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

=== 6.3.1 Potential of the integrated response options for delivering mitigation ===

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In this section, the impacts of integrated response options on climate change mitigation are assessed.

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<span id="integrated-response-options-based-on-land-management-1"></span>
==== 6.3.1.1 Integrated response options based on land management ====

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In this section, the impacts on climate change mitigation of integrated response options based on land management are assessed. Some of the caveats of these potential mitigation studies are discussed in Chapter 2 and Section 6.2.1.

''Integrated response options based on land management in agriculture''

Increasing the productivity of land used for food production can deliver significant mitigation by avoiding emissions that would occur if increased food demand were met through expansion of the agricultural land area (Burney et al. 2010 <sup>[[#fn:r238|238]]</sup> ). If pursued through increased agrochemical inputs, numerous adverse impacts on GHG emissions (and other environmental sustainability) can occur (Table 6.5), but, if pursued through sustainable intensification, increased food productivity could provide high levels of mitigation. For example, yield improvement has been estimated to have contributed to emissions savings of &gt;13 GtCO <sub>2</sub> e yr <sup>–1</sup>  since 1961 (Burney et al. 2010 <sup>[[#fn:r239|239]]</sup> ) (Table 6.13). This can also reduce the GHG intensity of products (Bennetzen et al. 2016a,b) which means a smaller environmental footprint of production, since demand can be met using less land and/or with fewer animals.

Improved cropland management could provide moderate levels of mitigation (1.4–2.3 GtCO <sub>2</sub> e yr <sup>–1</sup> ) (Smith et al. 2008, 2014; Pradhan et al. 2013 <sup>[[#fn:r240|240]]</sup> ) (Table 6.13). The lower estimate of potential is from Pradhan et al. (2013) for decreasing emissions intensity, and the upper end of technical potential is estimated by adding technical potentials for cropland management (about 1.4 GtCO <sub>2</sub> e yr <sup>–1</sup> ), rice management (about 0.2 GtCO <sub>2</sub> e yr <sup>–1</sup> ) and restoration of degraded land (about 0.7 GtCO <sub>2</sub> e yr <sup>–1</sup> ) from Smith et al. (2008) <sup>[[#fn:r241|241]]</sup> and Smith et al. (2014). Note that much of this potential arises from soil carbon sequestration so there is an overlap with that response option. (Section 6.3.1.1).

Grazing lands can store large stocks of carbon in soil and root biomass compartments (Conant and Paustian 2002 <sup>[[#fn:r243|243]]</sup> ; O’Mara 2012 <sup>[[#fn:r244|244]]</sup> ; Zhou et al. 2017 <sup>[[#fn:r245|245]]</sup> ). The global mitigation potential is moderate (1.4–1.8 GtCO <sub>2</sub> e yr <sup>–1</sup> ), with the lower value in the range for technical potential taken from Smith et al. (2008) <sup>[[#fn:r246|246]]</sup> which includes only grassland management measures, and the upper value in the range from Herrero et al. (2016) <sup>[[#fn:r247|247]]</sup> , which includes also indirect effects and some components of livestock management, and soil carbon sequestration, so there is overlap with these response options (Section 6.3.1.1). Conant et al. (2005) <sup>[[#fn:r248|248]]</sup> caution that increases in soil carbon stocks could be offset by increases in N <sub>2</sub> O fluxes.

The mitigation potential of improved livestock management is also moderate (0.2–1.8 GtCO <sub>2</sub> e yr <sup>–1</sup> ; Smith et al. (2008) including only direct livestock measures; Herrero et al. (2016) <sup>[[#fn:r249|249]]</sup> include also indirect effects, and some components of grazing land management and soil carbon sequestration) to high (6.13 GtCO <sub>2</sub> e yr <sup>–1</sup> ) (Pradhan et al. 2013 <sup>[[#fn:r250|250]]</sup> ) (Table 6.13). There is an overlap with other response options (Section 6.3.1.1).

