The Baron de Montesquieu’s magnum opus from 1748, The Spirit of the Laws, is a familiar Enlightenment text. This dizzying, panoramic analysis became, in effect, the first textbook of comparative politics, and helped establish political science as an identifiable field. The Baron also crafted hugely influential definitions of political law, civil law, and the law of nations, and his description of the “separation of powers” in democratic governments, based on a highly impressionistic reading of the Roman Republic and the British parliamentary system, wielded an immense impact on the framers of the U.S. Constitution.

All of this is well known by historians.

What is less well known, and less appreciated, is Montesquieu’s startling belief that climate not only affected a country’s ideal legal-political culture, but even dictated its form. The deep-rooted principles that guided the shape and character of governments were formed “in relation to the climate of each country, to the quality of its soil, to its situation and extent.” Everywhere Montesquieu returns to climate as the élément clé in explaining the world’s legal and political systems. In the process, he blends 18th-century conceptions of race, biology, climate, jurisprudence, and governance to decipher (or rather stereotype) a country’s “natural” legal values. In many ways, a country’s laws had to balance out the vices that were induced by particular climates.

Here’s one example: “When, therefore, the physical power of certain climates violates the natural law of the two sexes, and that of intelligent beings, it belongs to the legislature to make civil laws, with a view to opposing the nature of the climate and re-establishing the primitive laws.”1

Rough translation: when hot climates incite horniness and sluttiness, and people start having liberated, sweaty sex, then it’s a good idea to have laws that prevent such hedonism and return people to their natural, shame-filled modesty.

Some of this beguiling climate-based reasoning derived, in part, from Aristotle’s arguments about climate—namely, that the world was divided into three climatic zones, the frigid, the temperate, and the torrid, and that human bodies worked well only in the temperate zone. But Montesquieu’s heavy emphasis on the relationship between climate and human beings was essentially new, and sparked immense interest in the “science” of weather patterns, temperature, and microclimates.

In short, climate was now on the agenda for educated Europeans, who became accustomed to thinking about its effects on bodies, minds, and land.

This turn to climate in the 18th century is not entirely surprising given that Europeans dealt with the effects of the Little Ice Age in this period. This temporary cooling of the Northern Hemisphere was most likely caused by a temporary decline of sunspot activity that reduced solar-radiation activity, although some scholars believe that rapid ecological changes in the Americas exacerbated or even caused the cooling process in the Atlantic world. Whatever the ultimate cause, the Little Ice Age created erratic and frigid temperatures across Europe in the early modern period. The cold winters are immortalized artistically in the many Dutch Golden Age paintings of ice-skaters on frozen canals. (The canals rarely freeze any more.) The early modern period experienced numerous weather-related crop failures, too, including three devastating ones in France in 1693-1694, 1709-1710, and 1788. The climate was hard to ignore.

What’s even more striking, from out modern point of view, is that Europeans not only began to discuss the ways in which climate affected humans and land, but they also came to realize that human beings had the terrifying capacity to change the climate. That is, Europeans of the 18th century were perhaps the first people in world history to grasp that Earth’s seemingly impervious climate systems were in fact more mutable and more fragile than previously assumed. A single, benighted species such as mankind apparently had the capacity to disrupt large-scale environmental processes.

Let me be clear, though. I am not arguing here that Europeans shared our current consciousness about climate change. Ever since the 1970s and 1980s there’s been a growing awareness that fossil fuel emissions (mainly carbon dioxide and nitrous oxide), rampant deforestation, and the release of natural stores of methane have created a “greenhouse gas (GHG) effect” in our planet’s atmosphere, which traps heat (at infrared wavelengths) that would otherwise escape from the Earth’s atmosphere, and which results in the slow but steady warming of average surface temperatures. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” concludes the Fifth Assessment Report (2014) of the UN’s Intergovernmental Panel on Climate Change. The growth of GHG emissions can be charted over time by analyzing the chemical composition of long-frozen ice cores. More recent GHG levels are identified from direct atmospheric measurements. We now know that the pre-industrial world had about 280 parts per million of carbon dioxide in the atmosphere. That number has now surpassed the 400 mark.

