This article focuses on the future of UK climate action in light of thedecision to withdraw from the EU. The UK’s decision to leave the EU sentshockwaves through the UK and the EU political establishments and policy communities. Uncertainty marks the future of policy areas in which the UK previously demonstrated leadership. One area of particular importance is that of UK climate action. In 2006, a decade prior to the referendum in which 52% of voters chose to leave the EU, the UK began a period of intense and ambitious climate policy development and adoption. This period of ambition drove both the UK and the EU into a position of global climate leadership.Brexit has the potential for significant impact on the UK’s climate policy.However, political debates about the UK’s post-Brexit future have largely been devoid of references to climate change. Drawing on the agenda-setting literature, this article deploys the multiple streams model to analyze the problems, politics and policies of Brexit-era UK climate action. This is an innovative utilization of the multiple streams model, which is primarily used to explore policy change retrospectively. The application allows for the addressment of key issues – whether Brexit signals a definitive break in UK climate action, whether there is still support for climate action in Brexit Britain, and the future institutional capacity for climate policy. It is concluded that the UK is sleep-walking into diminished climate actorness after it leaves the EU.