Arguments
How does the Medieval Warm Period compare to current global temperatures?
What the science says...
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While the Medieval Warm Period saw unusually warm temperatures in some regions, globally the planet was cooler than current conditions. |
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Climate Myth...
Medieval Warm Period was warmer
"For now, though, it is enough just to see the Medieval WARM Period shown to be global, and warmer than today." (Musings from the Chiefio)
One of the most often cited arguments of those skeptical of global warming is that the Medieval Warm Period (800-1400 AD) was as warm as or warmer than today. Using this as proof to say that we cannot be causing current warming is a faulty notion based upon rhetoric rather than science. So what are the holes in this line of thinking?
Firstly, evidence suggests that the Medieval Warm Period may have been warmer than today in many parts of the globe such as in the North Atlantic. This warming thereby allowed Vikings to travel further north than had been previously possible because of reductions in sea ice and land ice in the Arctic. However, evidence also suggests that some places were very much cooler than today including the tropical pacific. All in all, when the warm places are averaged out with the cool places, it becomes clear that the overall warmth was likely similar to early to mid 20th century warming.
Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the globe. The National Academy of Sciences Report on Climate Reconstructions in 2006 found it plausible that current temperatures are hotter than during the Medieval Warm Period. Further evidence obtained since 2006 suggests that even in the Northern Hemisphere where the Medieval Warm Period was the most visible, temperatures are now beyond those experienced during Medieval times (Figure 1). This was also confirmed by a major paper from 78 scientists representing 60 scientific institutions around the world in 2013.
Secondly, the Medieval Warm Period has known causes which explain both the scale of the warmth and the pattern. It has now become clear to scientists that the Medieval Warm Period occurred during a time which had higher than average solar radiation and less volcanic activity (both resulting in warming). New evidence is also suggesting that changes in ocean circulation patterns played a very important role in bringing warmer seawater into the North Atlantic. This explains much of the extraordinary warmth in that region. These causes of warming contrast significantly with today's warming, which we know cannot be caused by the same mechanisms.
Overall, our conclusions are:
a) Globally temperatures are warmer than they have been during the last 2,000 years, and
b) the causes of Medieval warming are not the same as those causing late 20th century warming.
Figure 1: Northern Hemisphere Temperature Reconstruction by Moberg et al. (2005) shown in blue, Instrumental Temperatures from NASA shown in Red.
Basic rebuttal written by dana1981
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Last updated on 7 July 2015 by pattimer. View Archives
Tom,
I'm aware of no Viking Saga stating that grapes were grown in Greenland. Around A.D. 1,000 the Vikings sailed West from Greenland, coming across a barren land they called "Markland", presumably Labrador. They sailed South and, as I can recall, they called their southernmost discovery, "Vinland" or "land of the grapes". We believe this is present day Nova Scotia where a Viking settlement was discovered at L'anse d'Meadows.
Note: The Vikings never grew domestic grapes, at least not in North America. The "grapes" they found may have been wild grapes, presently found no farther north than New England.
Possible explanations: 1. The Vikings misidentified their wild 'grapes'. 2. We are misinterpreting the word "Vinland". 3. The Vikings did discover wild grapes but, since then, wild grapes have disappeared from Nova Scotia for reasons other than climate. 4. The Vikings sailed as far south as New England. 5. Nova Scotia was significantly warmer then than now. Take your pick.
Just a passing note: the first essay on history I did in college was over Helge Ingstad's Westward to Vinland. Well-written, but I can't recall what Helge said about the development of the name 'Vinland'.
DSL,
I forgot to list a sixth possibility i.e. the Vikings could have been lying. We were taught, as children that Erik the Red's naming of "Greenland" was a propaganda ploy to lure naive Icelandic and Norwegian settlers to Greenland [this is extraordinarily unlikely given the violent nature of the Vikings]. Conceivably, his successors might have been using propagandistic terms to describe the North American "Vinland".
