Earth System Science (ESS) encompasses scientists from different scientific disciplines who use a multitude of heterogeneous terms to describe processes and data. This volume of often ambiguous, duplicate, inconsistent terms presents numerous challenges regarding interoperability and standardisation, e.g. for automated data selection or searching for data in a repository. Terminologies such as ontologies, thesauri and controlled vocabularies can enable scientists and infrastructure providers to realise a machine-processable expression of the information contained in their research data and other scholarly outputs. However, selecting the most appropriate ontology is often difficult and requires support for data producers and curators.The  BITS1 project is building a Terminology Service (TS) for Earth System Sciences (ESS TS) as part of the existing Terminology Service2 (TIB TS) of the TIB – Leibniz Information Centre for Science and Technology3. It has implemented the ESS collection4 within the TIB TS, which already contains 40 terminologies that are relevant for the ESS and to which further relevant terminologies will be added. All terminologies in the TIB TS are quality controlled. New terminologies for the ESS collection can be suggested at any time via the ESS homepage. New terms for terminologies hosted on Github can also be suggested and forwarded to the developers of that terminology.One possible use case for the ESS TS is to support the annotation of data with terms from terminologies. A major challenge in this case is the breaking of annotations: this can happen if the term of a terminology used for the annotation is deleted - e.g. in a subsequent version of a terminology. Therefore, BITS is conducting a feasibility study: can we assign persistent handles to all classes and individuals of each future version of a terminology in the  ESS TS collection, so that the handles redirect to a landing page of the respective terms? These handles could then be used in annotations and the TIB will ensure that they are persistent.The integration of the ESS TS into the two different data repositories of the German Climate Computing Centre (DKRZ) and the Senckenberg - Leibniz Institute for Biodiversity and Earth System Research (SGN) is another task of BITS. The experience gained will be used to develop blueprints for connecting other ESS repositories to the TS. We also work closely with NFDI4Earth and the wider ESS community, and with the BASE4NFDI basic service TS4NFDI. Feedback from the wider ESS community on their expectations and needs for such a service is welcome and necessary for the project. Our goal is a terminology service that serves as a valuable resource for researchers, students, professionals and developers in ESS, providing them with accurate and consistent terminologies to enhance their work, improve communication and data sharing, and advance knowledge in their respective fields.1: https://projects.tib.eu/bits/home 2: https://terminology.tib.eu/ts 3: https://www.tib.eu/en/4:  https://terminology.nfdi4earth.de