area (over 3 Mkm2), mostly in Latin America and Sub-Saharan Africa.

Integrated water management to improve water availability and reliability of water for agricultural production is likely to become more challenging in future scenarios of water declines, which are likely to be regionally uneven (Sections 2.6 and 6.4.4).

Forest response options: The availability of forest management as a response option can be impacted on by climate-induced changes, including increased diseases, pests and fires (Dale et al. 2001 <sup>[[#fn:r988|988]]</sup> ; Logan et al. 2003) (Section 4.5.1.2). These impacts will affect reforestation and afforestation response options as well. Locatelli et al. (2015a) note that climate change will influence seedling establishment, tree growth and mortality, and the presence of invasive species and/or pests; these can be buffered with modified silvicultural practices, including species selection (Pawson et al. 2013 <sup>[[#fn:r990|990]]</sup> ). Climate change can also alter the sink capacity for vegetation carbon sequestration, reducing the potential for reducing emissions from deforestation and forest degradation (REDD), reforestation and afforestation (Bonan 2008; Malhi et al. 2002 <sup>[[#fn:r991|991]]</sup> ).

Soil management: Climate change can alter the sink capacity for soil carbon sequestration, reducing the potential for increased soil organic carbon as an option. Projected climate change can reduce soil resilience to extreme weather, pests and biological invasion, environmental pollutants and other pressures, making reduced soil erosion and reduced soil compaction as response options harder to achieve (Smith et al. 2015 <sup>[[#fn:r992|992]]</sup> ). Climate change will likely increase demand for irrigation in dryland areas, which can increase risks of salinisation, diminishing the effectiveness of this response (Smith et al. 2015 <sup>[[#fn:r993|993]]</sup> ). Biochar additions to soil may be affected by future climatic changes, such as rising soil temperatures, but little is known, given that most research on the subject is from laboratory and not in situ field experiments. There are also wide estimates of the stability and residence times of biochar from this literature (Gurwick et al. 2013 <sup>[[#fn:r994|994]]</sup> ).

Other ecosystem management: Fire management is likely to become more challenging in a changing climate; some studies suggest an 50% increase in fire occurrence by the end of the century in circumboreal forests (Flannigan et al. 2009 <sup>[[#fn:r995|995]]</sup> ). Landslide risks are related to climate through total rainfall, rainfall intensity, air temperature and the general weather system (Gariano and Guzzetti 2016 <sup>[[#fn:r996|996]]</sup> ); thus reduced landslides and natural hazards as a response option will be made more difficult by increasing storms and seasonality of rainfall events projected for many areas of the world. Reduced pollution is likely less affected by climate change and can continue to be an option, despite increasing temperatures.

Conversely, some invasive species may thrive under climate change, such as moving to new areas or being less susceptible to control protocols (Hellmann et al. 2008 <sup>[[#fn:r1265|1265]]</sup> ). Conversion of coastal wetlands will be more difficult to halt if loss of productive land elsewhere encourages development on these lands, but coastal wetlands will likely adapt to increased CO2 and higher sea levels through sediment accretion, which will also enhance their capacity to act as carbon sinks (Duarte et al. 2013 <sup>[[#fn:r998|998]]</sup> ). While subarctic peatlands are at risk due to warming, these are not the main peatlands that are at risk from agricultural conversion (Tarnocai 2006 <sup>[[#fn:r999|999]]</sup> ). Peatlands, such as those in the tropics, may be more vulnerable in hotter scenarios to water table alterations and fire risk (Gorham 1991 <sup>[[#fn:r1000|1000]]</sup> ). Biodiversity conservation, such as through protected areas or corridors, may be threatened by increased land expansion under agriculture in climate change scenarios, including the newly available land in northern climates that may become agriculturally suited (Gimona et al. 2012 <sup>[[#fn:r1001|1001]]</sup> ), lessening the effectiveness of this response option.

Carbon dioxide removal (CDR): The efficacy of enhanced weathering is not likely to be affected by future climate changes. On the other hand, climate change will affect the productivity of bioenergy crops (Cronin et al. 2018 <sup>[[#fn:r1002|1002]]</sup> ), influencing the mitigation potential of bioenergy and BECCS (Calvin et al. 2013 <sup>[[#fn:r1003|1003]]</sup> ; Kyle et al. 2014 <sup>[[#fn:r1004|1004]]</sup> ). There is uncertainty in the sign and magnitude of the effect of climate change on bioenergy crop yields. As a result, there is uncertainty in whether climate change will increase or decrease the potential of bioenergy and BECCS.

Demand management of value chains: For most response options in demand-side management, the tools are generally not made more difficult by future climate changes. For example, dietary change is not likely to be affected by climate change; in fact, the opposite is more likely, that diets will shift in response to climate change impacts as reflected in high prices for some staple grains and meats, the productivity of which may be reduced (Tigchelaar et al. 2018 <sup>[[#fn:r1005|1005]]</sup> ). However, there is some indication that fruit and vegetable production will also be reduced in future scenarios, making healthier diets potentially harder to achieve in some regions (Springmann et al. 2016 <sup>[[#fn:r1006|1006]]</sup> ). Reduced post-harvest losses and reduced food waste may become an even more important option if water or heat stresses under climate change reduce overall harvests. Material substitution does have risks related to the availability of products if there are declines in the growth of forest and other biomass in certain future scenarios over time, although some evidence indicates that biomass may increase in the short term with limited warming (Boisvenue and Running 2006 <sup>[[#fn:r1007|1007]]</sup> ).

Supply management of value chains: Sustainable sourcing relies on being able to produce consumer goods sustainably (palm oil, timber, cocoa, etc.), and these may be at risk; for example, areas suitable for oil palm production are estimated to decrease by 75% by 2100 (Paterson et al. 2017 <sup>[[#fn:r1008|1008]]</sup> ). Improved management of supply chains is likely to increase in importance as a tool to manage food security, given that climate change threatens to lead to more production shocks in the future (Baldos and Hertel 2015 <sup>[[#fn:r1009|1009]]</sup> ). For enhanced urban food systems, climate stresses like heat island effects or increased water scarcity in urban areas may reduce the viability of food production in certain urban systems (da Silva et al. 2012). Improved food processing and retailing and improved energy use in agriculture are not likely to be impacted on by climate change.

Risk management options: Most risk management response options are not affected by climate impacts per se, although the increased risks that people may face will increase the need for funding and support to deploy these options. For example, disaster risk management will likely increase in importance in helping people adapt to longer-term climate changes (Begum et al. 2014 <sup>[[#fn:r1010|1010]]</sup> ); it is also likely to cost more as increased impacts of climate change, such as intensification or frequency of storm events, may increase. Management of urban sprawl may also be challenged by increased migration driven by climate change, as people displaced by climate change may move to unregulated urban areas (Adamo 2010 <sup>[[#fn:r1011|1011]]</sup> ). Livelihood diversification can assist in adapting to climate changes and is not likely to be constrained as a response option, as climate-sensitive livelihoods may be replaced by others that are less so. Use of local seeds as an effective response option may depend on the specific types of seeds and crops used, as some may not be good choices under increased heat and water stress (Gross et al. 2017 <sup>[[#fn:r1012|1012]]</sup> ). Risk-sharing instruments are unlikely to be affected by climate change, with the exception of index and crop insurance, which may become unaffordable if too many climate shocks result in insurance claims, decreasing the ability of the industry to provide this tool (Mills 2005 <sup>[[#fn:r1013|1013]]</sup> ).

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