Study on paleo rainfall records clearly shows existence of MWP and LIA in Southern Hemisphere

This study from the University of Pittsburgh and SUNY-Albany set out to illustrate how rainfall patterns changes with global temperature in South America. They found the link they were looking for. At the same time, they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere, which is interesting since many claim the effects were regional, not global. See the image at left and press release below.

Delta-O-18 levels from Pumacocha correlate with geological temperature records, including solar radiation levels, titanium concentration at Cariaco Basin, and annual temperatures in the Northern Hemisphere and North Atlantic. Click to magnify the image

Pitt-led Team Unearths 2,300-Year Climate Record Suggesting Severe Tropical Droughts as Northern Temperatures Rise

A sediment core from a South American lake revealed a steady, sharp drop in crucial monsoon rainfall since 1900, leading to the driest conditions in 1,000 years as of 2007 and threatening tropical populations with water shortages, a team from Pitt, Union College, and SUNY-Albany reports in PNAS

PITTSBURGHA 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet’s densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.Laguna Pumacocha in the Peruvian Andes.

The researchers report in the Proceedings of the National Academy of Sciences (PNAS) that a nearly 6-foot-long sediment core from Laguna Pumacocha in Peru contains the most detailed geochemical record of tropical climate fluctuations yet uncovered. The core shows pronounced dry and wet phases of the South American summer monsoons and corresponds with existing geological data of precipitation changes in the surrounding regions.

Paired with these sources, the sediment record illustrated that rainfall during the South American summer monsoon has dropped sharply since 1900—exhibiting the greatest shift in precipitation since around 300 BCE—while the Northern Hemisphere has experienced warmer temperatures.

Study coauthor Mark Abbott, a professor of geology and planetary science in Pitt’s School of Arts and Sciences who also codesigned the project, said that he and his colleagues did not anticipate the rapid decrease in 20th-century rainfall that they observed. Abbott worked with lead author and recent Pitt graduate Broxton Bird; Don Rodbell, study codesigner and a geology professor at Union College in Schenectady, N.Y.; recent Pitt graduate Nathan Stansell; Pitt professor of geology and planetary science Mike Rosenmeier; and Mathias Vuille, a professor of atmospheric and environmental science at the State University of New York at Albany. Both Bird and Stansell received their PhD degrees in geology from Pitt in 2009.

“This model suggests that tropical regions are dry to a point we would not have predicted,” Abbott said. “If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet.”

The study compared the record in the Pumacocha sediment core (PC) to various geological records from South America—Cascayunga Cave (CC), the Quelccaya ice Cap (QIC), and the Cariaco Basin (CB)—as well as the annual position of the Intertropical Convergence Zone (ITCZ).
The study compared the record in the Pumacocha sediment core (PC) to various geological records from South America—Cascayunga Cave (CC), the Quelccaya ice Cap (QIC), and the Cariaco Basin (CB)—as well as the annual position of the Intertropical Convergence Zone (ITCZ).

The sediment core shows regular fluctuations in rainfall from 300 BCE to 900 CE, with notably heavy precipitation around 550. Beginning in 900, however, a severe drought set in for the next three centuries, with the driest period falling between 1000 and 1040. This period correlates with the well-known demise of regional Native American populations, Abbott explained, including the Tiwanaku and Wari that inhabited present-day Boliva, Chile, and Peru.

After 1300, monsoons increasingly drenched the South American tropics. The wettest period of the past 2,300 years lasted from roughly 1500 to the 1750s during the time span known as the Little Ice Age, a period of cooler global temperatures. Around 1820, a dry cycle crept in briefly, but quickly gave way to a wet phase before the rain began waning again in 1900. By July 2007, when the sediment core was collected, there had been a steep, steady increase in dry conditions to a high point not surpassed since 1000.

To create a climate record from the sediment core, the team analyzed the ratio of the oxygen isotope delta-O-18 in each annual layer of lake-bed mud. This ratio has a negative relationship with rainfall: Levels of delta-O-18 are low during the wetter seasons and high when monsoon rain is light. The team found that the rainfall history suggested by the lake core matched that established by delta-O-18 analyses from Cascayunga Cave in the Peruvian lowlands and the Quelccaya Ice Cap located high in the Andes. The Pumacocha core followed the climatological narrative of these sources between the years 980 and 2006, but provided much more detail, Abbott said.

The team then established a connection between rainfall and Northern Hemisphere temperatures by comparing their core to the movement of the Intertropical Convergence Zone (ITCZ), a balmy strip of thunderstorms near the equator where winds from the Northern and Southern Hemispheres meet. Abbott and his colleagues concluded that warm Northern temperatures such as those currently recorded lure the ITCZ—the main source of monsoons—north and ultimately reduce the rainfall on which tropical areas rely.

The historical presence of the ITCZ has been gauged by measuring the titanium concentrations of sea sediment, according to the PNAS report. High levels of titanium in the Cariaco Basin north of Venezuela show that the ITCZ lingered in the upper climes at the same time the South American monsoon was at its driest, between 900 and 1100. On the other hand, the wettest period at Pumacocha—between 1400 and 1820, which coincided with the Little Ice Age—correlates with the ITCZ’s sojourn to far south of the equator as Northern Hemisphere temperatures cooled.

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Levels of the oxygen isotope delta-O-18 from Pumacocha overlaid with corresponding levels from Cascayunga Cave (red) and Quelccaya Ice Cap (blue).h/t to reader Dennis via email
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84 Responses to Study on paleo rainfall records clearly shows existence of MWP and LIA in Southern Hemisphere

  1. Pingo says:

    It was clearly regional to south America and north-west Europe, move along nothing to see here.

    Meanwhile a single Calfornian tree can decipher global climate for hudnreds of years.

  2. Mike Bromley says:

    I read it twice….no reference to any link to CAGW?? Are my eyes happily deceiving me?
    In keeping with just how complex all of this is, just imagine a different continental confiuguration.

  3. Joe Lalonde says:

    Anthony,

    I love the way conclusions are made for little evidence support in a time frame that is extremely minor the time frame of the whole planet.

