Saturday, May 12, 2012

The Medieval Warming Period and the Climate Stasis Hypothesis

 Did Eric the Red really colonize Greenland?  If so, was the weather warmer back then, or was it all a conspiracy?

    The historicity of the Medieval Warming Period is a minor controversy these days.  Almost everyone accepts the data from the 20th Century which shows that global average temperature has increased by about 1.0 degrees Celsius since about 1908.  By the same token, there is only a minor embarrassment that the temperature rise leveled off from about 1946 through 1975, and that once again the temperature rise has slowed since 2002.  This data is not in serious dispute, or at least it is not disputed by the Village Elliot. 

   Given that global temperatures have risen, the next question is whether human activity has been the primary cause.  Conventional wisdome is that human activity is absolutely implicated, based on the presumption that the average temperature of the earth has remained constant, plus or minus about 0.5 degrees Celsius, for thousands of years (referred to as the Climate Statis hypothesis; i.e., that climate change is definitely not natural or at least not on the timescale of "only" 100 years or so).  Hence a temperature rise of 1.0 degrees Celsius is too much to attribute to non-anthropogenic causes, and thus the CO2 Greenhouse Effect can safely be identified as the sole cause for the temperature rise.  Moreover, many mainstream climatologists argue that the world is headed for a climate catastrophe, and major changes are required in the global hydrocarbon economy in order to avert disaster.  

    The Village Elliot is not on board with some of these key principles, despite the fact that the persons making these assements are much better qualified and well studied in these matters.  In particular, I suggested in my last blog that historical climatology is basically blind as a bat if it could not see much unusual about 1816, the Year Without a Summer, in which snow fell year round.  It is thought that tree ring data provides information about the temperature in any given year, which I find amazing, given that on three continents trees reportedly failed to even grow rings that year because they stayed dormant.  The cooling of 1816 was caused by a massive volcanic eruption at Tambora, Indonesia and does not directly affect the CO2 Greenhouse hypothesis.  It does call into account whether the historical records of the 19th century are worth a darn, and specifically whether they allow us to rule out climate change caused by factors other than carbon dioxide.  

    Let us then turn our attention to the Medieval Warming period.  As is the case with the Year Without  a Summer, the Medieval Warming period used to be a historical fact.  Eric the Red colonized Greenland  at the end of the 10th century.  The Vikings flourished there, so that by the 13th century there were over 3000 colonists in 300 farms.   

Some historians have suggested that Eric named Greenland simply as a propaganda ploy to attract new residents.  Maybe so, but someone had to convince crops to grow in a short growing season, and people and livestock to not freeze to death once they did settle there.  These seem close to being historical facts which can not be easily overturned. 

Yet, according to conventional wisdom, global average temperatures changed only slightly during this period, and even the localized temperatures in the North Atlantic were cooler than they are today.

The Village Elliot wonders how this could be true.   Even with today's agricultural technology, it is very difficult to farm in Greenland.  To think that thousands of Vikings could be farming in a wintry wasteland does not make sense.  Morever,  Antactic Ice core data supports the notion that this period was indeed warmer than the later period.  This, plus the general dominance of the Vikings during those centuries, strongly implies that the temperatures were much warmer during that period.

Moreover, the Vikings were not the only group that settled Greenland.  It turns out that the aboriginal Tuniit and Inuits also greatly expanded their territory in Greenland coming from from the northwest, and thrived for a time before receding significantly during what historians can the Little Ice Age (but which most climatologists call a 0.5 degree temperature dip).     

Why it Matters

   The existence or nonexistence of the Medieval Warming period does not contradict the reality of the CO2 Greenhouse effect.   Rather, the reality of absorption of thermal energy by carbon dioxide is pretty much undisputed.   The advancement of the Climate Stasis hypothesis, or the notion that the climate never changed much prior to the 20th century. mainly serves to confuse the modelers and perhaps impart some errors into the assumptions that go into current climate models.  Namely, we may be left with a model of a robust terrestrial climate, which suggest that the earth's average temperature is not strongly affected of volcanos such as Tambora.  The models further suggest that the Year Without a Summer and the Medieval Warming Period never happened, or at least that they were greately exaggerated.  Hence this might lead to understimation of effects other than carbon dioxide.  Moreover, most climate historians seem content with the view that recent climate has been fairly static. 

