How can anyone question man's significant role in global warming?

[Andre]

What about agitated clathrates as a possibility?

Not for the current warming, that appears to directly related to cloud forming interacting with solar activity.

When a clathrate field like the Amazon fan or that Canadian methane glacier goes unstable, it will release a lot of methane propably on decadal to century scale. The oxydation with a half time of about 20 years makes that we are not looking at many ppmv's in the total atmosphere. Much more effect may have the upwelling of cold water which spreads out over the ocean surface while releasing a lot of CO2 due to depressurizing. But we may be talking about an order of magnitude of 10-50ppmv. Not too shocking. But the usual surface water currents may severely be disturbing weather patterns-like El nino- causing flooding rains at one place and sun-burning arid deserts elsewhere. Tha't may very well be the real effect of clathrate bursts.

 

[Andre]

Dear Solin4 You have no idea. Tomorrow night I'm going to show in great detail here what is wrong with the perceptions of the Younger Dryas. (use babelfish language is dutch). I spend 5 years and over 1000 publications to read to figure it out.

You really should get some idea first about the opposition before citing obsolete textbooks,

Anyway, I did reflect a bit about that here:

https://www.physicsforums.com/showthread.php?t=79362
https://www.physicsforums.com/showthread.php?t=50130
https://www.physicsforums.com/showthread.php?t=113807
https://www.physicsforums.com/showthread.php?t=127240
https://www.physicsforums.com/showthread.php?t=126676
https://www.physicsforums.com/showthread.php?t=125669
https://www.physicsforums.com/showthread.php?t=95820
https://www.physicsforums.com/showthread.php?t=16702
https://www.physicsforums.com/showthread.php?t=29375
https://www.physicsforums.com/showthread.php?t=50130
https://www.physicsforums.com/showthread.php?t=15593

and a lot more, running out of time to find them all back. Now what were you saying?

 

[Andre]

How about the http://home.wanadoo.nl/bijkerk/extinctions_climate_refs.pdf of the big paper I'm working on; If Alley would have scrutinized as I have he would never have made the wrong choice about what his isotopes were saying.

Edit

the big mistake can be pinpointed exactly, that was http://home.wanadoo.nl/bijkerk/jouzeletal97.GIF

From:

Jouzel, J. Alley, R.B. Cuffey, K.M. Dansgaard W. Grootes, P. Hoffmann, G. Johnsen, S.J. Koster, R.D. Peel, D. Shuman, C.A., Stievenard, M. Stuiver, M. White, J, 1997. Validity of the Temperature Reconstruction from Water Isotopes in Ice Cores; Journal of Geophysical Research Vol 102, No C12 pp 26,471-26,487, November 30, 1997

Second edit. Just letting the post grow

See the problem? They have been warned by a previous publication of Steig et al about the logic of seasonal precipitation determining isotope signature, which was comfirmed by empiric evidence of a nearby station. They were also warned by the huge difference in precipitation at the boundaries of the Younger Dryas which should have been a big alarm bell; yet, they decided to run an artificial garbage in-garbage out type of gadget, usually adressed as simulation model, which was fed by the same data that would also be the output, a perfect circular reasoning with as result: temperatures not precipitation.

And with those alleged 10 degrees or so temperature jump started the real hype. Based on this, Alley wrote a price winning book, http://www.pupress.princeton.edu/titles/6916.html . Skillfully written but the conclusion was plainly wrong. If only they had consulted some already available geologic studies from the Northern hemisphere. for instance,

Haynes, C.V., Jr., 1991, Geoarchaeological and paleohydrological evidence for a Clovis age
drought in North America and its bearing on extinction: Quaternary Research, v. 35,
p. 438–450.

or

Dreimanis, A. 1968, Extinction of Mastodons in Eastern North America: Testing a New
Climatic Environmental Hypothesis, The Ohio Journal of Science Vol. 68: 6 pp 257 –
272

then they would have known that those precipitation changes were duplicated at least in North America and not the alleged big changes in temperature.

Unfortunately it was this mistake; the "10 degrees temperature change within a decade" that really fuelled the hype to incredible heights.

