Correction Appended

Columbus, Ohio

BEN FRANKLIN and GLOBAL WARMING

FEW would argue that the debate on global warming engenders a lot of emotion. What else are we to make of comments that “within the last 40 or 50 years there has been a very great observable change of climate,” that “a change in our climate ... is taking place very sensibly” and that “men are led into numberless errors by drawing general conclusions from particular facts”?

That these comments were actually tossed around back in the late 18th century by the Pennsylvania doctor Hugh Williamson, Thomas Jefferson and Noah Webster reminds us that history has a tendency to repeat itself. (One can imagine what television talk shows would have been like then. Would Jefferson have promoted “An Inconvenient Treatise” only to be acrimoniously contradicted by Webster on “Hard Quoits,” assuming either could get a word in amid the jabbering of the host?)

In the 1780s, Thomas Jefferson opined in his “Notes on Virginia” that “both heats and colds are become much more moderate within the memory even of the middle-aged,” expressing views articulated as early as 1721 by Cotton Mather: “Our cold is much moderated since the opening and clearing of our woods, and the winds do not blow roughly as in the days of our fathers, when water, cast up into the air, would commonly be turned into ice before it came to the ground.”

The weather historian James R. Fleming has noted that the vexing scientific challenge in the climate debate has always been “the response of a large, complex, potentially chaotic system to small changes in forcing factors.” Benjamin Franklin understood climatic forcing factors better than anyone, surmising in a 1763 letter to Ezra Stiles that “cleared land absorbs more heat and melts snow quicker.” Franklin, our meteorologist emeritus for his seminal work on everything from lightning to northeasters, later surmised (correctly) that a prevailing haze over parts of North America and northern Europe was associated with the eruption of the Laki volcano in Iceland in June 1783, and was possibly the source for the exceptional chill experienced in the winter of 1783-84 in the new United States.

On the other side of the developing weather controversy in the late 18th century, Webster quarreled with Jefferson, insisting that he relied too heavily on the memories of “elderly and middle-aged people” for his observation that the climate had moderated. While Webster conceded an anthropogenic influence might still be at work, he argued that it caused something less than climate change: “All the alterations in a country, in consequence of clearing and cultivation, result only in making a different distribution of heat and cold, moisture and dry weather, among the several seasons.”

Hugh Williamson, astute in his understanding of the hydrological cycle, a key component in any climate change debate, wrote, “The vapors that arise from the forests are soon converted into rain, and that rain becomes the subject of future evaporation, by which the earth is further cooled.” A century and a half later, land-use studies would confirm quantifiable relationships between clearing trees for extensive farmland and changes in soil temperature, moisture distribution and local and regional climate responses, as well as the urban heat-island effect. In our time, we have learned that tropical deforestation is linked to as much as 15 percent of the world’s global warming pollution, largely due to the release of carbon dioxide, one of several “greenhouse gases” that trap and re-radiate terrestrial heat.

But the primary goal of Jefferson and other colonials in the national climate discussion was to scuttle the European notion that the New World’s climate was too harsh and deleterious for settlement. From Mather to Williamson and Jefferson and many others, the debate was a reaction to European attitudes regarding the presumed rigorous and unhealthful climate of North America.

Instead, early American writers painted a far more favorable picture of the American climate and fauna. The notion took hold that manmade climate change, specifically clearing untamed land for cultivation, would prove beneficial, ameliorating health problems by draining standing water and wetlands thought to breed disease and lethargy.

Not until the middle of the 19th century would the debate on North American climate change finally be put to rest by early climatologists who had cranked out numbers by hand from sparse and slowly accumulating weather observations and phenological data.

The clearing and cultivation climate-change debate of Jefferson’s era was driven by literary and anecdotal evidence in the absence of solid data. Now we have satellites monitoring high-latitude snow cover, thinning sea ice and deep-layered atmospheric temperature increases, coupled with ground observations revealing the disappearing snows of Kilimanjaro (85 percent ice loss since 1912) and many other glaciers.

The wealth of data now at our disposal, enhanced by high-resolution computer models that pioneer climatologists would have craved, has, curiously, not turned down the thermostat on the centuries-old global climate change debate, quite likely because the stakes are so much higher.