Zomer et al. (2016) <sup>[[#fn:r251|251]]</sup> reported that the trees agroforestry landscapes have increased carbon stock by 7.33 GtCO <sub>2</sub>  between 2000–2010, which is equivalent to 0.7 GtCO <sub>2</sub> e yr <sup>–1</sup> . Estimates of global potential range from 0.1 GtCO <sub>2</sub> e yr <sup>–1</sup> to 5.7 GtCO <sub>2</sub> e yr <sup>–1</sup> (from an optimum implantation scenario of Hawken (2017) <sup>[[#fn:r252|252]]</sup> , based on an assessment of all values in Griscom et al. (2017), Hawken (2017) <sup>[[#fn:r253|253]]</sup> , Zomer et al. (2016) and Dickie et al. (2014) <sup>[[#fn:r254|254]]</sup> (Table 6.13).

Agricultural diversification mainly aims at increasing climate resilience, but it may have a small (but globally unquantified) mitigation potential as a function of type of crop, fertiliser management, tillage system, and soil type (Campbell et al. 2014 <sup>[[#fn:r255|255]]</sup> ; Cohn et al. 2017 <sup>[[#fn:r256|256]]</sup> ).

Reducing conversion of grassland to cropland could provide significant climate mitigation by retaining soil carbon stocks that might otherwise be lost. When grasslands are converted to croplands, they lose about 36% of their soil organic carbon stocks after 20 years (Poeplau et al. 2011 <sup>[[#fn:r257|257]]</sup> ). Assuming an average starting soil organic carbon stock of grasslands of 115 tC ha <sup>–1</sup> (Poeplau et al. 2011 <sup>[[#fn:r258|258]]</sup> ), this is equivalent to a loss of 41.5 tC ha <sup>–1</sup> on conversion to cropland. Mean annual global cropland conversion rates (1961–2003) have been around 47,000 km2 yr <sup>–1</sup> (Krause et al. 2017 <sup>[[#fn:r259|259]]</sup> ), or 940000 km2 over a 20-year period. The equivalent loss of soil organic carbon over 20 years would therefore be 14 GtCO <sub>2</sub> e = 0.7 GtCO <sub>2</sub> e yr <sup>–1</sup> . Griscom et al. (2017) <sup>[[#fn:r260|260]]</sup> estimate a cost-effective mitigation potential of 0.03 GtCO <sub>2</sub> e yr <sup>–1</sup> (Table 6.13).

Integrated water management provides moderate benefits for climate mitigation due to interactions with other land management strategies. For example, promoting soil carbon conservation (e.g., reduced tillage) can improve the water retention capacity of soils. Jat et al. (2015) <sup>[[#fn:r261|261]]</sup> found that improved tillage practices and residue incorporation increased water-use efficiency by 30%, rice–wheat yields by 5–37%, income by 28–40% and reduced GHG emission by 16–25%. While irrigated agriculture accounts for only 20% of the total cultivated land, the energy consumption from groundwater irrigation is significant. However, current estimates of mitigation potential are limited to reductions in GHG emissions mainly in cropland and rice cultivation (Smith et al. 2008 <sup>[[#fn:r262|262]]</sup> , 2014) (Chapter 2 and Table 6.13). Li et al. (2006) <sup>[[#fn:r263|263]]</sup> estimated a 0.52–0.72 GtCO <sub>2</sub> e yr <sup>–1</sup> reduction using the alternate wetting and drying technique. Current estimates of N <sub>2</sub> O release from terrestrial soils and wetlands accounts for 10–15% of anthropogenically fixed nitrogen on the Earth System (Wang et al. 2017 <sup>[[#fn:r264|264]]</sup> ).

Table 6.13 summarises the mitigation potentials for agricultural response options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.4.6, and indicative (not exhaustive) references upon which the evidence in based.

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'''Table 6.13'''

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'''Mitigation effects of response options based on land management in agriculture.'''