 

[Andre]

But eventually the reality overtakes, a first rebellious sign. As the isotopes of Antarctica started to "warm" up around 18000 years ago after the last glacial maximum and those of Greenland lagged to about 14500 years ago, this asymmetric "warming" has puzzled science and that is only to increase since:

http://www.sciencemag.org/cgi/content/abstract/312/5779/1510

Schaefer, J.M. et al 2006; Near-Synchronous Interhemispheric Termination of the Last Glacial Maximum in Mid-Latitudes Science 9 June 2006: Vol. 312. no. 5779, pp. 1510 - 1513

Isotope records from polar ice cores imply globally asynchronous warming at the end of the last glaciation. However, 10Be exposure dates show that large-scale retreat of mid-latitude Last Glacial Maximum glaciers commenced at about the same time in both hemispheres. The timing of retreat is consistent with the onset of temperature and atmospheric CO2 increases in Antarctic ice cores. We suggest that a global trend of rising summer temperatures at the end of the Last Glacial Maximum was obscured in North Atlantic regions by hyper cold winters associated with unusually extensive winter sea ice.

The second ad hoc hypothesis (extensive sea ice), the first one was from Bjorck et al with their fohn in the South Greenland lake. But this time, no dice since we have excellent sea surface temperature records of

Dolven J.K. Cortese G, Bjørklund K.R. 2002 A High-resolution Radiolarian-derived Paleotemperature Record for the Late Pleistocene-Holocene in the Norwegian Sea, Paleoceanography, Vol 17, No. 4 1072 pp 24-1

showing sea surface temperatures comparable with the Holocene around 16500 calendar years ago,(cal BP) just before they dropped a few degrees towards the Bolling Allerod period (14500-12800 cal BP)

and also:

Lagerklint M, J.D. Wright 1999 Late glacial warming prior to Heinrich event 1: The influence of ice rafting and large ice sheets on the timing of initial warming. Geology; December 1999; v. 27; no. 12; p. 1099–1102;

http://www.unige.ch/forel/PapersQG06/Lagerlint%20et%20Wright04.pdf

High-resolution faunal, isotopic, and sedimentologic data from North Atlantic core V29-191 show that sea-surface temperatures increased from 17.5 to 17.3 ka,

So no extensive sea ice in the warming period of the Antarctic warming. Moreover Kennett brings it rather ironical in his study:

Hill T.M., J.P. Kennett, D.K. Pak, R.J. Behl, C. Robert and L. Beaufort Pre-Bølling warming in Santa Barbara Basin, California: surface and intermediate water records of early deglacial warmth, Quaternary Science Reviews, article in press doi:10.1016/j.quascirev.2006.03.012

Abstract
A new piston core from Santa Barbara Basin, California provides evidence of the timing, magnitude, and character of deglaciation, including evidence of warming prior to Termination IA. ...findings are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific

There you go, a nice catastrophic warming in Greenland down the drain.

 

[reasonmclucus]

You're correct about the difficulty of determining the impact of clouds. An additional factor is the elevation and thickness (or density) of the clouds. Some clouds are sufficiently transparent/translucent that some sunlight reaches the ground.

The impact at night is not due to preventing radiation from leaving the earth. Light (electromagnetic radiation) travels at 186,000 miles per second and is quickly gone even if reflected many times. Instead clouds prevent warmer air from rising and thus keep it closer to the ground and prevent it from warming higher levels of the atmosphere.

The greater the distance of the base of the cloud to the ground the higher warm air can rise before being blocked.



.

 

[Bystander]

"Not bad!" No, genuinely, pathetically awful --- might as well put the model quality issue out of its misery.

Tambora, 1815, 100 km³, 5-6 K temperature drop, implies Pinatubo at 10 km³ is going to result in a 0.5-0.6 K temperature drop if we apply a simple linear model (temperature drop is proportional to volume of eruption). A temperature drop between 0.5 and 0.7 K was observed. http://www.andaman.org/BOOK/originals/Weber-Toba/ch4_climate/textr4.htm Simple linear model predicts a climate effect within 0.05 K; compare this to the Goddard prediction that has been declared "Not bad!"

 

[Mk]

What about nonlinear? Why would it have to be linear?

 

[Bystander]

What about nonlinear? Why would it have to be linear?

