Greenhouse Gases

The greenhouse gases now in the air do keep the Earth’s surface warmer than it otherwise would be, and adding more greenhouse gases will cause more warming. There is nothing new, surprising, or honestly controversial in any of this. With a calculation something like the one in The Simplest Climate Model (linked below), the French scientist Jean Fourier discovered in 1824 that something was keeping the Earth’s surface anomalously warm, and among the hypotheses he considered was that the atmosphere is acting something like glass holding heat in a container (perhaps the origin of the comparison to a greenhouse; see The Discovery of Global Warming. The British physicist John Tyndall showed in 1859 that gases in the air, including water vapor and carbon dioxide, were contributing to the greenhouse effect. And, in 1896, the Swedish physical chemist and Nobel Prize-winner Svante Arrhenius did a fairly good job of calculating the global warming from the carbon dioxide released by human burning of fossil fuels. (Through history, scientists have actually been better at calculating the effects of greenhouse gases than at realizing just how incredibly skillful fossil-fuel companies would become at supplying large quantities.) 

Timeline of climate science: 1824 Fourier, 1859 Tyndall, 1896 Arrhenius, 1900 Planck, 1905 Einstein, 1915 Wegener, as explained in text.
A brief history of some major advances in climate science and other fields. Climate science is NOT new. 
Source: Diagrams by Richard B. Alley

The science of the greenhouse effect thus is not some new discovery, but has a long history compared to such “recent” science as relativity (Albert Einstein, 1905) or quantum mechanics (Max Planck, 1900). The pioneers who explored radiation in climate science were giants of physics, chemistry and mathematics, who saw the strong interactions between laboratory studies and application to the atmosphere.

Much of the work on the details of interaction between radiation and gases in the air was done by the US Air Force just after World War II and applied to topics such as sensors on heat-seeking missiles, as told in the introduction to this chapter. A missile uses a sensor to “see” the infrared radiation from a hot engine, but greenhouse gases such as carbon dioxide and water vapor block the view in some wavelengths by absorbing that radiation. Because the gases interact with radiation traveling in any direction, and there is much more energy in those wavelengths going up from the sun-warmed Earth than coming down from military bombers, the warming influence of the greenhouse gases is unavoidable. 

Heat seeking missile.
Heat Seeking Missile - Infrared Radiation 
Source: U.S. Department of Defense film, 342-USAF-49391, courtesy of the U.S. National Archives and Records Administration, College Park, MD. Courtesy of Earth: The Operators’ Manual and Geoffrey Haines-Stiles. 

Earth: The Operators' Manual CO2 and the Atmosphere - This 9 minute clip will appear 3 times within lessons 4 and 5 this week. To see a short clip on the Air Force's role in understanding the physics of the atmosphere and the warming effect of CO2, watch the first 1 minute and 20 seconds. The material that follows this 1 minute and 20 seconds will be covered later in this lesson as well as in Module 5.


Learning Checkpoint

Multiple Choice: choose the best answer.

CO2 is a greenhouse gas.  This means:

a. It absorbs certain wavelengths of the incoming shortwave radiation from the sun
b. It reflects all wavelengths of the incoming shortwave radiation from the sun
c. It absorbs all outgoing wavelengths of infrared radiation from the Earth
d. It absorbs certain wavelengths of infrared radiation from the Earth that have approximately the right energy to cause particular oscillations of the CO2 molecules
e. It is used to make the glass of greenhouses

Click for answer.

The answer is d.  There is very little interaction between the sun’s shortwave radiation and CO2, but CO2 does absorb particular wavelengths of outgoing longwave radiation from the earth, that have the “right” energy to cause particular behaviors of the molecules.