As educators have begun to investigate new ways to promote student productivity and creativity by 'co-creating' with generative AI (GenAI), scholars have simultaneously warned against attributing creativity to GenAI given potential risks that anthropomorphizing AI could result in undermining the value of human creativity or in encouraging current extractive processes by AI development companies. In the context of this tension, this article uses a new materialist frame and observations from an original in-class activity to illustrate how the experience of speculatively co-creating with GenAI -- when situated within the social and environmental impacts of human-caused climate change -- can be a helpful resource for encouraging students to question historical assumptions of human exceptionalism and to imagine new forms of social and political organization. The article then discusses the implications of human-GenAI co-creativity in terms of social and environmental justice education and contemporary academic discourse on post-anthropocenic and post-capitalist imagination.