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{| class="wikitable"
|-
! Integrated response option
! Potential
! Confidence
! Citation
|-
| Increased food productivity
| &gt;13 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Low confidence
| Chapter 5<br />
Burney et al. 2010
|-
| Improved cropland managementa
| 1.4–2.3 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2; Chapter 5<br />
Pradhan et al. 2013; Smith et al. 2008, 2014
|-
| Improved grazing land managementa
| 1.4–1.8 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2; Chapter 5<br />
Conant et al. 2017; Herrero et al. 2016; Smith et al. 2008, 2014
|-
| Improved livestock managementa
| 0.2–2.4 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2; Chapter 5<br />
Herrero et al. 2016; Smith et al. 2008, 2014
|-
| Agroforestry
| 0.1–5.7 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2<br />
Albrecht and Kandji 2003; Dickie et al. 2014; Griscom et al. 2017; Hawken 2017; Zomer et al. 2016
|-
| Agricultural diversification
| &gt;0
| Low confidence
| Campbell et al. 2014; Cohn et al. 2017
|-
| Reduced grassland conversion to cropland
| 0.03–0.7 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Low confidence
| Note high value not shown in Chapter 2; calculated from values in Griscom et al. 2017; Krause et al. 2017; Poeplau et al. 2011
|-
| Integrated water management
| 0.1–0.72 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Low confidence
| IPCC 2014; Howell et al. 2015; Li et al. 2006; Rahman and Bulbul 2015; Smith et al. 2008, 2014
|}
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a Note that Chapter 2 reports mitigation potential for subcategories within this response option and not the combined total reported here.

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''Integrated response options based on land management in forests''

Forest management could potentially contribute to moderate mitigation benefits globally, up to about 2 GtCO <sub>2</sub> e yr <sup>–1</sup> (Chapter 2, Table 6.14). For managed forests, the most effective forest carbon mitigation strategy is the one that, through increasing biomass productivity, optimises the carbon stocks (in forests and in long- lived products) as well as the wood substitution effects for a given time frame (Smyth et al. 2014 <sup>[[#fn:r265|265]]</sup> ; Grassi et al. 2018 <sup>[[#fn:r266|266]]</sup> ; Nabuurs et al. 2007 <sup>[[#fn:r267|267]]</sup> ; Lewis et al. 2019 <sup>[[#fn:r268|268]]</sup> ; Kurz et al. 2016 <sup>[[#fn:r269|269]]</sup> ; Erb et al. 2017 <sup>[[#fn:r279|279]]</sup> ). Estimates of the mitigation potential vary also depending on the counterfactual, such as business-as-usual management (e.g., Grassi et al. 2018) or other scenarios. Climate change will affect the mitigation potential of forest management due to an increase in extreme events like fires, insects and pathogens (Seidl et al. 2017 <sup>[[#fn:r271|271]]</sup> ). More detailed estimates are available at regional or biome level. For instance, according to Nabuurs et al. (2017), the implementation of Climate- Smart Forestry (a combination of forest management, expansion of forest areas, energy substitution, establishment of forest reserves, etc.) in the European Union has the potential to contribute to an additional 0.4 GtCO <sub>2</sub> e yr <sup>–1</sup> mitigation by 2050. Sustainable forest management is often associated with a number of co-benefits for adaptation, ecosystem services, biodiversity conservation, microclimatic regulation, soil erosion protection, coastal area protection and water and flood regulation (Locatelli 2011 <sup>[[#fn:r272|272]]</sup> ). Forest management mitigation measures are more likely to be long- lasting if integrated into adaptation measures for communities and ecosystems, for example, through landscape management (Locatelli et al. 2011 <sup>[[#fn:r273|273]]</sup> ). Adoption of reduced-impact logging and wood processing technologies along with financial incentives can reduce forest fires, forest degradation, maintain timber production, and retain carbon stocks (Sasaki et al. 2016 <sup>[[#fn:r274|274]]</sup> ). Forest certification may support sustainable forest management, helping to prevent forest degradation and over-logging (Rametsteiner and Simula 2003 <sup>[[#fn:r275|275]]</sup> ). Community forest management has proven a viable model for sustainable forestry, including for carbon sequestration (Chhatre and Agrawal 2009 <sup>[[#fn:r276|276]]</sup> ) (Chapter 7, Section 7.7.4).

Reducing deforestation and forest degradation rates represents one of the most effective and robust options for climate change mitigation, with large mitigation benefits globally (Chapters 2 and 4, and Table 6.14). Because of the combined climate impacts of GHGs and biophysical effects, reducing deforestation in the tropics has a major climate mitigation effect, with benefits at local levels too (Alkama and Cescatti 2016 <sup>[[#fn:r277|277]]</sup> ) (Chapter 2). Reduced deforestation and forest degradation typically lead to large co-benefits for other ecosystem services (Table 6.14).

