In the context of climate emergency and growing mistrust in knowledge institutions, both science and documentary practice have often been positioned as neutral authorities. Yet the knowledge they produce is shaped by political, social, and material conditions. This paper presents a creative practice research project that uses speculative documentary to trouble dominant narratives of truth and objectivity. Rather than rejecting science, it critiques the authority of singular truth claims in both scientific and documentary domains, asking how knowledge is constructed and maintained. The analysis centres on It Will Not Be Pure, a multi-channel video installation created as a form of climate fiction. Set in a near-future where soil is scarce and arable land is gated for the privileged, the work follows a researcher documenting life beyond these enclosures. Fiction and documentary language are blended to examine environmental collapse, purity politics, and socio-economic exclusion. Accompanied by video documentation, this paper reflects on speculative documentary as both aesthetic strategy and research method. Within environmental education, such approaches offer critical ways of engaging with uncertainty and imagining otherwise. The work draws on feminist, queer, and anti-colonial scholarship to explore interdependence and alternative futures.