Intended nationally determined contributions (INDCs) for mitigation of greenhouse gas emissions are expected to be an important part of a post-2020 climate agreement under the UNFCCC. However, it is not certain yet what these INDCs will contain and how they will be assessed. The EU Emissions Trading System (EU ETS) faced similar challenges in its first years (2005-12). Thus, the mechanisms and lessons learned under the EU ETS could be applied to the INDCs to create a governance and assessment system that increases transparency and builds trust among parties to the UNFCCC.