Reducing Uncertainties in Net Carbon Capture to Advance Wetlands as Natural Climate Solutions

Wetlands play an integral role as natural climate solutions due to their potential to sequester carbon dioxide (CO₂) from the atmosphere. However, myriad factors influence the spatial heterogeneity of organic carbon (OC) sequestration rates, necessitating techniques to reduce uncertainty in these rates if they are to guide policy decisions to meet national climate action targets. In this study, we combined expert knowledge with statistical learning techniques to derive place-based estimates of OC sequestration rates for wetlands on agricultural landscapes. Expert knowledge revealed complex relationships between process controls and OC sequestration rates, including carbon quantity, carbon quality, bulk density, cation exchange capacity, aggregate reactivity, redox potential, and temperature for wetlands. GIS and remotely sensed data were used as proxies for these process controls, which, along with field-based OC sequestration rates, were input into a statistical learning-based random forest (RF) model. This RF model predicted OC sequestration rates within reasonable error bounds, achieving adjusted coefficient of determination (R²) of 0.93, a mean absolute error of 0.05 Mg ha-1 yr-1, and a root mean square error of 0.08 Mg ha-1 yr-1. The variable importance analysis indicated that human impact index, various soil properties, and inundation probability were the most influential variables. Our findings suggest that statistical learning-based models grounded in an understanding of process controls and their interactions can reliably estimate OC sequestration rates, providing essential data to inform policy development and implementation for managing wetlands as natural climate solutions.

Natural climate solutions can contribute to climate change mitigation and other environmental and social goals. An emerging body of academic and gray literature seeks to identify how governance ecosystems, inclusive of diverse actors, the mechanisms they employ, and the conditions they create, can actualize the potential of natural climate solutions. Enabling conditions are a critical component of these governance ecosystems as they describe the conditions needed to achieve a desired outcome. However, limited empirical research explores what conditions and combinations of conditions might promote the implementation of natural climate solutions across agricultural landscapes. This paper aims to identify and categorize enabling conditions for scaling natural climate solutions adoption in agriculture to address this gap. This objective is achieved through 51 semi-structured key informant interviews with diverse experts engaged in climate action in Canada's agriculture sector, which are corroborated with relevant literature. The expertise of key informants includes: agricultural production; agricultural technology; climate and environmental policy and markets; sustainable investment; sustainable sourcing and agri-food supply chains; measuring, reporting, and verification of ecosystem services; technical assistance; and ecosystem modeling. Findings from the interviews suggest that the potential for natural climate solutions adoption is currently limited by several critical barriers, including regulatory uncertainty, insufficient investment in measuring and monitoring infrastructure, and a lack of accessible and relevant resources to inform and guide actors. Aggregated findings point to four principal enabling conditions that together form the foundational conditions for an enabling governance ecosystem for natural climate solutions adoption in agriculture: (1) coordinated and coherent governance approaches; (2) favourable market conditions; (3) streamlined and robust measuring, reporting and verification; and (4) capacity among actors. This paper's contribution includes identifying and organizing enabling conditions for scaling the adoption of agriculture-based natural climate solutions, which can help better position actors to build an effective governance ecosystem in Canada's agriculture sector and elsewhere.

A framework for promoting natural climate solutions in the agriculture sector

Natural Climate Solutions (NCS) are climate mitigation approaches that aim to incorporate sustainable practices in forest, agriculture, wetland, and grassland management to increase GHG mitigation from land sectors and have been estimated to be highly effective from global to local scales. As more state and local governments seek to address climate change using a range of available techniques, the potential of NCS has gained increasing attention. As NCS directly involves land management by a range of actors (such as farmers and landowners) operating within resource-dependent communities (such as those dependent on the forest sector), it also has the potential to significantly alter the socioeconomic conditions and opportunities for these communities, necessitating a critical assessment of how NCS implementation interacts with socioeconomic systems. In this work, we focus on the implementation of NCS in Washington State to support its 2050 net-zero goals. Using a novel research approach, we compare recently estimated NCS potentials along multiple pathways with estimates of county-level socioeconomic sensitivities, exposures, and adaptive capacities to NCS-related changes and highlight the potential challenges that exist. These challenges can significantly limit the estimated GHG reduction and ecosystem co-benefits from NCS if they are implemented without due consideration of potential social interactions. We outline policies that can supplement NCS implementation to support just and equitable approaches that contribute to resilient communities and enhance human wellbeing while mitigating GHG emissions from the natural lands of Washington state.

