Cutting carbon emissions in half every decade through 20501 has become a benchmark for global2, national and corporate target-setting that delivers the Paris goal of limiting global warming to 1.5°C above pre-industrial levels. However, with a rapidly shrinking remaining carbon budget3, here we show that halving fossil emissions every decade alongside scaling negative emissions technologies (NETs) to balance remaining fossil CO2 emissions by 2050, is no longer enough to avoid significant and lengthy overshoot past 1.5°C, unless improvements in ecosystem stewardship are also accelerated beyond levels currently assumed in most 1.5°C-aligned climate scenarios. We further show that a decadal acceleration of natural climate solutions, reaching net-zero emissions from agriculture, forestry and land use by 2030 and -7 gigatons CO2e per year of net removals by 2050, is both consistent with sectoral (or “bottom-up”) estimates of cost-effective potential and can keep the window to 1.5°C decisively open, if delivered alongside decadal halvings of fossil-fuel emissions and scaling of NETs. This “Carbon Law for Nature” mitigation pathway can feasibly be achieved through a transformation of humanity’s land and coastal stewardship: protecting remaining intact ecosystems, climate-smart management of agricultural and forestry lands, restoring natural ecosystems where appropriate, and reducing excess demand for land-intensive products. Crucially, following this pathway also minimizes the magnitude and length of time of temperature overshoot, reducing both the chronic impacts of climate change4 and the risk of exceeding tipping points in the earth system5.

Integrated conservation and development efforts in low- and middle-income countries have emphasized the devolution of forest management to local communities. This approach is posited to benefit both communities and conservation, but those benefits may depend on community capacity to capture value added, e.g., by processing forest products. In Mexico, most forests are under community management, but only some communities have vertically integrated their wood products supply chain through the establishment of community sawmills. The different timing of sawmill construction allows us to test the hypothesis that vertical integration of the wood products supply chain under community management is protective of forests. We use detailed, spatially explicit panel data from southern Mexico that allow us to examine impacts on land use change (deforestation and forest regrowth) separately from temporary changes in tree cover within forest areas. We find that vertical integration, as indicated by the presence of community sawmills and corroborated by a government classification of ejidos, reduced deforestation while increasing forest regrowth. Our findings, thus, have a somewhat counter-intuitive policy implication: programs that increase financial resources for communities to invest in forestry operations could improve forest protection and restoration, with regional and global benefits for climate, biodiversity, and other ecosystem services.

Natural Climate Solutions (NCS) are the climate mitigation sector with the largest potential, yet the least investment. A major barrier to scaling NCS is lack of evidence-based scientific learning at the scale of actual interventions. To overcome this gap, we propose the world's largest field experiments, supported by a global data-sharing platform and guided by a clear framework of ethical principles and guidelines for delivering robust NCS evidence. This involves consistently reporting outcomes in units of MgCO2e $-1 yr-1 while describing direct and enabling actor groups and their financial, policy, and information interactions.

Extensive forest restoration is a key strategy to meet nature-based sustainable development goals and provide multiple social and environmental benefits. Yet achieving forest restoration at scale requires cost-effective methods. Tree planting in degraded landscapes is a popular but costly forest restoration method, which often results in less biodiverse forests when compared to natural regeneration techniques under similar conditions. Here, we assess the current spatial distribution of pantropical natural forest (from 2000-2016) and use this information to present the first model of the potential for natural regeneration across tropical forested countries and biomes at 30-meter spatial resolution. We estimate that 215 million hectares - an area greater than the entire country of Mexico - have potential for natural forest regeneration, representing an above-ground carbon sequestration potential of 23.4 Gt CO2 (range 21.1-25.7 Gt) over 30 years. Five countries (Brazil, Indonesia, China, Mexico, and Colombia) account for 52% of this estimated potential, showcasing the need for targeting restoration initiatives that leverage natural regeneration potential. Our results facilitate broader equitable decision-making processes that capitalise on the widespread opportunity for natural regeneration to help achieve national and global environmental agendas.

