Michael Mann says climate models cannot explain the Medieval Warming Period – I say they can’t even explain the present

Ice core data shows CO2 levels changed less than 10 parts per million from 1600-1800 during the MWP.

From the Hockey Schtick:  A new paper from Schurer et al (with Mann as co-author) finds that climate “models cannot explain the warm conditions around 1000 [years before the present, during the Medieval Warming Period] seen in some [temperature] reconstructions.”

According to Schurer et al, “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900.” They also claim, “but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800.” This claim is highly unlikely given that ice cores show CO2 levels only changed by less than 10 ppm from 1600-1800, and the effect of 10 ppm CO2 on the climate today remains undetectable even with modern instrumentation.

Separating forced from chaotic climate variability over the past millennium
Andrew Schurer,1 Gabriele Hegerl,1 Michael E. Mann,2 Simon F. B. Tett,1 and Steven J. Phipps3

Journal of Climate 2013 doi: http://dx.doi.org/10.1175/JCLI-D-12-00826.1

Abstract
Reconstructions of past climate show notable temperature variability over the past millennium, with relatively warm conditions during the ‘Medieval Climate Anomaly’ (MCA) and a relatively cold ‘Little Ice Age’ (LIA). We use multi-model simulations of the past millennium together with a wide range of reconstructions of Northern Hemispheric mean annual temperature to separate climate variability from 850 to 1950CE into components attributable to external forcing and internal climate variability. We find that external forcing contributed significantly to long-term temperature variations irrespective of the proxy reconstruction, particularly from 1400 onwards. Over the MCA alone, however, the effect of forcing is only detectable in about half of the reconstructions considered, and the response to forcing in the models cannot explain the warm conditions around 1000 [years before the present] seen in some reconstructions. We use the residual from the detection analysis to estimate internal variability independent from climate modelling and find that the recent observed 50-year and 100-year hemispheric temperature trends are substantially larger than any of the internally-generated trends even using the large residuals over the MCA. We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900, but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800. The proxy reconstructions tend to show a smaller forced response than is simulated by the models. We show that this discrepancy is likely to be, at least partly, associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations.

================================================================

Heck, the climate models can’t even explain the present, let alone the past, so this really isn’t a surprise:

IPCC_Fig1-4_models_obs

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113 thoughts on “Michael Mann says climate models cannot explain the Medieval Warming Period – I say they can’t even explain the present

  1. He is quick to avoid leaving anything stupid unsaid. Models only report back what we tell them and in a way we have told them. If climate models were self-modifying AI they would surely pull the pin before dishing out the trash they are told to create.

  2. MattS, That is no need for the /sarc, tag, as sadly, the alarmist warmists actually appear to believe that. They have more trust in the models, (which have had to be constantly re-engineered to retrospectively “predict” the past temperatures that they failed to predict in reality), than trust the actual real historical data. They will not believe the data until it has been adjusted to match the models.

    And they have the bare faced cheek to call themselves scientists?

  3. “They also claim, “but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800.”

    They find – as ever – just what they want to find.

  4. Wait, I thought Mann had proved conclusively that neither the Medeval Warm Period or the Little Ice Age had ever happened.
    I’m getting confused again.

  5. Nothing new,
    Already demonstrated many times.

    for example in
    Scafetta N., 2010. I cambiamenti climatici sono regolati da cicli naturali di origine astronomica (Climate change is regulated by natural cycles with an astronomical orogins). Il 21mo Secolo, Scienza e Tecnologia 1, 5-10 (2010). (figure 6)

    http://people.duke.edu/~ns2002/pdf/21mo-secolo.pdf

    and about the 20th century, look at

    Scafetta N., 2012. Testing an astronomically based decadal-scale empirical harmonic climate model versus the IPCC (2007) general circulation climate models. Journal of Atmospheric and Solar-Terrestrial Physics 80, 124-137.

    http://www.sciencedirect.com/science/article/pii/S1364682611003385

    For those who may be interested, I am keeping a comparison between the forecast made with my proposed astronomical based model of climate variation vs. the IPCC GCMs projection at my web-site where my proposed model clearly outperforms until now the IPCC GCMs.

    http://people.duke.edu/~ns2002/#astronomical_model_1

  6. Michael Mann says climate models cannot explain the Medieval Warming Period – I say they can’t even explain the present

    Yeah, but…

    You say it on a board read by thousands,

    while he says it where many less will read it but the main stream media will quote it as gospel everywhere.

  7. …A new paper from Schurer et al (with Mann as co-author) finds that climate “models cannot explain the warm conditions around 1000 …

    Umm.. therefore the MWP didn’t exist?

    Isn’t that how climate science works? ” I can’t see any other reason for what happened apart from the one I believe, so that MUST be the right one…”

  8. Ice core data shows CO2 levels changed less than 10 parts per million from 1600-1800 during the MWP.

    Can someone point me to the definitive work on how CO2 behaves under the sort of temperature and pressure conditions it experiences in an ice deposit? Specifically, how does it migrate through ice? Does it, for example, tend to an equilibrium point at about 285 ppm? I’m trying to work out just what it is I don’t trust about all these claims about the CO2-invariant paradise we had “before we messed it all up”.

  9. Dr. Nicola Scafetta,

    It would be interesting to have an ongoing chart of the -residuals- of all of the competing models. Or, at least, the running least-squared error between models and obvservations. Both as independent models and as the “ensemble”.

    This is a pretty stock method of comparing models with reality, I know of no legitimate reason to avoid this for climate science.

  10. To be blunt Mr Mann needs to learn the difference between his ares to his elbow. Before Mr Mann perpetrated the Hockeystick fraud, he first claimed MWP which did not was so insignificant it did not merit as much as a pimple bump on an elephants arse. Then he claimed it existed but only in northern Europe, therefore it wasn’t representative or have any effect on global temperatures. Mr Mann your wrong as usual 1-The MWP was warmer for a longer period than any present day warming. 2- there is a mountain of evidence it was worldwide in extent. Mr Mann how can we believe any thing you say, your track record is questionable at best and outright fraud at worst!

