Most nations recently agreed to hold global average temperature rise to well below 2 °C. We examine how much climate mitigation nature can contribute to this goal with a comprehensive analysis of “natural climate solutions” (NCS): 20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We show that NCS can provide over one-third of the cost-effective climate mitigation needed between now and 2030 to stabilize warming to below 2 °C. Alongside aggressive fossil fuel emissions reductions, NCS offer a powerful set of options for nations to deliver on the Paris Climate Agreement while improving soil productivity, cleaning our air and water, and maintaining biodiversity.

Better stewardship of land is needed to achieve the Paris Climate Agreement goal of holding warming to below 2 °C; however, confusion persists about the specific set of land stewardship options available and their mitigation potential. To address this, we identify and quantify “natural climate solutions” (NCS): 20 conservation, restoration, and improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We find that the maximum potential of NCS—when constrained by food security, fiber security, and biodiversity conservation—is 23.8 petagrams of CO 2 equivalent (PgCO 2 e) y −1 (95% CI 20.3–37.4). This is ≥30% higher than prior estimates, which did not include the full range of options and safeguards considered here. About half of this maximum (11.3 PgCO 2 e y −1 ) represents cost-effective climate mitigation, assuming the social cost of CO 2 pollution is ≥100 USD MgCO 2 e −1 by 2030. Natural climate solutions can provide 37% of cost-effective CO 2 mitigation needed through 2030 for a >66% chance of holding warming to below 2 °C. One-third of this cost-effective NCS mitigation can be delivered at or below 10 USD MgCO 2 −1 . Most NCS actions—if effectively implemented—also offer water filtration, flood buffering, soil health, biodiversity habitat, and enhanced climate resilience. Work remains to better constrain uncertainty of NCS mitigation estimates. Nevertheless, existing knowledge reported here provides a robust basis for immediate global action to improve ecosystem stewardship as a major solution to climate change.

The Paris Climate Agreement declared a commitment to hold “the increase in the global average temperature to well below 2 °C above preindustrial levels” (1). Most Intergovernmental Panel on Climate Change (IPCC) scenarios consistent with limiting warming to below 2 °C assume large-scale use of carbon dioxide removal methods, in addition to reductions in greenhouse gas emissions from human activities such as burning fossil fuels and land use activities (2). The most mature carbon dioxide removal method is improved land stewardship, yet confusion persists about the specific set of actions that should be taken to both increase sinks with improved land stewardship and reduce emissions from land use activities (3).

The net emission from the land use sector is only 1.5 petagrams of CO 2 equivalent (PgCO 2 e) y−1, but this belies much larger gross emissions and sequestration. Plants and soils in terrestrial ecosystems currently absorb the equivalent of ∼20% of anthropogenic greenhouse gas emissions measured in CO 2 equivalents (9.5 PgCO 2 e y−1) (4). This sink is offset by emissions from land use change, including forestry (4.9 PgCO 2 e y−1) and agricultural activities (6.1 PgCO 2 e y−1), which generate methane (CH 4 ) and nitrous oxide (N 2 O) in addition to CO 2 (4, 5). Thus, ecosystems have the potential for large additional climate mitigation by combining enhanced land sinks with reduced emissions.

Here we provide a comprehensive analysis of options to mitigate climate change by increasing carbon sequestration and reducing emissions of carbon and other greenhouse gases through conservation, restoration, and improved management practices in forest, wetland, and grassland biomes. This work updates and builds from work synthesized by IPCC Working Group III (WGIII) (6) for the greenhouse gas inventory sector referred to as agriculture, forestry, and other land use (AFOLU). We describe and quantify 20 discrete mitigation options (referred to hereafter as “pathways”) within the AFOLU sector. The pathways we report disaggregate eight options reported by the IPCC WGIII and fill gaps by including activities such as coastal wetland restoration and protection and avoided emissions from savanna fires. We also apply constraints to safeguard the production of food and fiber and habitat for biological diversity. We refer to these terrestrial conservation, restoration, and improved practices pathways, which include safeguards for food, fiber, and habitat, as “natural climate solutions” (NCS).