On the other hand--and directly apropo to this site--it all may have been the literal truth. Southwestern Greenland may, indeed, have been a Green Land i.e. grassy, during the warmer months, one thousand years ago. The sagas tell us that the settlers were able to graze cattle and goats close to their several settlements. Not only that, but they were able to overwinter their stock which means that the settlers were able to harvest enough forage during the warm months to feed their stock during the snow-bound winter.
The same is likely true of "Vinland". Not only did the Vikings describe a "grape land", but they also stood amazed at its bounty. Of course, everything may simply be comparative. Even if Greenland were relatively lush 1000 years ago, Nova Scotia, at some distance South of the Greenland settlements, must have seemed bounteous, indeed.
[DB] This is NOT a site to discuss speculative fiction. If you have a citation to a reputable source to support your claims, then please provide it.
Failing that, please refrain from such and instead discuss matters of science.
DSL,
I wrote "goats' when I should have written "sheep."
Spoonieduck
Instead of describing vague "sagas" you have read about on the internet you could refer to peer reviewed studies of Greenland. Jahred Diamond summarized much of this work in his book Collapse, on how societies in the past have collapsed from environmental change, some of it self inflicted. In spite of your vague suggestions, it is actually well known what conditions were in Greenalnd during Viking occupation. Why don't you do some serious reading and find out what is known?
As you have been told before, this is a scientific site. Vague descriptions of "sagas" without any references are handwaving and have no place in scientific discussion. Please start to present sources for your wild speculations.
spoonieduck @178, although at the time of Eric the red, some (small) sections of southern and western greenland were green (grass covered) in summer, they were less so than the settled areas of Iceland, and certainly less so than Norway and Denmark. Furthur, it is highly likely that Eric, having determined to establish an independent colony would want to attract fellow norsemen to his cause (thereby increasing his stature and power should he ever "go viking"). Of course, that explanation presupposes that some part of Greenland was at least sufficiently green that Eric wanted to settle there.
Spoonieduck... I just want to clarify something. You're not assuming the most of Greenland was actually green, are you?
Tom,
I thought I already addressed part of your statement. We were taught as children that Erik the Red falsely promoted Greenland as a Green Land to lure unwary and naive Scandinavians to his new colony.
Let's examine that belief a little more closely. The Vikings were truly violent people as retold in my of their Sagas and retold in the AngloSaxon Chronicle amongst others. Now let's say a group of Norwegian or Icelandic Vikings bought into Erik's propagandistic lie that Greenland was a Green Land and a great place to settle and raise a family. After sailing with their families--women and children--and livestock ater a long, nervous voyage in open Knorrs over dangerous northern seas, they come to southwestern Greenland, little more than frozen, barren rock with little more to eat than birds' eggs, fish and walrus blubber. How long do you reckon that Erik would have lasted?
Now, the Vikings did settle in southwestern Greenland. Archaeologists have found their settlements complete with church and structures that were probably animal overwintering facilities. I don't know if you have much experience with livestock but, obviously, they must be fed year round, not just in the summer. In northern climates, farmers put up hay in the plentiful summer months to feed their stock during the winter months. This presupposes the presence of quite a lot of grass and other forage during the warm months of the year.
No, Rob, I'm not. Apparently only parts of southwest Greenland were habitable by Europeans with European technologies at the time.
Spoonieduck,
Instead of speculating about what conditions were in Greenland in the 1,000's why don't we read something scientific about it!! What a novel idea, find out what is already well known instead of making up stories!! According to Collapse by Jahred Diamond, it was too cold to raise any vegetables in Greenland during the Viking settlements. They did collect forage during the summer for their cattle, but no plant farming. Currently there are over 100 tons of potatoes grown along with plentiful cabbages. It is only in the last 20 years that it has become warm enough to grow potatoes.
This is a scientific board. No-one cares what you remember from elementary school. Provide citations for your opinions or stop your nonsense.
The paleoclimate scientific community seems to agree that southern Greenland was warm during the Medieval Period. See the spatial pattern below from Mann (2009).
