Session by Simon Upton, Director, OECD Environment Directorate, 4 February 2016. The session presented the outcomes of COP21, main challenges in implementing the Paris Agreement and implications for future policy priorities on climate. COP21 represents an important milestone in the international community’s fight against climate change, but the true measure of success will be in how countries implement the Paris Agreement to move to low-carbon growth. Meeting the ambition of the Paris Agreement will require effective policy alignment and cost-effective action to implement country emissions reduction commitments, and dynamism to ensure nationally determined contributions (NDCs) evolve to become more stringent over time. Governments will also need to undertake and strengthen adaptation measures to protect the most vulnerable, continue efforts to build greater transparency on progress towards NDCs and means of implementation, and scale-up climate finance resources, addressing residual methodological challenges on measuring, monitoring and tracking climate finance as they go.