GeoCarb™: A Latitude-Based Carbon Absorption Model for Independent Pre-Verification of Nature-Based Solution Projects. (Species-Specific Gaussian Calibration and Application to Climate Finance Due Diligence)

Nature-based solution (NbS) projects are increasingly central to climate finance portfolios, yet no independent tool exists to verify the physical plausibility of carbon sequestration claims at the proposal stage. Existing verification frameworks-including Verra and Gold Standard-focus on ex-post verification, leaving a structural gap in GCF and MDB review processes where overstated carbon claims cannot be independently assessed prior to funding approval. This paper presents GeoCarb™ v1.1, a latitude-based carbon absorption model that predicts annual CO₂ sequestration for NbS projects using three inputs: latitude, vegetation species, and project area. GeoCarb™ employs species-specific Gaussian functions G(φ) = A•exp(-(φ-φ₀)²/2σ²) as its core equation, integrated with Liebig minimum correction and VaR-based risk adjustment. Literature-based calibration across seven vegetation types yielded an overall R² of 0.9883 and RMSE of 34.0 gC/m²/yr, validated against MODIS MOD17A3 satellite NPP data across 27 latitude bands. Applied to an actual GCF funding proposal, GeoCarb™ detected a 32.4% overstatement of carbon sequestration claims relative to physically achievable levels for a wildflower restoration project in Madagascar. Benchmark comparisons against registered NbS projects in Africa, together with one boundary-case test in Indonesia, confirmed prediction accuracy within ±10%. GeoCarb™ is immediately applicable to NbS proposal pre-screening by GCF and MDBs, geographic optimization of REDD+ investments, and exante estimation of carbon budget contributions. To our knowledge, it represents the first independent ex-ante verification model designed to address the structural gap in climate finance decision-making on the path to net-zero 2050.