The Parties to the Paris Agreement have committed to communicate successive ‘nationally determined contributions’ (NDCs) to the global response to climate change. Each NDC is expected to reflect the Party's ‘highest possible ambition’ (HPA) on the mitigation of climate change. This article envisages the possibility of taking HPA seriously: that is, of approaching it as an effective legal standard. It shows that, in some circumstances, the HPA standard can help to assess whether a State has complied with due diligence obligations on climate change mitigation.