For each pathway, we estimate the maximum additional mitigation potential as a starting point for estimating mitigation potential at or below two price thresholds: 100 and 10 USD MgCO 2 e−1. The 100 USD level represents the maximum cost of emissions reductions to limit warming to below 2 °C (7), while 10 USD MgCO 2 e−1 approximates existing carbon prices (8). We aggregate mitigation opportunities at the 100 USD threshold to estimate the overall cost-effective contribution of NCS to limiting global warming to below 2 °C. For 10 of the most promising pathways, we provide global maps of mitigation potential. Most notably, we provide a global spatial dataset of reforestation opportunities (https://zenodo.org/record/883444) constrained by food security and biodiversity safeguards. We also review noncarbon ecosystem services associated with each pathway.

These findings are intended to help translate climate commitments into specific NCS actions that can be taken by government, private sector, and local stakeholders. We also conduct a comprehensive assessment of overall and pathway-specific uncertainty for our maximum estimates to expose the implications of variable data quality and to help prioritize research needs.

Results and Discussion

Cost-Effective and Low-Cost NCS. We explore the proportion of maximum NCS mitigation potential that offers a cost-effective contribution to meeting the Paris Climate Agreement goal of limiting warming to below 2 °C. We define a <2 °C “cost-effective” level of mitigation as a marginal abatement cost not greater than ∼100 USD MgCO 2 −1 as of 2030. This value is consistent with estimates for the avoided cost to society from holding warming to below 2 °C (7, 25). We find that about half (11.3 PgCO 2 e y−1) of the maximum NCS potential meets this cost-effective threshold. To estimate the portion of NCS that are cost effective for holding warming to below 2 °C, we estimated the fraction of the maximum potential of each natural pathway (high = 90%, medium = 60%, or low = 30%) that could be achieved without exceeding costs of ∼100 USD MgCO 2 −1, informed by published marginal abatement cost curves. Our assignment of these indicative high, medium, and low cost-effective mitigation levels reflects the coarse resolution of knowledge on global marginal abatement costs for NCS. These default levels structured our collective judgment where cost curve data were incomplete (SI Appendix, Table S4). Using parallel methods, we find that more than one-third of the “<2 °C cost effective” levels for natural pathways are low cost (<10 USD MgCO 2 −1; 4.1 PgCO 2 e y−1; Fig. 1 and SI Appendix, Table S4). The “low-cost” and cost-effective NCS carbon sequestration opportunities compare favorably with cost estimates for emerging technologies, most notably bioenergy with carbon capture and storage (BECCS)—which range from ∼40 USD MgCO 2 −1 to over 1,000 USD MgCO 2 −1. Furthermore, large-scale BECCS is untested and likely to have significant impacts on water use, biodiversity, and other ecosystem services (2, 26). Our 100 USD constrained estimate (11.3 PgCO 2 e y−1) is considerably higher than prior central estimates (6, 14, 27, 28), and it is somewhat higher than the upper-end estimate from the IPCC Fifth Assessment Report (AR5) (10.6 PgCO 2 e y−1). Aside from our inclusion of previously ignored pathways as discussed above, this aggregate difference belies larger individual pathway differences between our estimates and those reported in the IPCC AR5. We find a greater share of cost-constrained potential through reforestation, forestry, wetland protection, and trees in croplands than the IPCC AR5, despite our stronger constraints on land availability, biodiversity conservation, and biophysical suitability for forests (14, 29).