Abstract. For wetlands to serve as natural climate solutions, accurate estimates of organic carbon (OC) sequestration rates in wetland sediments are needed. Dating using cesium-137 (137Cs) and lead-210 (210Pb) radioisotopes is commonly used for measuring OC sequestration rates in wetland sediments. 137Cs radioisotope dating is relatively simple, with calculations based on a single point representing the onset (1954) or peak (1963) of the 137Cs fallout. 210Pb radioisotope dating is more complex, as the calculations are based on multiple points. Here, we show that reliable dating of sediment cores collected from wetlands can be achieved using either 137Cs or 210Pb dating or their combination. However, 137Cs and 210Pb profiles along the depth of sediment cores need to be screened, analyzed, and interpreted carefully to estimate OC sequestration rates with high precision. To this end, we propose a decision framework for screening 137Cs and 210Pb profiles into high- and low-quality sediment profiles, and we compare dating using the 1954 and 1963 time markers, i.e., the rates of sedimentation and, consequently, OC sequestration over the past ∼ 60 years. Our findings suggest that 137Cs- and 210Pb-based OC sequestration rates are comparable, especially when using the 1963 (vs. 1954) time marker.

Novel carbon dynamics assessment framework reveals climate positive land management approaches across North America

Natural climate solutions (NCS) could provide over one-third of the climate mitigation needed between now and 2030 to limit warming below 2°C and support the Sustainable Development Goals. However, large disparities persist between the estimated biophysical climate mitigation potential (CMP) of NCS and their actual implementation. Social, political, informational, and economic factors contribute to this gap, but the spatial distribution of these constraints and their impacts on different NCS pathways remains poorly understood. Understanding these constraints is especially important due to the large uncertainties in NCS CMP and growing research on spatial prioritization of NCS, often based only on biophysical criteria. We identified and mapped nonbiophysical constraints to NCS implementation efficacy by conducting a systematic review of recent peer-reviewed literature across 10 high-CMP NCS pathways. From 1,821 papers, we identified 352 that provided 2,480 observations of 39 unique constraints from 135 countries. We mapped the spatial distribution of these constraints and analyzed patterns across NCS pathways and geographic classifications. Lack of funding, insufficient information on NCS management, and ineffective policies emerged as the most common constraints globally. However, each pathway and geography faced a distinct suite of interrelated constraints spanning multiple categories. These findings highlight the need for context-specific, equitable solutions, likely requiring transdisciplinary approaches and cross-sectoral collaborations. The results could also help increase accuracy of NCS CMP estimates. We discuss how adaptive management may be used for NCS initiatives at any scale to proactively diagnose co-occurring constraints at each implementation phase and to develop integrated, place-based solutions.

Mitigating climate change requires clean energy and the removal of atmospheric carbon. Building soil carbon is an appealing way to increase carbon sinks and reduce emissions owing to the associated benefits to agriculture. However, the practical implementation of soil carbon climate strategies lags behind the potential, partly because we lack clarity around the magnitude of opportunity and how to capitalize on it. Here we quantify the role of soil carbon in natural (land-based) climate solutions and review some of the project design mechanisms available to tap into the potential. We show that soil carbon represents 25% of the potential of natural climate solutions (total potential, 23.8 Gt of CO2-equivalent per year), of which 40% is protection of existing soil carbon and 60% is rebuilding depleted stocks. Soil carbon comprises 9% of the mitigation potential of forests, 72% for wetlands and 47% for agriculture and grasslands. Soil carbon is important to land-based efforts to prevent carbon emissions, remove atmospheric carbon dioxide and deliver ecosystem services in addition to climate mitigation. Diverse strategies are needed to mitigate climate change. This study finds that storing carbon in soils represents 25% of land-based potential, of which 60% must come from rebuilding depleted carbon stores.