A large range of estimates exist in the scientific literature for the mitigation potential of reforestation and forest restoration, and they sometimes overlap with estimates for afforestation. At global level, the overall potential for these options is large, reaching about 10 GtCO <sub>2</sub> e yr <sup>–1</sup> (Chapter 2 and Table 6.14). The greatest potential for these options is in tropical and subtropical climate (Houghton and Nassikas 2018 <sup>[[#fn:r278|278]]</sup> ). Furthermore, climate change mitigation benefits of afforestation, reforestation and forest restoration are reduced at high latitudes owing to the surface albedo feedback (Chapter 2).

Table 6.14 summarises the mitigation potentials for forest response options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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<span id="table-6.14"></span>
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'''Table 6.14'''

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'''Mitigation effects of response options based on land management in forests.'''

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{| class="wikitable"
|-
! Integrated response option
! Potential
! Confidence
! Citation
|-
| Forest management
| 0.4–2.1 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2<br />
Griscom et al. 2017; Sasaki et al. 2016
|-
| Reduced deforestation and forest degradation
| 0.4–5.8 GtCO <sub>2</sub> e yr <sup>–1</sup>
| High confidence
| Chapter 2<br />
Baccini et al. 2017; Griscom et al. 2017; Hawken 2017; Houghton et al. 2015; Houghton and Nassikas 2018; Smith et al. 2014
|-
| Reforestation and forest restoration
| 1.5–10.1 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2<br />
Dooley and Kartha 2018; Griscom et al. 2017; Hawken 2017; Houghton and Nassikas 2017<br />
Estimates partially overlapping with Afforestation
|-
| Afforestation
| 0.5–8.9 GtCO <sub>2</sub> e yr <sup>–1</sup>
| Medium confidence
| Chapter 2<br />
Fuss et al. 2018; Hawken 2017; Kreidenweis et al. 2016; Lenton 2010. Estimates partially overlapping with Reforestation
|}
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''Integrated response options based on land management of soils''

The global mitigation potential for increasing soil organic matter stocks in mineral soils is estimated to be in the range of 1.3–5.1 GtCO <sub>2</sub> e yr <sup>–1</sup> , though the full literature range is wider (Fuss et al. 2018 <sup>[[#fn:r1247|1247]]</sup> ; Lal 2004 <sup>[[#fn:r280|280]]</sup> ; de Coninck et al. 2018; Sanderman et al. 2017 <sup>[[#fn:r281|281]]</sup> ; Smith et al. 2008 <sup>[[#fn:r282|282]]</sup> ; Smith 2016 <sup>[[#fn:r283|283]]</sup> ) (Table 6.15).

The management and control of erosion may prevent losses of organic carbon in water- or wind- transported sediments, but since the final fate of eroded material is still debated, ranging from a source of 1.36–3.67 GtCO <sub>2</sub> e yr <sup>–1</sup> (Jacinthe and Lal 2001 <sup>[[#fn:r1268|1268]]</sup> ; Lal 2004 <sup>[[#fn:r284|284]]</sup> ) to a sink of 0.44–3.67 GtCO <sub>2</sub> e yr <sup>–1</sup> (Smith et al. 2001 <sup>[[#fn:r286|286]]</sup> ; Stallard 1998 <sup>[[#fn:r287|287]]</sup> ; Van Oost et al. 2007 <sup>[[#fn:r288|288]]</sup> ) (Table 6.15), the overall impact of erosion control on mitigation is context-specific and uncertain at the global level (Hoffmann et al. 2013 <sup>[[#fn:r289|289]]</sup> ).

Salt-affected soils are highly constrained environments that require permanent prevention of salinisation. Their mitigation potential is likely to be small (Wong et al. 2010 <sup>[[#fn:r290|290]]</sup> ; UNCTAD 2011 <sup>[[#fn:r291|291]]</sup> ; Dagar et al. 2016 <sup>[[#fn:r292|292]]</sup> ).

Soil compaction prevention could reduce N2O emissions by minimising anoxic conditions favourable for denitrification (Mbow et al. 2010), but its carbon sequestration potential depends on crop management, and the global mitigation potential, though globally unquantified, is likely to be small (Chamen et al. 2015 <sup>[[#fn:r293|293]]</sup> ; Epron et al. 2016 <sup>[[#fn:r294|294]]</sup> ; Tullberg et al. 2018 <sup>[[#fn:r295|295]]</sup> ) (Table 6.15).