    Evidence of the past suggest there was a GREAT deal more ocean water but current theories lump movements of huge rocks with Ice Ages considering snow and ice don’t actually move.
    Upland movements do NOT calculate out with the current science when brought back to the time frame of billions of years ago by many hundreds of thousands of meters.

  4. RayG says:

    What happens if you overlay these results on the dendro plots of NH temp, MM’s in particular? Do these results represent yet another falsification of treemometers?

  5. Luther Wu says:

    What’s this? They didn’t throw in so much as a paragraph, or even a sentence warning that it’s all our fault?
    Perhaps that all comes later, when the rhetoricians turn this report on it’s ear to show that ‘yes, there was no Little Ice Age’.

  6. henrythethird says:

    “…A 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet’s densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium…”

    Seems their main objective wasn’t to confirm the existance of the LIA, but to give us another “it’s gonna get worse” scenario, and blame the Northern Hemisphere as well.

    Unfortunately for them, it shows the GLOBAL impact of the LIA.

  7. Gary says:

    They claim a correlation with NH temperatures, but I don’t see a mechanism for the linkage proposed in the paper, just some references to other studies. They also state that decadal variation in rainfall is quite variable. Interesting, but needs more work to pin down the causes.

  8. P Gosselin says:

    This further confirms that Mann’s HS was a fraud throughout. The lion’s share of the climate science can be discarded onto the scrap heap.

  9. John Marshall says:

    According to 971 scientists from 562 research institutions the MWP is a fact of history. This research covers 43 different countries, Northern and Southern hemispheres.

    So the above report, important though it is, is not the first and doubtless not the last.

    IPCC please note.

  10. “since many claim the effects were regional, not global.”

    Gotcha Mann!

    Now tell us that the medieval warm period was just a small regional effect.

  11. Rick Bradford says:

    It won’t make any difference to the faithful, who are still waiting for the Climate Rapture (aka ‘tipping point’) which will instantly plunge us into planetary catastrophe.

    Making trillion-dollar economic decisions on the basis of the climate religion is the real apocalypse.

  12. tallbloke says:

    The graph shows pretty small temperature changes between the MWP -LIA and NOW

    Could easily be fully accounted for by solar, GCR and instrumental/interpretational/calculation errors.

    CO2 along for the ride methinks.

  13. tallbloke says:

    Gary says:
    May 23, 2011 at 5:48 am
    Interesting, but needs more work to pin down the causes.

    Here you go:
    http://tallbloke.files.wordpress.com/2010/08/shumidity-ssn96.png

  14. Amino Acids in Meteorites says:

    More data showing that climate always changes. It also shows we are living in a relatively mild time in climate. There are no unprecedented weather events happening now. Things have been worse in the past.

  15. richard verney says:

    I understand that there is little evidence in the various Southern Hemisphere proxy records suggesting that the MWP was not seen in the Southern Heisphere but rather due to a sparcity of proxy records, there was insufficient evidence to confirm that the MWP also extended into the Southern Hemisphere. In otherwords, the AGW proponents, in quite typical stance, used the sparcity of evidence as ‘proof’ that the MWP was not global.

    It is not known with any certainty as to precisely when Machu Picchu was built but it is thought to be around or shortly before 1450 and was inhabitated for about 100 or so years. Many archaeologists consider that crops were grown there and the site was abandoned when agriculture was no longer possible due to climate change.

    Obviously, such a theory is only a theory but if correct, it would suggest that Peru was considerably warmer in the mid 1400s than it is today and this therefore leads some historical support to the MWP being a global event (although the precise dates for the MWP may vary from hemisphere to hemisphere).

  16. Steve Keohane says:

    John Marshall says: May 23, 2011 at 5:51 am
    According to 971 scientists from 562 research institutions the MWP is a fact of history. This research covers 43 different countries, Northern and Southern hemispheres.

    John, it would help your argument if you linked to the source:

    http://www.co2science.org/data/mwp/mwpp.php

  17. “The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium”

    The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.

    It has a rising trend of 9.23 mm/annum.

  18. Don B says:

    In Jasper Kirkby’s “Cosmic Rays and Climate,” on page 3 is a graph of Venezuelan Andes glacier growth and shrinkage for eleven hundred years.

    http://aps.arxiv.org/PS_cache/arxiv/pdf/0804/0804.1938v1.pdf

    The MWP and the LIA are obvious, as is the correlation with cosmic rays.

  19. Alan the Brit says:

    “By July 2007, when the sediment core was collected, there had been a steep, steady increase in dry conditions to a high point not surpassed since 1000.”

    I’m sorry, are they saying this has happened before? Now there’s a surprise!

  20. Kevin Schurig says:

    Great, the drier period will be blamed on us in an attempt to weasel even more money out of us to give to those we have “screwed” through our causing AGW. As many have stated this report shows the world wide effect the MWP and LIA had, but that will be ignored in order to blame the industrialized nations for all the ills of the rest of the world. Fine, bring it on.

  21. Mike says:

    From the abstract: “Continued Northern Hemisphere and North Atlantic warming may therefore help perpetuate the recent reductions in SASM precipitation that characterize the last 100 years, which would negatively impact Andean water resources. ”

    The article is clearly a wake up call that continued AGW will damage the region.

    “Minimum δ18O values occurred during the Little Ice Age (LIA) between A.D. 1400 and 1820, reflecting a prolonged intensification of the SASM that was regionally synchronous. After the LIA, δ18O increased rapidly, particularly during the current warm period (CWP; A.D. 1900 to present), indicating a return to reduced SASM precipitation that was more abrupt and sustained than the onset of the MCA.” [MCA = medieval climate anomaly]

  22. Gary Pearse says:

    Interesting paper but no surprise to thinking scientists. The ludicrous position is that the LIA and MWP were “local” – this is a null hypothesis of a higher probability inference that such long-lasting and significnt events are global. Its a bit like sea ice in the Arctic being local until we make the surprising find that it also is to be found in the Antarctic (of course such a find then probably has them speculating there must be polar bears there too). Yet the CAGW types have no problem in pronouncing that that the future hell-on-earth with a 2C rise will be global. Yes, I’m happy they appear to have located the MWP and LIA in South America but I already predicted that myself.

