Why a 45 KB webpage can still damage your phone's lifespan, carbon models aside

Current per-byte carbon models used to rate webpage sustainability assign equal scores to pages with identical file sizes, regardless of how they actually perform on a device. Research from two independent sources — the Sustainable Web Design model and France's ADEME–Arcep study — agrees that end-user device manufacturing, not data transfer, accounts for the largest share of digital's carbon footprint. However, both models still calculate manufacturing impact as a proportion of bytes transferred, even though device lifespan is shortened by poor runtime performance, not page weight. A poorly optimised 45 KB page running continuous CPU loops or blocking the main thread can accelerate device obsolescence just as much as a much heavier page. Metrics like Interaction to Next Paint and CPU idle state are argued to be more meaningful proxies for real-world environmental impact than transferred kilobytes alone.