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The Moirai land data system, written in C and R, is designed to produce recent historical land inputs for an integrated human-Earth systems model. The primary function of Moirai is to combine spatially explicit input data (e.g., raster images) with tabular input data (e.g., crop price table) to generate spatially-referenced tabular data of crop production, crop harvested area, land value, irrigated and rainfed crop area, water footprint, soil and vegetation carbon density of unmanaged land, and historical land use/cover. These data are aggregated to user-defined geographic boundaries within 231 countries and the default boundaries are defined globally by 235 watersheds. The production, harvested area, and land value outputs reconstruct those available from the Global Trade Analysis Project, while the other outputs provide additional information for various applications, such as initializing or evaluating a land use change model or an economic general/partial equilibrium model. Furthermore, Moirai is a modular system that can be updated and customized through replacement and addition of source data.

Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO _2 ) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO _2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute $1.4_{0.7}^{2.1}$ % ( $ - 1.8_{ - 0.9}^{ - 2.7}$ Mt CO _2 eq y ^−1 ) and $4.6_{2.3}^{6.9}$ % ( $ - 6.0_{ - 3.0}^{ - 8.9}$ Mt CO _2 eq y ^−1 ) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO _2 eq y ^−1 ), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to $4.1_{2.5}^{5.6}$ % ( $ - 5.2_{ - 3.2}^{ - 7.3}$ Mt CO _2 eq y ^−1 ) and $13.5_{8.2}^{18.6}$ % ( $ - 17.5_{ - 10.7}^{ - 24.2}$ Mt CO _2 eq y ^−1 ), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

Land-use and -cover change (LUCC) is globally important to climate change mitigation. However, using land-based strategies to support aggressive subnational greenhouse gas emissions reduction targets is challenging due to competing land use priorities and uncertainty in ecosystem carbon dynamics and climate change effects. We used the California natural and working lands carbon and greenhouse gas model to quantify the direct ecosystem carbon emissions (CO _2 and CH _4 ) impacts, trade-offs, and climate change interactions of two policy scenarios identified by the State of California for fulfilling multiple land use goals, including the competing goals of mitigating wildfire severity and landscape carbon emissions, among others. Here we show that emissions from desired forest management to reduce the amount of combustible biomass (fuel reduction) initially outweighed emissions reductions from other strategies (e.g. less intensive forest management, restoration, land conservation); however, avoided emissions and enhanced carbon sequestration from the other strategies gradually outweighed fuel reduction emissions. Thus, in jurisdictions with large-scale wildfire mitigation goals, practices that reduce emissions and/or increase carbon sequestration can simultaneously offset fuel reduction emissions. Our analysis highlights the complexities inherent in LUCC planning, underscoring the need for governments to begin the task now.