Recent research has advocated for a broader conception of evaluation for Sustainable HCI (SHCI), using interdisciplinary insights and methods. In this paper, we put this into practice to conduct an evaluation of Sustainable Interaction Design (SID) of digital services. We explore how SID can contribute to corporate greenhouse gas (GHG) reduction strategies. We show how a Digital Service Provider (DSP) might incorporate SID into their design process and quantitatively evaluate a specific SID intervention by combining user analytics data with environmental life cycle assessment. We illustrate this by considering YouTube. Replacing user analytics data with aggregate estimates from publicly available sources, we estimate emissions associated with the deployment of YouTube to be approximately 10MtCO2e p.a. We estimate emissions reductions enabled through the use of an SID intervention from prior literature to be approximately 300KtCO2e p.a., and demonstrate that this is significant when considered alongside other emissions reduction interventions used by DSPs.