For biochar, a global analysis of technical potential, in which biomass supply constraints were applied to protect against food insecurity, loss of habitat and land degradation, estimated technical potential abatement of 3.7–6.6 GtCO <sub>2</sub> e yr <sup>–1</sup> (including 2.6–4.6 GtCO <sub>2</sub> e yr <sup>–1</sup> carbon stabilisation). Considering all published estimates by Woolf et al. (2010) <sup>[[#fn:r296|296]]</sup> , Smith (2016) <sup>[[#fn:r297|297]]</sup> , Fuss et al. (2018) <sup>[[#fn:r298|298]]</sup> , Griscom et al. (2017) <sup>[[#fn:r299|299]]</sup> , Hawken (2017) <sup>[[#fn:r300|300]]</sup> , Paustian et al. (2016) <sup>[[#fn:r301|301]]</sup> , Powell and Lenton (2012) <sup>[[#fn:r302|302]]</sup> .

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'''Table 6.15'''

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'''Mitigation effects of response options based on land management of soils.'''
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Dickie et al. (2014) <sup>[[#fn:r303|303]]</sup> , Lenton (2010) <sup>[[#fn:r1248|1248]]</sup> , Lenton (2014) <sup>[[#fn:r1249|1249]]</sup> , Roberts et al. (2009) <sup>[[#fn:r1250|1250]]</sup> , Pratt and Moran (2010) <sup>[[#fn:r1251|1251]]</sup> and IPCC (2018) <sup>[[#fn:r1269|1269]]</sup> , the low value for the range of potentials of 0.03 GtCO <sub>2</sub> e yr <sup>–1</sup> is for the ‘plausible’ scenario of Hawken, (2017) <sup>[[#fn:r304|304]]</sup> (Table 6.15). Fuss et al. (2018) <sup>[[#fn:r1254|1254]]</sup> propose a range of 0.5–2 GtCO2e yr–1 as the sustainable potential for negative emissions through biochar, similar to the range proposed by Smith (2016) <sup>[[#fn:r305|305]]</sup> and IPCC (2018) <sup>[[#fn:r1252|1252]]</sup> .

Table 6.15 summarises the mitigation potentials for soil-based response options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

''Integrated response options based on land management in all/other ecosystems''

For fire management, total emissions from fires have been in the order of 8.1 GtCO <sub>2</sub> e yr <sup>–1</sup> 1 for the period 1997–2016 (Chapter 2 and Cross-Chapter Box 3) and there are important synergies between air pollution and climate change control policies. Reduction in fire CO2 emissions due to fire suppression and landscape fragmentation associated with increases in population density is calculated to enhance land carbon uptake by 0.48 GtCO <sub>2</sub> e yr <sup>–1</sup> for the 1960–2009 period (Arora and Melton 2018 <sup>[[#fn:r306|306]]</sup> ) (Table 6.16).

Management of landslides and natural hazards is a key climate adaptation option but, due to limited global areas vulnerable to landslides and natural hazards, its mitigation potential is likely to be modest (Noble et al. 2014 <sup>[[#fn:r307|307]]</sup> ).

In terms of management of pollution, including acidification, United Nations Environment Programme (UNEP) and World Meterological Organization (WMO) (2011) <sup>[[#fn:r1253|1253]]</sup> and Shindell et al. (2012) <sup>[[#fn:r308|308]]</sup> identified measures targeting reduction in short-lived climate pollutant (SLCP) emissions that reduce projected global mean warming about 0.5°C by 2050. Bala et al. (2013) <sup>[[#fn:r309|309]]</sup> reported that a recent coupled modelling study showed nitrogen deposition and elevated CO2 could have a synergistic effect, which could explain 47% of terrestrial carbon uptake in the 1990s. Estimates of global terrestrial carbon uptake due to current nitrogen deposition ranges between 0.55 and 1.28 GtCO2 yr–1 (De Vries et al. 2006, 2009 <sup>[[#fn:r1254|1254]]</sup> ; Bala et al. 2013 <sup>[[#fn:r1255|1255]]</sup> ; Zaehle and Dalmonech 2011 <sup>[[#fn:r310|310]]</sup> ) (Table 6.16).

There are no global data on the impacts of management of invasive species/encroachment on mitigation.