Montesquieu and his acolytes knew absolutely nothing about any of this. Nonetheless, some eighteenth-century observers of the natural world began to observe more localized examples of man-made climate change, and they all cited Montesquieu as an inspiration. The best examples come from the writings of European imperial overlords in the 1760s and 1770s who colonized and deforested tropical islands. The historian Richard H. Grove has shown persuasively that colonial administrators on European-controlled islands in the Caribbean, Atlantic Ocean, and Indian Ocean developed an acute awareness about mankind’s ability to alter local climates. It was easier, in a sense, for European invaders to recognize environmental degradation and its consequences on isolated, self-contained tropical islands than it was to recognize such changes back in the homeland. France, the Netherlands, and England had been slowly deforested over thousands of years, and this degradation seemed natural and tolerable to many (but not all) Europeans. However, on tiny islands, it was much easier to notice the rapid disappearance of forests, and its effect on climate, native species, and local hydrological systems, since these observable changes took place over a shorter period of time and on smaller morsels of land.

In the seventeenth and eighteenth centuries, colonial powers from France, England, the Netherlands, Portugal, and elsewhere took over such islands as Mauritius, St. Helena, Barbados, St. Vincent, Montserrat, and Jamaica, all in the hopes of transforming them into profitable agricultural outposts. Within a few decades, most of these islands had been badly deforested by a combination of land clearance policies, overconsumption of wood for industrial purposes, and the introduction of destructive foreign livestock. Indigenous inhabitants were either killed off (and replaced by African slave laborers) or else severely diminished in population. In a process termed “ecological imperialism” by Alfred Crosby, new flora and fauna as well as foreign agricultural practices overwhelmed and forever changed the ecology of these lands.

However, in the middle and late eighteenth century, a series of reformist bureaucrats wound up on these islands and sought to reverse the trends of environmental destruction. (The irony here is that there would not have been a need for new conservation policies had early European settlers not destroyed island forests.) Many of these colonial bureaucrats opposed slavery, too, but they cared quite a lot about the economic interests of their respective home countries, and their early “environmentalism” (a term used by Grove) was rarely inspired by concerns for social well-being. Figures such as Pierre Poivre, who lived on French-run Mauritius, drew on Enlightenment science as well as Persian, Indian, and Zoroastrian botanical knowledge to protect old-growth forests. Poivre, along with other technocratic bureaucrats, realized that deforestation had economic and environmental impacts, too. It slowed agricultural output, since sugar production, for instance, required lots of wood.

But even more importantly for our purposes, Poivre and others began to realize that sudden deforestation made island climates drier and warmer. Rainfall seemed to diminish in areas that had been clear-cut; streams that had once run wild through sloped forests quickly dried up, removing vital freshwater resources for European colonials; soil erosion on hillsides and in riparian zones silted up rives, which in any case had become more desiccated. In the words of Grove, “Poivre marshaled the climatic arguments against deforestation which had emerged by the 1760s and then persuaded the French colonial authorities of their importance.” As a result of this growing environmental consciousness in the early modern period, and also out of a concern for agricultural profits, European powers began to put in place strict laws meant to encourage the sustainable use of forests: St. Helena (late 17th century), the Dutch Cape Colony (late 17th century), Montserrat (1702), Mauritius (1760s-1770s), Tobago (1763), and so on. The policies enacted later in the eighteenth century were meant explicitly, at least in part, to rehabilitate island climates, and make them more hospitable for human inhabitants and agriculture.

None of this meant as a defense or justification of Poivre or any other colonial administrator. At the end of the day, what these figures cared about was creating profitable cash-crop plantations meant to feed European markets and line the pockets of colonial investors. Their early brand of environmentalism and advocacy of sustained-yield forestry needs to be situated within that regrettable context. Their motives and morals were reprehensible, but I can at least concede that at least some colonial administrators began to recognize and react to anthropogenic climate change.

Even though eighteenth-century knowledge about climate change differed from our own, this early concern for climate science and conservation is certainly part of the history of sustainability. The chilling power of humans to change the climate has been recognized for over 250 years. We can learn something from these eighteenth-century figures who were less troubled than many of us are today by the realization that human behavior can alter the climate. Given our ongoing and rather vexed debates about climate change, it would be useful for the public to understand that even in the eighteenth century, climate change was already becoming an accepted reality. Moreover, there was an overriding belief that humans can and should reverse those changes.

1Ibid., p.119. Montesquieu comes down particularly hard on the indigenous inhabitants of warmer climates. “The inhabitants of warm countries are, like old men, timorous; the people in cold climates are, like young men, brave.” See p.102. Note, also, that he bases many of his arguments on experiments he conducted with a frozen and dissected sheep’s tongue. See pp.102-3.