In message <[email hidden]>, Roger
<[email hidden]> writes
Quoted message said:The message <[email hidden]>
from Stewart Robert Hinsley <[email hidden]> contains these words:Quoted message said:Quoted message said:Global warming sceptics are currently suffering from the First and
Second.Most global warming skeptics are suffering from a severe case of non
science and, in many cases, an ostrich approach to global warming as
well. The recent channel 4 program struck me as being about as fair and
balanced as B.Liar's initial justification for invading Iraq.Quoted message said:You mean that the "sceptics" are trying ridicule and violent opposition
because they lack reasoned arguments against a significant anthropogenic
contribution to the global warming trend of the last 50 or so years?I haven't got round to following it up yet but there was a recent report
that a scientist at the Cavendish Laboratory claims that the just 15% of
the CO2 currently in the atmosphere is all that is required to capture
all the IR in the main absorption band being reflected from the Earth's
surface. If that is right I can't see how wasting money restricting CO2
output is going to help prevent further warming.
I've just set up a simple spreadsheet model to get a qualitative
understanding of the effect of "saturation" on greenhouse warming.
The simplest model is one in which absorption is independent of
frequency. In this case saturation doesn't limit warming; the greenhouse
warming is linear with concentration.
In a model with a window with no absorption at all, and in which
re-emission by the atmosphere has a black-body spectrum, then warming
does saturate, but at a column density in excess of that required to
capture all the emitted IR. (What happens in this model is that at every
level in the atmosphere a proportion of the outgoing radiation is
converted into outgoing radiation in the no-absorption frequency window;
at a sufficiently high column density essentially all outgoing radiation
has been so converted, and hence the warming saturates.
The model was unfortunately unstable when I tried two different non-zero
absorption levels. However from consideration of the extreme cases it
can be inferred that greenhouse warming increases as long as there is a
frequency range in which the absorption is undersaturated, such as the
wings of the bands of which the cores are saturated, or minor bands.
(Note that Venus has several hundred degrees of greenhouse warming.)
The absorption spectrum of CO2 is known, and it's pretty much evenly
distributed in the atmosphere, so in principle it's relatively easy to
calculate the effects on radiative transport of CO2; numerically solve a
differential equation over altitude and frequency. I have my doubts that
the re-emission of IR by the atmosphere has a black-body spectrum
(consider Sodium lamps), but to the degree it is not it is more
plausible that it adds to the warming (re-emission correlated with
absorption frequency) than reduces it (re-emission anti-correlated with
absorption frequency).
I don't find it plausible that all the people working on climate models
would make the same error in modelling CO2 effects, so I have to accept
their evaluation that adding CO2 adds to warming.
Water vapour greenhouse effects are harder to model because the
variation in the water vapour content of the atmosphere, geographically,
chronologicall, and altitudinally.
Quoted message said:
Global warming is a fact whether it is manmade or natural and something
needs to be done if the natural trend doesn't reverse very soon but
concentrating on a convenient red herring is just what one would expect
from a bunch of politicians many of whom have degrees in the art of
lying convincingly (ie are lawyers) and none of whom (AFAIK) have any
scientific background whatsoever.Having written the above I thought I had better see if I can find some
trace on the Internet to back up my memory and came across the piece
reproduced below that almost matches the report that originally drew my
attention to the problem. The source for the report is a website called
Eureka."Global Warming: is CO2 the real culprit? 01/09/2005
A retired scientist, but one who should definitely know what he is
talking about, is questioning whether global warming is due to increased
carbon dioxide, or caused by other human induced effects.F James Cripwell now lives in Ottawa, Canada but started his scientific
career working in the Cavendish Laboratory in Cambridge under Sir Gordon
Sutherland, the UK's if not the world's leading expert in infra red
spectroscopy and the various interactions between infra red (heat)
radiation and other substances.Global warming is undoubtedly caused by visible light falling on the
earth's surface, which is re-radiated into the atmosphere, but is
increasingly being trapped there, undoubtedly as a result of increased
human activity. However, there is no complete agreement as to which
human activity or activities are mainly to blame.The culprit most widely considered to be responsible is carbon dioxide
but Jim Cripwell writes, "Assuming the earth is at 290 deg Kelvin,
Wien's law shows that the maximum radiation is emitted at 10 microns.
Water has a massive infrared absorption band centered on 8.5 microns,
and in sufficient quantities that can exist in the atmosphere, absorbs
all the radiation in a band from about 7 to 11 microns, accounting for
about 70 per cent of the radiation. By contrast, carbon dioxide and
methane have a very few intense, narrow absorption bands in this part of
the spectrum. Those for carbon dioxide are at about 4 and 14 microns.
However, the carbon dioxide absorptions are so intense that all the
radiation that it is ever going to absorb is done by about 15 per cent
of the atmosphere. So adding more carbon dioxide cannot increase its
greenhouse effectiveness. The same is true of methane, except that the
concentrations of methane in the atmosphere may be too low for it to
have reached its maximum." (According to the US EPA, methane is
considered to have a 100 year global warming potential about 21 times as
great as that of carbon dioxide, but that is mainly because once it gets
into the atmosphere, it tends to stay there). Jim Cripwell continues,
There's something wrong there; it's CO2 that has a longer lifetime in
the atmosphere, not CH4; CH4 is oxidised to CO2 in a relatively short
timescale. (CH4 has more effect per molecule per second than CO2, but
there's fewer molecules involved, and it has a shorter lifetime.)
Quoted message said:"Whatever is causing warming, it is not an increase in levels of carbon
dioxide. A more plausible theory is that it is water put into high
altitudes by aircraft; this would have roughly the same time line."
If saturation did occur adding more water vapour at altitude would not
have any affect - "absorbs all the radiation in a band from about 7 to
11 microns". However any radiation absorbed by another greenhouse gas
above the levels where water vapour is normally present, may be
re-emitted at water vapour frequencies, and reabsorbed by this
additional water.
However at high altitudes the low temperature means that little water
vapour can persist, and ice crystals form. This lowers the temperature
in the daytime and raises it at night. The overall effect of this, as of
clouds in general, is unclear. Apparently examination of historical
climate records indicates that the climate sensitivity (the ratio of the
overall temperature change to that which would result from the direct
effects of CO2 on radiative transfer) is roughly the same as that
resulting predicted from consideration of non-cloud effects, suggesting
that the effects of clouds (perhaps the biggest uncertainty in the
modelling of energy transport in the atmosphere) roughly cancels out.
But my impression is that the scientific consensus is that water
emissions from stratospheric aircraft flights is one of the
contributions to warming. (There are a dozen to a score significant
factors involved in the current warming trend; some anthropogenic, some
natural; some lowering the temperature, some raising it.)
Quoted message said:
That last sentence is telling (if true) but I can't see our Government
taking any notice of it when they are already hell-bent on expanding air
travel regardless of its CO2 output.
I would have thought that the proposals to tax air travel more heavily
was intended to discourage growth in air travel.
--
Stewart Robert Hinsley