The Paris Agreement of December 2015 is subject to much criticism of being inadequate. This however neglects its very ambitious objective, which limits legally-binding global warming to 1.5 to 1.8 degrees in comparison to pre-industrial levels. This article shows, based on the overlap of unanswered questions for prognoses in natural science and the legal precautionary principle, that this objective indicates a legal imperative towards zero emissions globally within a short timeframe. Furthermore, it becomes apparent that policies need to be focused on achieving the 1.5-degree temperature limit. From a legal standpoint with regard to existential matters, only those policies are justified that are fit to contribute to reaching the temperature limit with high certainty, without overshoot, without leaving the 1.5 limit aside and without geoengineering measures, in contrast to the tendencies of the IPCC. This creates a big challenge even for the alleged forerunners of climate policies, Germany and the EU; because, according to the objective, the EU and Germany have to raise the level of ambition in their climate policies rapidly and drastically.