Non-linear models are useful over the range of data to which they are fit. Extrapolate outside that range, and you're wasting time generating random numbers. Linear models "behave" when extrapolated outside the range of data to which they've been fit. Do they give "good" predictions? Depends on the quality of the data and the range of the extrapolation; fit a short, "noisy," data set and you're not going to get much more than "trend" information (this increases/decreases as that). Fit decent data, and you can extrapolate beyond the limits of the data by something like half the range of the data set and hang 10-20% uncertainty on the extrapolated values. Shove noisy data into a non-linear model and what do you get? A lot of unconstrained parameters, and no extrapolation capability --- not even trends. Shove decent data in and what? You may get an improvement in fit over the linear model (smaller residuals); do you get improved extrapolations? Only in the very few cases where the model accounts for every parameter of the system, and the data set is robust enough to constrain all the fit parameters.

 

[Skyhunter]

Standby to be surprised:

The first known accurate measurement of CO2 is:

Thenard, 1812 Traité élém. de chimie, 5 edit., vol1, p.303.

Value: 385,0 ppm

We also have:

W. Kreutz 1941, Kohlensäure Gehalt der unteren Luft schichten in Abhangigkeit von Witterungsfaktoren,” Angewandte Botanik, vol. 2, 1941, pp. 89-117
Average 1939-41: 438ppm.

(Current value ~381ppm)

The pile of ignored papers about measurements, before CO2 was structurally measured at Mauna loa, is about just under two feet high. Many are consistent with each other, showing two very weird short living decadal size spikes.

I wonder how it is possible that people still believe in mans significant role in global warming.

Well as your http://www.ipsl.jussieu.fr/GLACIO/hoffmann/hoffmannengl.html there is a huge problem with the credibility of these measurements, especially the 438ppm in 1939-1941.

A last comparison. Each year the entire terrestrial biosphere is exchanging about max. 60GTC with the atmosphere. That are all the leafs, stems, roots and champignons in the world (which of course is respired at the same time which is why the terrestrial biosphere is about in equilibrium). Now the scenario of Andre (720GTC within 16years) implies that the full global biosperic production is packed into little plastic bag and send into space so that no respiring flux comes back into our atmosphere. And this not for one year but effectively for each year between 1941 and 1957. An interesting hypothesis and a most interesting way of thinking. Thankyou for your contribution.

If you cannot explain where all that carbon went, why are you still advocating those data?

 

[Andre]

Skyhunter,

This is a most blatant example of ostrich politics. head in the sand. I can't explain it so, so it doesn't exist. Most of us can't explain Venus' enigmatic features, but it exists.

And those spikes most likely have existed, even after statistical processing, assuming that the largest environment noise errors apply. But for further confirmation, I have triggered the leaf stomata CO2 reconstruction people to see if they can replicate those spikes.

Where the spikes come and go? Well the oceans contain something like 70 times more CO2 than the atmosphere and it appears that the interchange between ocean and atmosphere is rather fast. A 200 ppm spike coming from the ocean would make that 69,5 times. Readsorption within some decade does not seem unreasonable if that spike event (which would sustain another pet idea) disturbed the balance.

 

[Skyhunter]

Where the spikes come and go? Well the oceans contain something like 70 times more CO2 than the atmosphere and it appears that the interchange between ocean and atmosphere is rather fast. A 200 ppm spike coming from the ocean would make that 69,5 times. Readsorption within some decade does not seem unreasonable if that spike event (which would sustain another pet idea) disturbed the balance.

Thank you,

You had offered no explanation in the other thread.

So you are suggesting that by some mechanism, the ocean releases carbon and then reabsorbs it in a very short time.

OK, nice to have a pet theory.

What does that have to do with AGW, and how is it relevant to this thread?

Has there been such an event recently?

Are you suggesting that the increase in CO₂ in recent years is natural , and not the result of a significant anthropogenic contribution?

Why don't we move past this and onto the broader discussion about what can be done about it. As Evo posted earlier, ill thought out solutions can create unintended consequences.

 

[culion]

Most of the discussions about global warming tend to go in circles after a relatively short time. The key question is how much of global warming is due to human forcings. It is not sufficient to simply claim that this is significant on the basis of unmeasured "consensus" which is of little importance in science. The climate has always changed and sometimes quite rapidly. However, actual changes are not consistent with the best available models that contain both human and natural driving forces. At this point, it looks like the effect of human activities is not substantial and should not be a major consideration in political and economic actions. Of course, other routes (e.g., conservation) might very well lead to the same end but would be done with the proper perspective with respect to the scope and rate of change of appropriate activities.

