Information and communications technology (ICT) has become an indispensable part of our lives. Prior research on climate impact of ICT devices and services mostly makes use of life cycle assessment and energy modeling frameworks focused on embodied greenhouse gas (GHG) emissions. Because these perspectives emphasize the GHGs emissions associated with the construction and distribution of digital devices along production supply chains, not much is known about the GHGs emissions monitored or facilitated by digital device use. In this study, we propose the concept of digital use supply chains (DUSCs) as an orthogonal dimension of digital devices’ life cycle. DUSC refers to the production activities and resource consumption recorded by digital devices. We propose a framework to conceptualize and quantify digital behavior-related GHGs emissions through use of the Screenomics paradigm, where users’ digital screen data are unobtrusively collected moment-by-moment. Through Screenomics’ granular recording of users’ digital behavior, we evaluate behavior-based GHGs emissions traced by the digital devices. DUSC connects individual’s digital behaviors to their global climate change impact, contributing to a more nuanced and complete evaluation of the climate impacts of the digital economy. Our single-case study indicates the estimated scale of the GHGs emissions linked to a user’s one-day digital activities could be three orders of magnitude (1000 times) higher than the emissions associated with the device life cycle alone. DUSC could enable climate change mitigation at a meaningful, actionable level through personalized educational or behavior change programs, and also facilitate novel data-driven feedback loops that may provide digital device users with insights into their personal climate impacts. Recognition and future study of DUSC could accelerate the quantification and standardization of a ‘carbon handprint’ of digital devices and create positive climate impacts from digital products and services.