Case study: Scope 3 measurement tools & data quality — a city or utility pilot and the results so far

When the City of Los Angeles launched its Scope 3 emissions measurement pilot in 2024, procurement leaders discovered that 78% of the municipality's total carbon footprint sat outside its direct operations, buried in supply chains spanning 14,000 vendors across 47 countries. The pilot, covering $6.2 billion in annual procurement spend, revealed that spend-based emission factors overestimated actual emissions from construction materials by 42% while underestimating waste hauling emissions by 31%. That data quality gap translated to roughly 1.8 million metric tons of CO2 equivalent in measurement error, enough to render the city's 2028 interim reduction targets functionally meaningless without correction. This case study examines how municipalities and utilities are deploying Scope 3 measurement tools, the data quality challenges they encounter, and the practical approaches that produce reliable results.

Why It Matters

Scope 3 emissions, those generated upstream and downstream in an organization's value chain, represent the largest share of greenhouse gas impact for most cities and utilities. The US Conference of Mayors' 2025 climate survey found that among 187 cities with active carbon reduction plans, 91% had measured Scope 1 and 2 emissions but only 23% had attempted comprehensive Scope 3 accounting (US Conference of Mayors, 2025). The gap is not from lack of ambition but from measurement complexity: a mid-sized city purchasing thousands of product categories from thousands of vendors faces a data collection challenge that dwarfs typical corporate Scope 3 programs.

Federal policy is closing the optional window. California's SB 253, effective for reporting year 2026, requires entities with annual revenues exceeding $1 billion (including large municipal utilities) to disclose Scope 3 emissions. The SEC's climate disclosure rules, while narrowed from their initial scope, establish materiality-based Scope 3 reporting expectations for publicly traded utilities. Cities and utilities that delay building measurement infrastructure face compressed timelines and higher implementation costs as compliance deadlines approach.

The financial stakes extend beyond compliance. Austin Energy's 2024 analysis demonstrated that accurate Scope 3 data identified $47 million in fuel supply chain cost reduction opportunities that aggregate spend-based estimates had obscured (Austin Energy, 2024). Seattle City Light found that supplier-specific emissions data revealed 14 vendors whose actual carbon intensity was 60% lower than industry-average emission factors suggested, creating opportunities for preferential procurement that advanced decarbonization goals without increasing costs.

Key Concepts

Scope 3 measurement relies on two fundamental methodological approaches. Spend-based methods apply emission factors (kilograms of CO2e per dollar spent) to procurement expenditure data, offering broad coverage with minimal supplier engagement. Activity-based methods use physical quantities (kilowatt-hours consumed, tons of material purchased, vehicle-miles traveled) combined with supplier-specific or product-specific emission factors, delivering higher accuracy but requiring detailed data collection. Hybrid approaches combine both: spend-based factors for low-materiality categories and activity-based measurement for high-impact procurement categories.

Data quality scoring, as defined by the GHG Protocol's Corporate Value Chain (Scope 3) Standard, rates data from Level 1 (supplier-specific primary data) through Level 5 (spend-based estimates using sector-average factors). Each level represents roughly a 30 to 50% improvement in accuracy over the level below it, according to analysis by the World Resources Institute (WRI, 2024). For municipal and utility procurement, the practical challenge is determining which of the GHG Protocol's 15 Scope 3 categories warrant the investment in higher-quality data and which can remain at screening-level estimates without compromising decision-making.

Emission factor databases, including EPA's Supply Chain GHG Emission Factors, the EXIOBASE multi-regional input-output model, and proprietary databases from platforms like Watershed and Persefoni, form the backbone of spend-based calculations. The accuracy of these factors varies dramatically: a 2024 peer-reviewed comparison found that emission factors for identical product categories differed by 2x to 5x across major databases, with construction materials, professional services, and IT equipment showing the widest divergence (Environmental Science & Technology, 2024).

What's Working

Los Angeles: Tiered Measurement Architecture

Los Angeles designed a three-tier measurement framework that allocated data collection intensity based on emissions materiality. Tier 1 (the top 200 vendors by spend, representing 62% of total procurement value) received direct engagement surveys requesting product-specific emission factors, energy consumption data, and transportation modes. Tier 2 (the next 800 vendors, representing 24% of spend) received simplified questionnaires focused on energy sources and primary material inputs. Tier 3 (the remaining 13,000 vendors) remained on spend-based estimation.

This tiered approach achieved Level 2 or Level 3 data quality for 86% of the city's procurement-related emissions while limiting the data collection burden. The city's Office of Sustainability reported a 67% supplier response rate for Tier 1 vendors after implementing contract language requiring emissions data disclosure as a condition of bid evaluation for contracts exceeding $5 million (City of Los Angeles, 2025). The program cost $2.8 million in the first year, including software licensing, staff time, and consultant support, but identified $12 million in procurement optimization opportunities.

