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This post was edited by sansukong at 2011-12-25 08:25|
Part: 1 of 2
February 25, 2010
The Hidden Flaw in Greenhouse Theory
By Alan Siddons
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."
To be continued ........