  11. DaveG says:
    Correction:

    To be blunt Mr Mann needs to learn the difference between his ares to his elbow. Before Mr Mann perpetrated the Hockeystick fraud, he first claimed the MWP was insignificant that it did not merit as much as a pimple bump on an elephants arse. Then he claimed it existed but only in northern Europe, therefore it wasn’t representative or have any effect on global temperatures. Mr Mann your wrong as usual 1-The MWP was warmer for a longer period than any present day warming. 2- there is a mountain of evidence it was worldwide in extent. Mr Mann how can we believe any thing you say, your track record is questionable at best and outright fraud at worst!

  12. Using plant stomata however the ice core levels may not be the best measure of CO2 levels.

    Studies of plant stomata show that the currently-held view of predominantly stable CO2 levels (260-280 ppm) before the Industrial Revolution (1750 AD, i.e. 200 years B.P.) may be an inaccurate view. CO2 levels appear to have regularly exceeded 280 ppm– the average of CO2 concentrations across the Holocene interglacial period (last 11,000 years) appears to have been approximately 305 ppm.

    and
    In the 1800’s direct air CO2 measurements were performed by various researchers. Interestingly, the CO2 levels reported by them were mostly in excess of 300 ppm. For reasons that are unclear, only a few of these tests were considered valid by G.S. Calendar (1898-1964)– the grandfather of the theory of man-made global warming. Today, the remaining data are largely ignored,

    http://www.geocraft.com/WVFossils/stomata.html

    Still do not understand how the magical CO2 decides how and when to affect the air temps.

  13. “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900.”

    … but now the lack of explosive volcanism and variations in solar output (solar maximum) is not the main drivers of 1900-today’s much better climate ?? … as if as if we were never suppose to rebound from that icy period in history ??

    Lopsided climate “science” is all they feed to us today. It is nothing but crap and should be called what it is.

  14. “…for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800.” ~ Mann, et al.

    Given the time frame and claimed resolution why doesn’t the model explain correctly the last 15 years?

  15. As this is ‘climate science’, is The Great Fire of London in 1666 of any relevance?

    It must have produced a lot of CO2, perhaps that might help Mann find his missing evil gas. It is just as good a reason as the other stuff he makes up.

  16. Cause or effect? Is there a relationship between decreases in atmospheric CO2 and/or temperature during the Little Ice Age and population declines at high altitudes (the Altiplano)
    at that time?

  17. I haven’t been able to find the paper I read it in, but I read years ago that modelers had to jack up sensitivity to Co2 to get the models to increase temps as measured, and while there’s nothing wrong with doing something like that to guide research for a physical mechanism, it’s not proof.
    But, the point is I don’t think Mann is a modeler, I think the wheels are starting to wobble, and Mann just threw the modeler (Hansen) under the bus.

  18. “Ice core data shows CO2 levels changed less than 10 parts per million from 1600-1800 during the MWP.”

    I think you meant LIA.

  19. Earth to Leif Svalgaard, comments?

    “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900″

  20. Every time I go to the store and pay for something I whip out a twenty dollar bill (or multiples thereof) and look at the person at the cash register with the most honest, sincere, and bland expression I can think of. As I hand the cashier the bill, making certain the expression I described is riveted to my face, I say, “This is not really a twenty dollar bill.” With genuine sincerity I then say, “It’s really a two hundred dollar bill.” And then with the tone of my voice just oozing honesty I immediately employ the ‘trick’, “It’s just that you can’t see the other zero, but trust me, it’s there.” I really do this. I’m not making this up. And the reason you can believe me when I say that I really do this is when I tell you that it never works. Ever. And, in fact, the cashiers tend to laugh at me. (Which is a little better outcome than being arrested.)

    It would be nice if the powers that be had the same sense of humor and practicality that these cashiers had for, if that was the case, Michael Mann would have had a career as an old fart trying to pan off twenty dollar bills which contain magic signals turning them into two hundred dollar bills, rather then the damaging career he has now.

  21. dp says:
    April 11, 2013 at 10:40 am
    He is quick to avoid leaving anything stupid unsaid. Models only report back what we tell them and in a way we have told them. If climate models were self-modifying AI they would surely pull the pin before dishing out the trash they are told to create.
    ——————————-
    I worked on inertial navigators during the 70’s. Great system but we had to update it every few days or so using GPS, sonar, LORAN, and a Type XI Periscope we used to get a star fix.
    We said it was a “multi-million dollar system that will tell you where you are as long as you tell it where it is.”
    Sounds a lot like Dr. Mann’s proxies. They’ll tell you what the temperature was if you know what you want the temperature to have been.
    So is Mann admitting previous research (no MWP) was a waste or lie or what?
    cn

  22. Alan S. Blue says:
    April 11, 2013 at 11:11 am
    It would be interesting to have an ongoing chart of the -residuals- of all of the competing models. Or, at least, the running least-squared error between models and observations. Both as independent models and as the “ensemble”. This is a pretty stock method of comparing models with reality, I know of no legitimate reason to avoid this for climate science.

    *******
    This was actually done (at least in part) in my paper

    Scafetta N., 2012. Testing an astronomically based decadal-scale empirical harmonic climate model versus the IPCC (2007) general circulation climate models. Journal of Atmospheric and Solar-Terrestrial Physics 80, 124-137.

    http://www.sciencedirect.com/science/article/pii/S1364682611003385

    see Figure 6.

    http://people.duke.edu/~ns2002/pdf/ATP3533.pdf

    ****************************
    by the way,

    for those who might be interested, I just published a new paper

    Scafetta, N., O. Humlum, J.-E. Solheim, and K. Stordahl, 2013. Comment on “The influence of planetary attractions on the solar tachocline” by Callebaut, de Jager and Duhau. Journal of Atmospheric and Solar–Terrestrial Physics. DOI: 10.1016/j.jastp.2013.03.007

    http://authors.elsevier.com/sd/article/S1364682613000837

    http://people.duke.edu/~ns2002/pdf/ATP_3797.pdf

    which rebuts a paper discussed on this website last year.

    http://wattsupwiththat.com/2012/04/15/new-paper-in-the-journal-of-atmospheric-and-solar-terrestrial-physics-demonstrates-that-planets-do-not-cause-solar-cycles/

  23. Just remember – these people are getting paid to write this stuff…and WE are footing the bill. I’m afraid the joke’s on us…

  24. “MiCro says:
    April 11, 2013 at 11:58 am
    I haven’t been able to find the paper I read it in, but I read years ago that modelers had to jack up sensitivity to Co2 to get the models to increase temps as measured, and while there’s nothing wrong with doing something like that to guide research for a physical mechanism, it’s not proof.”