   The Village Elliot, however, is a habitual contrarian.  Certainly I do not have the tools to prove or disprove the consensus views of professional climatologists.    Nevertheless, in my opinion--and it's just an opinion--future  more objective reviews of history will lead probably climatologists to conclude that there are indeed other factors worth worrying about in addition to  carbon dioxide.   From the standpoint of politics, however, this is a heretical prediction, as we've pretty much settled on a policy of reducing carbon emissions even if it retards economic growth.  

Oct 30, 2012 Post Script:  It turns out that at least one recent peer reviewed study in fact has in fact vouched for a warmer Warming Period and a cooler Little Ice Age.  You may read about  it here:

Additional Reading

Check out the present average monthly temperatures in Greenland, and tell us how Vikings were able to grow crops there if the temperatures were lower in the 10th century than they are now...

Kim, B.; Yoon, Ho Il; Kang, Cheon Yun; Bahk, Jang Jun (2002). "Unstable Climate Oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula". Quaternary Research 58 (3): 234

J. Fabres et al., Branfield Basin fine-grained sediments:  Late Holocene Sedimentary Processes and Antarctic Oceanographic Conditions, The Holocene vol. 10 no. 6 703-718

Intergovernmental Panel on Climate Change Working Group I: The Physical Science Basis of Climate Change    

Climate Change in the Baltic Sea Area, HELCOM Thematic Assessment in 2007, Baltic Sea Environment Proceedings No. 111 Helsinki Commission, Baltic Marine Environment Protection Commission



  1. Since my comment here is long, I will have to divide it into separate comments. Here is the first part:

    In my comment on your post "The Significance of the Year Without a Summer," I showed that ice core and tree ring proxies (and other types of proxy data) faithfully recorded evidence of the Tambora eruption and the years after it. In addition, data for dozens of eruptions were referred to in my comment unequivocally showing that paleoclimatologists not only are not blind as bats, but can see quite well events such as volcanic eruptions, including those that there are no human descriptions of and only show geologic evidence for now.

    Elliot, as I have never heard of the “Climate Stasis Hypothesis” I googled it and the only entries that I came up with that fit the whole term were from your blog. So I have to ask you, did this originate from you? In my review of the literature, I have found no mention anywhere of climate stasis, either in the last millennium, or in the Holocene in general. So what do you base your hypothesis on? Would you mind being a little more specific and detailed about your Climate Stasis Hypothesis? What literature did you review to arrive at this hypothesis? An example of Holocene climate variability report is Mayewski et al. (2004; These authors describe six periods of rapid climate change during the Holocene Period. Also there is Masson et al. (2000;, which suggests that there were 9 aperiodic millennial scale oscillations during the Holocene. Schulz and Paul (2002; describe temperature oscillations during the Holocene based on oxygen isotope data from Greenland ice cores, and suggest a 900-year periodicity of climate fluctuations, which they said could be correlated to climate fluctuations in northern and central Europe. There are dozens of other papers that describe Holocene variability based on everything from tree rings and ice cores to chironomid bugs and packrat midden. I think it’s pretty well established that paleoclimatologists acknowledge climate variability, both in the last millennium and the entire Holocene.

  2. Paleoclimatologists acknowledge climate variability in the last thousand years. Even the Mann Bradley Hughes (MBH), “Hockey Stick,” maligned for years by skeptics, acknowledges variability in the last 1000 years. They discussed the long term cooling trend before the Industrial Revolution in their 1999 paper, something people who have not read the paper seem to be unaware of, or perhaps skeptics who did read the paper have forgotten. At the time around 1100 AD, according to the hockey stick, global temperatures were about the same as the MBH calibration period (1902-1980). The years 1500 to 1900 were significantly cooler than the years 1000 to 1500 on the “Hockey Stick,” with a significant drop off of about 0.3°C around the year 1450 and a partial recovery by 30 to 40 years later.

