Insulated by an outer crust, the surface of the earth acquires nearly all of its heat from the sun. The only exit for this heat to take is through a door marked "Radiation." And therein lies a tale...
Recently, I chanced upon an Atmospheric Science Educator Guide [PDF] published by NASA. Aimed at students in grades 5 through 8, it helps teachers explain how so-called "greenhouse gases" warm our planet Earth. These guides are interesting on a number of levels, so I recommend that you look them over. But what caught my eye was this:
- Question: Do all of the gases in our atmosphere absorb heat?
- Answer: (Allow students to discuss their ideas. Don't provide the answer at this time.)
Indeed, that's a good one to think over yourself. Almost all of what we're breathing is nitrogen and oxygen -- do these gases absorb heat? Lakes and rocks absorb heat, after all, and thereby reach a higher temperature. So can nitrogen and oxygen molecules do the same?
Well, I won't keep you hanging. After allowing students to discuss it, the instructor is instructed to give them the final verdict.
- Answer: No. Only some gases have the unique property of being able to absorb heat.
These are the infrared-absorbing "greenhouse gases," of course, substances like carbon dioxide and water vapor, and not nitrogen and oxygen.
Now, is something wrong here? Most definitely, for NASA has a finger on the scale. Let's review a few basics that NASA should have outlined.
Heat consists of vibrating and colliding molecules. The motion of these molecules jostles their electrons around, and this emits light. Heat and light are thus strongly related, but they aren't the same. For instance, heat can't actually be radiated; only the light that heat brings about can. By the same token, light itself has no temperature because temperature is an index of molecular motion, and a beam of light isn't composed of molecules. In short, "heat" can be regarded as molecular excitement and light as electromagnetic excitement.
Observe how NASA describes this relationship, however.
- Question: What is the relationship between light and heat?
- Answer: Things that are hot sometimes give off light. Things under a light source sometimes heat up.
Utterly false. Heated masses always emit light (infrared). Always. That's a direct consequence of molecules in motion. And while it's true that some substances may be transparent to infrared light, it doesn't follow that they can't be heated or, if heated, might not emit infrared. Yet NASA's misleading formulation implies precisely that.
There are three ways for heat (better to say thermal energy) to move from one zone to another: by conduction, convection, and radiation. Conductive heat transfer involves direct contact, wherein vibrations spread from molecule to molecule. Convective transfer involves a mass in motion: expanded by heat, a fluid is pushed up and away by the denser fluid that surrounds it. Radiative transfer arises when molecules intercept the light that warmer molecules are emitting, which brings about a resonant molecular vibration -- i.e., heating.
Heat is transferred and absorbed in several ways, then, and no substance is immune to being heated, which means that all gases absorb heat -- contrary to what NASA tells children.
So how does NASA go wrong? By consistently confusing light and heat, as you see in the illustration below, where infrared light is depicted as heat. Elsewhere, NASA expresses heat transfer in terms that pertain to radiant transfer alone:
The Earth first absorbs the visible radiation from the Sun, which is then converted to heat, and this heat radiates out to the atmosphere, where the greenhouse gases then absorb some of the heat.
Nowhere in its teacher's guide are conductive and convective heat transfer even mentioned. By selective context and vagueness, then, NASA paints an impression that only light-absorbing substances can be heated. Thus, since nitrogen and oxygen don't respond to infrared, NASA feels justified to say that "only some gases have the unique property of being able to absorb heat."
But a mixup like this raises a deeper question: Why does NASA go wrong? Because it has a flimsy yet lucrative theory to foist on the taxpaying public, that's why. As the space agency explains in the Main Lesson Concept, the core idea of greenhouse theory is that downward radiation from greenhouse gases raises the earth's surface temperature higher than solar heating can.