    It is perfectly legitimate to modify all and any variables in any computer model to see what the projected output is. What is NOT legitimate is to then state that that model is reality. I am still astonished that the whole AGW scam is based on giving precedence to the output of models over real world data – even more so, that people don;t get that this is not science but dogma.

  25. ‘Medieval Climate Anomaly’

    I like it. Having refused to admit it’s existence for the last 15 years or so, they have to rename it something else. Note MWP still did not exist, but there was MCA at about the same time. LOL

    Then we note a nuance of the new spin , note the word “anomaly”, ie that which is abnormal. It can’t be “normal” because it was not produced by CO2. It is not a natural ‘warm period”, it is anomalous.

    Of course the models,being “tuned” to best match the last half of the 20th c record do not even hind-cast the first half. What hope of reproducing anything that far outside the calibration period?

    And to think these jokers are marking up career brownie points by publishing this drivel.

    Yet more evidence of the widespread corruption of science and abandonment of the scientific method.

  26. Why have they started calling it the Medieval Climate Anomaly? It lasted for over two centuries. Is it the same PR trick as changing AGW to Climate Change?

    How can they now be sure that that is not the normal state of climate, a state that existed for over four thousand years following the demise of the ice age, and repeated for half a century through the time of the Romans?

  27. Oh that this pin head were larger,
    Danceaway, Danceaway, Danceaway all,

    On prancer Mann, On fancy Gore,
    Danceaway danceaway, all

    Smaller feet, smaller reduced to
    Danceing small, all,, feet intangled

    Smile, Dance, show all, you can still
    Dance the hockey stick dance for all,

    Gold, fools gold, mine for all time,
    This CO2 fraud miss-minted rusty coin.

    Oh, that this pin head would just stop
    srinking, shrinking no room for all.

  28. Tez says:
    April 11, 2013 at 12:45 pm
    Why have they started calling it the Medieval Climate Anomaly? It lasted for over two centuries. Is it the same PR trick as changing AGW to Climate Change?
    =======================================================

    Why? Because they are fanatical ideologues. Ergo – extremely dangerous.

  29. @Chuck
    “We said it was a “multi-million dollar system that will tell you where you are as long as you tell it where it is.”

    LOL!

  30. Alternative abstract
    Reconstructions of past climate show notable temperature variability over the past millennium, with relatively warm conditions during the ‘Medieval Climate Anomaly’ (MCA) and a relatively cold ‘Little Ice Age’ (LIA). We have tweaked multi-model simulations of the past millennium together with a wide range of reconstructions of Northern Hemispheric mean annual temperature to separate model inconsistency from 850 to 1950CE into components attributable to external forcing and internal model variability. We find that external model tweaking contributed significantly to long-term temperature variations irrespective of the proxy reconstruction, particularly from 1400 onwards. Over the MCA alone, however, the effect of model tweaking is only detectable in about half of the reconstructions considered, and the response to forcing in the models cannot explain the warm conditions around 1000 [years before the present] seen in real data. We use the residual from the detection analysis of abberant models to estimate internal variability independent from climate and find that the recent observed 50-year and 100-year hemispheric model trends are substantially larger than any of the measured temperature trends even using the large residuals over the MCA. We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900, but for the first time we are also able to detect a complete lack of any contribution from greenhouse gas variations to the cold conditions during 1600-1800. The proxy reconstructions tend to show a smaller forced response than is simulated by the models. We show that this discrepancy is likely to be, at least partly, associated with the difference in the response to large volcanic eruptions between the complete lack of response of reconstructions and model simulations.

  31. Can the climate models explain Michael Mann? if not, can we really be sure he exists? Is it possible he’s just an epiphenomenon?

  32. So “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900, but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800.”…
    Thus the cold winters come from global warming. Next, glaciations are great whiffs of warming too… QED.

  33. So he admits that there IS a medieval warming period – what does that say about his hockey stick which denies it existed?

  34. “We show that this discrepancy is likely to be, at least partly, associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations.”

    Looking at the 1000 year climate simulations and focusing on the 1750 to present time segment,
    we can also see a discrepancy between observations( Berkeley Earth) and the model results.
    The discrepancy is systematic: models tend to overestimate the cooling response to volcanos and tend to predict a faster “rebound” than observations show. This would point to two areas that models need improvements in. go figure. you build a model. you run it. you find the systematic issues. you fix them.

  35. Mark W… right on: the Medieval Warm Period is gone so only the Medieval Climate Anomaly exists now!
    Isn’t that funny that everything is an “anomaly” supposedly deviating from a “normal” climate… that is stable? This reminds us of the “perturbations” supposed in meteorology to disturb a field that was normal, fine, healthy, clean, loving, happy and most importantly stable. This vision is so obsolete but very useful for the IPCC and other Mann and warm mongers.

  36. Steven Mosher:

    Your post at April 11, 2013 at 1:50 pm says

    “We show that this discrepancy is likely to be, at least partly, associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations.”

    Looking at the 1000 year climate simulations and focusing on the 1750 to present time segment,
    we can also see a discrepancy between observations( Berkeley Earth) and the model results.
    The discrepancy is systematic: models tend to overestimate the cooling response to volcanos and tend to predict a faster “rebound” than observations show. This would point to two areas that models need improvements in. go figure. you build a model. you run it. you find the systematic issues. you fix them..

    No, I will NOT build the climate model you suggest because I don’t understand climate sufficiently well to build one that will reveal systematic errors that can be corrected.

    Of course, I am not alone in this ignorance of climate. Everybody has it.
    NOBODY UNDERSTANDS CLIMATE SUFFICIENTLY TO BUILD A CLIMATE MODEL AND TO DO AS YOU SUGGEST.

    The problem is that the existing climate models have been built by people who pretend they do not share this ignorance of climate. They do.

    Richard

  37. “This claim is highly unlikely given that ice cores show CO2 levels only changed by less than 10 ppm from 1600-1800, and the effect of 10 ppm CO2 on the climate today remains undetectable even with modern instrumentation.”