    I know that you are aware that there are at least a dozen other studies, all of which graphically display data illustrating the warmer Medieval Climate Anomaly (MCA) and the cooler Little Ice Age, but with modern temperatures far exceeding even the warmest part of the MCA. I know you have seen the famous compilation of the graphs: And this compilation does not include numerous other studies which I am sure you are aware of, all of which indicate the existence of the MCA and the Little Ice Age (LIA). But for readers of your blog who might not be aware of them, here are links to a few of those studies, some of which only include the abstract:

    Attributes all of these studies have in common is that they show a warmer Medieval Climate Anomaly, a cooler Little Ice Age, and a rise in temperature in the 20th century far in excess of the MCA, and whose rate of rise is far faster than the MCA.

  3. The MCA has now been fairly well delineated, although much work remains to fill in details. Regional climate patterns that emerge for the MCA are an extended period of atypically dry climate in the southwest US, stronger than average Asian monsoons, wet conditions over much of tropical South America, dry conditions in equatorial East Africa, wet conditions in South Africa, a dry wetern Mediterranean region, and wet northwestern Europe (Seager and Burgman, 2011,; Seager et al., 2007,; Cook et al., 2009,; LeBlanc et al., 2004,; and other pubs). Coral oxygen isotope data from Palmyra in the central equatorial Pacific Ocean showed that sea surface temperatures were likely reduced throughout most of the MCA (Cobb et al., 2003, Evidence suggests that the warm climate in Greenland and northern Europe during the MCA was mainly due to a persistent positive North Atlantic Oscillation and a strong Atlantic Multidecadal Oscillation (Trouet et al., 2009, The regional patterns described above, along with the likelihood of relatively cool tropical Pacific sea surface temperatures, and a persistent positive North Atlantic Oscillation strongly suggests that during much of the MCA temperature and precipitation patterns fit a persistent La Niñ pattern, not conducive to overall global warmth.

    As far as southern Greenland is concerned, the postitioning of the Northern Annular Mode with respect to the North Atlantic Oscillation probably played a large role in the above average warmth. The Viking establishments were at the southwestern corner of Greenland, a location subject to the Foehn Effect.

  4. This comment has been removed by the author.

  5. This comment has been removed by the author.

  6. Elliot, to get an idea of the progress that has been made in Medieval Climate Anomaly (MCA) research, read the introduction to this paper by Graham et al., 2010 ( Here are a couple of excerpts from the introduction of that paper:

    "While many of these records show indications of notable climate shifts associated with the MCA, it became apparent that this period was characterized not by uniformly warmer temperatures, but rather by a range of temperature, hydroclimate and marine changes with distinct regional and seasonal expressions (Folland et al. 1992; Hughes and Diaz 1994; Bradley 2000; Bradley et al. 2003)."


    "Given the well established associations between winter North Pacific circulation patterns, cool season precipitation over the western US, and interannual-to-interdecadal SST variability in the tropical Pacific (Bjerknes 1969; Lau 1985; Schonher and Nicholson 1989; Mantua et al. 1997; Rajagopalan et al. 2000), the proxy evidence is consistent with the idea that MCA aridity in the American West (and contraction of the Aleutian Low) was a response, at least in part, to cooler central and eastern tropical Pacific SSTs. This idea has been explored by consideration of available proxy data and model results (Graham et al. 2007; Seager et al. 2007a, 2008)."

    And here is an excerpt from the review paper by Seager and Burgman, 2011 that I referred to earlier:

    "The hydroclimate of the Medieval period…features some dramatic anomalies with respect to the modern climate. Perhaps the most remarkable are the series of multidecadal “megadroughts” that struck vast areas of Southwest North America which combined to create a generally more arid climate in the region that lasted centuries. These are well documented from tree-ring records (Herweijer et al., 2007; Cook et al., 2007, 2010). In addition, there is evidence for a strong Asian monsoon during the Medieval period, wet conditions over much of tropical South America, dry conditions in equatorial East Africa, wet in South Africa, a dry western Mediterranean region and wet northwest Europe (see compilation of proxy data in Seager et al., 2007, Burgman et al., 2010 and Figure 1). What could have caused such a global reorganization of hydroclimate for such a long period of time? The North American megadroughts immediately suggest a link to tropical ocean sea surface temperatures (SSTs). Climate modeling has clarified that the historical droughts of the 19th and 20th centuries were forced by small variations in tropical SSTs. All were forced, wholly or in part, by a cold, La Niña-like tropical Pacific Ocean."

