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
bvangerven @224.
The talk of Romans and Alpine passes sounds like some of the nonsense that followed on from Kurt Nicolussi's "Green Alp" glacier theory that dates back to 2005. After a lot of noise, the evidence led to some better understanding of the microclimates in the Alps but had a big zero implications for climate on a regional or global scale.
Apparently the myth is "Medieval Warm Period was warmer
The Medieval Warm Period was warmer than current conditions. This means recent warming is not unusual and hence must be natural, not man-made." ...
Actually I think more the concern that many in the general public have is that the Medieval Warm Period was not mentioned by Al Gore in his inconvenient truth and that the Medieval Warm Period is usually not mentioned by those pushing global warming. I think people see this as selective reasoning or confirmation bias and therfore find it difficult to trust what they are being told.
MrN9
"Actually I think more the concern that many in the general public have is that the Medieval Warm Period was not mentioned by Al Gore in his inconvenient truth and that the Medieval Warm Period is usually not mentioned by those pushing global warming"
Leaving aside that what Al Gore may have said about something or other, which has no relevence, the premise of you argument is that there was a Medieval Warm Period. Given that the topic is Global Warming, the question is - was there a MWP Globally?
Read the Intermediate rebuttal. Was there actually a MWP? The evidence suggests no.
So what is your point?
MrN9, it's also going a bit too far to claim that "many in the general public" are concerned about Gore's non-mention of the MWP. I'd guesstimate that less than 2% of the general adult public knows anything about the MWP/MCA, and most of those people could care less one way or the other. I ask my first year students (highly selective university) each semester if they can describe how the greenhouse effect works--just the basics. No more than one or two in 30 gets close.
Glenn Tamblyn and DSL. What my point is that what is being discussed here is the wrong "myth". It's not about people thinking: "The Medieval Warm Period was warmer than current conditions. This means recent warming is not unusual and hence must be natural, not man-made." ... People think something more like... "Oh look, people who talk about global warming pick and choose the data which they tell us about, and omit that which does not support their view so as to make their own view sound more convincing". Exactly how warm or not the MWP may or may not have been is irrelevant. Most will never understand the complexities of the issues, this is about trust...
I'd say it's less about trust than cherry-picking on the part of the "people." People for whom critical thinking is not a matter of habit are going to cherry-pick the field of information according to what makes them comfortable. These people aren't trying to put together an understanding of the situation. I talk regularly with people who claim, all at the same time, that 1) climate has changed before, 2) it's been much hotter in the past, and 3) climate science is a fraud. (and how do we know about the past? Climate scientists — the same ones who are telling you that AGW is, in fact, quite real.) The information is not being put together into a coherent picture, and there's no desire to do so. The desire is to surround oneself with claims that block responsibility--responsibility for current activity and for future activity. Trust means going to sources that tell you what you want to hear (in the name of freedom).
When people hear that the MWP exists, they have a range of possible responses.
1. Those climate scientists are hiding stuff.
2. How warm was the MWP?
3. What was the cause of the MWP?
4. Really? I think I'll go check it out on Wiki and google scholar.
5. So? Stop talking to me about stupid crap. I'm trying to get into the game.
It would be less easy to automatically go with no. 1 if climate science communication wasn't primarily defensive. Sources that misrepresent the science are not legally bound in the US to represent the science accurately. Thus, we have some very good, very well-paid rhetoricians who frame the message in the most effective way. The sources don't simply point to Al Gore not talking about the MWP; instead, they create a narrative of persistent deceit, and they can do that because very few sources put together the actual science into a narrative, the narrative that scientists see. It's simply too complex for the general public. There will always be little bits of information that don't get included, bits that can be re-framed and blown out of proportion by experts. The so-called "climategate" is an excellent example, and it revealed the willingness of the "people" to jump all over anything that suited their interests, even while just a tiny effort toward critical thinking would have revealed the absurdity of the whispered claims.
The MWP is a good example for another reason. All due respect to Mike Mann, but his multi-proxy record of the last 1000 years of surface temperature is not fundamental to the theory of anthropogenic global warming. It's important, but one cannot work backward from it to confirm or refute the basic physical foundation of the theory, regardless of the accuracy of the work. Yet that is precisely what "denier" opinion shapers claim. At every step, they push the logic that one alleged inaccuracy causes a breakdown of the entire theory. The details are irrelevant; the logic is the message. It is the logic of doubt, the logic that says "You're right: you don't need to try to understand this, because everyone has an agenda, and you're never going to get good information."
In this sense, people "trust" Rush Limbaugh, but not blindly. They trust him until he rubs up against their own expertise and experience. And if he's just plain dumb where their expertise goes, it doesn't transfer to the stuff they don't know anything about. As long as his message is about not being responsible for the woes of others, everything is all good.
