The European Union (EU) has recognised the high-probability, high-impact threat climate change poses to international security, but is still formulating a response commensurate to the threat. This report outlines how the EU can meet a Responsibility to Prepare for unprecedented yet foreseeable threats to international peace and security. This involves routinising, institutionalising, elevating and integrating climate security considerations into policymaking processes and the policies and financial instruments of EU institutions, while honing rapid response capabilities and developing contingencies for unintended consequences.