Approach: The spend-based method estimates Scope 3 emissions by multiplying procurement expenditure by an emission intensity factor (kg CO₂e per USD spent). This is consistent with the GHG Protocol Scope 3 Technical Guidance and recommended for screening-level assessments.

Emission Intensity Factors: Base factors are sourced from the US EPA USEEIO v2.0 model — a peer-reviewed, environmentally extended input-output model published in 2021. USEEIO provides supply-chain GHG intensities across all US economic sectors, covering CO₂, CH₄, N₂O, and fluorinated gases (as CO₂e using AR5 GWPs).

Regional Adjustment: Country/region multipliers adjust for differences in electricity grid carbon intensity, industrial efficiency, and supply chain structure. Multipliers are calibrated against EXIOBASE 3.8 (a multi-regional I-O database covering 49 countries) and IEA CO₂ Highlights 2023. The US (USEEIO baseline) = 1.00.

Currency Conversion: Non-USD spend is converted to USD (approximate 2024 rates) before applying intensity factors. Exchange rate movements may affect results.

Climatiq Integration: When a valid Climatiq API key is provided, the app queries Climatiq's verified emission factor database for spend-based estimates, replacing embedded factors where available. Climatiq aggregates DEFRA, EPA, IPCC, and other authoritative sources.

Scope 3 Category Mapping: Each procurement category is automatically mapped to the relevant GHG Protocol Scope 3 category (Cat. 1: Purchased Goods & Services, Cat. 2: Capital Goods, Cat. 3: Fuel & Energy-Related Activities, Cat. 4: Upstream Transportation, Cat. 5: Waste, Cat. 6: Business Travel, Cat. 8: Upstream Leased Assets).

Uncertainty: Spend-based factors have typical uncertainty of ±40–60% per line item. Results are suitable for hotspot identification and high-level screening, not for verified emissions reporting without primary data validation.

Standards: GHG Protocol Corporate Value Chain (Scope 3) Standard · ISO 14064-1:2018 · TCFD recommendations.