Software Carbon Intensity Specification

Created by: Green Software Foundation

GitHub repo: https://github.com/Green-Software-Foundation/sci

Latest published version of the specification: https://github.com/Green-Software-Foundation/sci/blob/main/Software_Carbon_Intensity/Software_Carbon_Intensity_Specification.md

GSF Wiki: https://greensoftwarefoundation.atlassian.net/wiki/x/EYDz

SCI Score

Functional units: user, device, minute, API call, running a machine learning job, …

Methodology

Embodied emissions

See: https://github.com/Green-Software-Foundation/sci/blob/main/Software_Carbon_Intensity/Software_Carbon_Intensity_Specification.md#embodied-emissions

When software runs on a device, a fraction of the total embodied emissions of the device is allocated to the software. This is the value of M that needs to be calculated in the SCI equation.

This fraction consists of both a time- and resource-share. The length of time that the software runs on the device determines its time-share. The percentage of the device reserved just for that application during the time-share determines that application's resource-share.

To calculate the time-share, amortize the total embodied carbon over the expected life span of the device and then extrapolate based on the time reserved for the usage. For example, if the device’s embodied carbon was 1000kg with an expected lifespan of four years and it was reserved for use for one hour, the time-share embodied emissions would be 1000 * 1/(4_365_24) or around 28g of the total.

Guidance

SCI Guidance

The SCI Guidance project details various approaches on how to understand the different methodologies that are available for calculating energy, carbon intensity, embodied emissions and functional unit values which are the core components of the SCI calculation.

Use Cases

web shop

For this case study, we have considered R to be per 500 users over a 1 hour period with 50 concurrent users. Based on the load test approach we have taken, the functional unit is the scaling factor for this infrastructure and hence this is a compound functional unit.

🔗 References

Building green software with the Software Carbon Intensity Specification with Sara Bergman hosted by Green Tech South West

Software Carbon Intensity: Crafting a Standard | GSF

Software Carbon Intensity standard will empower consumers of software systems to make informed decisions.

Green software: 7 traps when calculating carbon emissions for software

This year in Kainos we've been applying the SCI to some of the digital services we've built on different clouds. This has given us an insight into the benefits and some of the pitfalls of applying the SCI to complex production enterprise software.