    And this excerpt from Graham et al. 2007 (

    "Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific sea surface temperatures during the Medieval Climate Anomaly, with warmer than modern temperatures in the western equatorial Pacific. This pattern of mid-latitude and tropical climate conditions is consistent with the hypothesis that the dry Medieval Climate Anomaly in the western United States resulted (at least in part) from tropically forced changes in winter Northern Hemisphere circulation patterns like those associated with modern La Niña episodes”"

    So, understanding of the MCA has dramatically changed since Lamb (1965, 1969) described general warmth in the North Atlantic-European sector during the MCA, and LaMarche (1974) used multi-elevation tree ring data analysis that indicated warmer drier conditions in the White Mountains of California from ~1000-1300 AD and cooler wetter conditions from ~1400-1800 AD. These works have largely been substantiated, but have been built upon by substantial amounts of later work indicating that the global picture during the MCA generally fits a combination of a persistent La Niña ENSO phase and a persistent North Atlantic Oscillation positive phase.

  7. Elliot, have you ever listened to Professor Richard Alley's talk on CO2 as the principal control knob on the earth's climate history. It's about an hour, but it's worth listening to. See what you think. Here is the link:

  8. BTW, even relatively early models took into account aerosols created by volcanic eruptions and their effect on the solar radiation (or temperature change) of the earth. Here is an excerpt from the abstract of Hansen, 1981 (

    "The global temperature rose by 0.2°C between the middle 1960's and 1980, yielding a warming of 0.4°C in the past century. This temperature increase is consistent with the calculated greenhouse effect due to measured increases of atmospheric carbon dioxide. Variations of volcanic aerosols and possibly solar luminosity appear to be primary causes of observed fluctuations about the mean trend of increasing temperature. It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980's."

    I think it's safe to say that that climate modelers have a realistic understanding of the climatic effects of volcanic eruptions (now with reams of data on actual eruptions) and a pretty clear global understanding of the Medieval Climate Anomaly, and paleoclimatologists are not rewriting history to fit inaccurate data. Well substantiated and much more clear data on a global scale (not just the synoptic scale of Lamb) are incorporated into the models. As paleoclimate has become more and more clear, the models have become more accurate (and the computing capacity for modeling has become far more powerful) Therefore models have become more realistic than Hansen's relatively accurate 1981 model projections. Still, there is always room for improvement.

    1. Steve, you and I agree what the consensus says. If there were a debate class, I am sure that I could argue the pro-CO2-greenhouse effect case rather effectively. Where we disagee is whether the consensus is, at the end of the day, acccurate in its projections for the future.

      I think where the science went wrong was in the 1999 IGCC Report in which as a group, climatologists declared that uncertainties had become greatly diminished, and they decided that they could confidently extrapolate the temperature rise of the 70's, 80's and 90's into the next century.

      In any normal science, you make predictions, and if you the data agree with the model predictions you tend to believe that the model may be accurate, but if the data diverge from the model predictions you doubt the model. In climatology however, the data since the 1999 report have had very poor agreement with the model. But, paradoxically the confidence in the model has continued to increase. I attribute that to political pressure (perhaps understandable in light of the importance of societal decisions that must be made on the basis of climate), but not really emerging new science.

  9. True enough that nearly all climate models overestimate recent global climate trends. ( but not all - From realclimate (2/8/2012) “People sometimes claim that “no models” can match the short term trends seen in the data. This is not true. For instance, the range of trends in the models for 1998-2011 are [-0.07,0.49] ºC/dec, with MRI-CGCM (run5) the laggard in the pack, running colder than observations.” It’s partly why Kevin Trenberth made his now famous statement “The fact is that we can't account for the lack of warming at the moment and it is a travesty that we can't.” a statement cherry picked by climate deniers and grossly misunderstood to mean that climate scientists were secretly admitting that they knew global warming had stopped. Of course, what he was really complaining about is the fact that earth’s surface temperatures were not rising as models had predicted, despite the fact that there is more radiant energy entering at the top of the atmosphere over than is leaving. In fact the rate of energy imbalance is increasing, as it was very small a few decades ago, but has now increased to nearly 0.9 W/m2. This fact is well documented by satellite observations and was described in Trenberth’s paper (2009; Modelers should be able to calculate how much heat the atmosphere and shallow oceans (ocean heat data is recorded down to 900 meters depth) should gain due to this energy imbalance. However, actual contributions fall short of calculations for reasons that were not yet clear when Trenberth wrote his paper, which is what he was complaining about.

