The Long History of Changing the Climate
Like many others before me, I’ve gone from being interested in the content of historical climate records for scientific analysis to also being fascinated by their context, and by the history of the idea of anthropogenic climate change found in these documents. The idea of humans changing the climate seems to have been around for a long time in the New World. Actually, the idea of humans changing the climate seems to have been around for a long time, period. Clarence Glacken traced the idea of human-induced climate change back Classical Antiquity, to shortly after Aristotle. The idea of humans changing the climate by modifying the environment winds its way through Roman historians, medieval monks, Enlightenment philosophers, and 19th century meteorologists.
By the middle of the 18th century, the idea of changing the climate by clearing forests and draining swamps (today we tend to use the somewhat more attractive term of “wetlands”) was bound up with the idea of phlogiston. I can’t claim to comprehensively understand the concept of phlogiston as it appears in the climate related theories, but the basic idea appears to be that heat was material, a substance, and that materials could lose this substance. When a log burned, it wasn’t the wood which was burning, but the phlogiston inside which was liberated into the air. Phlogisticated air (air which burns, which we now know contains oxygen) was necessary for breathing, while experiments showed that candles snuffed out and animals suffocated in “de-phlogisticated air” (mostly CO2). The concept of phlogiston was largely replaced by Lavoisier’s concept of the calorie around the 1790s.
The forests and swamps were held to lock in phlogiston, by reason of their being cold and damp: by removing the trees and draining the moisture of the swamps, the phlogiston would be released and warm the climate, especially in winter, as well exposing more of the surface to the sun. Not to worry about the summers becoming too warm, though, the removal of the trees would also generate more winds coming down from the mountains to circulate the liberated phlogiston around and relieve the oppressive heat of summer. (It’s at this point that I start to wonder if my fuzziness on the concept of phlogiston is due to my lack of comprehension or the way it seems to be used in a somewhat malleable way to support whichever vision of future climate the author is trying to present: More wind! Less damp! More rain! Warmer winters! But cooler summers! Not unlike some characterizations of current climate change).
A curious thing about the 18th century forests-and-phlogistion theory of anthropogenic climate change is that both proponents such as Hugh Williamson, Edward Gibbon and Theodore Mann, and detractors such as Daines Barrington appealed to the changes in climate and environment between their time and that of the Romans as a proof: since the times of the Romans, Europe in general and northern Europe in particular had been largely deforested and had grown warmer. The evidence that the mid-to-late 18th century was much warmer than the Roman period was taken from descriptions of weather and climate in the Classical Greek and Roman authors: advice on how to ice-fish in Rome, stories of the Black Sea freezing over; the allocation of soldiers’ wine rations having to be cut into chunks because the entire shipment of wine was frozen, Alpine passes that were open in the 18th century being recorded as impassable by the Romans; the frequent freezing over the larger rivers in Europe and their habitual use as roads by the barbarians. Mann in particular, writing during and shortly after the severe winter of 1788/89 in Europe, exhaustively described all references to climate, climate change and cold weather in the literature of classical antiquity in his 124 page treatise, observing that before looking for causes of climate change, it is first necessary to “prove by reliable authorities that these changes really happened”. (As an aside, Mann’s works might be among the first papers ever written in field of historical climatology: as well as his description of Roman climate from Classical sources, he described every cold winter from the 5th century AD to 1789 recorded in documentary sources).
Mann, as had Barrington and Gibbon before him, compared the Greek and Roman descriptions of the forested northern Europe to that of Canada, particularly the area around Hudson Bay, which spurred interest in the question of anthropogenic climate change in Canada. If these theories were true, then the 8-month long winters and short, mosquito-ridden summers could be eliminated, or at least mitigated, by cutting down the forests and draining the wetlands. Suddenly cutting down a tree became a patriotic duty to be undertaken for the common good of improving the climate.
I said earlier that this theory was curious: what I find curious about it from the 21st century viewpoint was the 18th century was supposed to be in the depths of the Little Ice Age (admittedly, the second half of the 18th century appears to have been a respite between some of the LIA’s severest periods, but still), while the “Roman Warm Period” has been documented in proxy records and some archaeological findings as a climatic optimum. How to reconcile the evidence of the proxy records with the documentary evidence of the classical authors as collated by Barrington, Williamson and Mann? Why did they think they were living in one of the warmest periods of the past 2000 years, while we think they were living in one of the coolest? To even try to answer these questions is another post in itself, but if any readers have access to records covering both the Roman period and the 18th century, especially in central and southern Europe, I would be very grateful for a reference. Many of the ones I’ve been able to track down seem to cutoff around the year 0.
A translation of Mann’s treatise can be found in the notebooks of John Samuel McCord, an amateur meteorologist who kept records of the climate in Montreal over much of his lifetime, starting as a boy in 1813. The question of whether or not the climate of Canada had changed as a consequence of deforestation was one of McCord’s main motivations for not only keeping his own record of weather and climate, but also for collecting as many observations of weather and climate from Canada as he could. His notes, copies of weather journals, and weather registers form the core collection of historical weather and climate documents for Canada which I’m trying to get typed up in digital format. Thanks the efforts of many volunteers, most of the McCord weather observations from 1794 to 1869 are in the process of being digitized. (See https://sites.google.com/site/historicalclimatedata/canadian-historical-data-typing-project).
So what was McCord’s evaluation of the forest-phlogiston theory, based on Mann’s papers and his records? This post is already too long, so for those who have managed to make it this far, the 19th century part of the story will in part 2.