 

[Andre]

So you are suggesting that by some mechanism, the ocean releases carbon and then reabsorbs it in a very short time.

The pet idea is this:
Every once and a while oceanic methane hydrate enters unstable conditions, with either water pressure dropping (tectonic uprising) or more like changing ocean currents bringing too warm water over the clathrate field.

If such an event is more massive and more prolongued then in the bubble stream the water is also forced up. You can observe that in the aquarium. This deeper water contains much more CO2 than the surface waters, it is brought there by putrifying of sinking biologic remains as bystander kindly pointed out.

Now as this water is forced up, the pressure drops and just like opening the soda bottle, the CO2 is forced out of solution, entering the atmosphere. That's how you can get a sudden CO2 spike. When this process stops, obviously the CO2 will drop again, readsorpted in the ocean and other sinks, until the original equilibrium has been restored. I'm a bit amazed how quick that went in those two events but there was an unbalance. Anyway, the models may need new parameters.

What does that have to do with AGW, and how is it relevant to this thread?

Those CO2 spikes were in the order of magnitude comparable to the termination of the glacial periods. Yet there was no 5-10-15 degrees of warming. Perhaps half a degree at best, looking at the global warming data. But this may have had another cause. As cold seawater in that hydrate event spreads over the ocean surface and pushes the original warmer surface waters to unusual places, the normal weather patterns will be disturbed; think of El Nino.

Consequently, since nothing serious happened, it proves that climate is much more stable than assumed and there will be little or no climate change due to CO2 spikes

Has there been such an event recently?

http://www.ukweatherworld.co.uk/forum/forums/thread-view.asp?tid=3254&posts=13 is such an event on a small scale.

Are you suggesting that the increase in CO₂ in recent years is natural , and not the result of a significant anthropogenic contribution?

No, obviously, there has been a steady increase in the antropogenic CO2 emission added to the carbon cycle causing an unbalance unlike the spikes of the hydrate event. But in terms of climate this looks to be meaningless.

Why don't we move past this and onto the broader discussion about what can be done about it. As Evo posted earlier, ill thought out solutions can create unintended consequences.

Wise words and spot on. The world problems in two sentences: climate and indefinately sustainable energy. Both suggest a termination of fossil fuel use.

The first seems most acute and appears to call for immediate and strong action, which may result in maximum conversion attemps to natural renewable energy sources. However this could give a negative outcome, when the complete life cycle costs of those renewables exceeds the energy production. That would be surely ill thought out solutions creating unintended consequences.

But climate isn't an acute problem at all. The deadlines may or may not be set by peak oil or something giving us time to avoid ill thought out solutions.

Even if that time is shorter than we think, we cannot hold climate hostage for doing the right thing for the wrong course. Science should be based on finding the truth, not on supporting politics with convenient global warming theories.

 

[Sinimod]

"Not bad!" No, genuinely, pathetically awful --- might as well put the model quality issue out of its misery.

Tambora, 1815, 100 km³, 5-6 K temperature drop, implies Pinatubo at 10 km³ is going to result in a 0.5-0.6 K temperature drop if we apply a simple linear model (temperature drop is proportional to volume of eruption). A temperature drop between 0.5 and 0.7 K was observed. http://www.andaman.org/BOOK/originals/Weber-Toba/ch4_climate/textr4.htm Simple linear model predicts a climate effect within 0.05 K; compare this to the Goddard prediction that has been declared "Not bad!"

Actually 0.29 is a misquote. The Goddard Model was actually off 0.09.

 

[Bystander]

Better --- 'nother Cray and a few more millions, they'll get it to where it beats a first order linear model.

 

[Andre]

Thanks, Evo

 

[Evo]

I haven't had a chance to read through the thread since the surgery. Anyone reading for the first time will probably be scratching their head.

 

[Bystander]

You made it fairly clear that there were going to be "missing" antecedents to various posts --- it ain't all that bad.

 

[Andre]

Anyway, here is a big questioner of man's significant role in global warming.

http://www.cei.org/pdf/5478.pdf

 

[Skyhunter]

The pet idea is this:
Every once and a while oceanic methane hydrate enters unstable conditions, with either water pressure dropping (tectonic uprising) or more like changing ocean currents bringing too warm water over the clathrate field.

If such an event is more massive and more prolongued then in the bubble stream the water is also forced up. You can observe that in the aquarium. This deeper water contains much more CO2 than the surface waters, it is brought there by putrifying of sinking biologic remains as bystander kindly pointed out.

