Greenhouse Gas Facts and Fantasies
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.