Coastal wetland restoration could provide high levels of climate mitigation, with avoided coastal wetland impacts and coastal wetland restoration estimated to deliver 0.3–3.1 GtCO <sub>2</sub> e yr <sup>–1</sup> in total when considering all global estimates from Griscom et al. (2017) <sup>[[#fn:r311|311]]</sup> , Hawken (2017) <sup>[[#fn:r1255|1255]]</sup> , Pendleton et al. (2012) <sup>[[#fn:r313|313]]</sup> , Howard et al. (2017) <sup>[[#fn:r314|314]]</sup> and Donato et al. (2011) <sup>[[#fn:r315|315]]</sup> (Table 6.16).

Peatland restoration could provide moderate levels of climate mitigation, with avoided peat impacts and peat restoration estimated to deliver 0.6–2 GtCO <sub>2</sub> e yr <sup>–1</sup> from all global estimates published in Griscom et al. (2017) <sup>[[#fn:r316|316]]</sup> , Hawken (2017) <sup>[[#fn:r1256|1256]]</sup> , Hooijer et al. (2010) <sup>[[#fn:r319|319]]</sup> , Couwenberg et al. (2010) <sup>[[#fn:r1257|1257]]</sup> and Joosten and Couwenberg (2008) <sup>[[#fn:r320|320]]</sup> , though there could be an increase in methane emissions after restoration (Jauhiainen et al. 2008 <sup>[[#fn:r321|321]]</sup> ) (Table 6.16).

Mitigation potential from biodiversity conservation varies depending on the type of intervention and specific context. Protected areas are estimated to store over 300 Gt carbon, roughly corresponding to 15% of terrestrial carbon stocks (Campbell et al. 2008 <sup>[[#fn:r322|322]]</sup> ; Kapos et al. 2008 <sup>[[#fn:r323|323]]</sup> ). At global level, the potential mitigation resulting from protection of these areas for the period 2005–2095 is, on average, about 0.9 GtCO <sub>2</sub> e yr <sup>–1</sup> relative to a reference scenario (Calvin et al. 2014 <sup>[[#fn:r324|324]]</sup> ). The potential effects on the carbon cycle of management of wild animal species are context dependent. For example, moose browsing in boreal forests can decrease the carbon uptake of ecosystems by up to 75% (Schmitz et al. 2018 <sup>[[#fn:r325|325]]</sup> ), and reducing moose density through active population management in Canada is estimated to be a carbon sink equivalent to about 0.37 GtCO <sub>2</sub> e yr <sup>–1</sup> (Schmitz et al. 2014 <sup>[[#fn:r326|326]]</sup> ).

Table 6.16 summarises the mitigation potentials for land management response options in all/other ecosystems, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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<span id="table-6.16"></span>
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'''Table 6.16'''

<span id="mitigation-effects-of-response-options-based-on-land-management-in-allother-ecosystems."></span>
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'''Mitigation effects of response options based on land management in all/other ecosystems.'''
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[[File:b3e5c39fc7a980bbdf74aa935f27dd47 table-6.16.png]]

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''Integrated response options based on land management specifically for carbon dioxide removal (CDR)''

Enhanced mineral weathering provides substantial climate mitigation, with a global mitigation potential in the region of about 0.5–4 GtCO <sub>2</sub> e yr <sup>–1</sup> (Beerling et al. 2018 <sup>[[#fn:r327|327]]</sup> ; Lenton 2010 <sup>[[#fn:r328|328]]</sup> ; Smith et al. 2016a <sup>[[#fn:r329|329]]</sup> ; Taylor et al. 2016 <sup>[[#fn:r330|330]]</sup> ) (Table 6.17).

The mitigation potential for bioenergy and BECCS derived from bottom-up models is large (IPCC 2018 <sup>[[#fn:r331|331]]</sup> ) (Chapter 2 and Cross- Chapter Box 7 in this chapter), with technical potential estimated at 100–300 EJ yr <sup>–1</sup> (Chum et al. 2011 <sup>[[#fn:r332|332]]</sup> ; Cross-Chapter Box 7 in Chapter 6) or up to about 11 GtCO2 yr–1 (Chapter 2). These estimates, however, exclude N2O associated with fertiliser application and land- use change emissions. Those effects are included in the modelled scenarios using bioenergy and BECCS, with the sign and magnitude depending on where the bioenergy is grown (Wise et al. 2015 <sup>[[#fn:r333|333]]</sup> ), at what scale, and whether nitrogen fertiliser is used.