Now as this water is forced up, the pressure drops and just like opening the soda bottle, the CO2 is forced out of solution, entering the atmosphere. That's how you can get a sudden CO2 spike. When this process stops, obviously the CO2 will drop again, readsorpted in the ocean and other sinks, until the original equilibrium has been restored. I'm a bit amazed how quick that went in those two events but there was an unbalance. Anyway, the models may need new parameters.

Interesting theory.

Two things right off the top of my head are;

1. This much CO₂ in the atmosphere would alter the PH in the upper oceans, leaving other evidence. If it happened a mere 60-70 years ago the evidence should be easy to find. A radical change in ocean acidity would have a devastating effect on about any sea animals that have shells.

2. There have been no observed events on a scale like the one you described, the event you linked claims to be the first conclusive proof that such events can even release carbon into the atmosphere.

Those CO2 spikes were in the order of magnitude comparable to the termination of the glacial periods. Yet there was no 5-10-15 degrees of warming. Perhaps half a degree at best, looking at the global warming data. But this may have had another cause. As cold seawater in that hydrate event spreads over the ocean surface and pushes the original warmer surface waters to unusual places, the normal weather patterns will be disturbed; think of El Nino.

El Nino is a cyclical event, and part of a normal weather pattern.

Consequently, since nothing serious happened, it proves that climate is much more stable than assumed and there will be little or no climate change due to CO2 spikes

Unless you can prove that these events happened, there are no consequences, and you are making assumptions based on a theorized event that has little scientific credibility.

Wise words and spot on. The world problems in two sentences: climate and indefinately sustainable energy. Both suggest a termination of fossil fuel use.

The first seems most acute and appears to call for immediate and strong action, which may result in maximum conversion attemps to natural renewable energy sources. However this could give a negative outcome, when the complete life cycle costs of those renewables exceeds the energy production. That would be surely ill thought out solutions creating unintended consequences

.
Renewable clean energy sources are not going to devastate the world economy, as has been claimed by many of your denialist sources. In fact the opposite, new energy technologies are fast becoming the driving force behind cutting edge technological development. As more and more companies see the bottom line benefits, the funds used to sponsor such organizations as CEI will dry up.

But climate isn't an acute problem at all. The deadlines may or may not be set by peak oil or something giving us time to avoid ill thought out solutions.

Even if that time is shorter than we think, we cannot hold climate hostage for doing the right thing for the wrong course. Science should be based on finding the truth, not on supporting politics with convenient global warming theories.

What ill thought solutions?

People have been thinking about this for a long time, and there are many good solutions that can be implemented today. Like shifting transportation money from highways to public transit. Designing our cities around pedestrians instead of cars. Increasing CAFE standards, encouraging zero emission vehicles, etc, etc, etc.

I find the most alarmism comes from those crying about how doing anything to combat GW will harm the world economically.

 

[Mk]

I haven't had a chance to read through the thread since the surgery. Anyone reading for the first time will probably be scratching their head.

Heh. I scratched my head where that huge chunk went. I don't remember what was there anymore either!

 

[Andre]

Explanation here

https://www.physicsforums.com/showthread.php?t=133399

If you follow the link you may recognize the posts of Fred, which were plagiarized into this thread. Evo has spent hours to delete all that illegal copying.

I'm known over there as the "real Mike"

 

[Sinimod]

The Competetive Enterprise Institute (CEI) recently released their Working Paper on the internet "A Skeptics Giude to An Inconvenient Truth" (AIT) in which they purported to refute much of what was said in that publication and movie. At the beginning of this paper, the authors summarized claims of AIT as one sided, misleading, exaggerated, speculative, or wrong. The first and only statement CEI claimed is wrong is as follows:

(AIT) "Claims glaciologist Lonnie Thompson's reconstruction of climate history proves the Medieval Warm Period was "tiny" compared to the warming observed in recent decades. It doesn't. Four of Thompson's six ice cores indicate the Medieval Warm Period was as warm as or warmer than any recent decade."

To actually settle this part of the debate, one should read the Thompson et al., 2006 publication "Abrupt tropical climate change: Past and present." (http://www.pnas.org/cgi/content/full/103/28/10536)
Thompson et al 2006 states "annually and decadally averaged delta O18 and net mass-balance histories for the last 400 and 2, 000 yr, respectively, demonstrates that the current warming at high elevations in the mid- to low-latitudes is unprecedented for at least the last 2 millennia."