Austin Energy: Utility Fuel Supply Chain Measurement

Austin Energy's Scope 3 pilot focused on Category 3 (fuel and energy-related activities not included in Scope 1 or 2), which constitutes approximately 40% of total utility value chain emissions. The utility deployed Persefoni's carbon accounting platform integrated with its existing SAP procurement system, enabling automated emissions calculation from purchase order data.

The critical innovation was establishing direct data-sharing agreements with its five largest natural gas suppliers, who collectively provided 78% of fuel volume. These suppliers shared well-level methane leak rate data, pipeline transmission loss factors, and processing facility emissions intensity. The result was a shift from EPA default methane leakage factors of 2.3% to verified supplier-specific rates ranging from 0.8% to 3.1%. This granularity revealed that one supplier's methane intensity was nearly four times that of the lowest-performing supplier, enabling procurement decisions that reduced upstream emissions by an estimated 180,000 metric tons of CO2e annually without changing total gas purchase volumes (Austin Energy, 2024).

Seattle City Light: Construction Materials Carbon Tracking

Seattle City Light implemented an activity-based Scope 3 measurement system for capital project materials, its second-largest Scope 3 category after purchased electricity losses. The utility required environmental product declarations (EPDs) for concrete, steel, and aluminum in all capital projects exceeding $10 million, covering roughly 70% of annual capital expenditure.

The EPD requirement, integrated into the utility's procurement management system, generated product-specific emission factors that replaced industry-average estimates. For concrete alone, the shift from American average emission factors to supplier-specific EPD data reduced estimated embodied carbon by 38% for projects using Pacific Northwest suppliers, whose lower-carbon grid electricity in cement production yielded materially lower emission intensity than national averages suggested. The program also created competitive incentives: three concrete suppliers invested in supplementary cementitious material capacity specifically to improve their EPD scores and win Seattle City Light contracts (Seattle City Light, 2025).

What's Not Working

Supplier Fatigue and Response Rate Decline

Initial supplier engagement campaigns achieve reasonable response rates, but sustaining data collection over multiple reporting cycles proves challenging. Los Angeles reported that its Tier 1 supplier response rate dropped from 67% in year one to 51% in year two as vendor sustainability teams faced competing disclosure requests from other customers. The proliferation of non-standardized questionnaires, with CDP, EcoVadis, and individual customer templates each requesting emissions data in different formats, creates duplication that erodes supplier willingness to participate. Until industry-wide data exchange standards mature, municipal programs face ongoing engagement costs to maintain data quality.

Emission Factor Uncertainty in Services Categories

Professional services, IT services, and financial services categories present persistent measurement challenges. These categories often represent 15 to 25% of municipal procurement spend but lack the physical unit basis (tons, kWh, vehicle-miles) that enables accurate activity-based measurement. Spend-based emission factors for services vary by a factor of 3x to 7x across databases, and supplier-specific data is difficult to validate because many professional services firms lack granular operational emissions data for individual engagements. Austin Energy's analysis found that its professional services Scope 3 estimate ranged from 45,000 to 310,000 metric tons of CO2e depending on which emission factor database was applied, a range too wide to inform procurement decisions.

Data Integration and System Compatibility

Municipal procurement systems were not designed for carbon accounting. Legacy ERP platforms often lack the product category granularity needed to match expenditures with appropriate emission factors. Los Angeles spent $400,000 on data mapping to align its 8,500 procurement category codes with the emission factor taxonomy used by its carbon accounting platform, a process that required manual review of thousands of product descriptions. Utilities using multiple procurement systems across divisions (generation, transmission, distribution, customer service) face additional integration costs. Without standardized procurement-to-emissions taxonomies, every implementation requires bespoke mapping that is expensive to maintain.

Key Players

Established Companies

• Persefoni: Enterprise carbon accounting platform deployed by Austin Energy and 30+ utilities for automated Scope 3 calculation from procurement data
• Watershed: Climate platform providing emission factor databases and supplier engagement tools used by municipal governments and Fortune 500 companies
• SAP: ERP provider whose Sustainability Control Tower module integrates emissions calculation into procurement workflows
• Sphera: Environmental data and software provider maintaining one of the largest lifecycle assessment databases used in Scope 3 measurement

Startups

• Climatiq: API-first emission factor platform aggregating 70,000+ factors from 30+ databases, enabling automated emissions estimation from procurement records
• CarbonChain: Supply chain carbon tracking platform specializing in commodity supply chains used by utilities for fuel and materials tracking
• Altruistiq: Sustainability data platform focused on supplier engagement and primary data collection for Scope 3 reporting

Investors

• Generation Investment Management: Growth equity investor in Persefoni and other climate data infrastructure companies
• Brookfield Renewable Partners: Strategic investor in utility decarbonization tools and infrastructure
• Energize Capital: Climate tech venture fund investing in emissions measurement and carbon accounting startups