  23. Olen says:

    I prefer BC rather than the new and not necessary BCE.

  24. KnR says:

    Of course the claim was that MWP was regional , but you notice no one side how big the region was just it was one . So as long as you can’t prove that the MWP existed in ever square cm of the planet , its ‘regional’ no matter how big the region . Climate science 101.

  25. Tom T says:

    Don’t count me as one who is happy to see no direct reference to AGW. Everything about this article implies that humans in the Northern Hemisphere are responsible for drought and probably every other bad thing that happens in the Southern Hemisphere.

  26. izen says:

    The research looked at proxy measures of rainfall, NOT temperature. The assumption is, from other research, that the change in rainfall corellates with temperature changes.

    That a Medieval climate anomaly exists is not in dispute. The controvesry arises over its magnitude and timing globaly. This reseach seems to show that the MWP was not as pronounced a warming in the S.H. as in in Northern latitudes, and with a peak around 1040 is later than the peak in the Northern hemisphere. The peak had already passed and the Vikings in Greenland were begining to suffer the effects of a cooling climate by this date.

    This research does seem to confirm that any MWP was not warmer, or at least dryer than the present; confirming that present conditions are exceptional.
    “The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.”

  27. richard telford says:

    “they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere”
    ———-
    They did no such thing.

    The Medieval Warm Period is a temperature anomaly. They don’t have a temperature-sensitive proxy, so they cannot, and did not try to reconstruct temperature. They have a precipitation proxy. To infer that the MWP of the North Atlantic region had far-field impact is a fair interpretation. To conclude that the MCA was a globally warm phase is to make the same fundamental mistake as Soon and Baliunas (2003).

    REPLY: Well, you are entitled to your opinion, but so much rides on making the MWP go away, I choose to side with Soon and Baliunas (2003) over your opinion, which isn’t peer reviewed. See the upcoming article for more things being said about the hockey stick that I’m sure will bother you. – Anthony

  28. Smokey says:

    Izen says:

    “That a Medieval climate anomaly exists is not in dispute. The controvesry arises over its magnitude and timing globaly.”

    There is no controversy. Let me correct your disingenuous little head: The MWP was a global event, as is verified by the strong corellation between both hemispheres.

    Note that this is empirical evidence, not George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies. Did you actually think you would get away with trying to sell your ‘medieval warming anomaly’ bullshit here? Run along to Skeptical Pseudo-Science or RealClimatePropaganda, they like dishonest language corruption like that. But here at the internet’s Best Science site, honest terminology matters, and peddlers of junk science are called out.

  29. Richard M says:

    Berényi Péter says:
    May 23, 2011 at 6:53 am
    “The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium”

    The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.

    It has a rising trend of 9.23 mm/annum.

    Yeah, but that would be due to the rotten water. The good water has decreased and it’s worse than we thought. ;)

  30. Professor Bob Ryan says:

    izen: logical fault. Even given your claims about the magnitude of the MWP the proposition that the peak temperature then was less than now does not confirm that the ‘present conditions are exceptional’. All it shows, if true, is that the warming in the modern era is greater than the most recent peak in global temperatures. However, my understanding of the uncertainties attaching to the proxy studies done so far is that they cannot resolve temperatures around 1000 AD to anywhere near the accuracy your statement would require to be true.

  31. Cathy says:

    Oh Smokey! I love it when you get smokin’ hot around the collar :-)

  32. richard telford says:

    Soon and Baliunas (2003) was of course peer-reviewed: four reviewers rejected it. It was only ever published because the editor sweet-hearted it in.

    REPLY: Yes, it had those dangerous ideas that didn’t go with the consensus wot dun it. Climategate shows us how that rolled. BTW Richard, will you ever be able to bring yourself to making a positive contribution here? You do nothing but complain. – Anthony

  33. Mike Bromley says:

    Joe Lalonde says:
    May 23, 2011 at 5:25 am
    Anthony,

    I love the way conclusions are made for little evidence support in a time frame that is extremely minor the time frame of the whole planet.

    Joe, can you please rephrase the above sentence? Right now it makes no literal sense.

  34. Dave says:

    John Marshall says:
    May 23, 2011 at 5:51 am

    According to 971 scientists from 562 research institutions the MWP is a fact of history. This research covers 43 different countries, Northern and Southern hemispheres.

    So the above report, important though it is, is not the first and doubtless not the last.

    IPCC please note.

    Hi John.
    Thanks for the info, any chance of referencing it with links?
    thanks.
    Dave

  35. Latitude says:

    richard telford says:
    May 23, 2011 at 8:15 am
    =================================
    Richard, you’re a hoot.

    The MWP was only in a suburb of Minneapolis…
    …happy now

    In spite of anything that has to do with sense, only certain parts of the planet got warmer, and had no effect on any other parts….
    There’s an invisible wall that stops it.
    …just like the GISS color coded temp maps

  36. Ryan Welch says:

    Why is there no data plotted for the Caricao Basin after about 1850? Are they attempting to “hide the decline?”

    This would make sense if the rainfall has been increasing since the 1900s as Berényi Péter pointed out in his link.

    “The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.”

    “It has a rising trend of 9.23 mm/annum.”

  37. Anthony Watts says:

    Telford replied to my question about why he can’t ever seem to say anything positive and always complains, citing that I was “spreading hate” so it was not approved. Try again Richard.

  38. Jimbo says:

    There are lots of studies indicating the MWP was global in nature. See the Medieval Warm Period Project.

  39. izen says:

    @- Smokey says:
    May 23, 2011 at 8:44 am
    “There is no controversy. Let me correct your disingenuous little head: The MWP was a global event, as is verified by the strong corellation between both hemispheres. ”

    I agree it was global, just not synchronous between the hemispheres.
    In the interests of using real data rather than ‘George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies,’ I was going to provide this link –

    http://pages.science-skeptical.de/MWP/MedievalWarmPeriod.html

    Which not only shows many of the proxy records from which you can detect a medieval climate anomaly, but also shows the differences in timing between different regions of the peak of the event.