They go on to say "Today most glaciers outside the polar regions are retreating at accelerating rates." And further "A sequence of maps ducuments the rapid and accelerating retreat of the glacier front. In the last 14yr (1991-2005), Qori Kalis has been retreating ~10 times faster (~60 m/yr) than during the initial measurement period of 15yr from 1963 to 1978 (~6 m/yr)." And: "The accelerating retreat of the Qori Kalis terminus is consistent with that observed for six other glaciers in the Cordillera Blanca that have been monitored by the power company ElectroPeru."

It seems to me the last 2, 000 years would include the Medieval Warm Period (~AD 800-1, 300). I guess you can judge for yourself whose right on this one.

 

[Sinimod]

I meant to say 'the first statement CEI claimed was wrong.' Obviously there were others. Sorry for the oversight.

 

[Andre]

"annually and decadally averaged delta O18 and net mass-balance histories for the last 400 and 2, 000 yr, respectively, demonstrates that the current warming at high elevations in the mid- to low-latitudes is unprecedented for at least the last 2 millennia."

Whilst it has been established a some time ago that tropical glacier isotopes within the equinoxes have a very erratic meaning as can be seen http://home.wanadoo.nl/bijkerk/GNIP-isotope-temp.gif , the graph showing the annual temperature / isotope correlation factor for each weather station in the GNIP database with an r2>50%. And that's only seasonal precipitation, whereas we have discussed already that changes in seasonal precipation predominate the isotope signature, much more than temperature.

All isotope proxies fail to show the Holocene Thermal Optimum whilst other proxies show an amazing warming deep into the arctic (which the Greenland ice sheet survived with flying colors)

Forget isotopes in ice sheets and glaciers, we don't understand what thses are saying.

 

[Andre]

http://www.ipsl.jussieu.fr/GLACIO/hoffmann/Texts/hoffmannGRL2003.pdf confirms that by the way:

Isotope records from Andean ice cores provide detailed and high-resolution climate information on various time scales. However, the relationship between these valuable isotope records and local or regional climate remains poorly understood. Here we present results from two new drillings in Bolivia, from the Illimani and the Sajama ice caps. All four high altitude isotope signals in the Andes now available (Huascara´n, Quelccaya, Illimani and Sajama) show near identical decadal variability in the 20th century. Comparison with general circulation model results and
meteorological data suggest that the Andean high altitude records are primarily controlled by precipitation variability over the Amazon basin.

 

[Mk]

"annually and decadally averaged delta O18 and net mass-balance histories for the last 400 and 2, 000 yr, respectively, demonstrates that the current warming at high elevations in the mid- to low-latitudes is unprecedented for at least the last 2 millennia."

Way to do it Andre!

All isotope proxies fail to show the Holocene Thermal Optimum whilst other proxies show an amazing warming deep into the arctic (which the Greenland ice sheet survived with flying colors)

Um. What?
How could this be? Why? Precipitation?

 

[Andre]

It is very obvious that after the failed assisination attempt on the medieval warming period (Overpeck 1997) there is now an cleary coordinated attempt to bury the Holocene Thermal Optimum and probably the Eemian next, all for the political target to declare the current period as the warmest in hundreds of thousands of years or millions of years.

All about the Holecene Thermal Maximum here:

http://www.ukweatherworld.co.uk/forum/forums/thread-view.asp?tid=5124&start=1

also with several clear proxies showing that South America was significantly warmer as well. But Lonny Thompson is in the team that listened very carefully to Schneider

 

[Skyhunter]

Forget isotopes in ice sheets and glaciers, we don't understand what thses are saying.

Which is exactly what this abstact does.

Although the factors driving the current 18O enrichment (warming) may be debated, the tropical ice core 18O composite (Fig. 6A) confirms that it is unusual from a 2,000-yr perspective. Regardless of whether 18O is interpreted as a function of temperature, precipitation, and/or atmospheric circulation, the important message clearly preserved in these high-elevation ice fields is that the large-scale dynamics of the tropical climate system have changed.

http://www.pnas.org/cgi/content/full/103/28/10536

Supporting the point of the thread.

How can anyone question man's significant role in global warming?

