A popular misconception of how
the "greenhouse effect" works is described in James Edward Oberg's
New Earths:
"... metaphorical[ly]
... sunlight streams through a protective screen (such as glass
on a greenhouse, or air over a planet) which is transparent
to visible light. This sunlight warms the surface below, which
attempts to reach a heat balance by giving off energy in the
infrared. That cooperative screen now balks; whereas it passed
the visible light without significant absorption, it is opaque
to infrared light--this occurs because of various atomic properties
of the materials--and hence absorbs it entirely, heating itself
and the surface below it."[1]
Oberg goes on to explain how
the "greenhouse effect" really works:
"But, as it turns
out, that's not how a greenhouse stays warm. Panes made of
material equally transparent to infrared, such as rock salt,
would work just as nicely. The key to greenhouse gardening
(which, after all, does work) is that the warmed air inside
is trapped by the walls and prevented from mixing with the
cold air outside.
"And Earth's
'greenhouse effect' is also obviously working ...
"The reason for
this is that heat is radiated into space at a rate proportional
to the fourth power of the absolute temperature of the radiating
object, be it the Sun or a desert, or a cloud. (Something
twice as hot radiates 2 x 2 x 2 x 2, or sixteen times, as
strongly.) Heat from the surface is absorbed by the atmosphere;
but the atmosphere itself can radiate heat. However, since
the temperature of the upper atmosphere is much colder than
the surface (on the average, 33°C colder), the heat loss
rate is much lower.
"Consequently,
the atmosphere keeps the heat in. It is primarily the water
vapor, and to a smaller degree the carbon dioxide, that contributes
the greatest portion of this 'greenhouse effect.' ...."[2]
However, while this explanation
corrects some widely held erroneous views about what constitutes
the "greenhouse effect," there is far more to the "greenhouse
effect" story that needs to be understood. In Global
Warming: The Origin and Nature of the Alleged Scientific Consensus
Dr. Richard S. Lindzen explains thus:
"Th[is]
simple picture of the greenhouse mechanism is seriously oversimplified.
Many of us were taught in elementary school that heat is transported
by radiation, convection, and conduction. The above representation
only refers to radiative transfer. As it turns out, if there
were only radiative heat transfer, the greenhouse effect would
warm the Earth to about seventy-seven degrees centigrade rather
than to fifteen degrees centigrade. In fact, the greenhouse
effect is only about 25 percent of what it would be in a pure
radiative situation. The reason for this is the presence of
convection (heat transport by air motions), which bypasses much
of the radiative absorption."[3]
In other words, atmospheric
convection (weather) diminishes the effect of the radiative
greenhouse effect by 75%. Yet proponents of anthropogenic CO2
as a culprit in "global warming" usually frame their arguments
in terms that suggest the greenhouse effect is a purely radiative
process, thereby grossly overstating the role CO2from all sources plays in the actual process.
Dr. Lindzen further discusses
how both convective (vertical) and advective (horizontal) atmospheric
motion significantly influence the greenhouse effect:
"...
The surface of the Earth is cooled in large measure by air currents
(in various forms including deep clouds) that carry heat upward
[convection]
and poleward [advection]. One consequence
of this picture is that it is the greenhouse gases well above
the Earth's surface that are of primary importance in determining
the temperature of the Earth. That is especially important for
water vapor, whose density decreases by about a factor of 1,000
between the surface and ten kilometers above the surface. ..."[4]
Yet, with all the knowledge
scientists have concerning the greenhouse effect, climate, and
climate change, they do not know it all. There remain many known
factors that are simply not well understood and there may well
be other factors yet to be discovered:
"Despite plenty of research,
when it comes to climate, we still know very little. We do
know that the surface temperature of the earth has warmed
by one degree Fahrenheit over the past century, but we also
know that most of the rise occurred in the early 1900s, long
before the big increase in carbon dioxide emissions from cars
and powerplants. Meanwhile satellites have found no atmospheric
warming over the past 20 years."[5]
"... the physics of unresolved
phenomena such as clouds and other turbulent elements is not
understood to the extent needed for incorporation into models."[6]
"... even the climate-change
panel [IPCC] could not hide the immense uncertainties concerning
such an elementary process as the greenhouse effect."[7]
In answer to a question
asking what we could do to purposefully effect a significant
climate change: "Let's start with the fact that
we do not know what the sensitivity of the climate is. We're
not in a position to even answer that. You will notice that
most of the statements have not really addressed that [question].