Most of the world was much cooler than present though (as shown above). This is why sea level in the equatorial regions was falling throughout the Medieval Period. No such thing is happening today because the current human-caused warming is globally coherent.
spoonieduck @185, ok, you have convinced me. How, after all, could this not be considered a greenland:
Whoops. Sorry, wrong picture. That is Iceland, where before Norse settlement "Birch and willow forests like this one at Lake Mývatn used to cover much of Iceland's interior." In contrast even the inhabitable portions of greenland have never sported more than grasses:
Oddly, Iceland was names as such because, during an early attempt at settlement, drift ice was spotted in the harbour in winter.
This is the first reason why your argument fails. No matter what else, Eric was trying to convince settlers (whether from Norway or from Iceland) to move into a harsher, less productive environment. If it were ill advised to do that due to the "Vikings were truly violent people", then it were ill advised whether he used a bit of subtle persuasion by his choice of name.
The second basis on which your argument fails is that the "Vikings" were not a truly violent people, or at least not more so than most other European peoples of the time. The norse have a reputation for violence because they went viking (ie, on naval expeditions for raiding). To conclude from that that they were unusualy violent would be like concluding the English were unusualy violent based on French accounts of Agincourt (or on reading Shakespears plays). Yes, the Norse could be violent at home, but were not unusually so.
The basic fact you must account for is that even those small parts of Greenland that are ever green are not so when compared to Iceland or Norway. Therefore the name Greenland, even if only confined to those locations, must involve some creative embelishment.
Tom,
How are photographs of Iceland apropo to conditions in southwestern Greenland between A.D. 1,000 and A.D. 1,400?
Detailed discussions of Viking violence are probably a bit afield for this specific topic but Erik didn't directly deceive anyone. He had been outlawed in both Norway and Iceland for successive murders, which is why he traveled west to Greenland [Saga of the Greenlanders].
Your other iteration that Erik was simply trying to convince.....etc. is simply a repeat of your previous statement. I'll try to put it another way. What if you were deceived into putting your entire family at the considerable risk of a hazardous sea voyage in an open boat? What if, on reaching your Greenland destination you found it a pile of frozen rocks fit only for arctic wildlife? Of course, I don't know how you would have reacted but I would have been truly upset. At a bare minimum, I would have packed up my family and left as soon as it was feasible--that is, if we didn't starve or freeze to death in the meantime. I certainly wouldn't have celebrated Erik as a great chieftain.
Michael,
I know that you don't care about my grade school recollections but the issue is nevertheless significant. This site shows abundant sophisticated charts, graphs and calculations and I am duly impressed. Still, most of these graphics are, in a real sense, highly indirect, when they apply to climatic events many hundreds of years ago.
Most of this evidence--tree rings, Sagasso Sea sediments even ice cores--is indirect and subject to various interpretations. Historical evidence, despite its problems, is more direct. Yes, there are problems with Viking Sagas. Most weren't written down until 300 years or so after the events, leaving plenty of room for error. Prior to this they were oral tales, probably recited for entertainment.
The other problem with the Sagas is that the events are very much local. It is quite conceivable that Southwestern Greenland was relatively warm, maybe even warmer than today, 1000 years ago. It is even possible that the frost line along the East coast of North America was farther north 1,000 years ago than it is at present. Maybe.
Even if true, none of this proves that the entire world was warmer then nor does it disprove that the earth is presently entering a dangerous warming trend. It certainly doesn't disprove that excessive atmospheric CO2 is contributiing to the current warming trend.
Spoonieduck:
The problem is that your "detailed discussions" of Vikings amount to uninformed speculations about behaviour you know nothing about. Your suggestions that your vague knowledge of Viking sagas, presented here without any documentation, is "historical evidence" is worthless. Have you ever read a Viking saga or a reasoned analysis by someone who has read them? I have. Link to a scholarly article summarizing the sagas and I will discuss it with you. Discuss what you learned in elementary school at WUWT. There is a wealth of archaelogical data and saga analysis about early Viking settlements, some of it referenced in Collapse (which I have read so I know more than an elementary school student).