    A paper by von Schuckmann et al., 2009 (, published just after the Trenberth paper (and after his famous statement) described data collected down to 2000 meters by Argo buoys that provided evidence supporting the idea that deeper ocean water had been building up heat at a rate of 0.77 W/m2, which brings the increased energy imbalance at the top of the atmosphere more in line with what would be calculated for heat energy gained by the earth.

    This partly explains why modelers are "paradoxically" more confident than before, because the enigma of where did the missing energy go has been largely explained. The new data has been incorporated into the models improving their accuracy for future projections.

    There are also other situations that climate modelers have become much better aware of in the last few years. The changes in water vapor in the lower stratosphere is one of those situations. Solomon et al., 2010 ( provided data showing that from about 1980 to 2000, lower stratospheric water vapor increased. But beginning around 2000, it began to decrease. I haven’t seen an update of this trend, so I don’t know how much progress scientists have made understanding this phenomenon. There have also been improvements in our understanding of meridional overturning circulation, which has a profound impact on the distribution of heat on the planet’s surface, but there is much left to learn ( It is the recent increasing understanding of these and other phenomena, and the monumental increase in model computing capacity are the main causes of the “paradoxical” increased confidence in modeling.

  10. There is yet another factor that plays a role in the increased confidence climate scientists have in the models. Here is the abstract of Kaufman et al., 2011, "Reconciling Anthropogenic climate change with observed temperature 1998-2008" (

    "Given the widely noted increase in the warming effects of rising greenhouse gas concentrations, it has been unclear why global surface temperatures did not rise between 1998 and 2008. We find that this hiatus in warming coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. As such, we find that recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects."

    An excerpt from the introduction to the paper:

    "Results indicate that net anthropogenic forcing rises slower than previous decades because the cooling effects of sulfur emissions grow in tandem with the warming effects greenhouse gas concentrations. This slow-down, along with declining solar insolation and a change from El Nino to La Nina conditions, enables the model to simulate the lack of warming after 1998."

    And an excerpt from the Results section of the paper:

    "Increasing emissions and concentrations of carbon dioxide receive considerable attention, but our analyses identify an important change in another pathway for anthropogenic climate change—a rapid rise in anthropogenic sulfur emissions driven by large increases in coal consumption in Asia in general, and China in particular."

    And an excerpt from the conclusion:

    "The results of this analysis indicate that observed temperature after 1998 is consistent with the current understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors that have well known warming and cooling effects."

    Aerosols produced from coal energy production, sulfate aerosols in particular, scatter the entire spectrum of solar radiation and change the net energy gain at the top of the atmosphere – the so-called direct effect of aerosols; and they modify the reflectance and lifetime of clouds – the so-called indirect effect.

    Whether you agree with these researchers or not as to the extent of the effect of sulfate aerosols on temperatures, there is no doubt that this is a contributory effect to the global temperature trend of the last decade. Incorporating the effect of sulfate aerosol production into climate models for this time improves agreement of models to actual temperatures, and is another reason for the increased confidence in climate models.

  11. So I would say that politics has nothing to do with the increased confidence of climate modelers, a rather cynical outlook. Rather it has to do with a better understanding of deeper oceanic heat storage, a better understanding of oceanic heat distribution, a better understanding of lower stratospheric water vapor trends and how it affects tropospheric temperatures, a better understanding of recent Asian sulfate aerosol production and how it effects recent temperature trends, and dramatically increased computing capacity. The computing capacity is primed to take another leap forward with the installation of the Yellowstone supercomputer by the National Center for Atmospheric Research. Yellowstone will be capable of performing 1.5 quadrillion calculations per second! ( and and

  12. Hi Steve, Thanks for your usual thoughtful comments. I think however that the authors are a bit disingenuous with their remarks. The level of CO2 has been on a linear rise since measurements were first made at Mauna Loa by the Air Force, and even show a bit of a positive exponential rise. So if you an engineer might be tempted to conclude that global average temperature is not keeping pace with CO2. Alternatively, you can consider explanations involving varabiability of aerosols and global dimming effects, nonlinear temperature feedback, and (as a last resort) non-anthropogenic transient effects.
    THe CO2 greenhouse effect looks very strong if you look only at data from 1945 till 2001 or so. In that case, you can say that particulate pollution resulted in dimming effects which overcame the warming effect and resulted in aslight decrease of global average temperature during this period. However, by the mid 1970's world governments started cleaning up particulate air pollution, leading to global un-dimming, and the CO2 effect took over. I could very easily believe that to be the case if that was all the data out there.