    You cannot talk about a 10ppm “change” without understanding the fundamentals

    A change from 10 to 20 is about 3.7 watts

    A change from 170 to 180 is about .3 Watts

    A change from 275 to 285 is about .2 Watts.

    A change from 380 to 390 is about .13 watts

    • Steven Mosher says:
      April 11, 2013 at 2:08 pm

      You cannot talk about a 10ppm “change” without understanding the fundamentals
      A change from 10 to 20 is about 3.7 watts
      A change from 170 to 180 is about .3 Watts
      A change from 275 to 285 is about .2 Watts.
      A change from 380 to 390 is about .13 watts

      But what’s not stated, is this difference is in the dry air temperature of the clear sky to space.
      On a 35F day that temp was measured with an IR thermometer as -40F, with e at 0.95 that is 159.17 watts/sq M, verses the 50 degree asphalt at 346 watts/sq M, you’re 0.13 watts is -39.91F, 0.09 degrees warmer.
      I measured a 9 degree drop in temps in 11 hours on a clear night, some 4.62-4.88 million joules/sq meter.

  38. Bill Illis, thanks for the link. It does show how they rigged the whole thing, not dissimilar to Marcott in order to show that the last 50 years are “unprecedented”: chose proxy reconstrutions that artifically smooth the past, adjust the models to replicates that stuff, pretend the slight differences can be explained by natural causes and then graft the HADcruT. Elementary my dear Watson!

  39. Assuming that MWP was a N. Hemisphere initiated event it could be reproduced from other natural climate independent events.
    It is variability in the Arctic Ocean’s currents that is the cause of the most of the climate’s natural variability. Extent of the cold Arctic waters outflow in turn regulates the inflow of Atlantic water warming the Arctic Ocean and consequently regulating the Arctic temperature, which is the main contributor to warming and the initiator of cooling.
    Crucial to this warm-to-cold oceanographic choreography is the Denmark Strait
    Denmark Strait is a bottleneck in a ‘superhighway’ in the oceans’ global circulation . The Arctic overflow water (about 3 Sv), the largest of the deep, overflow plumes that feed the lower limb of the conveyor belt and return the dense water south through gaps in the Greenland-Scotland Ridge.(WHOI)
    In this link

    http://www.vukcevic.talktalk.net/Arctic-NV.htm

    I reproduce temperature changes since 1660, to compare with the CET available data
    - first illustration shows The North Icelandic Jet current -NIJ. At its source the ocean heat loss to atmosphere is generator of the Icelandic Low atmospheric pressure system, determining latitude of the polar jet stream over the North Atlantic.
    The NIJ is a cold current that runs between Greenland and Iceland at a depth of about 600 meters at sea bottom, across the Icelandic plateau.
    The NIJ contributes to a key component of the Atlantic Meridional Overturning Circulation- AMOC.
    - second illustration shows the Denmark Strait’s bathymetry and its critical properties for the passage of the NIJ further south, as the main variable contributory component to the subpolar gyre, the home of the AMO.
    - third illustration shows correlation of the geological records in the area to the past solar activity (for time being an impenetrable geophysical quandary), but it does explain why many credit the sun for the climate’s natural variability.
    - forth illustration shows historic correlation between geological records, the CET and the trailing North Atlantic SST
    - fifth illustration shows the above in more detail.
    - sixth illustration shows change in the local magnetic field (proxy to the geological movements) and its correlation to the global temperature reconstruction.

  40. TomRude says:
    April 11, 2013 at 1:57 pm
    Mark W… right on: the Medieval Warm Period is gone so only the Medieval Climate Anomaly exists now!
    Isn’t that funny that everything is an “anomaly” supposedly deviating from a “normal” climate… that is stable?
    ============================================================

    It’s an abuse of language,.

    Capital offence in my book. A certain Mr. Orwell had much to say about this.

  41. No doubt we will soon be told that the other Holocene Warm Periods were also anomalous. Indeed, it will be that any warmth that is not directly CO2 generated will be anomalous.

    Mann truly is a clown.

  42. @ somebody says:
    April 11, 2013 at 12:01 pm
    “Ice core data shows CO2 levels changed less than 10 parts per million from 1600-1800 during the MWP.”

    I think you meant LIA.

    Garethman, yes, I noticed that, very confusing, is this poor processing or have I missed something?

  43. poooooooottototottitieirghuerhg says:
    April 11, 2013 at 12:05 pm
    Earth to Leif Svalgaard, comments?
    “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900″

    The effect of the solar driver [green line] in last slide of http://home.badc.rl.ac.uk/mjuckes/meetings/reading2012/pdf/schurer_variability.pdf
    is negligible [less than 0.1 degrees]. That leaves the real and large effect from volcanoes.

  44. Steven Mosher says:
    April 11, 2013 at 2:08 pm

    “You cannot talk about a 10ppm “change” without understanding the fundamentals

    A change from 10 to 20 is about 3.7 watts.”

    In some laboratory. Probably an imaginary one. No such calculation has ever been made in the earth’s atmosphere. Your contempt for empiricism is turning into fantasy.

  45. “Michael Mann says climate models prove Kennedy was shot by the CIA from the grassy knoll, also show moon landing was faked….”

    Uhh, right Michael. Perhaps you should tell your fan Stephan Lewandowsky about this.

  46. vukcevic says:
    April 11, 2013 at 2:22 pm
    - third illustration shows correlation of the geological records in the area to the past solar activity (for time being an impenetrable geophysical quandary),
    Not at all, just a spurious correlation without any physical basis

  47. Its politically acceptable to acknowledge a Little Ice Age, but not a Medieval Warm Period. Therefore by fiat, it becomes the ‘Medieval Climate Anomaly’ (MCA).
    What will they call it when the current “interglacial period” descends into the the next glaciation? The low density water period? (LDW)?

  48. ‘Oh! If the computer models can’t really explain it, then we will have to fabricate the gaps.’ So it becomes false!! Simple!