    Then I realised that you had already included the same link in your reply.
    Have you not examined that graphic of map and data? You can spend some time playing a version of the ma-jong tile-matching game trying to find two records with matching peak times. Very difficult if they are in different hemispheres!
    Perhaps you were not aware that the very data you linked to confirms my claim that the peak of any MWP was NOT globally synchronous.

    I have no idea why you included the other link, it shows data from both polar ice-cores, but with a timescale of kiloyears so the MWP is indistinguishable in the mass of lines on the extreme final few left-hand mm of the graph. The peaks marked are around 80,000 and 110,000 years ago during the last ice-age. Presumably this was linked in error.
    Perhaps you have some other evidence that refutes the research reported above that quite clearly states the detected rainfall changes associated with a southern hemisphere MWP peak after 1000AD.

    -”But here at the internet’s Best Science site, honest terminology matters, and peddlers of junk science are called out.”

    I would certainly hope so.
    It would be depressing if people could link to data and make claims that were not bourne out by the data. Would you care to present any research that supports a simultaneous MWP or would you concede that as the link we BOTH favour shows it peaked at different times in different regions?

  40. MattN says:

    This should bring an end to the continued misconception that the MWP and LIA were regional-only events. It is undeniably clear they were not…

  41. Jimbo says:

    The MWP was global. Here are links to the relevant papers concerned.
    http://sites.google.com/site/globalwarmingquestions/mwp

  42. Smokey says:

    Izen,

    Since you asked, here’s a chart with a much shorter time scale.

    And I would be glad to discard MWP and MWA in favor of the Medieval Optimum since it was a global warming similar to the Holocene Optimum, the Minoan Optimum and the Roman Optimum – not as warm as those three preceding, but warmer than today.

    The devious effort to downplay the MWP is so transparent to those who follow the issue that it is hard to conclude that it is anything but alarmist propaganda. See Jimbo’s link for refutation.

  43. izen says:

    @-Berényi Péter says:
    May 23, 2011 at 6:53 am
    “The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.
    It has a rising trend of 9.23 mm/annum.”

    That would make the river around a metre higher than when first measured against the steps of the local building used as the datum point.
    Are you sure that the only explanation for this rise is increased rainfall?
    Could water extraction in the town/city of Manaus have caused any subsidence of the two datum points?
    Or is river level also mediated by changes in the sediment deposition further down river at the confluence of the Negro and Amazon?

  44. Smokey says:

    The question of whether the MWP happened simultaneously over the globe is simply an attempt to muddy the waters. The central issue is: ‘was the MWP global?’ – not: ‘did the MWP begin and end at the same time everywhere?’ Avoiding the main issue is just misdirection [AKA: "Look over there! A kitten!]

    Dr Craig Loehle explains that the MWP was not simultaneous over the globe. He refers to it as “time transgressive”:

    “A good example is the warming at the last glacial termination. Because the ice sheets took so long to melt, the warming took longer to reach eastern Canada which still had ice. Thus a peak in warming moved across the northern regions, and individual records of climate will not agree on the date of the warming. To say this applies to the Holocene Optimum at 8,000 to 6,000 BP is not a documented result, and to say it applies to the MWP is without foundation at all, but is a ‘clever way to deal with a problem’ (that, and claiming it was only Europe that got warm at the MWP).”

    The alarmists’ consternation with the MWP is simply that it occurred prior to the industrial revolution. Mann tried to erase the MWP [the long shaft of his Hockey Stick] and was debunked. With a MWP, the current mild warming of only 0.7°C over a century and a half is unremarkable, and no different from past natural variability. Blaming CO2 is just a convenient way to tax all things “carbon”.

  45. izen says:

    @-Smokey says:
    May 23, 2011 at 11:13 am
    “Since you asked, here’s a chart with a much shorter time scale.”

    No it isn’t. It graphs the last ice-age going back 90,000 years with the present depicted in the last 10kyr division on the far left.

    “…The devious effort to downplay the MWP is so transparent to those who follow the issue that it is hard to conclude that it is anything but alarmist propaganda. See Jimbo’s link for refutation.”

    Is it ore devious than the effort to exaggerate the MWP which is so transparent to those who follow the issue that it is hard to conclude that it is anything but rejectionist propaganda.
    I have followed the links provided by Jimbo, here are some quotes –

    “Comparisons with selected temperature proxies from the Northern and Southern Hemispheres confirm that the MWP was highly variable in time and space. ”

    “This proxy suggests that during the late Middle Ages (ca. AD 1230–1410) the lake level was rather low representing a signal of the ‘Medieval Climate Anomaly’ in southeastern Patagonia.”

    “CH3Cl levels were elevated from 900–1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA).”

    The MWP clearly peaks at different times, it was just about over in Greenland by 1000AD but still rising in Patagonia. You can define the MWP as a vague, fuzzy period from 800AD to 1400AD which was global, but the timing of the peaks during those centuries was not globally synchronous. That makes it difficult to argue that it was an event with enough similarities to the present warming that IS globally synchronous and very difficult to maintain that the evidence shows it represents a similar gain in energy rather than the redistribution of energy between regions and hemispheres.

    There is a final irony in all this. IF the MWP was of similar magnitude to present warming it would indicate that climate sensitivity is greater because so much warming came from rather small solar/volcanic variations. That has serious implications for the magnitude of present warming from the increased energy returned to the surface as DLR from increased CO2. Presumably a conclusion you would not want ?

  46. phlogiston says:

    Several hundred peer reviewed papers recording the MWP from proxy studies from every continent on earth, are listed at CO2 Science, by continent and each summarised in a mini-abstract:

    http://www.co2science.org/data/mwp/mwpp.php

    Our troll guests should feel free to refute each one of these in turn.

  47. R. Gates says:

    Don B says:
    May 23, 2011 at 7:03 am
    In Jasper Kirkby’s “Cosmic Rays and Climate,” on page 3 is a graph of Venezuelan Andes glacier growth and shrinkage for eleven hundred years.

    http://aps.arxiv.org/PS_cache/arxiv/pdf/0804/0804.1938v1.pdf

    The MWP and the LIA are obvious, as is the correlation with cosmic rays.

