Overview of research framework.

The global effort to limit global warming to 1.5°C in line with the Paris Agreement is urgent, with just under five years left to act. The internet, and particularly websites, play a critical role in this challenge. While sustainable web design (SWD) is gaining attention, it is often overlooked, even by organisations central to climate action. This study examines the evolution of host country websites for the United Nations Framework Convention on Climate Change (UNFCCC), Conference of the Parties (COP), from COP1 (1995) to COP30 (2025). While COPs serve as the global focal point for climate negotiations, the environmental impact of their host websites has been largely unexamined. Motivated by concerns over the COP28 host website, criticised for potential “greenwashing”, we evaluated the environmental footprint of all available COP host websites using archival data from Internet Archive’s Wayback Machine. Our analysis reveals an exponential increase in website size, with average emissions rising over 13,000%, and many recent COP pages emitting roughly ten times the global average of approximately 0.36g of CO₂e per pageview. In-session participant homepage views drove emissions up by 83,400%, from 0.14 kg of CO₂e at COP3 (1997), roughly what a mature tree absorbs in two days at a standard sequestration rate, to 116.85 kg of CO₂e at COP29 (2024), requiring the annual carbon absorption of five to ten mature trees. This dramatic growth is largely driven by richer media content and scripts. We conclude with recommendations for integrating SWD principles into the Host Country Agreement and the How to COP handbook, ensuring that digital platforms align with the United Nations’ broader sustainability objectives. The code used in this study and the results are available via DOI: https://doi.org/10.5281/zenodo.15295396.