Nowadays, deforestation, chopping down loads of trees without replacing them, is generally considered to be detrimental to the local and global climate. But it was not always this way. Today we know that trees and forests, apart from providing nice habitats for a vast variety of species of wildlife, are important carbon sinks: they scrub the air clean of carbon dioxide, too much of which in the atmosphere can lead to a local warming effect, and they produce lots of lovely oxygen, which we enjoy breathing. Recent debates about anthropogenic climate change – whether or not humans can in fact have an impact on the environment on a global scale – have seen scientists argue back and forth over the past few decades about data, statistics, and interpretations in order to determine to what extent we really are making a mess of our planet. This is science which has been very heavily politicised indeed, especially around questions of the global economy. However, although our depth of knowledge may be new, our non-scientific motivations when it comes to understanding climate are not.
Based on an essay I wrote as a final year undergraduate, this article tells the story of a time when anthropogenic climate change, assumed to be a fact on a regional scale, was considered a very positive aspiration. This view, shaped as it was largely by anecdotal evidence and personal experiences, demonstrates very well how climate science can appear at first to be a very accessible field to observe and understand; everyone experiences the weather, and some keep notes, for example in diaries, which can be compared over time and from which it might seem possible to draw out general trends. It is possible that this was one reason for the belief, which became widespread in America in the eighteenth century, that the climate of the eastern states, especially Virginia, was improving. The seasons were observed to be becoming more moderate, and hence better for crops as well as people. However, other factors served to reinforce this conviction, which were not related to scientific matters at all, but rather were political, economic, or even religious in origin.
Early English settlers in America had arrived with an understanding of the nature of climate which was strongly challenged by the conditions which they found in the New World. The older conception was that climate was determined solely by latitude; indeed, the two words were often used interchangeably. The key factor which determined climate was the temperature and movement of the air, which was in turn determined by the amount of sunlight the area received, which depended on its latitude. By this logic, the climate of Virginia should have been similar to southern Spain and Portugal, which they believed was better suited to the English character than the hotter, more humid tropical regions of the southern American continent. However, in the sixteenth and seventeenth centuries these early settlers had been sorely disappointed by the conditions they found; the weather was wild and disagreeable, with storms more frequent and more violent than they had expected. Summers were too hot, and winters were too cold.
Even in the eighteenth century, one Church of England missionary to Rhode Island, James MacSparran (1693-1757), was warning potential colonists against emigrating to America at all, making his thoughts clear in a book published in 1753, titled, in full: “America Dissected, being a full and true account of all the American Colonies, shewing the intemperance of the climates, excessive heat and cold, and sudden violent changes of weather, terrible and mischievous thunder and lightning, bad and unwholesome air, destructive to human bodies.” The New World was not quite the paradise they had hoped for. However, as most were unwilling to abandon the ancient idea that climate could be reliably predicted from latitude, they needed another way to resolve the apparent discrepancy between theory and observation. The answer was that the climate should be as they expected, but some other factor was altering it away from the norm. Early observers drew connections between the problematic weather conditions and the forests. The solution, as proposed by some seventeenth century writers, was of course to remove the trees.
John Evelyn (1620-1706), a writer and amateur man of science, wrote in 1664 that the dense forests of North America caused rain, mists and high humidity. This in turn led to a greater incidence of disease amongst the colonists. Cutting down the forests, he argued, was already making a difference in New England. In 1688, the English clergyman John Clayton (1665-1737) wrote of Virginia that the colony was overgrown with forests, and speculated that this made the air stagnant by obstructing the movement of wind. Yet another John, this one a London physician and naturalist called John Woodward (1665/8-1728), followed Evelyn’s lead by encouraging the clearing of forests with the intention of improving the climate. In 1697 he gave a paper to the Royal Society in which he linked an abundance of trees with higher humidity in the air, resulting in frequent, inconvenient rains. When published several years later, this paper included the hope that as the north American forests were cleared to make way for habitation and cultivation, the climate would become drier, calmer, and generally more pleasant.
Many in eighteenth century America believed that the climate had been improving, their opinions derived from the anecdotal evidence of their own experiences and those of others. One contemporary and correspondent of Woodward’s, the very influential American Puritan minister Cotton Mather (1663-1728), claimed in 1721 that the climate was getting warmer and better. Having grown up in America he believed that the cold season had been moderated and the weather made more mild, with weaker winds. He attributed this change to settler efforts to cultivate the land by clearing the forests. Benjamin Franklin (1706-1790), the American statesman and man of science, wrote in 1763 that he thought the climate had been improving as the forests were cleared. He did however note that systematic observations and measurements would be the only way to really settle the issue of what was going on with the American climate. In 1770, the American physician and politician Hugh Williamson (1735-1819) read a paper to the American Philosophical Society in which he noted that those who had lived in Pennsylvania and the neighbouring colonies for the past forty or fifty years believed there had been an observable change for the better in the climate; winters were not so intensely cold, nor summers so uncomfortably hot. Thomas Jefferson (1743-1826) in 1784 would make similar recourse to such anecdotal evidence when discussing the improvement of the climate of Virginia.
