Eric,
Here is a good comparision of the temperature datasets and there is no
huge difference - I prefer the satellite based measures for obvious
reasons. RSS and UAH have converged in more recent times - which is
why NASA pays for 2 different analyses. There realistically have to
be checks.
Robert
> 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
>
>
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