 

[Andre]

Okay, so whenever:

18O is interpreted as a function of temperature, precipitation, and/or atmospheric circulation, the important message clearly preserved in these high-elevation ice fields is that the large-scale dynamics of the tropical climate system have changed.

which doesn't mean that you can interpret it as unpreceded warming in the Holocene. for that you'd need to have other proxies. So what else is new about South America and the Holocene Therman Optimum?

http://tinyurl.com/ezvgx

MH. Iriondo and NO. Garcia 1993. Climatic variations in the Argentine plains during the last 18,000 years,Palaeogeography, Palaeoclimatology, Palaeoecology Volume 101, Issues 3-4 , April 1993, Pages 209-220


Abstract
The last deglacial hemicycle was characterized by a general increase in temperature and precipitation in the region, with a few significant departures from this general trend. The present NE-SW climatic gradient was maintained throughout the entire period, except in the Upper Holocene. The following sequence of events is apparent if the present climate is taken as a reference base:

1. (a) 18,000–8500 yr B.P.: Arid and cool, with aeolian sand ad loess deposition. Patagonian fauna. Climatic isolines (temperature, precipitation, etc.) were located some 750 km northeast of their present positions.

2. (b) 8500-3500 yr B.P.: Humid subtropical, with Brazilian fauna. Pedogenesis and fluvial dynamics. Climatic limits migrated about 800/900 km southwest of their former positions...

http://tinyurl.com/lcnmy

Abarzúa et al 2004, Deglacial and postglacial climate history in east-central Isla Grande de Chiloé, southern Chile (43°S) Quaternary Research Volume 62, Issue 1 , July 2004, Pages 49-59


Abstract
Palynologic and stratigraphic data from Laguna Tahui (42°50′S, 73°30′W) indicate cool–temperate and humid conditions there between 14,000 and 10,000 14C yr B.P., followed by warmer and drier-than-present conditions between 10,000 and 7000 14C yr B.P....

,

http://tinyurl.com/gaxun

Ledru et al 1996 The last 50,000 years in the Neotropics (Southern Brazil): evolution of vegetation and climate Palaeogeography, Palaeoclimatology, Palaeoecology Volume 123, Issues 1-4 , July 1996, Pages 239-257


Abstract

In the “Lagoa Campestre” (Lake) of Salitre (19°S, 46°46′W, 970 m elev.),... .

The early Holocene, 9500 to 5000 yr B.P., is characterized by a more marked seasonal pattern and higher temperatures, reaching a maximum c. 5000 yr B.P...

Furthermore, Thompson could have cross checked the literature about the Medieval Warm Period in South America, being warmer than today or not and he could have found:

Rein B., Lückge, A., Reinhardt, L., Sirocko, F., Wolf, A. and Dullo, W.-C. 2005. El Niño variability off Peru during the last 20,000 years. Paleoceanography 20: 10.1029/2004PA001099.

The authors derived sea surface temperatures from alkenones extracted from a high-resolution marine sediment core retrieved off the coast of Peru (12.05°S, 77.66°W). The results indicated that the warmest temperatures of the past 20,000 years occurred during the late Medieval Period (AD 800-1250), and that they were about 1.5°C warmer than those of the Current Warm Period..

http://www.co2science.org/scripts/CO2ScienceB2C/data/mwp/studies/l1_perushelf.jsp

and

L Pérez-Cruz, 2006; Climate and ocean variability during the middle and late Holocene recorded in laminated
sediments from Alfonso Basin, Gulf of California, Mexico Article in Press, Quaternary Research Corrected
Proof -
Abstract
A laminated sequence (core BAP96-CP 24°38.12N, 110°33.24W; 390 m depth) from the Alfonso Basin in Bay of La Paz, southern Gulf of California, contains a record of paleoceanographic and paleoclimatic changes of the
past 7900 yr.

... Proxies indicate a warm scenario and the dominance of the Equatorial Surface Water in the Alfonso Basin from 2400 to 700 cal yr BP, suggesting the intensification of ENSO cycles.

suggesting that the current warm period is nothing unprecedent at al.

I keep wondering how people can think that man has a significant role in global warming.

Suppose that we can proof within a three sigma certainty that global CO2 levels were higher than today in the timeframe 1938-1949 and subsequently dropped against the increasing anthopogenic production, what would that say about the current climate paradigms?