Combating climate change and achieving the UN Sustainable Development Goals (SDGs) are two important challenges facing humanity. Natural climate solutions (NCSs) can contribute to the achievement of these two commitments but can also generate conflicting trade-offs. Here, we reviewed the literature and drew on expert knowledge to assess the co-benefits of and trade-offs between 150 SDG targets and NCSs within 12 selected ecosystems. We demonstrate that terrestrial, coastal, and marine NCSs enable the attainment of different sets of SDG targets, with low redundancy. Implementing NCSs in various ecosystems would therefore maximize achievement of SDG targets but would also induce trade-offs, particularly if best practices are not followed. Reliance on NCSs at large scales will require that these trade-offs be taken into consideration to ensure the simultaneous realization of positive climate outcomes and multiple SDG targets for diverse stakeholders.

Mitigating climate change cost-effectively requires identifying least-cost-per-ton GHG abatement methods. Here, we estimate and map GHG abatement cost (US$ per tCO2) for two common reforestation methods: natural regeneration and plantations. We do so by producing and integrating new maps of implementation costs and opportunity costs of reforestation, likely plantation genus and carbon accumulation by means of natural regeneration and plantations, accounting for storage in harvested wood products. We find natural regeneration (46%) and plantations (54%) would each have lower abatement cost across about half the area considered suitable for reforestation of 138 low- and middle-income countries. Using the more cost-effective method at each location, the 30 year, time-discounted abatement potential of reforestation below US$50 per tCO2 is 31.4 GtCO2 (24.2-34.3 GtCO2 below US$20-100 per tCO2)-44% more than natural regeneration alone or 39% more than plantations alone. We find that reforestation offers 10.3 (2.8) times more abatement below US$20 per tCO2 (US$50 per tCO2) than the most recent IPCC estimate. It is important to understand the cost-effectiveness of natural regeneration and plantations, which are common reforestation methods for mitigation. The authors estimate and map abatement costs for the two approaches across low- and mid-income countries, helping to guide reforestation initiatives.

Natural climate solutions can mitigate climate change in the near-term, during a climate-critical window. Yet, persistent misunderstandings about what constitutes a natural climate solution generate unnecessary confusion and controversy, thereby delaying critical mitigation action. Based on a review of scientific literature and best practices, we distill five foundational principles of natural climate solutions (nature-based, sustainable, climate-additional, measurable, and equitable) and fifteen operational principles for practical implementation. By adhering to these principles, practitioners can activate effective and durable natural climate solutions, enabling the rapid and wide-scale adoption necessary to meaningfully contribute to climate change mitigation.

Integrating trees into agricultural landscapes can provide climate mitigation and improves soil fertility, biodiversity habitat, water quality, water flow, and human health, but these benefits must be achieved without reducing agriculture yields. Prior estimates of carbon dioxide (CO2) removal potential from increasing tree cover in agriculture assumed a moderate level of woody biomass can be integrated without reducing agricultural production. Instead, we used a Delphi expert elicitation to estimate maximum tree covers for 53 regional cropping and grazing system categories while safeguarding agricultural yields. Comparing these values to baselines and applying spatially explicit tree carbon accumulation rates, we develop global maps of the additional CO2 removal potential of Tree Cover in Agriculture. We present here the first global spatially explicit datasets calibrated to regional grazing and croplands, estimating opportunities to increase tree cover without reducing yields, therefore avoiding a major cost barrier to restoration: the opportunity cost of CO2 removal at the expense of agriculture yields. The global estimated maximum technical CO2 removal potential is split between croplands (1.86 PgCO2 yr− 1) and grazing lands (1.45 PgCO2 yr− 1), with large variances. Tropical/subtropical biomes account for 54

Infestations of trees by woody climbing plants (i.e., lianas) are common and increasing in an estimated 250 Mha of the 1 billion hectares of mixed-species tropical and temperate forest subjected to selective logging. Cutting lianas that impede the growth of future crop trees (FCTs) in these forests would sequester carbon at low cost and increase timber yields. We estimate that application of this treatment to five liana-infested FCTs per hectare across the 250 Mha of selectively logged forest would result in 0.8 PgCO(2) of additional carbon removals by the liberated trees over 30 years at a direct cost of well less than $1.00 MgCO2-1. The same treatment could also be applied in forests not destined for logging where liana infestations were exacerbated by prior anthropogenic disturbances. If the numbers of trees liberated from lianas is kept small, undesired impacts on biodiversity will be minimized. One-Sentence Summary: Liberating future crop trees from lianas is a cost-effective way to increase rates of carbon sequestration, increase timber yields, and restore degraded forest.

