by Tom Kondis
May 21, 2008

To support their argument, advocates of man-made global warming have intermingled elements of greenhouse activity and infrared absorption to promote the image that carbon dioxide traps heat near earth's surface like molecular greenhouses insulating our atmosphere. Their imagery, however, is seriously flawed.

A greenhouse is simply a physical structure that traps hot air. Solar radiation initiates the heating sequence inside a greenhouse when photons in the visible region of the electromagnetic spectrum, entering through glass or transparent plastic panels, are absorbed by surfaces of opaque objects. Reflected photons exit freely; neither they, nor their "heat," are trapped inside. Drivers who regularly park their mobile greenhouses in sunny locations exploit this principle by placing reflective white cardboard behind their windshields to expel some before they're absorbed.

Although transparent to visible photons, greenhouse panels absorb weaker radiation in the infrared (IR) region of the spectrum. Solar IR photons can't enter. This fact requires spectroscopists to use exotic window materials such as polished rock salt in their IR pursuits. Visible radiation, not IR, energizes a greenhouse.

Advocates misuse the term "absorption" of photons by substances as being analogous to water sopped up by a sponge, unchanged, implying physical entrapment. Actually, it means that the photon smoothly transfers its radiant energy to kinetic form. Absorption is an energy transition, not a trap; photons don't occupy molecular cages. Similarly, emission is the reverse kinetic to radiant transfer.

An absorbed photon disappears as its discrete packet (quantum) of radiant energy dissipates into a diverse kinetic assortment of motion, vibrations or collisions involving atoms and molecules of the absorbing substance. Imagine one shot of your metabolic energy, through cue stick and cue ball, scattering a rack of balls on a pool table. These transfers obey the second law of thermodynamics, popularly stated as the spontaneous downhill flow from high to low energy, or hot to cold. Inside a greenhouse, visible photons define the hilltop from which this flow begins. IR photons, when emitted, are near the bottom of a typical greenhouse energy hill.

Continuing the sequence, the confined greenhouse atmosphere is convectively heated through molecular collisions with hotter opaque surfaces; its composition is at least 99.95% by volume nitrogen, oxygen, water vapor and argon. Carbon dioxide, only about 0.035% of the trapped hot air, is insignificant in this role. Drivers of mobile greenhouses recognize this principle too, when they crack open windows of their parked vehicles to partially disable the trap. Any gas can convectively transfer heat, but no gas can possibly mimic greenhouse-type entrapment of hot air. A greenhouse-carbon dioxide analogy has no logical basis.

Because a greenhouse obviously warms in the sunshine, the second law of thermodynamics is sometimes misconstrued. However, using the pool table analogy, if a person could repeatedly strike moving balls as rapidly as the sun pours visible photons into a greenhouse, the chaos on the table reasonably simulates greenhouse heating. But terminate the energy input, and the dissipation process mandated by the second law becomes obvious; a greenhouse cools, and the balls stop.

Advocates err when they equate absorption of IR photons by atmospheric carbon dioxide to absorption of exponentially higher intensity visible photons by objects inside a greenhouse. This exponential energy relationship, the Stefan-Boltzmann Law, is fundamental to thermal radiation and establishes the location of visible photons at the summit and IR photons near the base of typical greenhouse energy hills. For example, visible photons carry the intense energy representing solar surface temperatures. This intensity rapidly decreases with temperature of the emitter such that the human body liberally emits IR photons through our metabolic process, but is much too cold to emit visible photons. Even warm dirt emits IR photons from these lower temperature foothills of human habitation.

Consequently, carbon dioxide should properly be compared with water rather than with greenhouse contents. In all of its phases (gas, liquid and solid), water absorbs in the same region of the IR spectrum as carbon dioxide, and both are transparent to visible radiation. Significantly, the polar ice caps, glaciers and general snow cover all absorb this weaker radiation, obey the second law mandate, and remain frozen. However, advocates mistakenly claim that, despite existing for ages under direct solar IR bombardment, these frozen masses are melting now because carbon dioxide "traps" and leaks IR photons like soggy sponges. They offer no corroboration or experimental evidence to support their exaggeration.

The second law of thermodynamics prohibits carbon dioxide from arresting or reversing the spontaneous downhill flow of energy, putting advocates in the awkward position of insisting that a trace atmospheric component's innocent participation in a natural heat dissipation process is responsible for warming a planet. The fictitious "trapped heat" property, which they aggressively promote with a dishonest "greenhouse gas" metaphor, is based on their misrepresentation of natural absorption and emission energy transfer processes and disregard of two fundamental laws of physics. Their promotional embellishments have also corrupted the meaning of "greenhouse effect," a term originally relating the loose confinement of warm nighttime air near ground level by cloud cover, to hot air trapped inside a greenhouse.

Tom Kondis is a retired chemist and consultant with practical experience in absorption and emission spectroscopy.