NCS Contribution to a <2 °C Pathway. To what extent can NCS contribute to carbon neutrality by helping achieve net emission targets during our transition to a decarbonized energy sector? Warming will likely be held to below 2 °C if natural pathways are implemented at cost-effective levels indicated in Fig. 1, and if we avoid increases in fossil fuel emissions for 10 y and then drive them down to 7% of current levels by 2050 and then to zero by 2095 (Fig. 2). This scenario (14) assumes a 10-y linear increase of NCS to the cost-effective mitigation levels, and a >66% likelihood of holding warming to below 2 °C following a model by Meinshausen et al. (30). Under this scenario, NCS provide 37% of the necessary CO 2 e mitigation between now and 2030 and 20% between now and 2050. Thereafter, the proportion of total mitigation provided by NCS further declines as the proportion of necessary avoided fossil fuel emissions increases and as some NCS pathways saturate. Natural climate solutions are thus particularly important in the near term for our transition to a carbon neutral economy by the middle of this century. Given the magnitude of fossil fuel emissions reductions required under any <2 °C scenario, and the risk of relying heavily on negative emissions technologies (NETs) that remain decades from maturity (3), immediate action on NCS should not delay action on fossil fuel emissions reductions or investments in NETs. Fig. 2. Contribution of natural climate solutions (NCS) to stabilizing warming to below 2 °C. Historical anthropogenic CO 2 emissions before 2016 (gray line) prelude either business-as-usual (representative concentration pathway, scenario 8.5, black line) or a net emissions trajectory needed for >66% likelihood of holding global warming to below 2 °C (green line). The green area shows cost-effective NCS (aggregate of 20 pathways), offering 37% of needed mitigation through 2030, 29% at year 2030, 20% through 2050, and 9% through 2100. This scenario assumes that NCS are ramped up linearly over the next decade to <2 °C levels indicated in Fig. 1 and held at that level (=10.4 PgCO 2 y−1, not including other greenhouse gases). It is assumed that fossil fuel emissions are held level over the next decade then decline linearly to reach 7% of current levels by 2050. Half of this cost-effective NCS mitigation is due to additional carbon sequestration of 5.6 PgCO 2 e y−1 by nine of the pathways, while the remainder is from pathways that avoid further emissions of CO 2 , CH 4 , and N 2 O (SI Appendix, Fig. S4 and Table S1). Aggregate sequestration levels begin to taper off around 2060, although most pathways can maintain the 2030 mitigation levels we report for more than 50 years (Fig. 2 and pathway-specific saturation periods in SI Appendix, Table S1). The NCS scenario illustrated in Fig. 2 will require substantial near-term ratcheting up of both fossil fuel and NCS mitigation targets by countries to achieve the Paris Climate Agreement goal to hold warming to below 2 °C. Countries provided nationally determined contributions (NDCs) with 2025 or 2030 emissions targets as a part of the Paris Climate Agreement. While most NDCs indicate inclusion of land sector mitigation, only 38 specify land sector mitigation contributions, of 160 NDCs assessed (31). Despite these limitations, analyses indicate that if NDCs were fully implemented, NCS would contribute about 20% of climate mitigation (31) and about 2 PgCO 2 e y−1 mitigation by 2030 (31, 32). As such, a small portion of the 11.3 PgCO 2 e y−1 NCS opportunity we report here has been included in existing NDCs. Across all sectors, the NDCs fall short by 11–14 PgCO 2 e y−1 of mitigation needed to keep 2030 emissions in line with cost-optimal 2 °C scenarios (33). Hence, NCS could contribute a large portion—about 9 PgCO 2 e y−1—of the increased ambition needed by NDCs to achieve the Paris Climate Agreement. Our assessment of the potential contribution of NCS to meeting the Paris Agreement is conservative in three ways. First, payments for ecosystem services other than carbon sequestration are not considered here and could spur cost-effective implementation of NCS beyond the levels we identified. Natural climate solutions enhance biodiversity habitat, water filtration, flood control, air filtration, and soil quality (Fig. 1) among other services, some of which have high monetary values (34⇓–36) (see SI Appendix, Table S5 for details). Improved human health from dietary shifts toward plant-based foods reduce healthcare expenses and further offset NCS costs (37). Second, our findings are conservative because we only include activities and greenhouse gas fluxes where data were sufficiently robust for global extrapolation. For example, we exclude no-till agriculture (Conservation Agriculture pathway), we exclude improved manure management in concentrated animal feed operations (Nutrient Management pathway), we exclude adaptive multipaddock grazing (Grazing pathways), and we exclude soil carbon emissions that may occur with conversion of forests to pasture (Avoided Forest Conversion pathway). Future research may reveal a robust empirical basis for including such activities and fluxes within these pathways. Third, the Paris Agreement states goals of limiting warming to “well below 2 °C” and pursuing “efforts to limit the temperature increase to 1.5 °C.” Our analysis specifies a >66% chance of holding warming to just below 2 °C (30). Additional investment in all mitigation efforts (i.e., beyond ∼100 USD MgCO 2 −1), including NCS, would be warranted to keep warming to well below 2 °C, or to 1.5 °C, particularly if a very likely (90%) chance of success is desired.