Table 6.17 summarises the mitigation potentials for land management options specifically for CDR, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

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<span id="table-6.17"></span>
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'''Table 6.17'''

<span id="mitigation-effects-of-response-options-based-on-land-management-specifically-for-cdr."></span>
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'''Mitigation effects of response options based on land management specifically for CDR.'''
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[[File:e5cbabbf887d1af98db9d7a3144d1b5c table-6.17.png]]

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<div id="section-6-3-1-2-integrated-response-options-based-on-value-chain-management"></div>

<span id="integrated-response-options-based-on-value-chain-management-1"></span>
==== 6.3.1.2 Integrated response options based on value chain management ====

<div id="section-6-3-1-2-integrated-response-options-based-on-value-chain-management-block-1"></div>

In this section, the impacts on climate change mitigation of integrated response options based on value chain management are assessed.

''Integrated response options based on value chain management through demand management''

Dietary change and waste reduction can provide large benefits for mitigation, with potentials of 0.7–8 GtCO2 yr–1 for both (Aleksandrowicz et al. 2016 <sup>[[#fn:r334|334]]</sup> ; Bajželj et al. 2014b <sup>[[#fn:r335|335]]</sup> ; Dickie et al. 2014 <sup>[[#fn:r336|336]]</sup> ; Hawken 2017 <sup>[[#fn:r337|337]]</sup> ; Hedenus et al. 2014 <sup>[[#fn:r338|338]]</sup> ; Herrero et al. 2016 <sup>[[#fn:r339|339]]</sup> ; Popp et al. 2010 <sup>[[#fn:r340|340]]</sup> ; Smith et al. 2013 <sup>[[#fn:r341|341]]</sup> ; Springmann et al. 2016 <sup>[[#fn:r342|342]]</sup> ; Stehfest et al. 2009 <sup>[[#fn:r343|343]]</sup> ; Tilman and Clark 2014 <sup>[[#fn:r344|344]]</sup> ). Estimates for food waste reduction (Bajželj et al. 2014b <sup>[[#fn:r345|345]]</sup> ; Dickie et al. 2014 <sup>[[#fn:r346|346]]</sup> ; Hiç et al. 2016 <sup>[[#fn:r347|347]]</sup> ; Hawken 2017 <sup>[[#fn:r348|348]]</sup> ) include both consumer/retailed waste and post-harvest losses (Table 6.18). Some studies indicate that material substitution has the potential for significant mitigation, with one study estimating a 14–31% reduction in global CO2 emissions (Oliver et al. 2014 <sup>[[#fn:r349|349]]</sup> ); other studies suggest more modest potential (Gustavsson et al. 2006 <sup>[[#fn:r350|350]]</sup> ) (Table 6.18).

Table 6.18 summarises the mitigation potentials for demand management options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

<div id="section-6-3-1-2-integrated-response-options-based-on-value-chain-management-block-2"></div>

<span id="table-6.18"></span>
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'''Table 6.18'''

<span id="mitigation-effects-of-response-options-based-on-demand-management."></span>
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'''Mitigation effects of response options based on demand management.'''
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[[File:78fa23337d42ef1d2e565315f55e7e81 table-6.18.png]]

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<div id="section-6-3-1-2-integrated-response-options-based-on-value-chain-management-block-3"></div>

''Integrated response options based on value chain management through supply management''

While sustainable sourcing presumably delivers a mitigation benefit, there are no global estimates of potential. Palm oil production alone is estimated to contribute 0.038 to 0.045 GtC yr-1, and Indonesian palm oil expansion contributed up to 9% of tropical land-use change carbon emissions in the 2000s (Carlson and Curran 2013 <sup>[[#fn:r351|351]]</sup> ), however, the mitigation benefit of sustainable sourcing of palm oil has not been quantified. There are no estimates of the mitigation potential for urban food systems.

Efficient use of energy and resources in food transport and distribution contribute to a reduction in GHG emissions, estimated to be 1% of global CO2 emissions (James and James 2010 <sup>[[#fn:r352|352]]</sup> ; Vermeulen et al. 2012b <sup>[[#fn:r353|353]]</sup> ). Given that global CO2 emissions in 2017 were 37 GtCO2, this equates to 0.37 GtCO2 yr–1 (covering food transport and distribution, improved efficiency of food processing and retailing, and improved energy efficiency) (Table 6.19).