This is a scientific board. Speculations about how you might feel when you arrived in Greenland and it was too cold for crop farming are completely inappropriate. It is currently warmer in Greenland than it ever was for the Vikings. The Vikings were not able to grow vegetable crops like those currently grown in Greenland. They raised cattle and sheep.
A significant part of the reason Vikings went to Greenland was to obtain walrus ivory, polar bear skins and Gyrfalcons. Perhaps the settlers were ecstatic because of the Gyrfalcons and did not care about farming. Why havn't you mentioned these items which were available on Greenland? Because you don't know what you are talking about. Provide citations to support your opinions or stop bothering us. Looking back through this thread you have provided not a single reference to support your wild speculations.
Spoonieduck @189, the relevance of modern photos of Greenland and Iceland is that current temperatures in those nations are comparable to those in the MWP. If Iceland is more verdant now (as it clearly is), it follows that it was more verdant then - and the name "Greenland" is, therefore, not explicable by the unusual greenness of the land.
I am unsure why you want to explore a counterfactual hypthetical. Greenland (or at least, those portions of it colonized by the norse) was not "a pile of frozen rocks fit only for arctic wildlife". Colonies were established there, and survived several centuries. So Norse settlers decieved by Eric's clever naming would have found a land less verdant than those from which they came, contrary to what the name suggests - but one in which it was still possible to survive and make a living.
In any event, we do not need to speculate as to why Eric called Greenland "Greenland":
Eirik the Red's Saga
A counter argument based on assuming the alternative to a Greenland less verdant than Iceland is a Greenland having no colonizable lands at all is hardly a sound basis to reject the reasons given by the Nords themselves, and attributed directly to Eric.
Michael,
One of the primary justifications for this particular thread is historical accounts of a so-called medieval warming trend i.e. written histories. If it weren't for the histories--oral and written accounts--researchers [in my opinion] wouldn't be much concerned about anomalies in pollen samples, ice cores, sediments, tree rings from this period of time.
The Sagas i.e. Icelandic Sagas, Saga of the Greenlandders, Vinland Saga are some of the primary sources. Yes, Diamond wrote "Collapse" amongst other pop science histories. I haven't read it, yet, but reviewed his interesting "Guns, Germs and Steel." In a similar vein, I suggest "West Viking" by Mowat who supports the concept of the "Little Climatic Optimum."
Science is, of course, a generally materialistic approach to get at the truth and is usually best handled in a multidisciplinary fashion. It is not adequate to say "things were colder" in the face of historical testimony that things may have been "warmer". You may be right but you have to back it up.
Back to Diamond, Mowat and Dugamore et. al., Arctic Anthropology, 2007. None of these authors--including Diamons--dispute a medieval Greeland warming trend. After all there were two [East and West] Norse Greenland Settlements that existed for 450 years, from about A.D. 985 to at least A.D. 1427. Deteriorating cold weather was a major factor in the ultimate retreat from Greenland.
The various authors above also believe--entirely correctly--that the colony collapse was multifactorial. Political disruptions in Norway with reduced trade were possibly important. They also believe that the Norse were "slow learners" and might have hung on if they'd adapted eskimo lifestyles. I find the last contention amusing. It's almost like stating that the Aztecs might have defeated the Spaniards if they had guns.
Lastly, we just don't know. Unfortunately, and unlike today, the Norse didn't have thermometers. If they had them in Greenland, used them frequently, recorded the results for posterity, we wouldn't be having this discussion now.
Spooniduck@192
"Lastly, we just don't know. Unfortunately, and unlike today, the Norse didn't have thermometers. If they had them in Greenland, used them frequently, recorded the results for posterity, we wouldn't be having this discussion now"
Why do you expect the only way to get the temperature from past to be by the way of thermometers? Or reinterpreting the, initially oral, history tales?
It is as if you deliberately want to avoid looking at the multitude of reconstruction graphs, linked both to the article, as well as previous commenters.