    ______
    Thanks for this link. Of particular interest to me has been the Bond events (mentioned in the article you’ve referrenced). I’ve thought for quite some time that the MWP was global in nature based on my reading of the subject, and certainly involved changes in the ITCZ, but the excellent connections made in this this article between Solar Activity/GCR’s/Bond Events/ITCV etc was very useful. Thanks again…

  48. izen says:

    @-Professor Bob Ryan says:
    May 23, 2011 at 8:52 am
    “izen: logical fault. Even given your claims about the magnitude of the MWP the proposition that the peak temperature then was less than now does not confirm that the ‘present conditions are exceptional’. ”

    I agree, my apologies.
    ‘Exceptional’ requires some criteria of definition. The exceptional weather we are having at present in the UK would not be exceptional for mid-summer. It is necessary to define the context before a condition can be so labeled.

    “However, my understanding of the uncertainties attaching to the proxy studies done so far is that they cannot resolve temperatures around 1000 AD to anywhere near the accuracy your statement would require to be true.”

    Yes, The proxy studies of rainfall or temperature are ambiguous and I would accept that alone they lack the accuracy to definitively refute either hypothesis.
    The present warming is certainly not exceptional over long timescales, the Holocene maximum around 8000yrs BPE seems to have been warmer, but ice-mass and sea level indicate nothing comparable since.

    Modern industrial/technological civilisation got going during the LIA. The question of interest is how robust are such societies when the climate alters enough to disrupt agricultural systems. It may not require warming that could be described as exceptional over tens of kiloyears, but may be susceptible to variations, AGW or otherwise, of century scales.

  49. Stephen Wilde says:

    The air circulation systems clearly move cyclically poleward then equatorward then back again in both hemispheres in response to the battle between top down solar forcing and bottom up oceanic forcing. In that process the degree of meridionality shown by the jet streams alters total cloudiness and global albedo.

    All global climate change is a consequence of those movements.

    It’s just too obvious and too simple for anyone to accept.

  50. Gary Pearse says:

    Izen May 23, 2011 at 11:51 am

    “Comparisons with selected temperature proxies from the Northern and Southern Hemispheres confirm that the MWP was highly variable in time and space. ”

    Or temp proxies are only approximately dated or even invalid. They wouldn’t be the first proxies that have come to grief (to wit: those of the hockey stick). Also, note that comparisons here were made with selected temp proxies.

    The main support for the MWP and the LIA comes from historical documentation, not proxies – proxies followed and can be said to have been somewhat validated by the prior knowledge. Unfortunately this means that only those parts of the globe where cultures kept records have been highlighted ( nevertheless, North America, Greenland, Europe, Asia is a hell of a piece of territory to have experienced it all by itself for a couple of centuries). Speaking of the downside of “fuzzy MWP” in time and space, this “regional” kind of climate thinking has a downside for CAGW, too. If you are comfortable with MWP being a patch on the globe, then how can you argue so strongly that CAGW wouldn’t also be a patch in roughly the same place – they are approximately similar in temp. The wrongful thinking isn’t dissimilar to the idea that ice found in the Arctic first wouldn’t cause one to expect it to be found in Antarctica.

  51. Professor Bob Ryan says:

    izen: thank you and I agree with your final paragraph. That is, indeed, the question that matters.

  52. Billy Liar says:

    izen says:
    May 23, 2011 at 12:20 pm

    Perhaps you would care to define ‘exceptional’ with special reference to the current UK weather.

  53. rbateman says:

    Step one in reconstructing the MWP climate via one S.American lake.
    Lots of other lakebed sediments to check out.

  54. TonyG says:

    So, Mike, what caused the MWP, then?

    (And were they able to grow more or less crops during that time?)

  55. Smokey says:

    Izen says:

    “Modern industrial/technological civilisation got going during the LIA. The question of interest is how robust are such societies when the climate alters enough to disrupt agricultural systems. It may not require warming that could be described as exceptional over tens of kiloyears, but may be susceptible to variations, AGW or otherwise, of century scales.”

    More warmth has historically been very beneficial for civilization. Global cooling has been the real problem. A decade is a short trend, but it is still worrying.

  56. Christopher Hanley says:

    izen says:
    The peak had already passed and the Vikings in Greenland were begining to suffer the effects of a cooling climate by this date [1040]….
    ….and again:
    The MWP clearly peaks at different times, it was just about over in Greenland by 1000AD
    —————————————
    The Greenlanders don’t see it that way:
    http://www.greenland-guide.gl/leif2000/history.htm
    But of course data derived from proxies etc. always trump historical accounts because they carry that invisible aura of ‘science’.

  57. Geoff Sharp says:

    So temperature records follow solar output over thousands of years. This should put an end to the argument about solar forcing. At lower resolutions the influence of the PDO would also be important but is still linked to solar output. While the MWP and LIA are confirmed globally there is a likelihood that the northern hemisphere sees bigger shifts due to the topographic profile in the north, which affects jetstreams to a greater degree.

  58. Amino Acids in Meteorites says:

    Speaking of the Mann Hockey Stick graph:

    …….Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium”……

    -National Academy of Science

    -report on the Mann Hockey Stick graph, page 4

    http://www.nap.edu/openbook.php?record_id=11676&page=4

  59. Smokey says:

    Gates says:

    “Of particular interest to me has been the Bond events…”

    Then you may like this chart.

    # # #

    Also, since the temporal variations in the MWP in different regions is still being discussed here, it’s worth repeating Dr Loehle’s comment regarding the MWP:

    “Because the ice sheets took so long to melt, the warming took longer to reach eastern Canada which still had ice. Thus a peak in warming moved across the northern regions, and individual records of climate will not agree on the date of the warming.”

    I trust Lohle’s statement puts that question to rest. What matters is whether the MWP and other warm Holocene optimums exceeded current temperatures. The physical evidence shows that they did [and the reaction to the MWP by the "Team's" Jonathan Overpeck is about as unscientific as anyone can get: "We've got to get rid of the Medieval Warm Period!"].

    But at least Overpeck’s motivation to protect his gravy train is clear [so is his willingness to doctor the climate record]. If the public realizes that the current gentle warming cycle has happened repeatedly in the past, they will see that there is no adequate reason to assign the blame to a tiny trace gas – unless there is empirical evidence. But there is no evidence, none at all. The demonization of “carbon” is based on GCMs; computer climate models, which are even less accurate than economic models. And of course if econ models were accurate, their programmers and owners would be as rich as Croesus.

