Q&A: “The Jefferson Weather and Climate Records Digital Resource and the Digitization of American Weather Records”--A Virtual Discussion with Jim McClure

Select answers from Jim McClure, General Editor and project director of the Papers of Thomas Jefferson editorial project at Princeton University

Q. What do we know about what caused the little ice age? (Joella Clamen)

A. This is an interesting, big question that is beyond my expertise. It is the subject of ongoing investigation by climate history specialists. There were likely multiple factors contributing to that cooling period. For more information, I would recommend looking at some of the chapters in the Palgrave Handbook of Climate History edited by Sam White and others; White's A Cold Welcome; Anya Zilberstein's A Temperate Empire; Dagomar Degroot's The Frigid Golden Age; and an older work, The Little Ice Age by Brian Fagan.

Q. Can we conclude that the Little Ice Age explains severe conditions described at Valley Forge during the Revolution? Thank you! (Anonymous)

A. I don't know enough about the conditions at Valley Forge to say how they fit into larger patterns. I can say that there were some severe winters in Jefferson's time. One for which there is information in his meteorological record and correspondence was the winter of 1804-1805, for which we provide some supplementary information on the website (https://jefferson-weather-records.org/taxonomy/term/382).

Q. Which parts of Jefferson’s practice changed overtime? If they did change was it because he innovated or because he was influenced by someone else? (Anonymous)

A. This is an excellent question, but hard to answer. When he added a column to the record for a new category of information or made notes about something, we usually can't tell if it's because he became interested in a new problem, was motivated by something he read or learned in conversation, or was able to acquire a particular instrument (which could be hard to get). We know that there were particular problems he became interested in, such as the water cycle (what quantity of water came to a particular area of land from precipitation), effects of land elevation on air pressure, and wind. We have had less success in tracing the origins of those inquiries than one might expect to be the case with someone like Jefferson.

Q. I noticed on the data view it said “no animals mentioned” and “no plants mentioned.” In what context was he making such comments? (Anonymous)

A. This may have been answered later in the presentation. Jefferson sometimes made miscellaneous notations in the observation record that, in the case of plants and animals, usually related to seasonal activity (such as leafing out of trees in the spring). We created data fields to make that information discoverable on the site even though Jefferson usually didn't set it off in a column of his table.

Q. Surprised that rainfall records spotty—he was in charge of a farm. (Glorianne Robbi)

A. I was surprised by this also. I haven't looked into the question of what people at the time were thinking about quantification of precipitation (and relationships of rainfall to climate). My impression is that for Jefferson and many others, the relationship of rain to the cultivation of particular crops was, much of the time, a matter of fairly broad empirical categories: enough, not enough, too much. 

Q. Did Jefferson’s other family members and/or neighbors record similar observations?  And might these be included in some way in future? (Endrina Tay)

A. Hi Endrina, thanks for the question. As for family members, not so much. Jefferson urged one of his sons-in-law, Thomas Mann Randolph, Jr., to make some observations, but there was an issue finding a proper thermometer, so not a lot came of it. There was more luck with friends and acquaintances, particularly James Madison and members of this family, who made a significant weather record. Much of that is at the APS and is part of their excellent digitization effort. Jefferson's papers include some weather records by other people, and our goal is to get all of that up on the Jefferson Weather & Climate Records site, either in the daily observations dataset or in the Other Documents section, depending on the nature of the records.

Q. This is fantastic! I worked on the digital translation of Madison's weather and agricultural data for the APS last summer. I had interpreted Jefferson's reasoning behind this large climate/weather collection was not just to have information about Virginia's climate, but also to reinforce the argument that America is livable. Could you speak a bit more about what his reasons might have been to nudge people like Madison to collect this data on such a large scale? (Molly Nebiolo)

A. Yes, as can be seen in Notes on the State of Virginia, Jefferson wanted to counter a view of some Europeans that the American environment, including climate as a key factor, produced less robust plants, animals, and people. He wanted to get a fairly granular picture of the American climate and to be able to make comparisons with other regions such as Europe.

