The deluge of new software services we are facing is associated with an expansion of supporting infrastructures, including networks and data centers, and a rapid renewal of end- user devices. However, this surge is accompanied by significant environmental impacts and encompassing factors, such as CO2e emissions or the depletion of rare metals and minerals. Given systems’ complexity and rapid evolution, the ICT domain still struggles to understand its environmental impact and lacks openly available data to facilitate such assessments. Indeed, to the best of our knowledge, environmental impact assessments of ICT services have to deal with high margins of errors, which are insufficiently quantified and documented, yet wield a significant influence on the final estimation outcome. This paper, therefore, introduces an approach leveraging fuzzy logic to model and propagate uncertainties from the reference impact through the computations to the final results, encouraging their consideration by stakeholders. Adhering to the established 3-tier architecture used to conduct ICT services Life Cycle Assessments (LCA), we outline how assumptions can be mapped to fuzzy sets. We conclude with an illustrative example demonstrating the propagation of uncertainties throughout the environmental impact modeling process.