Editing IPCC:AR6/WGIII/Chapter-3 (section)

=== 3.4.7 Other Carbon Dioxide Removal Options ===

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This subsection includes other CDR options not discussed in the previous subsections, including direct air carbon capture and storage (DACCS), enhanced weathering (EW), and ocean-based approaches, focusing on the role of these options in long-term mitigation pathways, using both IAMs ( [[#Chen--2013|Chen and Tavoni 2013]] ; [[#Marcucci--2017|Marcucci et al. 2017]] ; [[#Rickels--2018|Rickels et al. 2018]] ; [[#Fuhrman--2019|Fuhrman et al. 2019]] , 2020, 2021; [[#Realmonte--2019|Realmonte et al. 2019]] ; Akimoto et al. 2021; [[#Strefler--2021a|Strefler et al. 2021a]] ) and non-IAMs ( [[#Fuss--2013|Fuss et al. 2013]] ; [[#González--2016|González and Ilyina 2016]] ; [[#Bednar--2021|Bednar et al. 2021]] ; [[#Shayegh--2021|Shayegh et al. 2021]] ). There are other options discussed in the literature, such as methane capture ( [[#Jackson--2019|Jackson et al. 2019]] ), however, the role of these options in long-term mitigation pathways has not been quantified and is thus excluded here. [[IPCC:Wg3:Chapter:Chapter-12|Chapter 12]] includes a more detailed description of the individual technologies, including their costs, potentials, financing, risks, impacts, maturity and upscaling.

Very few studies and pathways include other CDR options (Table 3.5). Pathways with DACCS include potentially large removal from DACCS (up to 37 GtCO 2 yr –1 in 2100) in the second half of the century ( [[#Chen--2013|Chen and Tavoni 2013]] ; [[#Marcucci--2017|Marcucci et al. 2017]] ; [[#Realmonte--2019|Realmonte et al. 2019]] ; [[#Fuhrman--2020|Fuhrman et al. 2020]] , 2021; [[#Shayegh--2021|Shayegh et al. 2021]] ; Akimoto et al. 2021) and reduced cost of mitigation ( [[#Bistline--2021|Bistline and Blanford 2021]] ; [[#Strefler--2021a|Strefler et al. 2021a]] ). At large scales, the use of DACCS has substantial implications for energy use, emissions, land, and water; substituting DACCS for BECCS results in increased energy usage, but reduced land-use change and water withdrawals ( [[#Fuhrman--2020|Fuhrman et al., 2020]] , 2021) (Chapter 12.3.2; AR6 WGI Chapter 5). The level of deployment of DACCS is sensitive to the rate at which it can be scaled up, the climate goal or carbon budget, the underlying socio-economic scenario, the availability of other decarbonisation options, the cost of DACCS and other mitigation options, and the strength of carbon-cycle feedbacks ( [[#Chen--2013|Chen and Tavoni 2013]] ; [[#Fuss--2013|Fuss et al. 2013]] ; [[#Honegger--2018|Honegger and Reiner 2018]] ; [[#Realmonte--2019|Realmonte et al. 2019]] ; [[#Fuhrman--2020|Fuhrman et al. 2020]] ; [[#Bistline--2021|Bistline and Blanford 2021]] ; [[#Fuhrman--2021|Fuhrman et al. 2021]] ; [[#Strefler--2021a|Strefler et al. 2021a]] ) (AR6 WGI Chapter 5). Since DACCS consumes energy, its effectiveness depends on the type of energy used; the use of fossil fuels would reduce its sequestration efficiency ( [[#Creutzig--2019|Creutzig et al. 2019]] ; [[#NASEM--2019|NASEM 2019]] ; [[#Babacan--2020|Babacan et al. 2020]] ). Studies with additional CDR options in addition to DACCS (e.g., enhanced weathering, BECCS, afforestation, biochar, and soil carbon sequestration) find that CO 2 removal is spread across available options ( [[#Holz--2018|Holz et al. 2018]] ; [[#Strefler--2021a|Strefler et al. 2021a]] ). Similar to DACCS, the deployment of deep-ocean storage depends on cost and the strength of carbon-cycle feedbacks ( [[#Rickels--2018|Rickels et al. 2018]] ).

'''Table 3.5 |Carbon dioxide removal in assessed pathways.''' Scenarios are grouped by temperature categories, as defined in [[#3.2.4|Section 3.2.4]] . Quantity indicates the median and 5–95th percentile range of cumulative sequestration from 2020 to 2100 in GtCO 2 . Count indicates the number of scenarios with positive values for that option. Source: AR6 Scenarios Database.

{| class="wikitable"
|-
! rowspan="2"| CDR option

! colspan="2"| C1: Limit warming to 1.5°C (&gt;50%) with no or limited overshoot

! colspan="2"| C2: Return warming to 1.5°C (&gt;50%) after a high overshoot

! colspan="2"| C3: Limit warming to 2°C (&gt;67%)

|-
! Quantity

! Count

! Quantity

! Count

! Quantity

! Count

|-
| CO 2 removal on managed land including Afforestation/Reforestation 1

| 262 (17–397)

| 64

| 330 (28–439)

| 82

| 209 (20–415)

| 196

|-
| BECCS

| 334 (32–780)

| 91

| 464 (226–842)

| 122

| 291 (174–653)

| 294

|-
| Enhanced weathering

| 0 (0–47)

| 2

| 0 (0–0)

| 1

| 0 (0–0)

| 1

|-
| DACCS

| 30 (0–308)

| 31

| 109 (0 – 539)

| 24

| 19 (0–253)

| 91

|}

1 Cumulative CDR from AFOLU cannot be quantified precisely because models use different reporting methodologies that in some cases combine gross emissions and removals, and use different baselines.

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