Overview
ISO/IEC 21031:2024 - Software Carbon Intensity (SCI) specification - defines a consistent, evidence-based methodology to calculate the rate of carbon emissions caused by a software system (its SCI score). The standard frames SCI as a rate (carbon per functional unit) to increase transparency of an application’s sustainability credentials and to support measurable reduction strategies. It covers both operational emissions (energy use × marginal carbon intensity) and embodied emissions (hardware manufacturing and disposal allocated to the software).
Key topics and technical requirements
- SCI as a rate: SCI = (O + M) per R, where O = operational emissions, M = embodied emissions, and R = functional unit.
- Operational emissions calculation: O = E × I
- E = energy consumed (kWh) for the defined functional unit.
- I = location-based marginal carbon intensity (gCO2eq/kWh) - use consequential/marginal rates, not market-based measures.
- Embodied emissions: allocate a time- and resource-share of device lifecycle emissions (manufacture, disposal) to software (M).
- Procedure for reporting: Bound (define software boundary), Scale (choose functional unit), Define (select quantification method - telemetry or models), Quantify (calculate per-component SCI), Report (disclose score, boundary, and methodology).
- Exclusions and principles: Offsets or market-based renewable claims do not reduce SCI; SCI focuses on elimination of emissions and uses location-based marginal rates.
- Units and granularity: Energy in kWh; carbon intensity in gCO2eq/kWh; supports diverse scales from single functions to distributed cloud systems.
Applications and who should use it
ISO/IEC 21031:2024 is practical for organizations and practitioners aiming to design, develop, operate, or procure lower-carbon software:
- Software developers and engineers - optimize code and runtime efficiency.
- AI/ML teams - reduce training emissions via model optimization and hardware choices.
- Architects and DevOps - choose architectures (serverless, event-driven), schedule workloads, and implement carbon-aware pipelines.
- QA and SRE - measure energy use in testing and production.
- Sustainability officers and product managers - set targets, compare baselines, and report SCI scores across products or services.
- Cloud providers and vendors - supply granular telemetry or modelled data to support accurate SCI calculations.
Related standards
ISO/IEC 21031:2024 complements broader sustainability and GHG accounting practices. Organizations should consider linking SCI reporting with corporate environmental management frameworks (e.g., ISO environmental standards) and established GHG reporting protocols when aligning software-level metrics with enterprise climate goals.