Q. Thank you for this fascinating talk. Could we think about Jefferson’s motives behind this project and how he kept up with meteorological research in his time by going through his library, the books he owned, his marginalia (if any)? For instance, did he own copies of Louis Cotte’s Treatise on Meteorology, De Luc’s writings on hygrometers, the Palatine Society’s Ephemerides, etc? Did he present his observations to the Royal Society or other organizations? (Jin-Woo Choi)

A. As my colleague Bland Whitley helpfully noted later in this thread, we do know of particular published works relating to weather and climate that Jefferson owned. We have not found, so far in our work, as many direct lines from such works to his own activity and thinking on these topics as one might expect to see. However, there are some connections. For example, Jefferson's investigations into relationships between land elevation and barometric pressure were informed by articles he saw in the Encyclopedie Methodique. We know that from sets of notes that are not yet up on our site (but will be once we are able to get to them). As for publication of his data, Jefferson may have incorporated some of his own observations in Notes on the State of Virginia. In the 1810s he made compilations of data that were published later, after his death, in a serial called the Virginia Literary Museum. He did not present his observations to the APS or other organization.

[From Bland Whitley: Not a question, but a partial answer to the previous query about Jefferson's reading on the subject. Sowerby's catalogue of his collection indicates that he owned the works of DeLuc, Dumont de Courset, and several more specialized pamphlets, etc.]

Q. Were the weather observations in the Broadway play and film 1776 based on Jefferson's actual observations do you think? (Some of the play used lines from actual letters for example). (Scott McKinley)

A. No, these records would not have been as readily available to the creators of 1776 as Jefferson's and his contemporaries' correspondence. (It's interesting that in popular depictions, July 1776 is often portrayed as hot. According to Jefferson's record, the highest temperatures in Philadelphia in the early days of July 1776 was 82 degrees F.)

Q. Are there any opportunities for archives or history students to volunteer for the project in any way? Thank you. (Anonymous)

A. Most of the transcription of Jefferson's daily observations was by two undergraduate students working as paid summer interns. In our current phase of work there is less opportunity for student involvement, but feel free to send us an inquiry using the "Contact Us" link at the foot of the Jefferson Weather & Climate Records home page. 

Q. Do the records reveal an increase in temperature over the five decades Jefferson covered (1776-1826)? (Nathalie Caron)

A. We haven't done a real analysis ourselves. We do provide a data visualization of maximum and minimum temperatures (https://jefferson-weather-records.org/visualization/41015) and the dataset is available for downloading from the Search page (https://jefferson-weather-records.org/search) for anyone interested in working with the numbers.

Q. Have you also collaborated with volcanic eruptions—around the globe as I have done some demographic research with tiny Italian town in the 1809-1860 era and the impact of Tambora is very self-evident in the death records. (Katherine Condon)

A. Excellent question! We have not looked for evidence of effects of the Tambora eruptions in Jefferson's observation records. If someone does that and finds something, we would love to hear about it. We might at some point add Tambora to the Weather Events section of the site.

Q. How interested was Jefferson in understanding the climate in North America at a particular latitude as compared to the same latitude in Europe (where it remains warmer further north)? Is there evidence he thought his data would help to study this difference? (Lawrence Dritsas)

A. He was very interested in comparisons of North America and Europe. They were only beginning to figure out that there were other factors than latitude affecting climate.

Q. Could Jefferson simply have wanted to accumulate weather records for his own agricultural knowledge and for its productivity? (Michael Little)

A. I haven't seen evidence that this was the primary driver for him to keep these records. I would have to spend more time with his Farm Book to say that for certain, however. Whenever he tried to get someone else interested in making a weather record, he didn't put it into a frame of practical agricultural information, but rather a frame of building a picture of climate.