Horace is absolutely right here, what greenhouse gases block, just like
glass panes do in actual greenhouses, is not reflected radiation (mostly
visible wavelengths, to which they are just as transparent on their way
up -reflected- than on the way down -incident-) but thermal radiation (infra
red, emitted including at night when there is no incident radiation to
reflect). Steve I am afraid your description needs revising.
Michel
----- Original Message -----
From: "Horace Heffner" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Thursday, March 02, 2006 8:32 AM
Subject: Re: global warming: spin or not spin?
On Mar 1, 2006, at 3:51 PM, Steven Krivit wrote:
It was my understanding that greenhouse gases are only those which have
the particular characteristic of absorbing "the wavelengths of reflected
radiation."
It is not the absorption of *reflected* radiation that is key. It is the
absorption of infra-red radiation that is key. H2O and CO2 both are
absorbers of infra-red radiation, both coming directly from the sun, and
that which results from black-body radiation from the heated Earth
surface and atmosphere. That black-body radiation is not reflected, it
is merely the byproduct of hot molecules. O2 and N2 are not absorbers of
infra-red, which makes both the H2O and CO2 concentrations critical.
It was told to me that only specific gasses, not water vapor, have this
characteristic. Comments? Disagreements?
The role of H2O in the greenhouse effect, especially a runaway greenhouse
effect, is profound.
The Wiki article states: "Water vapor (H2O) causes about 60% of Earth's
naturally-occurring greenhouse effect. Other gases influencing the effect
include carbon dioxide (CO2) (about 26%), methane (CH4), nitrous oxide
(N2O) and ozone (O3) (about 8%). Collectively, these gases are known as
greenhouse gases." See:
http://en.wikipedia.org/wiki/Greenhouse_effect
As I noted earlier, the DOE simply ducks the atmospheric water issue on
its Global Warming Potentials page by saying:"Short-lived gases such as
water vapor, carbon monoxide, tropospheric ozone, and other ambient air
pollutants (e.g., nitrogen oxide, and non methane volatile organic
compounds), and tropospheric aerosols (e.g., sulfur dioxide products and
black carbon), however, are present in very different quantities
spatially around the world, and consequently it is difficult to quantify
their global radiative forcing impacts. GWP values are generally not
attributed to these gases that are short- lived and spatially
heterogeneous in the atmosphere.11 "
As I have emphasized many times, the key to this issue is at *what
altitude* the water vapor is found. The amount of water vapor at high
altitudes will increase at a horrific and generally unappreciated rate as
sea temperature rises. See:
http://www.nasa.gov/centers/ames/news/releases/2002/02_60AR.html
which states: "Rabbette analyzed clear-sky data above the tropical
Pacific from March 2000 to July 2001. She determined that water vapor
above 5 kilometers (3 miles) altitude in the atmosphere contributes
significantly to the runaway greenhouse signature. She found that at 9
kilometers (5.6 miles) above the Pacific warm pool, the relative humidity
in the atmosphere can be greater than 70 percent - more than three times
the normal range. In nearby regions of the Pacific where the sea surface
temperature is just a few degrees cooler, the atmospheric relative
humidity is only 20 percent. These drier regions of the neighboring
atmosphere may contribute to stabilizing the local runaway greenhouse
effect, Rabbette said."
Additionally, methane is lighter than air. As far as I know, little has
been made of this fact. In the atmosphere, methane ultimately oxidizes
to form CO2 and water vapor. Methane released directly into the air can
thus be assumed to oxidize mostly at a high altitude. The coming arctic
methane release will have a significant effect in the upper atmosphere
due to methane's atmospheric life of 12 years. (For methane life see
Table G1 in
http://www.eia.doe.gov/oiaf/1605/gg02rpt/pdf/appendixg.pdf).
A high moisture content at low altitudes does increase infra-red
absorption, but also typically results in clouds which reflect light
above that altitude, thus increasing Earth's albedo, thus reducing the
energy which is absorbed by the dense lower atmosphere and by the
surface. Water at high altitude absorbs infra-red radiation before it
can be relected from the clouds, and absorbs infra-red radiation
reflected from both the clouds and from the surface of the earth, as well
as black body radiation from the surface and the lower atmosphere.
This is what I wrote in "The Rebirth of Cold Fusion":
The problem of global warming predominantly results from the combustion
of fossil fuels. According to the U.S. Environmental Protection Agency,
"fossil fuels burned to run cars and trucks, heat homes and businesses,
and power factories are responsible for about 98 percent of U.S. carbon
dioxide emissions, 24 percent of methane emissions, and 18 percent of
nitrous oxide emissions." These are the so-called "greenhouse gasses."
Carbon dioxide is the greatest culprit. It is odorless and invisible;
for the most part, it does its damage without our awareness. Carbon
dioxide and other greenhouse gasses collect in the upper part of the
Earth's atmosphere and remain trapped there. When solar radiation passes
through the Earth's atmosphere, most of this radiation is absorbed by
the earth's surface. However, some of the solar radiation is reflected
back to the atmosphere. Ordinarily, part of this radiation would
continue onward to outer space, and part would be reflected back to
earth.
However, as a blanket of greenhouse gasses accumulates in the upper
atmosphere, it absorbs the wavelengths of reflected radiation and
converts it into thermal energy. The gasses remains trapped, upsetting
the delicate energy balance as the Earth makes its yearly journey around
the sun, and contributing to an increase in global temperature
worldwide.
The above description is not accurate. It ignores the critical
wavelength shift to the red that occurs on the earth's surface and in the
atmosphere. Much radiant energy critical to the greenhouse effect is
initially high frequency and passes readily through the atmosphere and
results in warming of either molecules in the atmosphere or on the
surface. These warmed molecules emit black body radiation in the
infra-red band. The greenhouse effect is due to the ability of
greenhouse gasses to absorb incoming infra-red while passing high
bandwidth (visible and UV) energy and then to block the returning
infra-red that occurs due to the black body radiation increase caused by
warming due to light absorption. H2O and CO2 absorb this black body
radiation that would otherwise radiate out to space. Black-body
radiation making it to space results in a lower Earth temperature. If
black-body radiation is increasingly absorbed, on the way back to space,
by increased concentrations of H2O, then the atmosphere warms up.
Thermal equilibrium can only be reached by returning to space the same
amount of radiation power as absorbed from the sun, even though that
radiation is returned at a much lower frequency. If the total radiated
power is less that that incoming from the sun then Earth's temperature
will continue to rise until the equilibrium point is reached.
Horace Heffner