    More problematic is why global warming occured from 1907 to 1945 (at approximately the same rate as 1976 to 2001), but leveled off from 1946-1975.

    Some amateur climatologists look at the 2002-2012 period and draw a parallel to the 1976-2001 period. If this view of the 20th century is close to correct, it may be possible to consider past history in a similar light. The Medieval Warming Period and Little Ice Age might have been associated with real changes in global temperature.

    Global temperature then be understood as a composite of natural and anthropogenic contributions, rather just one or the other.

    1. One ought not fail to see the political pressures on this problem. The Village Ellliot is a bit of an oddball (you knew this already), because he tends to vote Democratic, and was trained as a nuclear engineer and physicist, but is anti-nuclear (failing to agree with the near universal consensus that meltdowns can not happen) and a climate skeptic. But I am the exception. As an educator, I see young people interested in climate and ecology becomeing climatologists and environmentalists, whereas young people who are more concerned about energy become engineers and go to work for energy companies. They usually form these opinions first, and get the academic training second. There are very few from the Tea Party who are climatologiests, and few from the Green Party who work for BP. It's not that anybody is dishonest or lying. Nevertheless in my opinion each side can very clearly see the biases and influences on the other side, but much less so on their own position. That's something we all have to strive to work on, I suppose.

  13. This comment has been removed by the author.

  14. Elliot, clearly the sun does play a significant role in earth’s climate. Interestingly, during the 1907-1945 period, the sun’s total solar irradiance was also rapidly rising. There are probably no climatologists who would question that the sun contributed to the global temperature rise during that period. But the sun’s role is also limited; total solar irradiance continued to rise until 1958’s solar maximum, long after global temperatures began to fall in 1945, suggesting the limited influence of changes in total solar irradiance. So during the 1907-1945 warming period, both the sun and increases in CO2 contributed to the warming. However, since the maximum of solar cycle 19 in 1958, total solar irradiance has either decreased or leveled off ( And, as you well know, global temperatures have risen significantly since 1976, reaching a high mark in 2010, a year of near historic low solar activity.

    I have already discussed multiple probable reasons for the slow down in the rate of temperature rise in the last decade, all contributing to varying degrees. I expect that since these are all temporary influences, when their effects wane or abate, the rate of global temperature rise will begin to dramatically increase and life will become much more harsh for all species on the planet. In addition, since the ocean only gradually gives up the additional heat it has gained, it is probable that the deepening of ocean warming will keep global temperatures higher for decades after the cessation of fossil fuel caused CO2 emissions.

  15. As far as the global temperature decline in the period from 1945 to 1976, I contributed a series of posts to the Science Forum of the Manpollo website (under the pseudonym sinimod) concerning that time if you want to read it. Here is the link:

    1. Yes I think we both understand that the 1945-1976 time period is troubling to those who advocate the consensus view but not necessarily fatal to that argument. The consensus view is that global dimming as well as the factors you cite provide an adequate explanation of the data. In response, my prediction is that by 2017, other refereed publications will seriously consider alternative explanations along the lines I have described. What might be fun is to track the numerical estimates of climate forcings as a function of the publication date.

  16. My friend Professor Scott Mandia, professor at SUNY Suffolk Community College in NY ( has posted some information about the Vikings in Greenland during the Medieval Climate Anomaly at this site: Please take a look at it. Here is an excerpt:

    "The Greenland Vikings lived mostly on dairy produce and meat, primarily from cows. The vegetable diet of Greenlanders included berries, edible grasses, and seaweed, but these were inadequate even during the best harvests. During the MWP, Greenland's climate was so cold that cattle breeding and dairy farming could only be carried on in the sheltered fiords. The growing season in Greenland even then was very short. Frost typically occurred in August and the fiords froze in October. Before the year 1300, ships regularly sailed from Norway and other European countries to Greenland bringing with them timber, iron, corn, salt, and other needed items. Trade was by barter. Greenlanders offered butter, cheese, wool, and their frieze cloths, which were greatly sough after in Europe, as well as white and blue fox furs, polar bear skins, walrus and narwhal tusks, and walrus skins. In fact, two Greenland items in particular were prized by Europeans: white bears and the white falcon. These items were given as royal gifts. For instance, the King of Norway-Denmark sent a number of Greenland falcons as a gift to the King of Portugal, and received in return the gift of a cargo of wine (Stefansson, 1966.) Because of the shortage of adequate vegetables and cereal grains, and a shortage of timber to make ships, the trade link to Iceland and Europe was vital (Hermann, 1954.)"

  17. This comment has been removed by the author.

  18. Scott has read this blog post and comments and said this to me: "I think the burden of proof is now on him [meaning you, Elliot] to show how massive increases in CO2 are NOT caysing [sic] [t]he warming especially given that the pattern of warming matches a reduction of outgoing energy and not an increase in incoming energy. Of course, if the MCA/MWP were warmer than we think then it means the climate is MORE sensitive to [sic]forrcings/feedbacks and it will get even warmer than the estimated 3C for 2xCO2."

  19. Hi Steve, please clarify the meaning of "the pattern of warming matches a reduction of outgoing energy and not an increase in incoming energy." Not sure what that means. Does he mean the pattern of global average temperature in the late 20th century is consistent with a reduction in radiated energy from the earth and inconsistent with an increase in incident energy from the sun? In any case, I am very impressed with the website link that you provided. I especially liked the data on grain prices in Europe, and the singularity that seems to have existed in 1816, which is the subject of another blog in which I suggest that there was probably a very significant transient at that time.

    As far as revising the current model of global temperature vis a vis CO2 effects, there are several chapters yet to be written in this story. Basically I am a believer in some influence of carbon dioxide on global climate, but I also think there are other effects which are underestimated. I doubt whether we are headed to a 3 C temperature global increase at the end of the 21st century however. I am flattered that you referred my blog to Professor Mandia, and even more so that the burden of proof might fall on me in such an important matter. However, what I think should happen is that Congress should appoint a peer review panel of experts without a vested interest in the outcome, to review the global climate model and to estimate the uncertainties. It should be headed by Nobel Prize winner. People who work on hydrodynamics codes for nuclear weapons, astrophysicists, quantum theorists etc should comprise the panel. They would be from the National Labs, Military Labs and academia. These are people who are smart enough to understand the climatologists are doing, while still retaining an alternate perspective. I've served on a National Academy of Sciences panel before, and would be grateful if you were to recommend me for such a panel if it should ever take place. The committee should be broad minded enough to be able endorse the findings of the IPCC if they believe them to be accurate; or to take issue with them if they believe that there are inaccuracies.

    Yes I am troubled by recent tendencies in the scientific community to downplay evidence of past climate change due to non-CO2 causes, while forcefully recommending strategies that many economists think would dismantle the current global economy. Before making decisions that influence trillions of dollars of the world economy, they ought to be reviewed by a number of perspectives, not just like-minded persons with similar viewpoints.

    You might well admonish me, however, not to spend too much time refuting flawed arguments. What really needs to be done is find out where the current model breaks down, and how to fix it. I hope to cover that in detail in a future blog. But to make a long story short, I suspect there is a problem in the energy transport model, which seeks to describe the fate of photons which interact with carbon dioxide and other absorbing molecules at different places in the atmosphere. A number of poets have chided me that this is just basic physics, but regrettably it is not. It's roughly the same level of complexity as a nuclear weapons calculation. This would be a Monte Carlo (i.e., particle-by-particle) energy and mass transport calculation. I know that this code exists, but I've never been given access to it, so it's hard to vouch for how bulletproof it actually is.

    1. To clarify, I don't mean that your arguments are flawed, but rather to agree with you that there is a limit to the value of refutation (in any discussion, but especially climatology where there are a number of misconceptions out there). Sorry if that came out sounding a little snippy. Also, I should have said that I assume that such a Monte Carlo code exists, and I'm inquiring about how to get access. If such code doesn't exist, it needs to be written.