Governments worldwide are seeking natural climate solutions that can provide economic stimulus while meeting climate goals. Forests provide essential carbon dioxide (CO 2 ) sequestration services, but their potential may be limited by elevated liana densities often resulting from human disturbance. Here we report the first estimate of liana ( Vitis spp.) impacts on CO 2 removal rates by trees in temperate Appalachian forests and suggest liana removal with biodiversity safeguards as a potential strategy for improved forest management. Shade‐intolerant tree species without lianas removed CO 2 20% faster than conspecifics with lianas ( p = 0.025). We did not detect significant impacts of liana presence on the CO 2 removal rates for shade‐tolerant species ( p = 0.838). Additionally, the merchantable boles of trees without lianas increased in volume 9% faster annually compared to trees with lianas, for all species ( p = 0.003). Our findings indicate that thinning lianas—particularly from light‐loving species such as Liriodendron tulipifera— may improve sustainability of forest management and increase carbon storage while mitigating climate change.

Carbon dioxide removal (CDR) figures prominently in modelled pathways to achieve the Paris Agreement's goal of limiting global warming to 1.5-2°C compared to pre-industrial levels. However, national roles and responsibilities to deliver CDR have been informed with CDR quota analyses that focus on developed economies and global major emitters. This study extends the discussion to implications for developing countries. For that purpose, we employ a diverse set of allocation methods on a wide range of global emissions scenarios to address equitability and uncertainty in sharing the burden of climate change mitigation. We further focus on tropical developing countries due to their large potential for natural climate solutions (NCS) that deliver CDR. Our analysis indicates the potential for stringent CDR quotas for the top seven countries that contribute ∼60% of pantropical cost-effective NCS potential, with median national quotas across emissions scenarios ranging from 0.1-29 GtCO2. However, the results reveal strong heterogeneity of quotas and inherent bias across allocation methods making agreement on an 'equitable' quota unlikely. Competition among NCS and non-NCS CDR options may arise when ambitious CDR quotas are implemented in countries with vast forest areas or large potential for expansion of tree cover. Therefore, it is important to not use CDR quotas to evaluate national climate actions or to inform climate targets that could exacerbate trade-offs between emissions reduction, biodiversity and ecosystem services in these NCS-rich countries. Instead, results from burden-sharing exercises could foster higher ambition if used to inform voluntary cooperation mechanisms. Discrepancy between perceived fairness and CDR quotas should be critically and transparently embraced to encourage acknowledgment of socio-ecological co-benefits as compensation. Such an approach will allow tropical developing economies to prioritise protection and restoration of nature in their climate change mitigation pathways.

This repository contains spatial and tabular data central to the analysis reported by Walker et al. (2022) on the global potential for increased storage of carbon on land. All maps provided here are global (excluding Antarctica) in geographic scope at a spatial resolution of ca. 500 meters in the MODIS sinusoidal projection (SR-ORG:6842). Maps are stored individually as single-band GeoTIFFs. Grid cell units for carbon density maps are megagrams of carbon per hectare (MgC/ha). Water has been masked out as NoData (-32768). Associated computer code is available for download from https://github.com/whrc/Global-Potential-Carbon.

