While the formal re-entry of the agreement is simple, the biggest challenge for a Biden administration would be to propose a new US NDC, widely seen as ambitious and credible. Many countries have stated in their NDCs that they intend to use some form of international emissions trading to implement their contributions. In order to ensure the environmental integrity of such transactions, the agreement requires the parties to adhere to accounting practices in order to avoid double counting of “internationally transferred mitigation results”. In addition, the agreement establishes a new mechanism that will contribute to mastery and support sustainable development that could produce or certify tradable emission units based on its design. The implementation of the agreement by all Member States is assessed every five years and the first evaluation will take place in 2023. The result will be used as a contribution to member States` new national contributions.  The inventory will not be one of the contributions/performance of each country, but of a collective analysis of what has been achieved and what remains to be done. Negotiators for the agreement said the INDCs presented at the time of the Paris conference were insufficient and noted, “with concern, that estimates of aggregate greenhouse gas emissions in 2025 and 2030, resulting from projected national contributions, do not fall into the least costly scenarios of 2°C, but end up at a projected level of 55 gigatonnes in 2030”, and also recognise that “much greater efforts will be needed to reduce emissions in order to keep the global average temperature rise to less than 2°C by reducing emissions to 40 gigatonnes or 1.5°C”.  [Clarification needed] The EU and its Member States are among the nearly 190 parties to the Paris Agreement. The EU formally ratified the agreement on 5 October 2016, allowing it to enter into force on 4 November 2016. .