  49. davidgmills says:
    April 11, 2013 at 1:53 pm
    Is Mann saying that the hockey stick for the last thousand years was shaped like a U?
    ———————————–
    Yes, it’s now a warped hokeystick.
    cn

  50. lsvalgaard says: April 11, 2013 at 3:00 pm
    vukcevic says:April 11, 2013 at 2:22 pm
    – third illustration shows correlation of the geological records in the area to the past solar activity (for time being an impenetrable geophysical quandary),
    …………..
    Not at all, just a spurious correlation without any physical basis

    You may call it spurious because either you don’t understand reasons for it (I do not) or it doesn’t suit your science presentation politics (which is your own business), either way it is of no consequence to the correlation’s existence.
    Does it matter?
    It does if true, sunspot as such appears do not have required power to move ocean’s temperature, tectonics does via effect on the ocean currents.
    Shown is the period (1880-2012) where there are good data

    http://www.vukcevic.talktalk.net/SSN+NAP.htm

  51. Steven Mosher says:
    April 11, 2013 at 1:50 pm

    Looking at the 1000 year climate simulations and focusing on the 1750 to present time segment,
    we can also see a discrepancy between observations( Berkeley Earth) and the model results.
    The discrepancy is systematic: models tend to overestimate the cooling response to volcanos and tend to predict a faster “rebound” than observations show. This would point to two areas that models need improvements in. go figure. you build a model. you run it. you find the systematic issues. you fix them.

    This discrepancy is well known. However, ‘fixing’ it requires the CO2 sensitivity to be reduced, which is why it hasn’t been fixed to my knowledge. Although in the, anything is possible, wonderful world of climate science, they may have reduced the CO2 sensitivity in the models and not told anyone, as it’s really not that important.

  52. Steven Mosher says:
    April 11, 2013 at 1:50 pm

    “Looking at the 1000 year climate simulations and focusing on the 1750 to present time segment,
    we can also see a discrepancy between observations( Berkeley Earth) and the model results.
    The discrepancy is systematic: models tend to overestimate the cooling response to volcanos and tend to predict a faster “rebound” than observations show. This would point to two areas that models need improvements in. go figure. you build a model. you run it. you find the systematic issues. you fix them.”

    Mosher’s New Model-Specific Scientific Method. Here it is:

    1 Construct your model.
    2 Run and get results.
    3 Check the results against reality.
    4 If the model failed to predict reality, it is falsified. NO, NO, NO, says Mosher.

    In the New Model-Specific Scientific Method, you change the model. Wow. Amazing. Just add some ad hoc hypothesis and you are on your way. No more old fuddy duddy falsification.

    Mosher, The Galileo of Climate Science.

  53. “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900, but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800. ”

    Aren’t these the same bunch of geniuses who have been giving anyone who has even suggested the Sun might play a role in driving the climate the big horse laugh? And how exactly does “explosive volcanism” drive the climate to something like the MCO? It has been my impression that “explosive volcanism” is considered to be a significant driver of global cooling, not warming.

    I am once more, for more times now than I can even approximate, struck by the towering irony that any Hollywood celebutard, MSM human press release fax machine, or brain dead politician in the world feels free to step in front of any available microphone, camera or keyboard and boldly declare that anyone like myself, who is not willing to be an epistemological mattressback for all of this hyperbolic climate catastrophism, must be some kind of a congenital moron.

    From the beginning of my attempts to understand this topic I have always been seriously underwhelmed by the quality level of the science that has generated this controversy and frankly that view extends to all sides. I have found myself firmly in the “skeptical” camp for several fairly simple reasons

    !) From my study of the philosophy of science, skepticism seems to be the primary and ultimate duty of anyone who seeks to “know” anything about the world and universe we inhabit. Personally I tend toward the view that science, even when done with ultimate rigor and integrity, can only allow us to have slightly stronger suspicions that what has been presented is the best available guess at the moment and that providing actual “knowledge” is beyond its logical capabilities.

    2) The people who inhabit the skeptical side of this controversy seem to do their work with much more of the humility that 1) above suggests to me is the second leading requirement to be a true scientist. They exhibit much less of a tendency to declare that the work they have done definitively “demonstrates” or “proves” anything and generally seem to operate in a manor that cleves much closer to what I think of as the scientific method i.e. openness about methodologies and data including inconvenient or countervailing data which might weaken their argument.

    3)Though I list this third, if I am truly honest with myself, it is probably my number one concern. It is that no one from the skeptical side suggests that their work demands that the world transform itself in ways that are profoundly detrimental to personal liberty, human prosperity, human wellbeing, and in fact the wellbeing of almost all of life on the planet. The “believers” on the other hand act as if the dogmatic certitude of their ends justifies absolutely any means necessary to enforce them on the rest of us. In a sense they are quite correct in their belief that AGW will necessarily turn into CAGW, but they seem incapable of seeing that the real catastrophes have occurred and will continue to occur because of the hugely damaging and ultimately ineffectual remedies for which they demand docile acquiescence from the rest of us. Biofuels, windfarms, carbon taxes and credits and the whole plethora of supposed AGW cures foisted on the world have already inflicted much more damage on human prospects and the global environment than any but the most hyperbolic of AGW catastrophe scenarios have any possibility of matching.

    4) I will add this one even though it will tend to undercut my presentation of myself as an objective observer. In all my time as a denizen of this and other related sites I have never had the pleasure of meeting any of the contributors or commenters whose views on this topic seem anywhere close to my own, but I have always felt that there were a great number I could envision spending a pleasant day or evening with, gathered around a table somewhere, sharing appropriate beverages and perhaps some good cigars and conversing about the climate or any other topic that might arise. Though my personal familiarity with the purveyors of climate dogmatism is no greater than for the folks here, almost none of them have engendered a similar sympathetic response. In fact, I would hesitate to be in the same room with most of them because of a very real fear that I would be faced with a commanding Ben Santer-like compulsion to push a fist through their faces. I haven’t actually struck anyone in anger since I was in the second grade, so I could probably restrain myself, but the prospect of having any fun around these dolts is so slim that it”s not worth the chance that I might not. In the end, even if they should somehow miraculously convince me of the correctness of their position, I would still have a difficult time aligning myself with them, because they almost all strike me as a bunch of j**koffs!

  54. vukcevic says:
    April 11, 2013 at 3:52 pm
    Does it matter?
    Yes, because it leads you to ill-founded conclusions. Next question: so what? And indeed, so what that you draw ill-founded conclusions? That matters because it dilutes the science-content of WUWT.