Natural climate solutions (NCS) are recognized as an important tool for governments to reduce greenhouse gas emissions and remove atmospheric carbon dioxide. Using California as a globally relevant reference, we evaluate the magnitude of biological climate mitigation potential from NCS starting in 2020 under four climate change scenarios. By mid-century NCS implementation leads to a large increase in net carbon stored, flipping the state from a net source to a net sink in two scenarios. Forest and conservation land management strategies make up 85% of all NCS emissions reductions by 2050, with agricultural strategies accounting for the remaining 15%. The most severe climate change impacts on ecosystem carbon materialize in the latter half of the century with three scenarios resulting in California ecosystems becoming a net source of carbon emissions under a baseline trajectory. However, NCS provide a strong attenuating effect, reducing land carbon emissions 41–54% by 2100 with total costs of deployment of 752–777 million USD annually through 2050. Rapid implementation of a portfolio of NCS interventions provides long-term investment in protecting ecosystem carbon in the face of climate change driven disturbances. This open-source, spatially-explicit framework can help evaluate risks to NCS carbon storage stability, implementation costs, and overall mitigation potential for NCS at jurisdictional scales.

Natural Climate Solutions (NCS) – protection, restoration, and improved management of lands and waters that reduce greenhouse gasses – have large climate change mitigation potential. However, a lack of comprehensive information on NCS implementation challenges hinders NCS adoption and delivery of near-term mitigation. Using a global survey of NCS projects and a systematic review of recent NCS studies, we map 46 constraints in eight categories, yielding 15,572 geo-referenced NCS pathway-constraint observations from 501 studies and projects in 137 countries covering 20 of 22 UN subregions. Social-behavioral, Knowledge, and Government-organizational are the most-reported constraint categories, and lack of policy coordination or implementation capacity the most-observed constraint and most frequently top-ranking constraint for pathways and subregions. Despite broad congruence, top constraint and category rankings vary among subregions and pathways, respectively. NCS projects generally encounter multiple constraints in multiple categories, indicating complex challenges. Without enabling efforts, near-term NCS mitigation may remain well below its biophysical potential.

Natural climate solutions. The way forward

Future land-use competition constrains natural climate solutions

Increasing concentrations of greenhouse gases (GHGs) are causing global climate change and decreasing the stability of the climate system. Long-term solutions to climate change will require reduction in GHG emissions as well as the removal of large quantities of GHGs from the atmosphere. Natural climate solutions (NCS), i.e., changes in land management, ecosystem restoration, and avoided conversion of habitats, have substantial potential to meet global and national greenhouse gas (GHG) reduction targets and contribute to the global drawdown of GHGs. However, the relative role of NCS to contribute to GHG reduction at subnational scales is not well known. We examined the potential for 12 NCS activities on natural and working lands in Oregon, USA to reduce GHG emissions in the context of the state’s climate mitigation goals. We evaluated three alternative scenarios wherein NCS implementation increased across the applicable private or public land base, depending on the activity, and estimated the annual GHG reduction in carbon dioxide equivalents (CO2e) attributable to NCS from 2020 to 2050. We found that NCS within Oregon could contribute annual GHG emission reductions of 2.7 to 8.3 MMT CO2e by 2035 and 2.9 to 9.8 MMT CO2e by 2050. Changes in forest-based activities including deferred timber harvest, riparian reforestation, and replanting after wildfires contributed most to potential GHG reductions (76 to 94% of the overall annual reductions), followed by changes to agricultural management through no-till, cover crops, and nitrogen management (3 to 15% of overall annual reductions). GHG reduction benefits are relatively high per unit area for avoided conversion of forests (125–400 MT CO2e ha-1). However, the existing land use policy in Oregon limits the current geographic extent of active conversion of natural lands and thus, avoided conversions results in modest overall potential GHG reduction benefits (i.e., less than 5% of the overall annual reductions). Tidal wetland restoration, which has high per unit area carbon sequestration benefits (8.8 MT CO2e ha-1 yr-1), also has limited possible geographic extent resulting in low potential (< 1%) of state-level GHG reduction contributions. However, co-benefits such as improved habitat and water quality delivered by restoration NCS pathways are substantial. Ultimately, reducing GHG emissions and increasing carbon sequestration to combat climate change will require actions across multiple sectors. We demonstrate that the adoption of alternative land management practices on working lands and avoided conversion and restoration of native habitats can achieve meaningful state-level GHG reductions.