Action Checklist

• Conduct a Scope 3 screening assessment using spend-based methods to identify the top 5 to 10 emission categories by magnitude
• Design a tiered supplier engagement strategy that concentrates primary data collection on vendors representing 60 to 80% of total Scope 3 emissions
• Embed emissions data disclosure requirements into procurement contracts for major spend categories, starting with new contracts and renewals
• Select and implement a carbon accounting platform that integrates with existing ERP and procurement systems to minimize manual data handling
• Establish supplier-specific data-sharing agreements with the largest 10 to 20 vendors, prioritizing fuel, construction materials, and fleet services
• Develop a procurement category-to-emission factor mapping and document the data quality level for each category to track improvement over time
• Require environmental product declarations for concrete, steel, and other high-embodied-carbon materials in capital projects exceeding a defined threshold
• Set annual data quality improvement targets (e.g., increase the share of Scope 3 emissions measured with Level 2 or better data by 10 percentage points per year)
• Train procurement staff on carbon accounting fundamentals so that purchasing decisions can incorporate emissions data alongside cost and performance criteria

FAQ

Q: How long does it take a city or utility to move from spend-based Scope 3 estimates to activity-based measurement for key categories? A: Based on the Los Angeles and Austin Energy experiences, the transition from spend-based screening to activity-based measurement for the top 5 to 10 categories typically requires 12 to 18 months. The first 3 to 4 months focus on data mapping and platform implementation. Months 4 through 10 involve supplier engagement and initial data collection. Months 10 through 18 cover data validation, gap analysis, and methodology refinement. Ongoing annual effort to maintain and improve data quality runs approximately $500,000 to $1.5 million for a mid-to-large municipality, depending on the number of suppliers engaged and the complexity of procurement systems.

Q: Which Scope 3 categories should municipalities prioritize for higher-quality measurement? A: For most cities, the highest-impact categories are Category 1 (purchased goods and services, especially construction materials), Category 3 (fuel and energy-related activities), and Category 4 (upstream transportation and distribution). Utilities should add Category 11 (use of sold products) if they sell electricity or gas to end users. These categories typically account for 70 to 85% of total Scope 3 emissions. Starting with categories that have readily available physical activity data (tons of concrete, therms of gas, vehicle-miles) rather than services categories produces faster accuracy improvements and more actionable procurement insights.

Q: What supplier response rate is realistic for emissions data requests? A: First-year response rates of 50 to 70% are achievable for top-tier suppliers when emissions disclosure is linked to procurement evaluation criteria. Response rates drop significantly without contractual leverage: voluntary requests typically achieve 15 to 25% response rates. Maintaining response rates above 50% in subsequent years requires simplifying data requests, providing feedback to suppliers on how their data is used, and aligning questionnaire formats with existing disclosure frameworks (CDP, EcoVadis) that suppliers may already complete. Automated data exchange through APIs or standardized digital formats significantly reduces supplier burden and improves long-term participation rates.

Q: How do cities handle the cost of Scope 3 measurement programs? A: Implementation costs range from $500,000 to $3 million in the first year depending on scope and existing data infrastructure. The most successful programs fund themselves by demonstrating procurement cost savings: Los Angeles identified $12 million in optimization opportunities from its $2.8 million first-year investment. Federal grants through the EPA's Climate Pollution Reduction Grants program and DOE technical assistance provide supplementary funding. Several cities have structured their programs as shared services across departments, spreading platform licensing and staff costs across multiple budget lines to reduce the burden on any single agency.

Sources

• US Conference of Mayors. (2025). Municipal Climate Action Survey: Scope 3 Measurement Readiness Assessment. Washington, DC: USCM.
• City of Los Angeles, Office of Sustainability. (2025). Scope 3 Procurement Emissions Pilot: First-Year Results and Methodology Report. Los Angeles, CA.
• Austin Energy. (2024). Value Chain Emissions Measurement: Fuel Supply Chain Carbon Accounting Program Report. Austin, TX: Austin Energy.
• Seattle City Light. (2025). Capital Projects Embodied Carbon Tracking: Environmental Product Declaration Program Results. Seattle, WA: Seattle City Light.
• World Resources Institute. (2024). Scope 3 Data Quality Hierarchy: Accuracy Improvements Across Measurement Levels. Washington, DC: WRI.
• Environmental Science & Technology. (2024). "Divergence in Supply Chain Emission Factor Databases: Implications for Corporate Scope 3 Reporting." ES&T, 58(12), 5234-5247.
• US EPA. (2025). Supply Chain Greenhouse Gas Emission Factors for US Industries and Commodities: 2025 Update. Washington, DC: US EPA.
• GHG Protocol. (2024). Corporate Value Chain (Scope 3) Accounting and Reporting Standard: 2024 Amendments and Guidance. Geneva: World Resources Institute and WBCSD.