Sunday, July 24, 2011

Jefferson vs Webster: America's First Global Warming Debate

Interesting article in the Smithsonian describing an early debate over human impact on the climate. Jefferson, measured the temperature on his farm twice daily for 50 years.
In his 1787 book, Notes on the State of Virginia, Jefferson launched into a discussion of the climate of both his home state and America as a whole. Near the end of a brief chapter addressing wind currents, rain and temperature, he presented a series of tentative conclusions: “A change in our climate…is taking place very sensibly. Both heats and colds are become much more moderate within the memory of the middle-aged. Snows are less frequent and less deep….The elderly inform me the earth used to be covered with snow about three months in every year. The rivers, which then seldom failed to freeze over in the course of the winter, scarcely ever do so now.” Concerned about the destructive effects of this warming trend, Jefferson noted how “an unfortunate fluctuation between heat and cold” in the spring has been “very fatal to fruits.”

Jefferson was affirming the long-standing conventional wisdom of the day. For more than two millennia, people had lamented that deforestation had resulted in rising temperatures.

Daniel Webster, best known for his dictionary, disputed the argument -- both in its traditional anecdotal/historical form and in the more empirical/scientific version that Jefferson and others made subsequent to the invention of the thermometer.
Webster concluded by rejecting the crude warming theory of Jefferson and Williams in favor of a more subtle rendering of the data. The conversion of forests to fields, he acknowledged, has led to some microclimatic changes—namely, more windiness and more variation in winter conditions. But while snow doesn’t stay on the ground as long, that doesn’t necessarily mean the country as a whole gets less snowfall each winter: “We have, in the cultivated districts, deep snow today, and none tomorrow; but the same quantity of snow falling in the woods, lies there till spring….This will explain all the appearances of the seasons without resorting to the unphilosophical hypothesis of a general increase in heat.”

Webster's arguments basically ended the debate and the idea that human activity significantly affected the climate was forgotten until the middle of the 20th century.

1 comment:

  1. Well that's ancient history. Now for some updated science, Scientific American has a report on the study of the last great rapid warming: the Paleolithic-Eocene Thermal Maximum. During that period, 2 [units] of carbon per year were put into the atmosphere and ocean, caused primarily by volcanic emissions related to the separation of the continents. During the current period of warming, we are putting out 9 [units] of carbon per year because of human activity. As well, the last warming happened over a period of 20,000 years. This current warming is happening 5 times faster. The last warming was reversed by the earth's own negative feedback loops that stopped the warming and returned it to a cooler climate, but that process took 200,000 years, well beyond the limits of human civilizations.

    The full article is NOT available online (that I know of).
    http://www.scientificamerican.com/article.cfm?id=the-last-great-global-warming

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