Specific Pathway Contributions. Forest pathways offer over two-thirds of cost-effective NCS mitigation needed to hold warming to below 2 °C and about half of low-cost mitigation opportunities (SI Appendix, Table S4). Reforestation is the largest natural pathway and deserves more attention to identify low-cost mitigation opportunities. Reforestation may involve trade-offs with alternative land uses, can incur high costs of establishment, and is more expensive than Avoided Forest Conversion (38). However, this conclusion from available marginal abatement cost curves ignores opportunities to reduce costs, such as involving the private sector in reforestation activities by establishing plantations for an initial commercial harvest to facilitate natural and assisted forest regeneration (39). The high uncertainty of maximum reforestation mitigation potential with safeguards (95% CI 2.7–17.9 PgCO 2 e y−1) is due to the large range in existing constrained estimates of potential reforestation extent (345–1,779 Mha) (14, 16, 40⇓–42). As with most forest pathways, reforestation has well-demonstrated cobenefits, including biodiversity habitat, air filtration, water filtration, flood control, and enhanced soil fertility (34). See SI Appendix, Table S5 for detailed review of ecosystem services across all pathways. Our maximum reforestation mitigation potential estimate is somewhat sensitive to our assumption that all grazing land in forested ecoregions is reforested. If we assume that 25%, 50%, or 75% of forest ecoregion grazing lands were not reforested, it would result in 10%, 21%, and 31% reductions, respectively, in our estimate of reforestation maximum mitigation potential. While 42% of reforestation opportunities we identify are located on lands now used for grazing within forest ecoregions, at our <2 °C ambition mitigation level this would displace only ∼4% of global grazing lands, many of which do not occur in forested ecoregions (20). Grazing lands can be released by shifting diets and/or implementing Grazing-Feed and Grazing-Animal Management pathways, which reduce the demand for grazing lands without reducing meat and milk supply (43). Avoided Forest Conversion offers the second largest maximum and cost-effective mitigation potential. However, implementation costs may be secondary to public policy challenges in frontier landscapes lacking clear land tenure. The relative success of Brazil’s efforts to slow deforestation through a strong regulatory framework, accurate and transparent federal monitoring, and supply chain interventions provides a promising model (44), despite recent setbacks (45). We find relatively low uncertainty for Avoided Forest Conversion (±17%), reflecting considerable global forest monitoring research in the last decade stimulated by interest in reducing emissions from deforestation and forest degradation (REDD) (46). Improved forest management (i.e., Natural Forest Management and Improved Plantations pathways) offers large and cost-effective mitigation opportunities, many of which could be implemented rapidly without changes in land use or tenure. While some activities can be implemented without reducing wood yield (e.g., reduced-impact logging), other activities (e.g., extended harvest cycles) would result in reduced near-term yields. This shortfall can be met by implementing the Reforestation pathway, which includes new commercial plantations. The Improved Plantations pathway ultimately increases wood yields by extending rotation lengths from the optimum for economic profits to the optimum for wood yield. Grassland and agriculture pathways offer one-fifth of the total NCS mitigation needed to hold warming below 2 °C, while maintaining or increasing food production and soil fertility. Collectively, the grassland and agriculture pathways offer one-quarter of low-cost NCS mitigation opportunities. Cropland Nutrient Management is the largest cost-effective agricultural pathway, followed by Trees in Croplands and Conservation Agriculture. Nutrient Management and Trees in Croplands also improve air quality, water quality, and provide habitat for biodiversity (SI Appendix, Table S5). Our analysis of nutrient management improves upon that presented by the IPCC AR5 in that we use more recent data for fertilizer use and we project future use of fertilizers under both a “business as usual” and a “best management practice” scenario. Future remote sensing analyses to improve detection of low-density trees in croplands (47) will constrain our uncertainty about the extent of this climate mitigation opportunity. The addition of biochar to soil offers the largest maximum mitigation potential among agricultural pathways, but unlike most other NCS options, it has not been well demonstrated beyond research settings. Hence trade-offs, cost, and feasibility of large scale implementation of biochar are poorly understood. From the livestock sector, two improved grazing pathways (Optimal Intensity and Legumes) increase soil carbon, while two others (Improved Feed and Animal Management) reduce methane emission. Wetland pathways offer 14% of NCS mitigation opportunities needed to hold warming to <2 °C, and 19% of low-cost NCS mitigation. Wetlands are less extensive than forests and grasslands, yet per unit area they hold the highest carbon stocks and the highest delivery of hydrologic ecosystem services, including climate resilience (47). Avoiding the loss of wetlands—an urgent concern in developing countries—tends to be less expensive than wetland restoration (49). Improved mapping of global wetlands—particularly peatlands—is a priority for both reducing our reported uncertainty and for their conservation and restoration.