  60. Gneiss says:

    Scottish Sceptic writes,
    “Gotcha Mann!
    Now tell us that the medieval warm period was just a small regional effect.”

    Smokey writes,
    “Note that this is empirical evidence, not George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies.”

    Smokey writes,
    “Mann tried to erase the MWP [the long shaft of his Hockey Stick] and was debunked.”

    Amino Acids in Meteorites writes,
    “Speaking of the Mann Hockey Stick graph”

    Since we’re speaking of Mann … look again at that colorful graphic, Fig. 5 from the article, that Anthony reproduces above. The second plot in Fig. 5 compares the authors’ Pumacocha reconstruction (gray) alongside the Northern Hemisphere temperature reconstruction of Moberg et al (2005). The fourth plot compares it with another well accepted reconstruction, North Atlantic sea surface temperatures from Mann et al (2009), which like many other studies (including Moberg and this one) report geographically widespread evidence of the Medieval Climate Anomaly and Little Ice Age.

  61. barry says:

    “they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere, which is interesting since many claim the effects were regional, not global. See the image at left and press release below.”

    I don’t think this accurately characterises mainstream understanding. The MWP and LIA are not in doubt regarding their existence. The dispute is about whether the global temperature was higher durig the MWP than now, and the mainstream response is that while the globe was warm, the effects were not uniform temporally and spatially, indicating that current temps are higher. There are plenty of studies of different parts of the world that demonstrate this lack of uniformity, but the ensemble of these does point to a warm medieval period and a cold LIA.

    IOW, Anthony’s right about the regional effects, but wrong to suggest that this has been used to deny the existence of the MWP.

  62. barry says:

    The full version of the paper is online:

    http://www.pitt.edu/~mabbott1/climate/mark/Abstracts/Pubs/Birdetal11PNAS.pdf

    Reading through the comments and keeping in mind the issue at stake, these excerpts sprang out of the paper.

    After the LIA, δ18O increased rapidly, particularly during the current warm period (CWP; A.D. 1900 to present), indicating a return to reduced SASM precipitation that was more abrupt and sustained than the onset of the MCA [Medieval Climate Anomaly]

    The timing and direction of mean state changes in these records are similar during the LIA and CWP, although the Quelccaya ice core shows greater variability and slightly later minimum δ18O ice values during the LIA. The MCA is less pronounced in the Quelccaya δ18O ice record than in the Pumacocha δ18O cal
    record, although δ18O ice increased between A.D. 980 and 1100 with two peaks
    centered on A.D. 990 and 1080…

    Volcanic and solar forcing are included because changes in radiative forcing from these sources have been identified as leading influences on NH temperature variability during the MCA and LIA…

    Weakening of the SASM observed in the Pumacocha δ18O cal record during the MCA is contemporaneous with generally elevated radiative forcing and warm NH temperatures (Fig. 5 A and B; ref. 29). At the same time, SST reconstructions from the North Atlantic show warmer, although variable, conditions
    (32, 33), whereas those from the equatorial Pacific indicate La Niña-like cooling (32).

    The latter appear to support the notion of regional differences during the MCA (MWP), while the current warm period is more uniform, abrupt and sustained.

  63. R. Gates says:

    Smokey says:
    May 23, 2011 at 6:15 pm

    Gates says:

    “Of particular interest to me has been the Bond events…”

    Then you may like this chart.

    ______
    Very interesting chart. Made even more so by the association of these events with longer term solar cycles and GCR variations. Thanks…

  64. Christopher Hanley says:

    It’s encouraging to note that followers of ‘IPCC science’ have reluctantly accepted the existence of the MWP, although comically, as yet, they cannot allow themselves to use that label, preferring Medieval Climate Anomaly (MCA) instead.
    But the period c.900-c.1300 was not anomalous (climate-wise) within the Holocene so far.
    It was the period c.1400-c.1800 which was anomalous in that it was about the coldest since the Younger Dryas.
    http://muller.lbl.gov/pages/iceagebook/history_of_climate.html (Muller).

  65. Al Gored says:

    Smokey says:
    May 23, 2011 at 11:33 am

    “The question of whether the MWP happened simultaneously over the globe is simply an attempt to muddy the waters. The central issue is: ‘was the MWP global?’ – not: ‘did the MWP begin and end at the same time everywhere?’ Avoiding the main issue is just misdirection [AKA: "Look over there! A kitten!]

    Dr Craig Loehle explains that the MWP was not simultaneous over the globe. He refers to it as “time transgressive”:”

    There’s a wonderful irony here. On the one hand, the Team is using this ‘trick’ question and fixating on any deviations from THEIR monolithic MWP… if it didn’t simultaneously warm up everywhere, it must be CO2, or something like that.

    On the other hand, now when things are highly variable across the planet it is a sure sign of the Planetary Fever.

    Was there no warmcold in the MWP?

  66. Mark says:

    KnR says:

    Of course the claim was that MWP was regional , but you notice no one side how big the region was just it was one . So as long as you can’t prove that the MWP existed in ever square cm of the planet , its ‘regional’ no matter how big the region . Climate science 101.

    On the other hand anything detected by “climate scientists” must be “global”. No matter how small a part of the planet it actually applies to :)

  67. stumpy says:

    FYI – Every paleo type study I have seen in New Zealand also confirms a MWP and LIA, so it definitely was not confined to the northern hemisphere. That includes species distribution (for example Totara remains are found further south than the current distribution), stalagmite records, Maori history, records of glacier recession / growth etc… it all supports it.

    The Ministry for the Environment even published a “best estimate” record in a 2004 climate change report that clearly documented it plus further past warm episodes. (they omit the graph in the reports since though – made the current climate look cooler than normal – wasn’t a good look for the warmist brigade!)

    Good to see further studies confirming a SH LIA and MWP – maybe Mann being an impartial scientist should update his prior studies to include all these SH proxies with a MWP?

