This thesis explores the role of the catastrophic imaginary in shaping environmental praxis in the UK. Confronted by the threat of a looming climate change catastrophe, environmentalism in the global North is caught in a state of impasse. Despite numerous organising attempts no mass climate change movement has emerged to confront the threat. This absence of a political movement is compounded by the failure of legislative campaigns and the inadequacy of government responses. Environmental praxis appears caught between ineffective practices and a catastrophic imaginary. It is this state of impasse, one as yet to be critically analysed, that this thesis sets out to explore. The thesis argues that the impasse in environmental praxis emerges from the intersection of the catastrophic imaginary and the limits of activism as a mode of liberal politics that I term liberal utopianism. Exploring a number of specific environmental organisations through a nomadic methodology framed by the practices of multi-sited ethnography, this thesis contends that the failure of liberal utopianism to adequately engage with climate change is in part due to the form climate change takes as a sociotechnical problem and not only an outcome of political practice itself. Exploration of responses to this state of impasse suggests that it is possible to break from the impasse by transforming the material grounds of the imaginary and envisioning catastrophe as a process of slow violence, and thus amenable to situated political action. This thesis explores the potential recent moves towards a politics of collapse, one I call radical fatalism, hold for environmental praxis. The thesis concludes by suggesting the need for a turn away from the politics of the event and the over-determining valuation of global scales within environmental praxis.