Table 6.19 summarises the mitigation potentials for supply management options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence in based.

<div id="section-6-3-1-2-integrated-response-options-based-on-value-chain-management-block-4"></div>

<span id="table-6.19"></span>
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'''Table 6.19'''

<span id="mitigation-effects-of-response-options-based-on-supply-management."></span>
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'''Mitigation effects of response options based on supply management.'''
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[[File:40ab5df7ca9f89b471aae9e245c3ca92 table-6.19.png]]

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<div id="section-6-3-1-3-integrated-response-options-based-on-risk-management"></div>

<span id="integrated-response-options-based-on-risk-management-1"></span>
==== 6.3.1.3 Integrated response options based on risk management ====

<div id="section-6-3-1-3-integrated-response-options-based-on-risk-management-block-1"></div>

In this section, the impacts on climate change mitigation of integrated response options based on risk management are assessed. In general, because these options are focused on adaptation and other benefits, the mitigation benefits are modest, and mostly unquantified.

Extensive and less dense urban development tends to have higher energy usage, particularly from transport (Liu et al. 2015 <sup>[[#fn:r354|354]]</sup> ), such that a 10% reduction of very low-density urban fabrics is correlated with 9% fewer emissions per capita in Europe (Baur et al. 2015 <sup>[[#fn:r355|355]]</sup> ). However, the exact contribution to mitigation from the prevention of land conversion in particular has not been well quantified (Thornbush et al. 2013 <sup>[[#fn:r356|356]]</sup> ). Suggestions from select studies in the USA are that biomass decreases by half in cases of conversion from forest to urban land uses (Briber et al. 2015 <sup>[[#fn:r357|357]]</sup> ), and a study in Bangkok found a decline by half in carbon sinks in the urban area in the past 30 years (Ali et al. 2018 <sup>[[#fn:r358|358]]</sup> ).

There is no literature specifically on linkages between livelihood diversification and climate mitigation benefits, although some forms of diversification that include agroforestry would likely result in increased carbon sinks (Altieri et al. 2015 <sup>[[#fn:r359|359]]</sup> ; Descheemaeker et al. 2016 <sup>[[#fn:r360|360]]</sup> ). There is no literature exploring linkages between local seeds and GHG emission reductions, although use of local seeds likely reduces emissions associated with transport for commercial seeds, though the impact has not been quantified.

While disaster risk management can presumably have mitigation co- benefits, as it can help reduce food loss on-farm (e.g., crops destroyed before harvest or avoided animal deaths during droughts and floods meaning reduced production losses and wasted emissions), there is no quantified global estimate for this potential.

Risk-sharing instruments could have some mitigation co-benefits if they buffer household losses and reduce the need to expand agricultural lands after experiencing risks. However, the overall impacts of these are unknown. Further, commercial insurance may induce producers to bring additional land into crop production, particularly marginal or land with other risks that may be more environmentally sensitive (Claassen et al. 2011a). Policies to deny crop insurance to farmers who have converted grasslands in the USA resulted in a 9% drop in conversion, which likely has positive mitigation impacts (Claassen et al. 2011a <sup>[[#fn:r361|361]]</sup> ). Estimates of emissions from cropland conversion in the USA in 2016 were 23.8 MtCO2e, only some of which could be attributed to insurance as a driver.

Table 6.20 summarises the mitigation potentials for risk management options, with confidence estimates based on the thresholds outlined in Table 6.53 in Section 6.3.6, and indicative (not exhaustive) references upon which the evidence is based.

<div id="section-6-3-1-3-integrated-response-options-based-on-risk-management-block-2"></div>

<span id="table-6.20"></span>
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<!-- TABLE IMG -->
<!-- IMG TITLE -->
'''Table 6.20'''

<span id="mitigation-effects-of-response-options-based-on-risk-management."></span>
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'''Mitigation effects of response options based on risk management.'''
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[[File:e906c9471e5bcf0cb5442ba0218b5ca4 table-6.20.png]]

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<span id="potential-of-the-integrated-response-options-for-delivering-adaptation"></span>