Member Story
How Chris Adams of the Green Web Foundation, Emma Horrell of the University of Edinburgh, and 14 assembly members from across the industry are building SCI for Web — a standard for measuring website carbon intensity that covers the full delivery chain: servers, networks, third-party services, and end-user devices.
Organisations involved
13 tonnes
CO₂ saved per year at the University of Edinburgh from homepage image optimisation alone
14
Assembly members from 15 organisations — tech giants, data providers, academics, and practitioners
W3C
Formal collaboration with the world's web standards body — bridging two communities for the first time
The Problem
Almost everyone uses the web daily. Yet no standard existed for measuring a website’s carbon intensity. Tools like the Sustainable Web Design Model, CO2.js, and the W3C Web Sustainability Guidelines had made web emissions visible and established foundational methodologies that thousands of practitioners used. But as organisations moved from awareness to accountability, they needed something more rigorous: a measurement approach with clear boundaries, carbon per functional unit rather than totals, and disclosed methodology so results were comparable and defensible.
The fragmentation ran deep. Modern web applications depend extensively on third-party services — analytics, advertising, CDNs, authentication — which consume energy on both servers and client devices. Without a standard that defined what to include and how to attribute emissions across this chain, any measurement was partial. Organisations could not compare results, validate reduction claims, or make informed decisions about where to invest optimisation effort.
The University of Edinburgh discovered the scale of the opportunity first-hand: through changes to homepage images alone, Emma Horrell and her team achieved 13 tonnes of CO₂ reduction per year. But they had no systematic framework to measure the rest — or to know if their approaches were right.
The Journey
2024–2025
As the SCI specification matured into ISO/IEC 21031:2024, GSF members recognised that a domain-specific, SCI-aligned approach was needed for web applications. The parent SCI standard was powerful but general. Web applications had unique characteristics — browser rendering, third-party dependencies, content delivery networks, user device diversity — that required specific guidance on boundaries and functional units. Tools like CO2.js and the Sustainable Web Design Model had made web emissions visible, but results weren't comparable and organisations couldn't validate reduction claims.
Beyond single-dimensional metrics for digital sustainability →September 2025
Chris Adams of the Green Web Foundation, active in both communities, brokered a strategic collaboration between GSF and W3C. GSF would manage the SCI for Web specification; W3C's Sustainable Web Interest Group would provide feedback. The collaboration included joint knowledge sharing, development of training materials, and Impact Framework templates. As the announcement stated: "Almost all of us use the web daily, and like everything else, we need to make using it more sustainable."
Read about the GSF and W3C collaboration →September 2025
Emma Horrell, User Experience Manager at the University of Edinburgh, had led an investigation into the university's digital estate — numerous websites each managed by different teams. They found image formats were "unnecessarily heavy," and through changes to homepage images alone, achieved 13 tonnes of CO₂ reduction per year. Their experience demonstrated that sustainable digital transformation is "fundamentally about behavioural change, not just technical solutions." The university joined GSF to contribute their ground-level implementation experience to SCI for Web.
Meet Emma Horrell of the University of Edinburgh →September–November 2025
Fourteen GSF members piloted an AI-assisted assembly process. Participants answered structured questions about measurement accuracy and adoption complexity. An LLM synthesised responses into draft content. The group reviewed and refined through multiple rounds. In contentious areas, participants revised until all objections were resolved. In ten weeks, the assembly moved from a blank page to a consensus design document — resolving the core tension: "A specification that is technically accurate but unused won't serve its purpose, and a widely used metric that lacks credibility also won't serve the purpose."
About the SCI for Web assembly →February 2026
The full consensus document was published. Scope: web applications delivering value through browser interfaces via HTTP/HTTPS, covering static sites, SPAs, server-rendered apps, e-commerce, and streaming services. Third-party services — analytics, advertising, CDNs, authentication — must be included within the measurement boundary because they consume energy on both servers and client devices.
Read the SCI for Web assembly report →Q1 2026
The SCI for Web specification entered active development under the Software Standards Working Group, led by Chris Adams. Built on the consensus design document, the specification will define how to measure the carbon intensity of web applications across the full delivery chain.
Learn about the SCI for Web standard →Sustainable digital transformation is fundamentally about behavioural change, not just technical solutions. When colleagues understand that unused content with heavy PDFs and videos has a real environmental impact, they make more thoughtful decisions about what they create and maintain.
Emma Horrell, User Experience Manager, University of Edinburgh
Who came together
Chris Adams
Director of Technology and Policy
Green Web Foundation
Leads the SCI for Web project and brokered the W3C collaboration as an active member of both communities. Participated in the AI-assisted assembly as one of the fourteen expert members.
Emma Horrell
User Experience Manager
University of Edinburgh
Brought practical implementation experience from two years of ground-level web sustainability work, including the 13-tonne CO₂ case study, to inform the standard's real-world applicability.
Daniel Schien
Academic
University of Bristol
Brought academic rigour on web measurement methodology, drawing on published research into the environmental impact of internet infrastructure.
In their words
"Almost all of us use the web daily, and like everything else, we need to make using it more sustainable. By defining a standard for measuring website emissions, we make it easier for people to request greener digital services, for responsible technologists to build them, and to reach the fossil-free internet we all need. "
GSF–W3C collaboration announcement
September 2025
"Digital sustainability is a relatively new area for us. We faced uncertainty about whether our approaches were correct, which experts to engage, and where to find guidance. The GSF provides the expertise and community we needed. "
Emma Horrell
User Experience Manager, University of Edinburgh
A consensus-built methodology for measuring the carbon intensity of web applications
Through this agreement, the GSF and W3C aim to promote the adoption of sustainable web development best practices and standards.
Turning sustainability goals into measurable action by rethinking digital practices.
GSF members can become a project co-chair to support Chris Adams in leading the specification work, or join the Software Standards Working Group to help through draft review, implementation testing, and technical feedback.
Contact sci-for-web@greensoftware.foundation to get started
