Robert,
You raise several points in one post. It's very difficult to attempt
to answer all these comments at once. I am probably not the best
person to do so.
So, you mention the changes seen in the paleo record over the last
several cycles of Ice Ages. However, you did not mention the
Milankovich orbital cycles, which are widely considered to be the
source of the basic forces which drive the longer term cycles seen in
the Antarctic ice core data. Perhaps you should spend some time
reading the literature on the subject, which goes back several
decades. You might find Broecker's comments regarding the THC as a
major component of this process. He pointed out that there was no THC
before the closure of the Isthmus of Panama some 3 million yr BP. His
suggestion was that the THC began as the result of the transport of
fresh water across the Isthmus, resulting in a saltier Atlantic
compared with the Pacific.
As for Spencer's analysis of the TLT, last I was aware of it, the UAH
data produced a smaller trend than that of the other data sets. The
RSS group simply tried to duplicate the UAH analysis to check of their
calculations, as I understand it. They used the UAH algorithm but
excluded coverage over the highest mountains and over Antarctica for
the same reason. RSS also used a different process to link the data
sets between the different satellites. Other researchers have found
greater trends in the MSU/AMSU data that that of UAH. I see no reason
to accept the UAH analysis as the gold standard, especially as Christy
and Spencer insist on including these areas which they have admitted
to be problematic. You may also find some discussion of this in the
literature or thru RealClimate.
I also worry about abrupt climate change and have suggested that we
are seeing changes in the North Atlantic which are not unlike that
which may have produced the Younger Dryas, although the mechanism is a
bit different. I think that the scenario of global warming leading to
another Ice Age can not be rejected, if the THC is already beginning
to move toward the "OFF" position. The recent focus on the AMOC at
lower latitudes and the efforts to measure the flows can not pick out
whether the THC sinking is occurring in the open waters of the Nordic
Seas or in the Arctic Ocean under the sea-ice, as the deep flows would
be similar. The difference would be that the replacement waters
flowing into the Arctic Ocean would flow in at some depth and not add
to the salt on the surface of the Greenland Sea. As the sea-ice cycle
can be expected to exhibit even lower levels of extent in future, I
would not be surprised that the THC in the Greenland Sea would be
suppressed, and perhaps that in the Labrador Sea as well as more fresh
surface water and sea-ice moves from the Arctic thru the Fram Strait
into the Nordic Seas.
This scenario is not a positive one for Northern Europe and it's one
which the weather people tend to ignore, since their focus is short
term atmospheric fluctuations and indices such as the NAO. But, we
are now in the third winter in which data shows one area associated
with the THC to be weakening. If this continues for several years, I
think we may call it a trend. But, I'm an engineer, not an
oceanographer, and my data is very thin, so I can't add much more
than that...
E. S.
----------------------------------------------
Robbo wrote:
> Dear Eric,
>
> I had unsubscribed from this forum because of a lack of polite
> discourse. You at least show a measured response - in possibly the
> last update I get - which I appreciate.
>
> I did begin by quoting the IPCC to the effect that past climates do
> not provide analogues for the near future. That should be the take
> away point.
>
> Just another quick point - I am not sure there is an obvious problem
> with the UAH temp record. It is showing about a 0.13 degree C rise in
> recent decades similar to the RSS, GISSTEMP and CRUTEM records. Much
> of a muchness I would have thought. I am not sure that the
> temperature rise in recent decades is all CO2. I have discussed ENSO
> dynamics and the relation to cloud cover. On cloud cover and albedo -
> see for instance some of the bibliography at the Big Bear Solar
> Observatory Project Earthshine site. Kevin Trenberth et al - not a
> notorious 'denialist' - discuss in a recent paper some of effects of
> cloud change on Earth’s recent radiation balance. Amy Clement and
> colleagues suggest that cloud decline between the mid 1970’s and the
> end of last century was a global warming feedback but both ISCCP and
> Project Earthshine records suggest more cloud since 1999 – about 2.7 W/
> m2 less shortwave radiation at the surface since 1999. The direction
> of causation is very obscure.
>
> It is agreed generally that CO2 and methane lag temp. This makes
> sense biologically and chemically. Warmer water holds less CO2 more
> biological activity increases the mass of CO2 being cycled through
> organisms and the atmosphere as well as biologically mediated (always)
> methogenisis. The reverse is true also. It obviously a positive
> biological feedback (in both directions) in a complex system. Peatland
> has also been suggested as a vegetative succession positive feedback
> in both directions.
>
> So other effects are important in both the initiation and recovery
> from glaciation. For instance - collapse of the west Antarctic ice
> shelf is implicated in the recovery from the last interglacial.
> Cessation of deep water formation in the Artic is implicated in the
> initiation of ice ages. Snow accumulates, ice melts and THC slows and
> one or other of the poles cools enough to initiate rapid growth in ice
> cover. Snow and ice cover is obviously an important factor in Earth
> albedo - and this changes signs. Cloud cover and snow accumulation
> change significantly - perhaps largely in response to ENSO - on
> decadal and longer timescales. Airborne dust may also be important in
> cloud dynamics but this also seems to lag temp changes.
>
> It is all speculative but something in the past 1.88 million years
> results in recurrent glaciation. It may be a combination of orbital
> changes, tectonic uplift and drift and dynamic internal climate
> processes. The fall into glaciation is interesting. What could cause
> carbon dioxide and methane to decline other than declining temps? The
> decline in temperature in the early stages of a glacial also proceeds
> the fall in CO2 and methane. This is a point that Roy Spencer made
> and it suggests that other factors are involved. Something that would
> seem obvious to me. Snow and ice are the essence of glacial
> periods.
[cut]
> I linked to Roy Spencer because I agree with the conclusion about the
> speculative nature and partial treatment of factors in abrupt ice age
> climate transitions - and not because he is a so called 'denialist'.
> I don't know if it is even a useful classification. What is being
> denied? That CO2 is a greenhouse gas? I don't think so. That we will
> be sent to the saltmines for expressing an opinion? IMHO (I had to
> google it) - I think they can go get rooted as we say in Oz.
>
> I have quoted elsewhere in this forum Wally Broecker on climate being
> an unpredictable and capricious angry beast which we shouldn't poke
> with a stick. But I think that dire predictions of global warming are
> an 'all in' ploy that risks complete loss of the policy debate and
> potentially does a great disservice to the cause. Indeed, I think it
> has already happened.
>
>
> Cheers
> Robert
>
>
--
You received this message because you are subscribed to the Google Groups
Global Change ("globalchange") newsgroup. Global Change is a public, moderated
venue for discussion of science, technology, economics and policy dimensions of
global environmental change.
Posts will be admitted to the list if and only if any moderator finds the
submission to be constructive and/or interesting, on topic, and not
gratuitously rude.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/globalchange
