Challenges of Climate Engineering under International Law - Classification and Outlook: The 27th Conference of the Parties to the UN Framework Convention on Climate Change (COP27) in Sharm el-Sheik at the end of 2022 once again demonstrated the relentless advance of climate change and biodiversity loss, and showed how the protection, conservation and restoration of ecosystems is becoming indispensable. While the reduction of emissions must remain the primary focus of climate action, the international community is turning towards Climate Engineering (CE) as an additional element of climate policy. The Intergovernmental Panel on Climate Change (IPCC) now even deems climate goals unachievable without CE. In absence of an international agreement governing the use of CE, the legal admissibility of CE will be analysed against the backdrop of various legal instruments, e.g. the UN Framework Convention on Climate Change (UNFCCC) and its Paris Agreement, the Convention on Biological Diversity (CBD) as well as the United Nations Convention on the International Law of the Sea (UNCLOS). Given the fragmentation of international law concerning CE, legal hurdles arise especially with regard to its admissibility under biodiversity and nature protection law. Approaches to overcome these hurdles may lie within an interpretation of the precautionary principle allowing “risk-risk trade-off” considerations between the risks of insufficiently abated climate change and CE to take place. Additionally, the design of a market for the trading of negative emissions certificates could encourage states to create legal certainty.