Ocean fertilization is, at least theoretically, perceived as an option to mitigate climate change. However, theoretical assumptions could not be proved by experiments, in fact recent experiments have endorsed existing doubts. On international level seems to be a far-reaching—at least political—consensus that ocean fertilization should not be applied as climate change mitigation measure, based inter alia on unknown risks for the marine environment. Currently the Contracting Parties of the London Protocol are negotiating an international ban of ocean fertilization projects. Only “legitimate scientific research” shall be exempted from the prohibition provided negative effects on the marine environment can be excluded in this field. There is an ongoing discussion on whether a prior permission regime for research projects would be an adequate and reasonable approach and—finally also—legally admissible.