The sky in the northern hemisphere had been darkened, the winters unusually harsh, and the summers barely arriving for decades when the German Lutheran author Johann Arndt published his Four Books on True Christianity in 1610. Arndt warned his readers that:

when the sky burns like this, and the sun turns blood-red, it is telling us: Behold, one day I will perish in fire. In this way, all the elements speak to us, announcing our wickedness and punishments.

Despite being a staggeringly popular work of Lutheran devotionalism, Arndt’s book was unorthodox: there was very little of Luther’s theology, and quite a lot of alchemical philosophy. He borrowed heavily from the work of the Swiss alchemist Paracelsus, often simply excerpting large portions of the latter’s writing without attribution. In doing so, Arndt injected early modern Protestantism with a heavy dose of Hermetic philosophy, a belief that God is actively present within creation itself. A philosophical belief with roots in the Antique Mediterranean world, this perspective was entirely absent from orthodox Lutheranism, in which the cosmos was a fallen world of mere matter and divine knowledge was only accessible in scripture. For his readership, Arndt’s book of alchemical Christian devotion seems to have been a welcome explanation of the worrying changes in their climate.

Environmental historians and climate scientists now recognise the 17th century as a period of intense climate change, the peak of the Little Ice Age – a period of severe cooling between the 16th and late 18th centuries – in which average yearly temperatures in the northern hemisphere plunged by as much as two degrees Celsius. While such a number might seem small, it had massive local effects. The m