There is no evidence that Thomas Jefferson, or any other American scientist, made the connection between the eruption of Mount Tambora, the most prodigious volcanic eruption in the history of civilization, and subsequent drastic changes in weather in the United States—and elsewhere in the Northern Hemisphere. Credible scientific evaluations can be made only on the basis of reliable data. Data collection is the time-proven starting point for all scientific inquiry. But the utility of data collection is not always evident at the time measurements and observations are entered in a record book; the payoff from a plodding exercise may be latent.  Such is the case with Jefferson’s routine observations of weather at Monticello. On May 17, 1816, Jefferson wrote:

[T]he spring has been unusually dry and cold. our average morning cold for the month of May in other years has been 63° of Farenheit. in the present month it has been to this day an average of 53° and one morning as low as 43°. repeated frosts have killed the early fruits and the crops of tobacco and wheat will be poor.^[1]

On April 10, 1815, the volcano Tambora in Indonesia had erupted violently, killing 100,000 islanders and discharging the largest volume of sulfurous gases and volcanic ash from one natural source in recorded history. The blanket of fine particles that hung in the atmosphere reflected a substantial portion of solar radiation, causing what New Englanders referred to as the “Year of No Summer.”^[2]

The fact that Jefferson did not connect the dots between cause and effect—he surely had heard of the Tambora disaster—does not diminish the importance of his data to science. Whenever scientists discuss the impact of Tambora, they tend to refer to Jefferson’s data, knowing that Jefferson used good weather instruments and was consistent in observing and recording.^[3]

In September 1816, Jefferson scanned his rainfall records and considered weather reports from elsewhere as he continued to puzzle over the drastic change in weather. From his correspondence with Albert Gallatin, we read:

We have had the most extraordinary year of drought & cold ever known in the history of America. in June, instead of 3 3/4 I. our average of rain for that month, we had only 1/3 of an inch, in Aug. instead of 9 1/6 I. our average, we had only 8/10 of an inch. and it still continues. the summer too has been as cold as a moderate winter. in every state North of this there has been frost in every month of the year; in this state we had none in June & July. but those of Aug. killed much corn over the mountains. the crop of corn thro’ the Atlantic states will probably be less than 1/3 of an ordinary one, that of tob[acc]o still less, and of mean quality.^[4]

The eruption of Mount Tambora offers only one instance of the payoff to science from Thomas Jefferson’s passion for collecting basic data on natural phenomena.

- Edgar A. Imhoff, 5/09

Further Sources

• Klingaman, William K. and Nicholas P. Klingaman. The Year Without Summer: 1816 and the Volcano that Darkened the World and Changed History. New York: St. Martin's Press, 2013.
• Thomson, Keith. Jefferson's Shadow: The Story of His Science. New Haven: Yale University Press, 2012.
• Look for further sources in the Thomas Jefferson Portal.