The Supreme Court of the Netherlands construed the state’s positive human rights obligations as requiring a 25 per cent reduction of its greenhouse gas emissions by 2020 compared with 1990 levels. This article explores how judges can decide the level of state effort required to mitigate climate change. To date, judges have predominantly approached this issue by seeking to identify an elusive benchmark, either by deduction from global objectives or induction from state conduct. This article shows that the judicial assessment of a state’s requisite efforts inevitably relies on equity infra legem. Acknowledging this, judges could learn from the international courts’ experience with establishing clarity in the midst of vague legal rules.