And if your objection to them is that they are too general (being global or NH-centric), then I would point out that Kobashi et al. 2011, did reconstruct the temperature located on Greenland.
It is considered poor form to disregard other evidence and just concentrate on one detail in order to carry on an argument.
Tom,
I don't believe that Iceland then or now is "less verdant" than Greenland. Quite the contrary. Even during the medieval period, the Greenland settlements' total population hovered at 10% that of Iceland. I'm not saying that temperatures aren't warmer now than they were 100 years ago. One poorly documented internet site I've come up with claims that the growing season in southwestern Greenland is 3 weeks longer now than it was not so many years ago. Then again, I came up with another not so well-documented site, that claims that temperatures now--in the same area--have plunged 1.0-1.6 C, although they predict that temperatures will rise 2.0C by 2100.
I'll refer you to Dugmore et al, Arctic Anthropology, 2007. Dugmore is supportive of climate change theory and believes the colony collapse to be multifactorial, although he believes Greenland cooling, with reduced growing season and increased sea ice--tougher for trade vessels and harder for Norse hunters to access herds of Walrus--was a major factor.
Dugamore and Rachel Bold [Norse Utilization of Archaebotanical Resources with the Myvatssvert locale, Northern Iceland, Dept. of Arch., Durham University, 2011] describe a biota in what became the Eastern and Western colonies far different than today. Bold: [I'm paraphrasing]: "Greenlad attracted settlers with its wide open grassy spaces close to the coast. Remaining land deemed suitable for occupation was predominantly covered in dense scrub--birch and willow in the Eastern Settlement, with the addition of alder in the Western Settlement. Land clearing, manually, and by burning was necessary to increase agricultural utility as evidenced by a thin black deposit underlying the occupational layer of the Western Settlement." Note: There is only one tiny "National Forest" today in southern Greenland composed of dwarf birch and willow.
Therefore evidence suggests the possibility that southwestern Greenland was undergoing a warm period before the Vikings ever arrived. We can't know for certain, of course, because, as I wrote to Michael Sweet, "The Vikings didn't carry thermometers."
On to Erik or Erik. You are correct and quoted the Saga accurately, but I'll paraphrase Dugmore, who references the same line. I'd like to quote him perfectly but my printer is on the fritz so I had to scribble it down. "Despite Erik's sales pitch, it is unlikely that the traditionally strong-willed Viking women and mothers could have been lured to go to and/or stay in a marginal land." My point exactly. Certainly, Erik wanted to see his settlements grow but an outright lie would have provoked a blood feud that he couldn't have survived. Erik's "Green Land" was--at least in a few isolated areas--a "Green Land" suitable for settlement.
I think the problem that some people are having with the Little Climatic Optimum concept is not so much as to whether temperatures were a little warmer then than now or vice versa. That is largely irrelevant. The real problem is that the temperature seems to have undergone a long, hundreds of years cycle, in Greenland in which human produced atmospheric carbon couldn't have played much of a role.
[JH] You are now skating on the thin ice of sloganeering and excessive reptition -- both of which are prohibited by the SkS Comment Policy. Please cease and desist, or face the consequences.
Spoonieduck@194
"I think the problem that some people are having with the Little Climatic Optimum concept is not so much as to whether temperatures were a little warmer then than now or vice versa. That is largely irrelevant."
I don't know about the other commenters here, but as far as my view goes, you have a serious problem of being myopic in your arguments. And as such it is strictly your and not my problem. Maybe you should actually read what other commenters respond to your writings, instead of 'thinking' what their motivations might be?
"The real problem is that the temperature seems to have undergone a long, hundreds of years cycle, in Greenland in which human produced atmospheric carbon couldn't have played much of a role."
'Seems'? Based on what? Do you even realize that you are solely arguing for a warm(er) Greenland in the time of ca. 1200-900 bp? And that your basis is only in the anecdotal oral stories which were only later written down? If you still fail to show any actual material to support your assertions, then you are merely mixing in two other often recited myths, "It's a natural cycle" and "It's not us" through the non sequitur-fallacy.
