In message , Gianna
writes
Bob Martin wrote:
in 221785 20070309 124614 Gianna wrote:

As the proportions of atmospheric gases vary over time, the term
'excess' is
subjective. They stated that temperatures, and CO2 levels, have been higher
than they presently are, and that was long before industrialisation etc..
Other sources claim that CO2 today is higher than at any time in the
last 600,000 years.

Yes, they do.
As in any scientific debate, each camp is producing evidence in support
of their conclusions. I would have no idea which set of evidence is
true in some theoretical absolute sense. Unless someone on this group
is a qualified climate scientist with access to the primary source raw
data (somewhat unlikely), then none of us will know which side is
'correct' (if any).

From the posts I have read here, we are all reliant on the secondary
sources (or worse). So, we weigh up each case and decide which we
think the most plausible.
We may then state which body of evidence and conclusion we believe - we
may not state which body of evidence is 'true' or 'correct' as we
cannot know.


If the person(s) you quote is not disputing that then he must be
referring to an earlier
period - in which case how does he know?

There was a blip in temperature and CO2 at the Palaeocene/Eocene
boundary, for example. That blip resulted in a pulse of extinctions
sufficient to cause geologists to draw a period boundary coincident with
that.

There is also a long term decrease in atmospheric CO2 levels, roughly
compensating for the increased brightness of the sun. Some time, in the
millions, or perhaps tens or hundreds of millions, years range, that
will put the


I rather had the impression that the climate scientist(s) on the
programme were disputing that. If you want more detail than was
provided in the programme, you would have to ask those who took part. I
can only report what I saw/heard.

I seem to recall that they suggested that CO2 from decaying vegetable
matter, including autumn leaves, was greater in volume than that
generated my human activity. I have not sought to check that.

Yes. That's true. It's also pretty much irrelevant as to whether global
warming is caused by human emissions. The annual oscillation due to
fixation of carbon in the northern hemisphere summer and release in the
northern hemisphere winter (the northern hemisphere biota is more
productive or more seasonal that the southern hemisphere biota) is
greater than the annual increase in CO2 level. However the natural
processes are in balance, leaving the anthropogenic emissions to change
the atmospheric CO2 level.
--
Stewart Robert Hinsley