  55. Theo Goodwin says:
    April 11, 2013 at 4:12 pm
    Steven Mosher says:
    April 11, 2013 at 1:50 pm

    “Looking at the 1000 year climate simulations and focusing on the 1750 to present time segment,
    we can also see a discrepancy between observations( Berkeley Earth) and the model results.
    The discrepancy is systematic: models tend to overestimate the cooling response to volcanos and tend to predict a faster “rebound” than observations show. This would point to two areas that models need improvements in. go figure. you build a model. you run it. you find the systematic issues. you fix them.”

    Mosher’s New Model-Specific Scientific Method. Here it is:

    1 Construct your model.
    2 Run and get results.
    3 Check the results against reality.
    4 If the model failed to predict reality, it is falsified. NO, NO, NO, says Mosher.

    In the New Model-Specific Scientific Method, you change the model. Wow. Amazing. Just add some ad hoc hypothesis and you are on your way. No more old fuddy duddy falsification.

    Mosher, The Galileo of Climate Science.

    Really, this type of mockery ill-becomes you. I guess if you had your way, the first time someone attempted to model physical reality using finite element analysis and failed, they should have just packed it up and gone home, rather than gather data and attempt to refine the model. Current climate models may be wrong, inelegant, and prone to belching in polite company for all I know. The crucial objection is that the current crop of not-ready-for-prime-time computer programs are ill-suited for determining how we intend to spend the public’s money, not that they are a condemnation of models per se.

  56. Is it just me or does their presentation seem less than professional? The conclusions might be wrong too, but the pictures and the like remind me of a term paper.

  57. Theo Goodwin says:
    April 11, 2013 at 4:12 pm

    ——

    I don’t know Theo, I use successive approximation so often that it’s practically my philosophy for living. :) I’ve got to admit that I very rarely get anything complicated right the first time.

  58. D.J. Hawkins says:
    April 11, 2013 at 5:11 pm

    “Really, this type of mockery ill-becomes you. I guess if you had your way, the first time someone attempted to model physical reality using finite element analysis and failed, they should have just packed it up and gone home, rather than gather data and attempt to refine the model.”

    I don’t know about Theo’s view, but as for me my objections are based on my own perception that they seem to spend much less time trying to refine their models to match the data from physical reality than they do trying to “refine ” the data to match their models.

  59. Like it or not, She is in control.
    No amount of taxes paid to soothsayers will calm Her tempests.
    Maybe, She works in (unpredictable) cycles.
    Best to be prepared for Her fits.

  60. Wow! On Tom Nelson’s blog you can find a ClimateGate email exchange between Mann and Phil Jones where they discuss how to manage the problem of the MWP. The exchange took place in 2003, ten years ago, where they talked about enlisting the assistance of staff at the AGU’s EOS publication in helping to “contain” the “putative” MWP. Here: http://tomnelson.blogspot.com/2011/12/mann-would-be-nice-to-try-to-putative.html

    Now he is admitting that the MWP existed?

    It has been obvious that Mann has been aware of the problems that the MWP and LIA present for the theory of Global Warming for years. Still he presses on because, for some reason, people want to buy what he is selling. How this guy has been able to maintain his job as a scientist, and why people continue to publish what he says completely baffles me. If people simply stopped listening or paying any attention, that would be the end of it.

    It is like a medieval belief in witches and spells. The people who attend to this nonsense are as guilty of perpetuating it as the alarmists themselves.

  61. Dave Wendt said:
    ,“[T]hey seem to spend much less time trying to refine their models to match the data from physical reality than they do trying to “refine ” the data to match their models.”

    To which I would add: “And then refine their models to match reality.” Rinse and repeat.

  62. D.J. Hawkins says:
    April 11, 2013 at 5:11 pm
    Mark Bofill says:
    April 11, 2013 at 5:23 pm

    I did not have time to make an extended comment. I took for granted that the context is scientific theory. Models are great analytic tools but cannot substitute for scientific theory. Models are wonderful in many contexts and essential for solving many important problems.

    However, if you want to argue that models can substitute for scientific theory, I will argue to the death on that one.

  63. There is no point in gearing the models to reproduce reality because it cant be done..
    Im sure they have tried and tried again to input the past and every variable under the sun, including the sun to find a pattern.. A constant state of flux and balance in a living organism (our climate) is like trying to model what Im going to do next.. Bathroom, fridge or shopping, maybe another glass of wine.. I dont even know until the urge hit me..

    Ever think our climate operates in the moment, for the moment, in spite of the moment..
    Effortlessly regulating its needs for no apparent reason.. No rules no roads, just energy transfer because there is so damn much of it there is nothing else for it to do..

    How do you model that?

  64. Dave Wendt says:
    April 11, 2013 at 5:50 pm
    D.J. Hawkins says:
    April 11, 2013 at 5:11 pm

    “Really, this type of mockery ill-becomes you. I guess if you had your way, the first time someone attempted to model physical reality using finite element analysis and failed, they should have just packed it up and gone home, rather than gather data and attempt to refine the model.”
    – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
    I don’t know about Theo’s view, but as for me my objections are based on my own perception that they seem to spend much less time trying to refine their models to match the data from physical reality than they do trying to “refine ” the data to match their models.

    Theo either has a serious issue with Mosher or a bad night’s sleep recently. He mocked what I view as a simple, straightforward presentation of the proper way to go about modelling in general, simply because it came from Mosher. I don’t disagree that there appears to be a great deal of “don’t look at the man behind the curtain” attitude amongst the warmanistas, but let’s try not to match their rigidity, eh?

  65. I’m still hung up on volcano’s..
    Our planet and all the life on it, including our climate has been able to handle eruptions big and small.. One medium eruption can put out more CO2 than the entire industrial revolution to date..

    How can you come to the conclusion that Mann’s industrial eruption over the last 150 years is any different than any other volcanic eruption? CO2 is simply CO2 isnt it..

    Never mind the ash and what it does over the short term.. We are talking about 150 years worth of Mann’s CO2 put into our atmosphere in 18 months..

    Again and again..

    It makes absolutely no logical sense at all that CO2 drives AGW..

    Volcano’s came first with life and our climate coming second.. The fact that we are here is proof positive that our climate can regulate CO2..

    AGW is green political nonsense..

