Tompkins Weekly 5-26-14

By Richard Franke

The Earth’s atmosphere, up to about 18 kilometers (or 11 miles), is 78 percent nitrogen and 21 percent oxygen. The remaining 1 percent includes the gas argon and about .04 percent carbon (CO2). Small percentages are sometimes written as parts per million, or ppm, and thus the Earth’s lower atmosphere currently holds about 400 ppm of CO2. Very small amounts of helium, neon and methane are also present. The atmosphere contains small and varying amounts of water vapor, too, that we experience as humidity or as precipitation.

The incredibly small amount of CO2 in Earth’s atmosphere has a large impact on the average surface temperature. Scientists did not predict this; they discovered it starting in the 1850s.

The Irish physicist John Tyndall (1820-93) was a surveyor for the British government went to night school to become a mathematics teacher and eventually studied in Germany with Robert Bunsen, inventor of the Bunsen burner now used in laboratories all over the world.

In the mid and late 19th century, chemists were discovering the many uses of heat. During this same period the British physicist James Joule had discovered and quantified the relationship between heat and work that led to the field of thermodynamics. One result of learning more about heat was the development of steel—first produced in China—that facilitated so much of the industrial revolution.

Tyndall decided to examine the heat-related properties of atmospheric gases. He built innovative equipment in his lab and discovered that nitrogen and oxygen allowed heat radiation to pass through them. However, he found that CO2, water vapor and methane (the main component of natural gas) partly blocked infrared heat radiation. Infrared radiation itself had been discovered only in 1800 by the astronomer William Herschel.

Tyndall realized that his discovery helped explain Earth’s climate, as well as the existence of life on our planet. The three gases allow the sun’s light to pass through them in the earth’s atmosphere and arrive at the earth’s surface. The earth then bounces back some of the infrared light. Infrared is a low-frequency light that can’t be seen by the normal eye—it’s below the frequency of red, the lowest frequency visible light—but accounts for more than half of the energy transferred from the sun to the earth.

The three gases block and reflect much of the infrared energy back toward Earth, thus holding it in the lower atmosphere. Because this process resembles the way a greenhouse maximizes absorption of solar heat, the process came to be called “the greenhouse effect.” More precise recent studies show that the greenhouse gasses, along with some other processes, have kept the earth’s surface temperature in recent millennia at an average of about 57.2 degrees Fahrenheit (14 degrees Celsius). Without those gases, the temperature would be below freezing, as most of the sun’s energy hitting the earth would bounce back into space. Under those conditions it’s unlikely that life could have emerged. We would not be here.

If the earth’s temperature is regulated by the light-related properties of these greenhouse gases, it follows that the earth’s temperature is also regulated by the amounts of these gases in the atmosphere. And, if those amounts were to change significantly, would the earth’s temperature change with them? This question was taken up in the 1890s by the Swedish chemist Svante Arrhenius, whose work will be examined in the next installment.

Richard W. Franke writes about the history of sustainability. He is professor emeritus of anthropology at Montclair State University, a resident of Ecovillage at Ithaca and a board member of Sustainable Tompkins.