"Steve Schulin" wrote in message
...
In article vApqf.934$AP5.273@edtnps84,
"Coby Beck" wrote:

"Eric Swanson" wrote...
says...

A lag of 800-1,000 years might mean that recent rise in CO2
is a response to Medieval Warm Period.

It's this "theory" of yours that I find not even remotely plausible and
prompted my reply to this thread. What happened during the so-called
WMP has nothing to do with today's ongoing increase in CO2, AIUI.
You have posted a notion that has no merit, which I think you realize
as you have not provided any scientific foundation for the claim.

It's unlikely that Steve really thinks this is the case, but regardless
there is another big problem with that notion, and that is the magnitude
of
the CO2 rise now vs the magnitude of the temperature rise in the MWP.
Looking he
http://en.wikipedia.org/wiki/Image:C...ide_400kyr.png
if one really wants to claim the mechanism for CO2 rise now is the same
lagged response as the other rises in the glacial record one would have
to
think that the MWP was a ~10oC skyrocketing of global temps rather than a
~1oC bump.

That's a fair point to raise, Coby. But I urge you to think in terms of
the question "What would the CO2 concentration be today if we had not
been burning carbon-based fuels during industrial era?

This is of course a hypothetical question, but nevertheless, absent any
observed mechanism of flow in or out of the atmosphere and given the
stability of CO2 levels since finishing the last climb out of glacial lows,
I see no reason to suppose it would not have stayed stable around ~280ppm.
Look at the stability of CO2 in the 600-1000 yrs after the Holocene Climatic
Optimum, perhaps a period as warm as today. There was no rise then AFAIU.

Well, I have done a bit of googling on CO2 in the Holocene and came across
this:
http://www.pnas.org/cgi/content/full/99/19/12011
"Abstract: By applying the inverse relation between numbers of leaf stomata
and atmospheric CO2 concentration, stomatal frequency analysis of fossil
birch leaves from lake deposits in Denmark reveals a century-scale CO2
change during the prominent Holocene cooling event that occurred in the
North Atlantic region between 8,400 and 8,100 years B.P. In contrast to
conventional CO2 reconstructions based on ice cores from Antarctica,
quantification of the stomatal frequency signal corroborates a distinctive
temperature–CO2 correlation. Results indicate a global CO2 decline of 25 ppm
by volume over 300 years. This reduction is in harmony with observed and
modeled lowering of North Atlantic sea-surface temperatures associated with
a short-term weakening of thermohaline circulation."

Skimming through that and noting references to conclusions of other papers
it appears that CO2 has fluctuated up and down between 275 and 325ppm with
things like the 8200yr cooling event and the LIA. But I note that this is a
short term response and not a 600-1000yr lagged response to a more
persistent trend like in the glacial cycles. It would appear that ice core
records tend to smooth over these short term flucuations as I have heard you
saying before.

So back to the hypothetical question: let's say that everything else is the
same (ie temperature has risen just as it has in reality) except no
anthropogenic CO2 or CH4 emissions. I would then expect CO2 to have risen
since 1900 by about 20-30ppm. I confess I did not read the paper or
references closely enough to know if I should add a lagtime of nothing,
decades or centuries to that expectation, probably many decades or a
century, which would lower the level we should see today. So if you can set
up an alternate planet and run the experiment, I will bet we should be
around 290ppm in 2000 absent fossil fuel burning.

Now back to the glacial record. ISTM that this record shows long term CO2
response to persistent temperature trends over multi-century time frames and
therefore offers us no insight into what the MWP might have to do with CO2
today. The MWP, the LIA and today's GW (thus far) are not long term enough
changes to show in the glacial record.

Even a small
change in that expected value could have a big effect on narrowing down
the uncertainty in atmospheric lifetime value assigned to CO2. The
alarmists typically refer to a century or more. I've seen the data fit
to a 67-year value. IPCC presents an even wider possible range. But if
there's a process change now like might have been the cause of the
observed 800-1,000-year lag, even the 67-year value would be overly
pessimistic.

I have to confess I do not follow you here at all.

--
Coby Beck
(remove #\Space "coby 101 @ bigpond . com")