  20. You said: Hi Steve, please clarify the meaning of "the pattern of warming matches a reduction of outgoing energy and not an increase in incoming energy."

    An increase of incoming energy specifically means an increase in total solar irradiance. Atmospheric scientists know that if this were the case there would be heating of the stratosphere as well as the troposphere. ( due to the increased absorption of ultraviolet radiation by ozone.

    The reduction in outgoing energy is specifically due to reduced infrared radiation escaping the atmosphere in the part of the spectrum that is absorbed by carbon dioxide and methane (Harries et al., 2001;; Griggs, J. A., J. E. Harries, 2007;; Chen et al., 2007, All of these researchers confirmed that there has been a reduction in outgoing infrared radiation in the spectrum range that is absorbed by carbon dioxide and methane. No other spectrum has been as significantly reduced, although there has also been a slight reduction of escape of the water vapor absorption spectrum since there has been about a 4% increase in atmospheric water vapor since 1950 due to the warming troposphere and according to the Clausius Claperyon relation.

    This reduction in outgoing infrared radiation at the CO2 and methane spectrums perfectly follows what would be expected to occur with the increased concentration of atmospheric CO2 and methane.

    In addition to the reduced infrared radiation escaping the atmosphere in the CO2 absorption spectrum, we would also expect an increase in returned infrared in the CO2 spectrum. This is indeed what has been observed (Philipona et al., 2004,; Wang and Liang, 2009,; Evans, 2006, All of these researchers observed an increase in the downward directed CO2 absorption spectrum at the earth’s surface.

    The result of the reduced escape of infrared radiation at the top of the atmosphere is reduced temperatures in the lower stratosphere ( Granted, the reduced ozone in the lower stratosphere also lowers temperatures there, but not enough to account for the fairly dramatic temperature reduction occurring in the lower stratosphere. This is effective confirmation that CO2 is significantly affecting surface, tropospheric and lower stratospheric temperatures. It is also effective confirmation of the relative insignificance of solar radiation in the increase in tropospheric temperatures and the reduction of lower stratospheric temperatures. The anthropogenic global warming greenhouse gas model precisely explains these phenomena, and the solar heating model does not.

    1. We need to be very careful about where the thermodynamic boundaries are being drawn.

      For example, when you talk about outgoing infrared radiation, are you thinking of radiation leaving the earth's surface, or the outer atmosphere? As I understand it the CO2 warming scenario assumes first of all that infrared energy is absorbed by CO2 in the atmosphere, which causes the atmospheric temperature to increase. This in turn implies that the temperature on the ground must increase because of the adiabatic compression relationship between P and T. But, in steady state at least, an observer on the moon would see the same amount of IR radiation from the earth, but the IR photons reaching space originate at a higher altitude than they would have without CO2 being present. In other words the observer on the moon sees the same temperature because he is looking at the gas molecules emitting energy. The gas molecules may be emitting IR from a higher altitude than they used to, but the total amount of energy out equals the mount of energy in if steady state has been reached. The observer on the earth, on the other hand, sees the surface of the earth being warmed, along with the atmosphere. If there really is a deficit of photons witnessed by the observer on the moon, this implies that the internal energy U of the earth is increasing by some appreciable dU/dT, and so something somewhere has to get hotter.

      I think that an individual IR photon is not likely to be reflected back to earth. An increase in CO2 results in absorption of photons, with collisional excitations and de-excitations taking place. It is not simple reflection. More likely the excited state that results is collisionally dissipated. What is the lifetime of the excited state versus the mean time between collisions with a nitrogen molecule? I think the collisions must be very frequent, like on the order of 10^-10 sec, so that most of the CO2 does usually not have time to decay radiatively. On the other hand, if CO2 has an absorption cross section it also has an emission cross section, and so my guess is that the observed increase in IR photons may involve collisional excitation from nitrogen. The net transport is not limited to radiation, but must also include convection terms. You may suppose that it is obvious that photon absorption in the atmosphere (which we agree on) leads to a 3 degree per century increase in surface temperature, but I remain a long way from that point.

      The photon data proves that absorption events are real, but I think we knew that already. I'll try to get around to really reading the article to see if I think that the difference in incoming versus outgoing energy is related to kinetic energy processes, or if it is the "smoking gun" that allows the world to calculate global surface temperature rise.