Many of us today might understand the relationship between carbon dioxide (CO2), the atmosphere, and climate change. However, we have been provided with little historic background on how the idea of global warming gained traction.
Historian and physicist John Perlin joins me in an enlightening interview about this little-understood subject. Perlin, for those who recall our past interview series on photovoltaics, is author of a comprehensive work on solar energy history: Let It Shine: The 6,000-Year Story of Solar Energy.
Mr. Perlin also provides key insight here involving Eunice Foote, who wrote for Scientific American in 1856, importantly contributing to advancing the role of women in science — not an easy undertaking at all in that era.
Meyers: In speaking with you, I learn there is considerable history about understanding carbon dioxide and its relationship to global warming. Tell me about some of the original modeling work that took place.
Perlin: The modeling of carbon dioxide gas and its contribution to global warming got its start in 1767. As Europe became wealthier, the use of clear glass for covering window openings proliferated and people soon became aware of its ability to trap solar heat. As Horace de Sausurre, one of Europe’s leading 18th century scientists, observed, “It is a known fact and a fact that has probably known for a long time, that a room, a carriage, or any other place is hotter when the rays of the sun pass through glass.” Saussure then built what he called a helio-thermometer and later became popularly known as a hot box.
Meyers: This was a very simple device, correct?
Perlin: Very simple. It was a rectangular insulated pine box with sheets of glass covering the top, and small enough to be held in one’s hands. When the glass-covered top was exposed to sunlight, the temperature inside the box rose above the boiling point of water. Saussure’s success with this new solar device led to him attempting to answer a question on the minds among learned people of his day
Meyers: And what was that question?
Perlin: Many wondered what made the peaks of the nearby Alps colder than the adjoining plains. Some argued the differing angles of the sun hitting these mountains was the reason; others suggested that both receive the same amount of solar radiation but its heat in the mountains dissipates more readily due to the lack of atmosphere as elevations increase.
Meyers: Enter Saussure’s hot box?
Perlin: He believed the hot box would accurately measure the true temperature of the sun at both higher and lower altitudes as he called his instrument a helio-thermometer because it would measure the true temperature o the sun. So, he carried his helio-thermometer to the top of Mount Carmon. On the following day he descended with it to the Plains of Cournier. While the altitude differed by almost 5,000 feet and the outside temperature on the plains was 30 degrees Fahrenheit higher, the temperature in the hot box remained the same at both places. These experiments demonstrated that the atmosphere, or the lack thereof, largely determined the temperature on the earth’s surface.
Meyers: Did Sausurre’s contemporaries appreciate the implications of this discovery?
Perlin: No, but other scientists later did. In the 1820s Joseph Fourier, well regarded for his contribution to mathematical physics, attempted to use his computational skills to figure out, in his words, “to what extent the atmosphere affects the mean temperature of the globe?” He eventually admitted the guidance of rigorous mathematical theory ceased to be of any help. He then lauded Saussure’s experiment for illuminating the role the atmosphere plays in influencing temperatures on earth.
Meyers: Please elaborate on this discovery.
Perlin: The glass sheets covering the top of Saussure’s box act in the same way as our atmosphere. It allows sunlight to enter. Eventually, the rays strike the earth, just as they would hit the bottom of the hot box. In both cases they get transformed into thermal energy. The subsequent longer heat waves cannot as easily exit through the atmosphere or glass as the shorter light waves had entered and therefore accumulate below, causing the interior of the box or the surface of the earth to become hotter.
Saussure’s helio-thermometer served as the model to explain the importance of atmosphere in the warming and cooling of the earth’s surface led scientists to ask a more complex question: Which of the constituent atmospheric gases absorb the most heat radiating into the sky from the surface of our planet. The answer came in an article, “Circumstances Affecting the Heat of the Sun’s Rays,” published by the American Journal of Science in the winter of 1856. The author, Mrs. Eunice Foote, once again used sealed glass containers exposed to sunlight in her experiments to find the answer.
Meyers: A woman in that far-ago time? She must have faced numerous difficulties in a universe overwhelmingly dominated by male scientists.
Perlin: She did, indeed. Eunice Foote required a male to present her work at the 1856 American Association for the Advancement of Science annual meeting, Scientific American, in its September issue of that year had a special article titled, “Scientific Ladies,” which featured her work. It began by criticizing the notion common among many males, who “have not only entertained, but expressed the mean idea, that women do not possess the strength of mind necessary for scientific investigations. Owning to the nature of women’s duties,” the article continued, “few of them have had the leisure or opportunities to pursue science experimentally, but those of them that had the opportunity to do so have shown as much power and ability to investigate and observe correctly as men.”
Images via John Perlin