Williamson, Franklin and Jefferson all appealed to the argument that cleared land had a different albedo to forested land, that it is it had a different capacity to absorb and retain heat. Cleared land would stay warmer for longer, thus heating the air which moved over it for longer periods. Williamson and Franklin both argued that the newly cleared land was warmer in winter, and Williamson believed that in the summer this warmer land would better facilitate atmospheric mixing of warmer and cooler air, thus leading to cooler summer temperatures. Later, in 1794, one author, Samuel Williams, observed the temperature of cleared land and forested land using buried thermometers, and concluded that cleared land was indeed warmer. He predicted that, as deforestation continued, the cold would decrease, the air would become warmer, and the overall climate would become more moderate.
Others, following Clayton’s earlier speculations regarding forests as an obstruction to wind flow, recommended that the clearing of forests would improve the climate by removing the impediments to the free movement of air; this would produce milder summers and winters. Jefferson’s explanation for the recent milder climate combined the ideas about the changing albedo of land surface with air flow theories. He argued that, as the land was cleared, it heated the air which moved over it more than the forests had done, and this mass of air then rose. It was replaced by cooler air from two sources: the mountains to the west and the sea to the east. However, the air from the west was slowed down by the rougher, uncultivated, forested terrain, and thus the sea air, moving faster over the cleared land, penetrated further inland. This greater incursion of sea breezes, Jefferson believed, was responsible for the improvements in the climate. Similarly, in 1798, Benjamin Henry Latrobe (1764-1820), a British architect and engineer who had recently moved to America, told the American Philosophical Society that he believed deforestation in Virginia was allowing ocean winds to travel further inland, reducing summer temperatures.
These opinions, predictions and suggestions were all aimed at improving the uncomfortable climate of the region. Many at the turn of the eighteenth century were still trying to hold on to the old conception that climate was determined by latitude. Removing the forests would result in the climate changing to what it was expected to be, and this was very important for many reasons, political, economic, and even religious. The key was making the North American continent appear habitable, and hospitable to English sensibilities. The early settlers had hoped, given their latitude, that the American colonies would be capable of producing commodities such as England was then importing from southern Europe, and thus release the English from the need to trade with their political enemies. For example, a reliable supply of a nice smelling oil was particularly important for the English economy as it was used in the manufacture of soap employed in the production of woollen cloth. Without a colonial supply, the English economy was very heavily reliant on the Spanish and the Portuguese, with whom they had recently been at war.
Early promoters expected to find gold, silver and pearls, and to be able to produce wine, silk, olive oil, sugar and spices. They had particularly hoped to be able to grow tropical and Mediterranean crops such as oranges, lemons and sugar cane in Virginia, and had not been discouraged by early failures. Winters tended to be too harsh for tropical plants, but decades into the seventeenth century promoters continued to hope for the kinds of produce and commodities which could be expected if climate was strictly determined by latitude. A good climate was vital, both for growing the necessary crops and for attracting potential colonists to make the long and dangerous journey across the Atlantic, and subsequently to stay and make their lives in the New World. By the middle of the seventeenth century, when it was quite definitely ascertained that North American weather was not going to live up to European expectations of it, the answer was to adapt the land in order to change the climate, and one of the most obvious things to do seemed to be what was being done already: namely to chop down the forests.
Cotton Mather, the aforementioned influential Puritan minister, had another reason for stressing how good the climate of the colonies was becoming, and how good he thought it could become. In his 1702 magnum opus The Ecclesiastical History of New England, Mather wrote about how he envisaged the centre of the Christian religion moving from Europe to America. Of course, this would not occur as he foresaw it if the climate continued to be so far from the anticipated ideal of Eden. It seems to me not unreasonable to infer that part of Mather’s encouragement of deforestation resulted from this desire to ensure that North America would grow to be the Christian haven he hoped for, and he, like so many others, placed his faith in the removal of the forests.
Although there were different ideas about the specific mechanism involved, including the effect of forests on humidity, the free movement of air, and the albedo of cleared ground, many in eighteenth century North America shared the belief that deforestation had been improving the climate, making it more agreeable by European standards. Most of these ideas were based on the anecdotal evidence of those who believed they had experienced first-hand the changes in the climate, but there was little in the way of systematic observation or measurement until the end of the eighteenth century. By the turn of the nineteenth century, there was much more uncertainty, with more voices arguing that the cold harsh winters of some of those years were evidence of a more complicated picture. Noah Webster (1758-1843), for example, argued that forests were no impediment whatsoever to the movement of air over terrain. Some even argued that the climate was actually getting colder.
As more emphasis was placed on observation, measurements, and the gathering and comparing of data, a clearer picture began to emerge about the connections between deforestation and climate, and in the nineteenth century the advice was, more often than not, to plant new forests in order to make the dry expanses of the American west more habitable. Then, as now, an understanding of climate, and how human activity could affect it, was important for political and economic reasons. From the eighteenth century onwards, the science required for an effective study of climate change was being consolidated, developed, and finally, understood to require more extensive data than was then available. Many people had come to the question of the connection between forests and climate with preconceived ideas of what they would find based on their political or economic bias; but they left us with the questions and the tools to better understand the impact human beings can have on our planet.
When writing this article, I have relied heavily on the following sources, which may provide interesting further reading:
- Fleming, James Rodger, Historical Perspectives on Climate Change, (Oxford University Press, 1998)
- Kupperman, Karen Ordahl, ‘The Puzzle of the American Climate in the Early Colonial Period‘, in The American Historical Review, Vol. 87, No. 5 (December 1982)
- Thompson, Kenneth, ‘Forests and Climate Change in America: Some Early Views‘, in Climatic Change 3 (1980)
- The Oxford Dictionary of National Biography, which you can access online (subscription required)