Challenges. Despite the large potential of NCS, land-based sequestration efforts receive only about 2.5% of climate mitigation dollars (50). Reasons may include not only uncertainties about the potential and cost of NCS that we discuss above, but also concerns about the permanence of natural carbon storage and social and political barriers to implementation. A major concern is the potential for Reforestation, Avoided Forest Conversion, and Wetland/Peatland pathways to compete with the need to increase food production. Reforestation and Avoided Forest Conversion remain the largest mitigation opportunities despite avoiding reforestation of mapped croplands and constraints we placed on avoiding forest conversion driven by subsistence agriculture (SI Appendix, Table S1). A large portion (42%) of our maximum reforestation mitigation potential depends on reduced need for pasture accomplished via increased efficiency of beef production and/or dietary shifts to reduce beef consumption. On the other hand, only a ∼4% reduction in global grazing lands is needed to achieve <2 °C ambition reforestation mitigation levels, and reduced beef consumption can have large health benefits (51). A portion of wetland pathways would involve limited displacement of food production; however, the extremely high carbon density of wetlands and the valuable ecosystem services they provide suggest that protecting them offers a net societal benefit (52). Feedbacks from climate change on terrestrial carbon stocks are uncertain. Increases in temperature, drought, fire, and pest outbreaks could negatively impact photosynthesis and carbon storage, while CO 2 fertilization has positive effects (53). Unchecked climate change could reverse terrestrial carbon sinks by midcentury and erode the long-term climate benefits of NCS (54). Thus, climate change puts terrestrial carbon stocks (2.3 exagrams) (55) at risk. Cost-effective implementation of NCS, by increasing terrestrial carbon stocks, would slightly increase (by 4%) the stocks at risk by 2050. However, the risk of net emissions from terrestrial carbon stocks is less likely under a <2 °C scenario. As such, NCS slightly increase the total risk exposure, yet will be a large component of any successful effort to mitigate climate change and thus help mitigate this risk. Further, most natural pathways can increase resilience to climate impacts. Rewetting wetlands reduces risk of peat fires (56). Reforestation that connects fragmented forests reduces exposure to forest edge disturbances (57). Fire management increases resilience to catastrophic fire (58). On the other hand, some of our pathways assume intensification of food and wood yields—and some conventional forms of intensification can reduce resilience to climate change (59). All of these challenges underscore the urgency of aggressive, simultaneous implementation of mitigation from both NCS and fossil fuel emissions reductions, as well as the importance of implementing NCS and land use intensification in locally appropriate ways with best practices that maximize resilience. While the extent of changes needed in global land stewardship is large (SI Appendix, Tables S1 and S4), we find that the environmental ambition reflected in eight recent multilateral announcements is well aligned with our <2 °C NCS mitigation levels. However, only four of these announcements are specific enough for quantitative comparison: The New York Declaration on Forests, the Bonn Challenge, the World Business Council on Sustainable Development Vision 2050, and the “4 pour 1000” initiative (SI Appendix, Table S6). The first three of these have quantitative targets that are somewhat more ambitious than our <2 °C mitigation levels for some pathways, while the 4 pour 1000 initiative is considerably more ambitious for soil carbon storage. More explicit and comprehensive policy targets for all biomes and natural pathways are needed to clarify the role of NCS in holding warming to below 2 °C.