Increasing concentrations of greenhouse gases (GHGs) are causing global climate change and decreasing the stability of the climate system. Long-term solutions to climate change will require reduction in GHG emissions as well as the removal of large quantities of GHGs from the atmosphere. Natural climate solutions (NCS), i.e., changes in land management, ecosystem restoration, and avoided conversion of habitats, have substantial potential to meet global and national greenhouse gas (GHG) reduction targets and contribute to the global drawdown of GHGs. However, the relative role of NCS to contribute to GHG reduction at subnational scales is not well known. We examined the potential for 12 NCS activities on natural and working lands in Oregon, USA to reduce GHG emissions in the context of the state's climate mitigation goals. We evaluated three alternative scenarios wherein NCS implementation increased across the applicable private or public land base, depending on the activity, and estimated the annual GHG reduction in carbon dioxide equivalents (CO2e) attributable to NCS from 2020 to 2050. We found that NCS within Oregon could contribute annual GHG emission reductions of 2.7 to 8.3 MMT CO2e by 2035 and 2.9 to 9.8 MMT CO2e by 2050. Changes in forest-based activities including deferred timber harvest, riparian reforestation, and replanting after wildfires contributed most to potential GHG reductions (76 to 94% of the overall annual reductions), followed by changes to agricultural management through no-till, cover crops, and nitrogen management (3 to 15% of overall annual reductions). GHG reduction benefits are relatively high per unit area for avoided conversion of forests (125-400 MT CO2e ha-1). However, the existing land use policy in Oregon limits the current geographic extent of active conversion of natural lands and thus, avoided conversions results in modest overall potential GHG reduction benefits (i.e., less than 5% of the overall annual reductions). Tidal wetland restoration, which has high per unit area carbon sequestration benefits (8.8 MT CO2e ha-1 yr-1), also has limited possible geographic extent resulting in low potential (< 1%) of state-level GHG reduction contributions. However, co-benefits such as improved habitat and water quality delivered by restoration NCS pathways are substantial. Ultimately, reducing GHG emissions and increasing carbon sequestration to combat climate change will require actions across multiple sectors. We demonstrate that the adoption of alternative land management practices on working lands and avoided conversion and restoration of native habitats can achieve meaningful state-level GHG reductions.

In recent years, increasing attention has been directed to “natural climate solutions” to mitigate climate change through the protection, restoration, and improved management of carbon-storing ecosystems. In practice, Indigenous Peoples have been implementing natural climate solutions for millennia through land stewardship. As Indigenous nations and communities in Canada reassert stewardship roles through Indigenous Guardians programs, the question arises: what possibilities emerge when natural climate solutions are driven by Guardians, guided by multifaceted community priorities and Indigenous knowledge? This paper responds to this question, drawing upon collaborative research with Wahkohtowin Development, a social enterprise based in Treaty 9 territory (Ontario, Canada), made up of Chapleau Cree First Nation, Missanabie Cree First Nation, and Brunswick House First Nation. We engaged youth Guardians in workshops that generated insights on the role of youth, cross-cultural collaboration, and holistic conceptualizations of climate action rooted in Indigenous ontologies (such as the Cree philosophy of wahkohtowin, embodying kinship and interconnectedness). Our analysis reveals that Indigenous Guardians are well positioned to advance natural climate solutions and to do so in an integrative manner that addresses intersecting challenges—with benefits for communities, ecosystems, climate action, and reconciliation.