Huge areas of tropical forests are degraded, reducing their biodiversity, carbon, and timber value. The recovery of these degraded forests can be significantly inhibited by climbing plants such as lianas. Removal of super-abundant climbers thus represents a restoration action with huge potential for application across the tropics. While experimental studies largely report positive impacts of climber removal on tree growth and biomass accumulation, the efficacy of climber removal varies widely, with high uncertainty as to where and how to apply the technique. Using meta-analytic techniques, we synthesize results from 26 studies to quantify the efficacy of climber removal for promoting tree growth and biomass accumulation. We find that climber removal increases tree growth by 156% and biomass accumulation by 209% compared to untreated forest, and that efficacy remains for at least 19 years. Extrapolating from these results, climber removal could sequester an additional 32 Gigatons of CO2 over 10 years, at low cost, across regrowth, and production forests. Our analysis also revealed that climber removal studies are concentrated in the Neotropics (N = 22), relative to Africa (N = 2) and Asia (N = 2), preventing our study from assessing the influence of region on removal efficacy. While we found some evidence that enhancement of tree growth and AGB accumulation varies across disturbance context and removal method, but not across climate, the number and geographical distribution of studies limits the strength of these conclusions. Climber removal could contribute significantly to reducing global carbon emissions and enhancing the timber and biomass stocks of degraded forests, ultimately protecting them from conversion. However, we urgently need to assess the efficacy of removal outside the Neotropics, and consider the potential negative consequences of climber removal under drought conditions and for biodiversity.

Nature-based efforts could further climate mitigation and help limit warming to 1.5°C, given that proper and immediate solutions are implemented with similar ambition as in energy and industry sectors; however, omission of natural solutions or delays in overall climate action would substantially undermine the climate target of Paris Agreement.

Governments worldwide are seeking natural climate solutions that can provide economic stimulus while meeting climate goals. Forests provide essential carbon dioxide sequestration services, but their potential may be limited by elevated liana densities often resulting from human disturbance. Here we report the first quantification of climate impacts, in the form of CO 2 removal, from liana presence in Appalachian forests. We investigated the impact of lianas ( Vitis spp.) on carbon storage in central Appalachia. We found that liana presence significantly reduced carbon sequestration rates of all trees (p=0.0227) and other metrics of tree growth. More specifically, we detected significant impacts of liana presence on shade-intolerant tree species (p=0.0354), but we did not find significant impacts on shade tolerant tree species (p=0.393). Our findings indicate that thinning abundant grape vines from trees—particularly species that are less shade tolerant such as Liriodendron tulipifera and Quercus rubra— may offer an important natural forest management strategy to increase timber value while mitigating climate change.

Significance Despite increased interest in land-based carbon storage as a climate solution, there are physical limits on how much additional carbon can be incorporated into terrestrial ecosystems. To effectively determine where and how to act, jurisdictions need robust data illustrating the magnitude and distribution of opportunities to increase carbon storage, as well as information on the actions available to achieve that storage. Here, we provide globally consistent maps for directing additional carbon storage under current and future climate, as well as a framework for determining how that storage could be gained through restoration, improved management, or maintenance of woody biomass and soil organic matter. Our estimates provide an upper bound on how improved land stewardship can mitigate the climate crisis.

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25 000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (⩽20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0–7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps.

Limited time and resources remain to constrain the climate crisis. Natural climate solutions represent promising options to protect, manage and restore natural lands for additional climate mitigation, but they differ in (1) the magnitude and (2) immediacy of mitigation potential, as well as (3) cost-effectiveness and (4) the co-benefits they offer. Counter to an emerging preference for restoration, we use these four criteria to propose a general rule of thumb to protect, manage and then restore lands, but also show how these criteria explain alternative prioritization and portfolio schemes. This hierarchy offers a decision-making framework for public and private sector actors to optimize the effectiveness of natural climate solutions in an environment in which resources are constrained, and time is short. Natural climate solutions, along with reduction in fossil fuel emissions, are critical to mitigating climate change and meeting climate goals. This Perspective outlines a hierarchy for decision-making regarding protecting, managing and then restoring natural systems for climate mitigation.

Analysis suggests that to limit global temperature rise, we must slash emissions and invest now to protect, manage and restore ecosystems and land for the future. Analysis suggests that to limit global temperature rise, we must slash emissions and invest now to protect, manage and restore ecosystems and land for the future.