The 1890s have a special significance in the literary history of the Anthropocene, and the fin de siècle has traditionally been understood as a moment when artifice triumphed over nature. Reexamining the period today, we can instead see how literature and art of the 1890s reckons with the idea of an indeterminate nature without design, purpose, or end – a nature profoundly shaped by human forces and yet beyond human reckoning and control. The concentrated finitude of the era, as framed in literary and historical study, actually reflects the period’s own grasp of the finitudes and vicissitudes of the natural world. This chapter aims to tease out the environmental and ecological inheritance of the decadent 1890s while simultaneously teasing apart the complex conceptual contestation among rival assaults on the category of the “natural” in the 1890s, assaults that can be roughly grouped around Oscar Wilde’s 1895 denaturalizing of heterosexuality and Svante Arrhenius’s 1896 denaturalizing of the atmosphere in his landmark essay “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground.”