As for the irrelevance that you talked earlier, your arguments are irrelevant as long as you continue repeating the same stuff over and over again, without providing any actual material.
[JH] Spoonieduck has now been officially warned about excessive repitition and sloganeering.
Spoonieduck,you are an extraordinaryly selective reader. When I read Dugmore et al 2011, I saw that Greenalnd never raised crops, only pastoral animals. Today they raise cabbages and a number of other crops in Greenalnd. It must be warmer in Greenalnd now since they were unable to raise crops in 1200 that they can raise now. Dugmore states:
"the Greenlandic economy seems from the outset to have been geared to obtaining and exporting rare and prestigious commodities such as walrus tusk and hide, narwhal teeth, and live polar bears."
It would have taken years or decades to build barns for herds and to breed sufficient animals to support a society. The original settlers were primarily engaged in hunting and exporting high value objects. You ignore this completely. Dugmore goes on to say:
D'Andrea et al, using the 'alkenone thermometer' as applied to lake core sediments reported in Geophysical Research, vol. 13, 2011: "We generated a 5,000 year long, decadally resolved record of summer water temperature from the annually-laminated sediments of Lower Murray Lake on Ellesmere Island in the Canadian high Arctic.........Most notably, the alkenone record reveals warm lake water temperatures beginning approximately 800 A.D. and persisting until approximately 1200 A.D., with temperatures up to 2-3 deg C warmer than the mean temperature for the last 100 years. This distinct warm period of Ellesmere Island interrupted a Neoglacial cooling trend that began approximately 2,000 years earlier."
Using similar alkenone studies, D'Andrea and colleagues studied cores from the bottoms of Lake Braya So and E, close to the original Norse Greenland settlements. In 2011 they reported that, during the time of earliest Vikng coloniation, the weather was relatively mild, similar to today. Around 1100 A.D. the temperatures dropped 4 deg C in 80 years..... D'Andrea et al. reported these findings to the National Academy of Sciences.
Peter Steen Henrickssen, an archaeobotonist doing research--digging into middens left by the Greenland Norse--for the National Museum of Copenhagen claims to have found a few grains of charred barley in the lowest level of one of the middens. Because of the context and the presence of extraneous chaff, he believes that this was barley cultivated in the early days of the Greenland colonies. Today, no cereal grains can be grown in Greenland.
As you correctly noted, a few potatos are grown in southern Greenland today. Potatos weren't grown in Norse Greenland because potatos were only grown in the Andean mountains at the time. They weren't 'discovered' and brought to Europe until after 1528.
Does the D’Andrea et al. 2011 research say anything about what the authors believe their findings indicate about the general temperature of the arctic region during the medieval warm period? These are excerpts from the abstract for D’Andrea et al. 2012 published in GSA that indicate at the locations investigated were not as warm in the MWP as recent (not average for last 100 yrs.) temperature.
“The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability.”
“We find that the summer warmth of the past 50 yr. recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr., including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent.”
Spoonieduck
Since you did not link your study I searched D'Andrea et al and found this study published in May 2012. It studies lakes in Svalbard, which is about as close to Greenland as Ellesmere Island. Here D'Andrea says:
"We find that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent."
The past 50 years are the warmest in the record. Many more crops are currently grown in Greenland than were attempted during the Viking settlements. The original settlers were hunters and not farmers. Greenland was never full of trees. A few barley grains in a midden could have been imported. They could grow barley today but it is cheaper to import from Denmark.
You only referenced one study. The others you describe without referencing or linking. How can I check what you say the studies claim? When I read DeAndrea et al 2011, I do not see the claim that the weather in 1100 was similar to today in Greenland. I see that it was warmer than earlier but no reference to current temperatures. Direct links allow me to read the study also.
Your assertion that since Greenland was named "Green" that it was warmer in 1000 AD than it is now is incorrect.
[JH] I deleted your duplicate post of this comment.
My interpretation of D'Anrea's studies is that he believes in present day CO2 induced global warming.