They're saying what will we have to do to stabilize the amount
of CO2. There's no conclusion as to whether this
will have any impact on climate."[8]
"... the National Academy
of Sciences' report highlights the difficulty in understanding
natural climate changes. And if we can't understand
those, then we can't figure out the human effect."[9]
Just recently, Dr. Lindzen and
a group of NASA scientists conducted a study that discovered
how the tropics act as a thermostat to help regulate heat:
"...
a paper that's just coming out this month [March 2001] that
I've written with two colleagues at NASA was looking at data
to see how clouds respond to temperature. And we find, in effect,
what we referred to as the 'Iris Effect,' namely that in the
tropics, when you have a warm region, the clouds coverage contracts
to let out more heat. And when the temperature is less, the
clouds expand to hold heat in. They act as a very effective
thermostat. And we estimate on a global basis that this will
take models that are predicting between 1.5 and 4.5 degrees
warming due to doubling carbon dioxide and cut it back to about
a half to one [degree]."[10]
In "The
Truth About Global Warming", some of the serious problems
with scientific knowledge about even current-day weather are
described:
"When
it comes to meteorology, data can be very iffy. The United Nations
specifies that thermometer readings in harsh polar climates,
for instance, should be taken in a shelter that is freshly painted,
of a specified height, ventilated in a certain way and so forth.
When the Soviet Union fell and Siberian data collectors stopped
being paid, did they continue to maintain the shelters? In the
oceans, sometimes data collectors take the temperature of water
drawn in a bucket over the side of a ship. Other times they
put their thermometers in the water that enters the ship’s engine
intakes. Such inconsistent practices may have something to do
with why observations show a warming at the North Pole but not
at the South, while some areas even seem to be cooling. The
overall warming trend of 0.6 degrees centigrade in the past
100 years is just discernible above these messy readings. 'The
observations are not great, but there’s a consistency in the
trend,' Lindzen[11] says."
[12]
Add all this uncertainty to
the crude state of climate modeling, and you have no hope for
any proper scientific foundation for the predictions of catastrophic
global warming due to human activity. More about climate simulations
in "Part 5: Warming - Human Influence, Simulations, & Uncertainty."
Natural Climate Warming
As described in Part 3: "there
are a host of known natural influences on climate whose effects
dwarf those of human origin. This section will concentrate on
what seems to be emerging as a powerful and convincing explanation
of underlying short-term variability (spanning decades or centuries)
in global average temperature - Solar Variability
Solar Variability
While our sun seems to us a fairly
benign star, recent studies have shown our closest star is far
from a model of perfect stability. "In half a billion years,
more or less, rising solar heat will transform global warming
into planetary purgatory. Earth will be simply too hot to sustain
human life."[13] But it isn't
necessary to wait 500 million years to experience the affects
of solar variability. Such variability has apparently characterized
our sun during its earth's entire existence. Recent data confirm
the solar/climate linkage:
"One
major natural component in changing the climate is -- not surprisingly
-- the sun. New findings, based on satellite measurements, suggest
that heat emanating from the sun to the earth changes significantly
on time scales of decades to centuries. NASA satellites have
uncovered the fact that the sun's changing magnetism over the
course of its sunspot cycle is accompanied by a change in total
energy output.
"This may be
the simple explanation for temperature change on earth:
The amount of energy reaching us increases or decreases as
the sun brightens and fades. And the change in solar magnetism,
or total energy output, is highly correlated with changes
in the temperature of the Northern Hemisphere going back 240
years (records of the entire earth over this period are not
accurate enough to study). The sun is today as magnetically
active as it has been in 400 years of direct telescope observations.
In other words, the mystery of global warming may have a simple
solution -- it's the sun that's heating the earth, with its
heat rising and falling in fairly regular cycles. If so, there's
nothing humans can do about it.
"The temperature
records of the Medieval Warm Period and the Little Ice Age
are not precise, but the larger trends of those centuries
are clear. The pattern of widespread warming followed by strong
cooling also tracks the measured changes in the sun's magnetism.
That information is captured in tree ring measurements of
radiocarbon, whose formation in the upper air by cosmic rays
-- fast moving particles from the galaxy -- is modulated by
the swings in the sun's magnetism. That record reveals that
the sun's activity waned at the onset of the Little Ice Age,
then recovered to its current energetic state."[14]