To make this idea seem plausible, therefore, it's crucial to fix people's attention on the 1% of the atmosphere that can be heated by radiant transfer instead of the 99% and more that is heated by direct contact with the earth's surface and then by convection. NASA is stacking the deck, you see. If they made it clear that every species of atmospheric gas gets heated mainly by conductive transfer, and that all heated bodies radiate light, then even a child could connect the dots: "Oh. So the whole atmosphere radiates heat to the earth and makes it warmer. All of the atmosphere is a greenhouse gas."
Crash, boom, there goes the theory. And there goes the abundant funding that this fear-promoting "science" attracts so well. For what CO2 and water vapor emit is miniscule compared to the buzzing multitude of heated nitrogen, oxygen, and even argon, all of it radiating infrared, too. Keep in mind that thermal radiation from this forgotten 99% has never been proposed or imagined to increase the earth's temperature, although by the theory's very tenets, it should. You simply take the NASA formulation:
Greenhouse gases absorb heat that radiates from Earth's surface and release some of it back towards the Earth, increasing the surface temperature ...
...and make allowance for conductive transfer, too...
All gases in the atmosphere absorb heat from the Earth's surface and radiate infrared back towards the Earth, increasing the surface temperature.
Consider too that since most air molecules are infrared-transparent, they can't be heated by the infrared that CO2 and water vapor emit. This means that downward radiation from "greenhouse gases" can only explain how the earth's surface might get warmer, not the rest of the atmosphere. This underscores, of course, how much the surface is heating this 99% by conduction and convection alone, since radiative transfer can't do the job.
To repeat: Irrespective of the manner of transfer, all gases absorb heat, and all heated gases radiate heat (infrared light) in close proportion to their temperature. Major gases like nitrogen and oxygen, then, do not just radiate heat to the earth below, but the total of this radiation vastly exceeds what minor players like carbon dioxide and water vapor contribute. Ironically, another NASA publication [PDF] reinforces this point.
In solids, the molecules and atoms are vibrating continuously. In a gas, the molecules are really zooming around, continuously bumping into each other. Whatever the amount of molecular motion occurring in matter, the speed is related to the temperature. The hotter the material, the faster its molecules are vibrating or moving.
Electromagnetic radiation is produced whenever electric charges accelerate - that is, when they change either the speed or direction of their movement. In a hot object, the molecules are continuously vibrating (if a solid) or bumping into each other (if a liquid or gas), sending each other off in different directions and at different speeds. Each of these collisions produces electromagnetic radiation at frequencies all across the electromagnetic spectrum.
... Any matter that is heated above absolute zero generates electromagnetic energy. The intensity of the emission and the distribution of frequencies on the electromagnetic spectrum depend upon the temperature of the emitting matter.
Accordingly, any heated gas emits infrared. There's nothing unique about CO2. Otherwise, substances like nitrogen and oxygen would truly be miracles of physics: Heat 'em as much as you wish, but they'd never radiate in response.
Yet this amounts to a double-whammy. For meteorologists acknowledge that our atmosphere is principally heated by surface contact and convective circulation. Surrounded by the vacuum of space, moreover, the earth can only dissipate this energy by radiation. On one hand, then, if surface-heated nitrogen and oxygen do not radiate the thermal energy they acquire, they rob the earth of a means of cooling off -- which makes them "greenhouse gases" by definition. On the other hand, though, if surface-heated nitrogen and oxygen do radiate infrared, then they are also "greenhouse gases," which defeats the premise that only radiation from the infrared-absorbers raises the Earth's temperature. Either way, therefore, the convoluted theory we've been going by is wrong.
An idea has been drummed into our heads for decades: that roughly 1% of the atmosphere's content is responsible for shifting the earth's surface temperature from inimical to benign. This conjecture has mistakenly focused on specifically light-absorbing gases, however, ignoring heat-absorbing gases altogether. Any heated atmospheric gas radiates infrared energy back toward the earth, meaning that the dreadful power we've attributed to light-absorbing molecules up to now has been wildly exaggerated and must be radically adjusted -- indeed, pared down perhaps a hundred times. Because all gases radiate the heat they acquire, trace-gas heating theory is an untenable concept, a long-held illusion we'd be wise to abandon.