🚀 go-pugleaf

niche@tartarus.uwa.edu.au (Nicole Heng) writes:

>Does anyone know any points that support the subject title?  There seems
>to be heaps on the net against, but hardly any supporting it, and I have a
>debate to do in a weeks time!  Can anyone help?

<Soapbox on>

All this from memory, OK? 8-)

1. Carbon dioxide

In the early 1930s, a carbon dioxide (CO2) monitoring program was begun by
Keeling (?) at the Mauna Loa observatory in Hawaii. Over the next thirty-odd
years, it was clear that the level of CO2 in the atmosphere was increasing,
with a pronounced seasonal fluctuation. Comparison with occasional records
from the nineteenth century indicated that the trend had been noticeable
since before the start of this century. Possible explanations were 
industrialisation, etc. The evidence for this is fairly conclusive and
incontrovertible.

2. Global warming

In the mid-70s, Ann Henderson-Sellers and her colleagues developed computer
models of the circulation of the earth's atmosphere which led them to
predict that increases in atmospheric concentrations of certain gases, in 
particular methane and carbon dioxide, would lead to a global temperature 
rise. The models used were comparatively primitive, but they predicted that 
by 2000 there would be a 0.3 degree rise in average temperature, and that
one consequence would ultimately be a rise in sea level. Other researchers
pointed to the possibility of changes in vegetation zones and forest cover.

3. Why global warming?

The initiating reason behind the belief in a global warming scenario rests
on a particular physical characteristic of 'greenhouse gases'. A glass
greenhouse lets sunlight through, allowing most of the transmitted light
not absorbed to escape again. Heat, however, is not released and the
greenhouse becomes warmer than the outside. Greenhouse gases act the same
way, transmitting visible light and other wavelengths, but not infra-red.
Carbon dioxide and methane are two gases with this characteristic.

4. Why not global warming?

The earth has experienced numerous ice ages and warm periods in the past.
Glaciers in various countries advance and retreat in response to local 
phenomena. In view of the substantial changes in CO2 concentrations in 
the atmosphere, we might have expected to see some evidence of change 
by now. It's hard to see any. It is possible the changes are still too
small and subtle.

It's also possible that the models (which are the only *actual* evidence
available for the theory) are wrong, and that the mechanisms which
control the earth's heat balance are far more complex and synergistic
than the still-simple models of the greenhouse brigade can tell.

Choudhury (years ago, about 1981) pointed out that increased dust levels
have reduced total irradiation of the earth, and the volcanic eruptions of 
the past twenty years (St. Helens, Pinatubo, etc.) have added their
share. This would mitigate the greenhouse effect.

As CO2 levels rise, so also does the net primary productivity of plants, 
which depends to a great extent on both CO2 concentration and temperature. 
This would have the effect of withdrawing more CO2 from the atmosphere
and storing it as plant material.

So we know of at least one or two feedback mechanisms which would mitigate 
the putative greenhouse effect. There may be many others.

5. Greenhouse laws

The current rash of greenhouse gas emission laws reflect a political
climate in which more weight is being given to environmental issues
than in the past. This is reflected, in OECD nations anyway, in attention
to recycling, nature conservation, river restoration, etc.

Where such laws are running into trouble is that the principal product of
complete combustion is carbon dioxide. The cleanest industrial processes
(as opposed to those which produce smoke, dust, carbon monoxide, etc)
cannot avoid these emissions, yet they are being required to limit
their operations even though there is relatively little they can do
to improve the efficiency of the effluent output except by vast expense.

The difficulty is that the basis for greenhouse laws, which is supposedly
scientifically-validated theory, is a theoretical model of atmospheric
circulation rather than a tangible result of experimentation. It may well
be a will-of-the-wisp instead of a real problem, much like the nuclear
winter scenarios which we never hear of now (they were big in the mid-1980s).

Politically, though, it is as though the greenhouse effect is a proven fact.
For industry, trying to fight against something that 'everyone' knows
is true is extremely difficult. The great fear is that the greenhouse 
effect is just 'the latest thing' and will soon be replaced by 'the 
next latest thing', but industry will still be saddled with the
consequences. Some of these fears are reasonable, some less so.

<Soapbox off>

-- 
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Mike McBain                                 Faculty of Business & Economics
mjm@silas.cc.monash.edu.au                  Monash University - Caulfield
+61 3 9903 2646                             Australia    3145