  68. Jimbo says:

    izen says:
    May 23, 2011 at 8:03 am

    This research does seem to confirm that any MWP was not warmer, or at least dryer than the present; confirming that present conditions are exceptional.

    Let me agree with you for just 1 minute. Now do you also agree that the Minoan and Roman warm periods were also exceptional?
    http://climate.geologist-1011.net/HoloceneTemperatures.png

  69. izen says:

    @- Jimbo says:
    May 24, 2011 at 3:04 am
    “Let me agree with you for just 1 minute. Now do you also agree that the Minoan and Roman warm periods were also exceptional?”

    No, as I mentioned on the issue of ‘exceptionality’ before it depends on context.
    I would accept that proxy records of past temperature are not sufficiently accurate or global to define the present climate as exceptional in relation to the MCA or LIA or any of the other past putative warmings except perhaps the Holocewne maximum after the big thaw ~8000 years ago.

    What puts present conditions into the exceptional class is the concurrent sea level rise and ice-mass loss which is unprecendented since the Holocene maximum. The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.

  70. liza says:

    izen says::
    “Holocewne maximum after the big thaw ~8000 years ago.”

    That’s not the “maximum”.

    “The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.”

    You can’t know that. Nobody knows exactly how long it took between the peaks (warm period-no ice) and troughs (cold period-ice) in the Milanknovitch Cycles. The data resolution isn’t good enough. You can only approximate. The data resolution is plus or minus thousands of years or more. The f[ur]ther you go back in time the margin for error gets even larger.

    The last big interglacial period ~125,000 yrs ago, which geologists know quite a lot about; sea level high stands were 15-20 ft higher then today. We are no where near that right now.

    http://www.ncdc.noaa.gov/paleo/globalwarming/paleobefore.html

  71. izen says:

    @- liza says:
    May 24, 2011 at 6:22 am
    “The last big interglacial period ~125,000 yrs ago, which geologists know quite a lot about; sea level high stands were 15-20 ft higher then today. We are no where near that right now.”

    But we are getting closer.
    The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
    Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
    There may also be arid deserts over large inland areas of the continents.

  72. Smokey says:

    “The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
    Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
    There may also be arid deserts over large inland areas of the continents.”

    Wow. That sounds just like Algore.

    Unfortunately for the believers in CO2=CAGW, the planet isn’t cooperating.

  73. tty says:

    Izen says

    “The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.”

    Not really, the last (Eemian, MIS 5e) interglacial for example was double-peaked with a cool episode with significant ice accumulation (lower sea levels) in between. The one before that (MIS 7) had three marked peaks (MIS 7.1, 7.3 and 7.5). It is true that the first interglacial peak is usually the warmest, but that is true of the current one too (we are a long way from the climatic optimum at the moment)

    Also claiming that the MWP had peaked by 1040 in Greenland is very doubtful. Climate there was warmer than at present (with grain growing marginally possible) as late as the thirteenth century (ref. Kónungs Skuggsjá). In Iceland where historical data are very good the main temperature decline (and the end of grain production) came in the fifteenth century.

    By the way it is interesting to note that while the last (Eemian) interglacial, which was a lot warmer than the present one, was also wetter than the present almost throughout the tropics. Just about the only exception was the Andean altiplano which was hyperarid.

    Also the usual claims about 20-30 feet higher sea levels during the last interglacial are very shaky. They are based on just a few sites of often questionable tectonic stability (like Hawaii and Bermuda). The best data from the very stable Australian craton indicates that 10 feet is a more likely figure .

  74. tty says:

    “The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
    Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
    There may also be arid deserts over large inland areas of the continents.”

    During the Eemian most deserts actually disappeared. There were lakes in the driest parts of Sahara and Rub al-Khali and Lake Eyre was a permanent lake rather than a playa.

  75. izen says:

    @-Smokey says:
    May 24, 2011 at 7:03 am
    “Unfortunately for the believers in CO2=CAGW, the planet isn’t cooperating.”

    Perhaps it is, this appears to be the first time since the Holocene maximum that ice-fields and glaciers are LOSING mass, that more ice is melting from the surface than is being added.
    There is no evidence in the ice-cores that this has ever happened before since the melt at the end of the last ice-age.

    http://researchnews.osu.edu/archive/radsignl.htm

    http://e360.yale.edu/feature/unlocking_secrets_from_the_ice_in_a_rapidly_warming_region/2268/

  76. Smokey says:

    Out of all the hundreds of predictions that purport to show that CAGW is happening – accelerating sea level rise, tropospheric hot spot, permanent coral bleaching, hurricanes increasing, disappearing polar ice caps, ocean acidification, frog extinctions, rapidly rising global temperature, etc., etc., etc. – none of them have actually happened. None.

    A broken clock is still right twice a day, and the climate alarmist claque is currently arm-waving over the natural variability of the Arctic [not mentioning the Antarctic, of course], the only event that even comes close to their hundreds of failed predictions. But Arctic ice has been even lower in the early 1800′s, well before industry started emitting significant amounts of CO2. Taking Occam’s Razor into account, the simplest explanation is that the Arctic ice cover is naturally variable. There is no evidence that CO2 has anything to do with Arctic ice.

    In any branch of the hard sciences a completely failed conjecture that has zero supporting evidence, and that cannot make correct predictions, and that has reams of contrary evidence would be universally ridiculed, and its funding would be cut off. The reason that the falsified claims of the “carbon” cultists are not laughed off stage is because CAGW is political, not scientific.

    Folks like Izen, who has at least some science background, apparently do not realize how ridiculous they sound making predictions of 20-foot sea level rises, and predictions that Eemian temps will be reached next century – conveniently far enough in the future that they can’t be proven wrong now. But the declining temperature trend over the past decade makes their unscientific claims of runaway global warming based on a harmless trace gas sound increasingly preposterous.

  77. Matt says:

    Interesting thread here in the form of a he said, she said debate. I don’t mean to demean the intellect here, for I myself am limited to BS Degree in Geology with over 25 years of environmental consulting and compliance. Not as much as most of you here I am sure. Through my work, I investigate/research issues and provide solutions, just as some of you do in your work. Root causes of local events/issues are important to identify to prevent recurrence. Why an event occurred can not be overemphasized as we seek understanding.

