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