  66. Jay says:
    “One medium eruption can put out more CO2 than the entire industrial revolution to date..”

    And here’s what the USGS says:

    “Gas studies at volcanoes worldwide have helped volcanologists tally up a global volcanic CO2 budget…. and studies show that globally, volcanoes on land and under the sea release a total of about 200 million tonnes of CO2 annually. seems like a huge amount of CO2, but…while 200 million tonnes of CO2 is large, the global fossil fuel CO2 emissions for 2003 tipped the scales at 26.8 billion tonnes. Thus, not only does volcanic CO2 not dwarf that of human activity, it actually comprises less than 1 percent of that value.”

    Jay, could you explain that monumental discrepancy. Where did you come up with that ‘information’? JP

  67. I have a question for Dr Mann:

    If as you say you found external forcings (solar/volcanism) pushed the temperatures down between 1400-1900, in the absence of these external forcings (1900-present) should we not expect temperatures to then bounce straight back up?

    It’s like a ball floating in water. Apply force to the ball and it sinks. Remove the force and it rises again back to its natural state.

  68. thesdale says:

    “… should we not expect temperatures to then bounce straight back up? It’s like a ball floating in water. Apply force to the ball and it sinks. Remove the force and it rises again back to its natural state.”

    Thesdale, the atmosphere is more complex than the water in your analogy. And there are ‘forcingS’, whereas your analogy has only one forcing. The ‘ball’ will come back up, but it doesn’t necessarily “…bounce straight back up… JP

  69. dynam01 says:
    April 11, 2013 at 6:03 pm
    To which I would add: “And then refine their models to match reality.” Rinse and repeat.

    To which I would observe if that were the case the models would converge on reality when in fact they are in parabolic free flight away from reality. You have surely seen the charts that depict this.

  70. John Parsons says:
    April 11, 2013 at 8:31 pm

    thesdale says:

    “… should we not expect temperatures to then bounce straight back up? It’s like a ball floating in water. Apply force to the ball and it sinks. Remove the force and it rises again back to its natural state.”

    Thesdale, the atmosphere is more complex than the water in your analogy. And there are ‘forcingS’, whereas your analogy has only one forcing. The ‘ball’ will come back up, but it doesn’t necessarily “…bounce straight back up… JP

    So apply 37 different forcings (that should be enough, eh?), all components resolving to the same vertical temperature force and you’d have “thesdale’s” base case without pontificating needlessly to obfuscate his point. But confusing the issue was your main objective, wasn’t it, John?

    Or should I simply state that the overall results are the same whether it’s one or 37 forcings. Once the negative forcings are eliminated, temperature has but one general way to go–and that is up. And since the bottom of the LIA, that’s pretty much what temperature has done (with a few plateaus along the way just to make it interesting). We haven’t seen it go down significantly, which proves “thesdale’s” point.

  71. Mosher writes “You cannot talk about a 10ppm “change” without understanding the fundamentals”

    I find that statement slightly ironic when you’ve assumed 3.7W when doubling from 10ppm to 20ppm. Who said the response was linear over such a wide range of doublings? For example would you also expect a 3.7W effect going from 1 to 2ppm? How about 0.001 to 0.002ppm?

  72. lsvalgaard says: April 11, 2013 at 4:35 pm
    Yes, because it leads you to ill-founded conclusions. Next question: so what? And indeed, so what that you draw ill-founded conclusions?
    ………….
    ill-founded conclusions?
    Nonsense, more likely it doesn’t suit your science presentation politics.

  73. DD More says:
    April 11, 2013 at 11:28 am
    //////////////////////////////////////////////
    Further to your comment.

    Despite claims to the effect that CO2 is a well mixed gas, CO2 is not particularly well mixed and its concentration varies quite substantially between seasons, and even the time of day.

    The experiments to which you refer (performed in the 1800s and early 1900s) appear to have been conducted to a high standard with fairly accurate equipment. These experiments appear to have been dismissed without (in my opinion) a well and sound reasoned explanation. If their findings were valid, it would destroy the CO2 induced warming conjecture (this may be the motive behind their dismissal).

    I am of the view that those experiments should be replicated today. The same sites should be sampled, at the same time of year (and time) and the results analysed using the same equipment and methodology.

    If these experiments were replicated, we would have a much better appreciation of the comparison of today’s levels of CO2 with past levels of CO2 in the 1800s and early 1900s. This would be useful and valuable.

  74. TimTheToolMan says:
    April 11, 2013 at 11:36 pm
    ///////////////////////////////////////////
    Sensitivity to CO2 (if Earth’s climate is at all sensitive to that gas) must have varied greatly over time, and over concentration levels otherwise the oceans would not have formed or would have boiled away, long ago. The earth would be like Venus (not necessarily for the same reasons).

    How many doublings of CO2 have there been over the entire history of our planet?

    It appears that the earliest atmosphere was hydrogen and helium, and it was only through later volcanic activity that CO2 was spewed into the atmosphere. During the first eruptions, CO2 must have been a minimal component in the atmosphere. So logic suggests that there must be literally hundreds of doublings.

  75. fobdangerclose says:
    April 11, 2013 at 12:46 pm

    Oh that this pin head were larger,
    Danceaway, Danceaway, Danceaway all,

    On prancer Mann, On fancy Gore,
    Danceaway danceaway, all

    Smaller feet, smaller reduced to
    Danceing small, all,, feet intangled

    Smile, Dance, show all, you can still
    Dance the hockey stick dance for all,

    Gold, fools gold, mine for all time,
    This CO2 fraud miss-minted rusty coin.

    Oh, that this pin head would just stop
    srinking, shrinking no room for all.

    ——————————————————————————————————————-

    Very GOOD! Smiling as I write. Conjures the image beautifully.

  76. D.J.Hawkins, I agree that Mosher gave a pretty tepid view of what modeling should be about. However, I think the problem is, that is not what we have been seeing from the modeling community. What we have seen is blatant apptempts to support “The CAUSE”. In real science we should see competing methodologies from the various modeling camps. Instead, we see a rigid approach where GHGs are the only possible driver of climate change. I think that is what drove Theo’s disdain for Mosher’s comment. Mosher’s comment ignored reality. Dave Wendt hit the nail on the head.

