of Vicky Slonosky's "The Long History of Changing the Climate"
The deforestation-climate change idea seems to have been very popular and much discussed in early 19th century Canada, although the links to phlogiston were dropped as Lavoisier’s revolution in chemistry led towards our current theories of heat. James Flemming and Hans (von Storch of this blog) have discussed deforestation and climate theories in the US and Germany. As most of my work has been on Canadian observers, my examples will come from there.
Mention of the land-clearing climate change idea seems to have been obligatory for anyone writing a travel memoir, some of whom report that debate on whether the climate had improved was typical tavern discussion. It’s also a common theme in works sponsored by various governments trying to attract immigrants: yes, the climate was harsher than in Europe, but a bit of hard work cutting down trees and planting crops will quickly transform the harsh Canadian climate into a mild European one. After all, north-western Europe was farther north than Canada, so Canada ought to be warmer than Europe. What was the main difference between the colonies and northern Europe? The forests and swamps. Remove those, and the climate would be transformed. (True, a few natural philosophers mentioned the Gulf Stream and wrote of northern Europe basking the warm waters of that current, but nothing could be done about changing the ocean currents, while clearing the forests could be done with an axe.)
The land-clearing climate improvement theory seems to have been as much, if not more, of a popular belief as one put forward by the early scientists, possibly because it was the settlers and farmers who had the labour of clearing the forests. The physician Jean-Francois Gaultier, whose temperature weather observations from 1742 to 1754 are among the earliest systematic observations in Canada, wrote in 1746 that “The inhabitants of Canada claim that the winters are not as cold as they used to be, this they attribute to the large quantity of land which has been cleared”. An 1827 editorial from the Nova Scotian stated that “It is a theory which now almost universally obtains that the climate of a young country is undergoing, with the progress of improvement, a slow but gradual amelioration. We are satisfied ourselves that the former opinion is correct: but at the same time it would be more satisfactory if we could refer to actual observations and found our reasonings upon meteorological tables.” Around 1836, McCord wrote that “I had not made up my mind as to the fact of the climate having materially altered but was impressed generally with the belief that the climate had improved, or become warmer, as it had increased in population and cultivation. “
It was time to turn to observations to test the theory. As one who has spent nearly 20 years working on finding, transcribing and analyzing observations of climate, McCord’s next words are my favourite climate quotation:
" I resolved to make diligent search for such records as might be found …The difficulty of the experience was even greater than I had anticipated. Few individuals had turned their attention to this (even now) infant science … and of those which I was fortunate enough to discover, many were unsuitable from the irregular manner in which they were kept... No-one but the most zealous meteorologist knows how very difficult it is to obtain observations in this science which can be depended upon” (circa 1836).Despite this, McCord managed to collect observations from several locations around the St-Lawrence Valley and the Ottawa River Valley between 1790s and the 1860s, many of which have been typed up by volunteers in past four years. He even managed to convince the British Army to keep weather observations at the local garrison from 1839 to 1841. He had been hoping for hourly observations, but military routines and the schedule of the changing of the guard meant the observations could only be recorded every two hours. His conclusion was that:
“My own observations, supported by many curious and ancient records of the climate of Canada, corroborate the [Dr.’s] opinion that there has been no essential amelioration in its climate since the period of its first discovery … I am distinctly of the opinion that if the extremes are less intense and long (which I believe), the mean temperature of these Provinces has not materially changed”.The “Dr.” mentioned above was naval surgeon William Kelly, who noted:
“The general opinion is, that the climate of a country becomes milder, as it is cleared of forests, and cultivated. The application of this doctrine to Canada is not at all new, for I find it entered into the speculation of a writer on this country towards the end of the 17th century. It is founded on the generally admitted fact, that the climate of Europe is much milder now, than at the commencement of the Christian era … inferred from the … Roman writers. … This explanation seems to have been generally received without a very strict examination into the facts connected with it, and kept for want of a better.”Kelly looked into the journals kept by the early explorers of Canada such as Jacques Cartier (whose voyages to Canada were between 1534 and 1542) and Samuel de Champlain (who founded Quebec City in 1608) for climate indicators such as the melting of the river ice and the flowering of fruit trees to decide that “from the little evidence we have here … the conclusion that the climate has undergone no change, may I think be safely drawn”.
The clearing-climate improvement theory was definitively dismissed in John Disturnell’s 1867 book, “Influence of Climate in North and South America”. Disturnell quoted extensively from Dr. Lillie’s “Essay on Canada”, which examined the documentary records of Canadian climate since the 16th century and like Kelly, concluded that the timing of the seasons hadn’t changed over the centuries. I haven’t been able to find a copy of Lillie’s essay.
I’ve tried to evaluate the deforestation-climate-improvement theory using energy budgets from 20th century observations. On balance, in a climate with winter snow cover, I think the forest clearing would actually tend to cool the local climate due to the high albedo of snow covered fields compared to forest. Even in summer the albedo of cultivated fields is higher than that of a mixed forest, although sensible and latent heat exchanges complicate the picture.
It’s interesting that this theory of anthropogenic climate change was active in Canada for over a century (or even several centuries, according to Kelly), and was one of the main motivating forces behind the systematic recording and collecting of weather observations in 18th and 19th century Canada. It’s also interesting to compare attitudes towards anthropogenic climate change then and now. In the past, actively trying to change the climate was viewed as something positive and an improvement, even if it turned out in the end to be ineffective, whereas today human-induced changes to climate are inadvertent and considered as something negative, even potentially dangerous.