Dodgy NASA Pages Undermines Scientific Education
The educational troubles at NOAA are well known. Now I have stumbled by accident into one set of misleading NASA-hosted pages allegedly set up in order to help teachers and students understand the greenhouse effect.
The starting page of the set “Measuring the Temperature of the Sky and Clouds” by a Forrest M. Mims III and part of teacher-focused “My NASA Data” website, claims to describe a project where “you will learn about the greenhouse effect by measuring the temperature of the sky and clouds far overhead with an infrared thermometer“.
The project is described across four pages and it might be easily misinterpreted as showing that clouds are warmer than the cloudless atmosphere because of the greenhouse properties of water vapor (one needs to read the text very carefully). But that’s not the real problem.
The real problem is that it is claimed that:
The temperature in outer space approaches absolute zero, which is -273 degrees Celsius. But you will measure a much warmer temperature if you point an infrared thermometer at the sky directly overhead (the zenith). Depending on the season and your location, the temperature will likely be near or below zero degrees Celsius. While this is very chilly, it’s far from being as cold as absolute zero. The difference is caused mainly by water vapor in the sky that has become warm by absorbing infrared radiation emitted by the Earth below. The warmed water vapor returns some of the infrared back to the Earth, and this helps keep the Earth warmer than space.
The statement above is wrong. Says who? Says mainstream scientific consensus on the behavior of atmospheres. Here’s an excerpt from a University of Texas page explaining it all:
Of course, we know that the atmosphere is not isothermal. In fact, air temperature falls quite noticeably with increasing altitude. In ski resorts, you are told to expect the temperature to drop by about 1 degree per 100 meters you go upwards. Many people cannot understand why the atmosphere gets colder the higher up you go. They reason that as higher altitudes are closer to the Sun they ought to be hotter. In fact, the explanation is quite simple. It depends on three important properties of air. The first important property is that air is transparent to most, but by no means all, of the electromagnetic spectrum. In particular, most infrared radiation, which carries heat energy, passes straight through the lower atmosphere and heats the ground. In other words, the lower atmosphere is heated from below, not from above. The second important property of air is that it is constantly in motion. In fact, the lower 20 kilometers of the atmosphere (the so called troposphere) are fairly thoroughly mixed. You might think that this would imply that the atmosphere is isothermal. However, this is not the case because of the final important properly of air: i.e., it is a very poor conductor of heat.
Note that there is not a single mention of any greenhouse property of anything. Later on the UTexas text contains a reference to water vapor but for different reasons than the greenhouse effect:
As air rises, expands, and cools, water vapour condenses out releasing latent heat which prevents the temperature from falling as rapidly with height as the adiabatic lapse rate would indicate
So if the ground is at whatsoever temperature and you point a thermometer to the sky, you’ll read “the temperature through a cone-shaped column of the troposphere“, as determined by the properties of air and water vapor. The value you will read will be far above absolute zero independently from the greenhouse effect.
It is rather worrying to see such a poorly-designed experiment getting NASA approval (well, that might explain a few things…) and who knows how many pupils have now got it all wrong. Hopefully, there’s two or twenty science teachers out there capable to use critical reasoning.