This thesis is concerned with literature’s engagement with the environment, specifically ecosystems and climate change. Literature of the fantastic, works that break from the tradition of mimetic literature and the limits of realism, are the focus of this thesis, which argues, alongside ecocriticism, that literature must be part of the interdisciplinary drive towards greater ecological awareness. Speculative literature adds fantastic elements or draws on scientific extrapolations into the future, and offers a platform to engage with the science of environmental issues alongside philosophical engagements with the relationship between humans and the more-than-human world around them. This thesis draws on ecocriticism to examine the role of reading and criticism in constructing more ecologically sustainable societies. From this position, it asks how fantasy can be used to convey these themes. As a result, this thesis is interested in definitions of fantasy, drawing on science fiction and fantasy to examine Kathryn Hume’s framework of the fantastic impulse. Placing fantastic texts on two axes, Hume examines the ways texts support or subvert the reader’s expectations, and encourage or discourage reflection on their extratextual worlds. This thesis contends that, texts that encourage engagement are most transformative, but that the spectrum of engagement and disengagement challenges authors to navigate between didacticism and emotive imagery. To show this, this thesis examines four series of novels drawing on the fantastic impulse. Frank Herbert’s Dune Chronicles, Kim Stanley Robinson’s Mars Trilogy and Science in the Capital, and George R.R. Martin’s A Song of Ice and Fire. The first two are on opposite ends of both of Hume’s axes, and imagine the challenges of constructing Earth-like ecosystems on other planets, asking questions about the sustainability of such a project as well as the possibilities of transforming society. The latter two engage with rapid climate change, Robinson’s looking at contemporary climate change and Martin’s engaging with historical climate change. They interrogate the impact of the climate on human and more- than-human life, and reveal the tension between comforting didactic revisions of human- environment interactions and framework-disturbing alternate ways of relating to the environment. This tension is where the fantastic is powerful, allowing alternate visions to pierce sceptical readers’ defences