This chapter explores climate change negotiations and nuclear diplomacy. Climate and nuclear risks are both defined as “existential threats” given their threat towards human life on a planetary scale. Both are considered complex problems that require a fully global response. As such, both bring challenges of an unprecedented magnitude for decision-making. The chapter aims to identify central themes in the climate negotiation literature to inform future comparisons with nuclear diplomacy, highlighting the distinct challenges and frameworks of each field. It reviews the evolution and key themes of climate diplomacy, such as framing, scientific input, power dynamics, the role of non-state actors, and transparency. It then contrasts these with the more secretive and compliance-focused character of nuclear diplomacy.