Arguing that environmental sustainability is a growing concern for digital information systems and services, this article proposes a simple method for estimation of the energy and environmental costs of digital libraries and information services. It is shown that several factors contribute to the overall energy and environmental costs of information and communication technology (ICT) in general and digital information systems and services in particular. It is also shown that end‐user energy costs play a key role in the overall environmental costs of a digital library or information service. It is argued that appropriate user research, transaction log analysis, user modeling, and better design and delivery of services can significantly reduce the user interaction time, and thus the environmental costs, of digital information systems and services, making them more sustainable.