    In climate we all seek to understand as well. It really is simplistic to me (and you can rip me if you want) that the Earth warms up, cools down, and goes through wet and dry periods – sometimes extremes. I think we can all agree on that. Here is the issue so pay attention. How are we going to control the Earth’s processes and the relationship with the Sun’s processes? Ding Ding Ding. The answer is we can not on such a grand scale. All the information presented above and all the other information presented elsewhere, accurate/true or inaccurate/false, has no bearing on what Earth’s climate will do. It will do so as it has before our existence and will do so after our existence. That’s the bottom line on a grand scale of things. On a smaller scale we can prepare and react to climate changes (see investigate events/issues above).
    The past couple of years in the North, I have prepared by looking to the Southern Hemisphere. Surprisingly it was somewhat accurate looking back. Tough cold winters and floods. Will it work again? I have know idea as I can not control the Earths processes.

    So please, quit wasting taxpayer money and using AGW (its a punchline to me), as a means to line your pockets. Don’t tell me how to live my life. After all, this really is about obtaining wealth and power over others. Recorded human history tells us such.

  78. phlogiston says:

    izen says:
    May 24, 2011 at 6:50 am

    …The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
    Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
    There may also be arid deserts over large inland areas of the continents.

    Does a warmer world always mean more arid? Putting the CAGW hypothesis in a palaeo-climate context always seems problematic for the hypothesis. For most of the history of multicellular life (from the Cambrian onwards, the Phanerozoic eon) the earth has been much warmer than now. And it has not been arid. The Silurian, Devonian and Carboniferous gave us our oil and coal organic fossil deposits, with rich vegetation over most continents including Antarctica.

    Plus of course CO2 was through the roof then compared to now. If anything, life on earth appears to have been MORE vibrant, fecund and verdant then than now. Not less.

    I keep coming back to this graph:

    http://img801.imageshack.us/img801/289/logwarmingpaleoclimate.png

    There is a message in this graphic to any with an open mind – to me it seems to suggest clearly that we are in fact at the low, not the high – end of a “healthy” range of atmospheric CO2 concentrations which is wide and extends up to 8,000 ppm and maybe further. We know for instance that somewhere below 150-180 ppm CO2 plant photosynthesis starts to be limited and then we’re all up a gum tree.

    It is quite possible that a future, more enlightened and less politicised scientific community will welcome CO2 emission as a beneficial medicine for the planet’s thermal well being, and remain incredulous of the historic period of the dominance of the CAGW catastrophist alarmism driven by misanthropic Luddite politics.

  79. R. Gates says:

    Smokey,

    You’ve correctly identified the Arctic as the one region that we should be seeing the earliest signs of global warming and that you feel might even come close to the “failed” predictions of the AGW “alarmists”, but then you make this claim:

    “Arctic ice has been even lower in the early 1800′s…”

    Please substantiate this with lots of scienfiically verified studies with complete references and links, which will need to be extraordinary since your claim is quite extraordinary.

  80. R. Gates says:

    Response to phlogiston:
    May 24, 2011 at 1:38 pm

    ____
    It is absurd to think that a world of several thousand ppm of CO2 would be more conducive to supporting the 7+ billion human beings who largely rely on the millions upon millions of cultivated grain crops for their daily food supply in one way or another. Tropical rain forests may enjoy higher CO2 levels, at least some species of plants, but the vast open wheat fields of N. America, Russia, southern Brazil, Australia, etc. might be serioiusly threatened by such higher levels and the rather disputive weather changes that would probably ensue. Far from bringing a great bonanza of increased food supplies, CO2 levels at several thousand ppm would probably even further restrict the ability of humanity to feed itself.

  81. Steve Keohane says:

    R. Gates says: May 24, 2011 at 4:30 pm

    Response to phlogiston: May 24, 2011 at 1:38 pm

    ____
    It is absurd to think that a world [...] might be serioiusly threatened [...] would probably even further [...]

    You really nailed this time Gates! Do you have anything to “substantiate this with lots of scienfiically verified studies with complete references and links, which will need to be extraordinary since your claim is quite extraordinary.”?
    We know 2000 ppm of CO2 is more typical for life on this planet, and we currently reside in a time of historically low CO2.
    http://i55.tinypic.com/11awzg8.jpg
    http://i46.tinypic.com/2582sg6.jpg

  82. phlogiston says:

    R. Gates says:
    May 24, 2011 at 4:30 pm

    Steve Keohane says:
    May 25, 2011 at 6:36 am

    Response to phlogiston:
    May 24, 2011 at 1:38 pm

    I’m not suggesting that several thousand ppm CO2 is a desirable end. But as Steve K reiterated, the palaeo record makes it a challenge, to say the least, for the AGW camp to justify alarm over CO2 levels a few hundred ppm higher than today.

    Of course data on both temperature and CO2 from deep time – 10^8-10^9 yrs ago, has to be taken with a pinch of salt. We only have indirect estimates. But enough of them seem to agree for a probable picture to emerge.

    In any case even if industrial CO2 emissions continue as today indefinitely, atmospheric CO2 will not increase indefinitely but will equilibrate depending on the lifetime of CO2 in the atmosphere, which is finite; probably at somewhere in the 1000-2000 range. Grasses evolved in the late cretaceous in such CO2 levels so grasses such as wheat, barley etc should not find a problem to back-evolve a little to such levels, Dollo’s Law notwithstanding.

    I believe a worse problem than CO2 is loss of vegetation. Photosynthesis by plants and the effect of natural vegetation on water tables and the hydrological cycle are such that the artificial desertification that extensive urbanisation represents, is a threat to the homeostasis of the biosphere. Plant metabolism over the Phanerozoic have reduced both temperature and CO2 concentration to levels conducive of a healthy biosphere (I happen to believe that Lovelock’s Gaia is a serious scientific hypothesis, and largely correct, and should not be ridiculed).

    BTW deforestation in this context is a red herring. If Brazilian farmers cut down forest and replace them with grasses for agriculture, the end result is not less photosynthesis but more, due to the more efficient c4 photosynthesis of grasses and other monocots. But if they use the land for shopping malls and car parks – then that’s a problem…

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