This article argues that environmental issues confront us as an ongoing emergency. The epistemic features of serious environmental issues – the fact that we cannot reliably distinguish ex ante between benign policy choices and choices that may lead to environmental catastrophe – are the same features of an emergency. This means that, like emergencies, environmental issues pose a fundamental challenge for the rule of law: they reveal the necessity of unconstrained executive discretion. Discretion is widely lamented as a fundamental flaw in Canadian environmental law, which undermines both environmental protection and the rule of law itself. Through the conceptual framework of the environmental emergency, this article offers a critique of the current understanding of discretion in environmental law and suggests how an alternative conception of the rule of law can both constitute and constrain the state’s regulative authority over the environment.