Measuring the Embodied Carbon of Continuous Integration Pipelines

Abstract

Continuous integration (CI) pipelines run millions of ephemeral build and test jobs every day, yet sustainability assessments of software development almost exclusively consider the operational energy of these jobs, ignoring the embodied carbon of the hardware they run on. This poster presents CICarbon, a measurement methodology and open-source tool that attributes both operational and embodied emissions to individual CI jobs. Embodied carbon is amortised over device lifetime and allocated to jobs in proportion to their exclusive occupation of CPU, memory, and storage resources, following the principles of the Software Carbon Intensity specification but adapted to the bursty, short-lived nature of CI workloads. We apply CICarbon to 14 months of CI history from 27 open-source repositories (1.9 million jobs) executed on a mix of cloud-hosted and self-hosted runners. Our results show that embodied carbon accounts for 43-61% of total CI emissions on typical cloud runners — a share that rises for short jobs, where machine provisioning dominates useful work. We identify three practical reduction levers: test selection cuts total carbon by 29% in our subject repositories, runner right-sizing by 17%, and extending runner hardware lifetime from four to six years by 22%. The poster includes an interactive dashboard demonstration and a call for repository-level carbon budgets in open-source projects.