  77. fobdangerclose says:
    April 11, 2013 at 12:46 pm

    You’ve stuck this picture in my head! If this was the late 19th century I’d expect to see a tin kids game with all this prancing and precarious balance! How about an Ap? The Climate Science Ap? Updated as they fall off?

  78. ****
    richard verney says:
    April 12, 2013 at 3:23 am

    Despite claims to the effect that CO2 is a well mixed gas, CO2 is not particularly well mixed and its concentration varies quite substantially between seasons, and even the time of day.
    ****

    Richard, the GHG effect of CO2 is only important at high altitudes (say, above 30000 ft). Ground CO2 has little GHG effect.

  79. Theo Goodwin says:
    April 11, 2013 at 6:07 pm

    However, if you want to argue that models can substitute for scientific theory, I will argue to the death on that one.

    ————

    No, I’m only addressing this because I don’t want you walking away thinking that’s my position. All I was saying is, I don’t see anything unreasonable about refining a model by comparing it to reality, looking for systemic shortcomings, and correcting them. It’s not like they’re going to be able to ‘black box’ it, by fiddling with knobs until they get it empirically correct without understanding what’s really going on. You can make it match the past that way but you’ll never get it to predict the future at all doing that. Maybe we will never get it right; maybe we don’t understand enough of what’s going on. Still, looking at where why and how the models fail to match reality can provide valuable insight into what we don’t know about the system.

    People who make claims based on climate models irritate me as much as they irritate you, just so you know. :)

  80. beng says:
    April 12, 2013 at 5:55 am
    ****
    “richard verney says:
    April 12, 2013 at 3:23 am

    Despite claims to the effect that CO2 is a well mixed gas, CO2 is not particularly well mixed and its concentration varies quite substantially between seasons, and even the time of day.
    ****

    Richard, the GHG effect of CO2 is only important at high altitudes (say, above 30000 ft). Ground CO2 has little GHG effect.”

    So, the calculation of PPM is made at high altitude only? And the PPM reported does not include the CO2 that is lower than the high altitude?

  81. D.J. Hawkins says:
    April 11, 2013 at 6:40 pm

    I am depending on my prior knowledge that Mosher believes that models can substitute for scientific theory. I should have stated as much. Having done so, I now repeat that anyone who believes that models can substitute for scientific theory understands neither of them.

  82. Volcanoes seem to be the dark energy hole where model error can be assigned as needed, more in some cases and ignored in others. I will remind readers that there is no global index of volcano emissions, it is a model dumping ground instead.

  83. Jay says April 11, 2013 at 7:11 pm

    Volcano’s came first …

    What? Pls, for future use, the plural form (meaning or indicating two or more of something) of volcano is “volcanoes” (I double checked that too!)

    If you were to refer to a volcano’s plume or ash cloud, in this case the singular possessive form “volcano’s” is appropriate (the plume essentially belongs to the volvaco!)

    (Pls bear with me on this; it is the one of the few pet peeves grammatically that sets me off … as not all who post here are native-English speakers/writers, please pardon me if this interruption in the dialog seems unwarranted.)

    Plural and Possessive – usage and syntax

    .

  84. Dave Wendt said:
    ,“[T]hey seem to spend much less time trying to refine their models to match the data from physical reality than they do trying to “refine ” the data to match their models.”

    dynam01 says April 11, 2013 at 6:03 pm
    To which I would add: “And then refine their models to match reality.” Rinse and repeat.

    Intractable solution. That is, “problems that can be solved in theory (e.g., given infinite time), but which in practice take too long for their solutions to be useful, are known as intractable.”

    Take the last seven days here in Texas, the first four days we had low-overcast over half the state (and on northward into Oklahoma) and clear skies for the remainder, resulting in 90 degree high temperatures over those areas that saw ‘sun’ … while the overcast portion saw only 70’s as the high temp; with the cloud deck resulting in near 100% albedo for insolation (save for that small portion absorbed since we had _low_ overcast) for that large area and four-day timeframe … and THAT’S a lot of Energy! … Now, how is that accounted for macro-scale-wise in a GCM (model) given Hadley Cell circulation and Rossby waves and all?

    Are misc fudge factors utilized? Are arbitrary ‘confidence’ figures and various ‘odds’ values used to calculate the chance occurrence of a ‘system’ as I described above? How predictable, how often do meteorological conditions allow such a setup, followed by a cold front and upper-level low initiating a *wide* band of showers having just today moved off the eastern shore but still affecting New England states and Canada in the models? Two, three, half a dozen a season? The same goes for hurricanes and other large, synoptic scale * ‘events’.
    .

    * Synoptic scale: In meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 km – 620 miles or more.
    .

  85. Theo Goodwin says:
    April 12, 2013 at 8:12 am
    //////////////////////////////
    Further to your post, Mauna Loa is about 13,500ft, so quite a bit under half the 30,000ft suggested by Beng.

    What about the CO2 measurements obtained from ice? From what height was this CO2 sequestered? Once again, probably considerably less than 30,000 ft.

  86. Could the 1,000,000 °C temperature a mile under the earth according Al the Gore have anything to do with global warming?

  87. Hey Penn State, you fired the wrong guy…hello, Happy Valley…yes somebody please pick up…Hello Mcfly, you there???

  88. A rather late comment to this thread, so I guess it is one for the archives.

    Further evidence that the MWP was a global event, see: http://www.dailymail.co.uk/sciencetech/article-2308225/Mayans-wiped-drought-say-scientists-tests-temple-beam-confirm-accuracy-ancient-calendar.html

    There is debate as to whether the Mayan civilisation collapsed sometime before 1100AD because of climate change, and in particular drought.

    I have on a number of occasions mentioned the Incas of Peru, whose civilisation peaked in the 14th century, and the settlement at Machu Picchu. In and around this settlement, there are stepped plateaus which many archaeologists consider were made for farming/agriculture. These archaeologists consider that the Incas farmed at height. It is not possible today to farm at this height in these latitudes, and the inevitable conclusion is that at the peak of the Inca settlement, the climate must have been warmer than today. Again, it is mooted that the settlement collapsed when this warm period was over and when the climate began to cool so that farming and agriculture was no longer viable.

    The Archaeological evidence of both the Mayan and Inca civilisation suggests that there was a warm period in the Southern Hemisphere, and it would appear that the climate must have been warmer than today.

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