Cutting down the Liberty Tree: Climate Change and Despotism in Enlightenment Thought

In the eighteenth century, European thinkers began to suspect that the climate of their continent had warmed considerably since antiquity. Jean-Baptiste Dubos noted Juvenal’s remarks on the Tiber river freezing over and Horace’s references to the streets of Rome being filled with snow—events that no longer occurred in the Rome of his own day. Hume argued that this apparent change in temperature was due to human activity, particularly deforestation: “the woods are cleared, which formerly threw a shade upon the earth, and kept the rays of the sun from penetrating to it. Our northern colonies in America become more temperate, in proportion as the woods are felled.”  This observation on the transformation of the American climate dovetailed with the testimony of colonists ranging from Cotton Mather to Thomas Jefferson.

Claims about the effects of human activity on climatic temperature did not occur in an intellectual vacuum: contemporaneous with this discussion of climatic variability, political theorists including Montesquieu and Rousseau debated the effect that climate had on human behavior and governance. Many in Britain and its North American colonies believed that Europe was losing its ancient liberty and sliding towards tyranny, and gradual deforestation and continental warming provided one causal mechanism to explain that drift. Contemporary beliefs about heat and “enervation” also tapped into anxieties about a perceived declension in masculine virtue.

In this paper, I will discuss the intersection of climate change and political theory in Atlantic thought, drawing on a variety of sources which discuss whether “Time makes change in climates.”  I hope to show how the eventual rejection by Europeans and Americans of these theories of continental warming and climatic influence on human behavior eliminated a nascent rationale for political pluralism and closed the door on more fluid conceptions of race at the dawn of the nineteenth century.