Any why was Mann attacked so ferociously? Because he scored a rhetorical home run with his graphed results. Easy to understand. No one puts an attack on Lacis et al. 2012 in front of the general public. It's a fine publication, and works through the fundamentals in a readable way, but it didn't produce any easy-to-get visuals. Once you see the 'hockey stick' graph, it can't be unseen, and so denierville's experts have to attack, attack, attack. Same thing happened to Marcott et al. 2013. They shape public opinion, and, given the enormous amount of money going into the opinion shaping campaign, it's a credit to the people of the US that perhaps only a third of them have fallen for it hook, line, and sinker.
MrN9 wrote: "Exactly how warm or not the MWP may or may not have been is irrelevant."
Only to people who place their "trust" with no concern for reality. The only way to show that their 'trust' is misplaced is to provide the facts... i.e. 'exactly how warm or not the MWP' was. If you show that there was no global MWP (as the article above does) and people still respond that you are 'hiding' this thing which does not exist (as you argue they will) then those people are delusional. They aren't engaging with the facts, but operating solely on 'who they trust'... even when those trusted sources are shown to be false.
realiscience wrote (in 2012): "Did you look at Oppo's data points. Some are clearly at this level, meaning that it is within the margin of error that sea surface temperatures could have been higher. ?"
I read the paper. Did you see this part? " The modern rate of Pacific OHC change is, however, the highest in the past 10,000 years (Fig. 4 and table S3)." OHC = ocean heat content
Steven Sullivan @233.
The 2012 comment by realscience @148 referred to Oppo, DW, Y Rosenthal, BK Linsley, 2000-year-long temperature and hydrology reconstructions from the Indo-Pacific Warm Pool, Nature, 460 1113-1116, doi:10.1038/nature08233, 2009. You are referring to a more recent paper - Rosenthal, Y., BK Linsley, Oppo, DW, Pacific Ocean Heat Content during the past 10,000 years, Science, 342 617-621, 2013.
The quote you make from this later paper has been bandied about by contrarians, mainly because they rather enjoyed the paper saying "The inferred similarity in temperature anomalies at both hemispheres is consistent with recent evidence from Antarctica (30), thereby supporting the idea that the Holocene Thermal Maximum, MWP, and LIA were global events," but felt the sentence you quoted needed a bit of trashing as it spoiled their interpretation of what the paper was saying. So some branded your quote "a single sentence of genuflection to CAGW." Reading this contrarian blather, I think it's fair to say that the contrarians inabilities in understanding 'CAGW' are also persent in their understanding of the relationship between OHC & surface temperatures.
This is a response to Angusmac elsewhere.
Angusmac, I distinguished between three different meanings of the claim "the MWP was global":
In response you have not stated a preference to any of the three, and so have not clarrified your usage at all. In particular, while your citing of the AR5 graphs suggests you accept this first meaning, you then go on to cite the Luning and Varenholt google map app, which suggests you accept also the third, false meaning. Your question as to whether or not I believe the MWP was global remains ambiguous as a result, suggesting you are attempting to play off agreement on the first definition as tacit acceptance of the third, and false position.
With regard to the Luning and Varenholt google map app, KR's response is excellent as it stands and covers most of what I would have said. In particular, as even a brief perusal of Luning and Varenholt's sources shows, the warm periods shown in their sources are not aligned over a set period and include colder spells within their warm periods which may also not align. Because of the possible failure of alignment, any timeseries constructed from their sources proxies will probably regress to a lower mean - and may not be evidence of a warm MWP at all. (The continuing failure of 'skeptic' sources such as Soon and Baliunas, CO2Science and now Luning and Varenholt to produce composite reconstructions from their sources in fact suggest that they are aware that doing so will defeat their case - and have taken a rhetorically safer approach.)
In addition to this fundamental problem, two further issues arise. The first is that Luning and Varenholt do not clarrify what them mean by "warm" on their map legend. One of their examples helps clarrify, however. This is the graph of a temperature reconstruction from Tasmanian tree rings by Cook et al (2000) that appears on Luning and Varenholt's map:
(Expanded version)
They claim that it shows a "Warm phase 950-1500 AD, followed by Little Ice age cold phase." Looking at that warm phase, it is evident that only two peaks within that "warm phase" rise to approximately match the 1961-1990 mean, with most of the warm phase being significanly cooler. It follows that, if they are not being dishonest, by "warm phase" they do not mean as warm as the mid to late twentieth century, but only warmer than the Little Ice Age. That is, they have set a very low bar for something to be considered warm. So much so that their google map app is useless for determing if the MWP had widespread warmth relative to late 20th century values or not.
As an aside, Cook et al stated "There is little indication for a ''Little Ice Age'' period of unusual cold in the post-1500 period. Rather, the AD 1500-1900 period is mainly characterized by reduced multi-decadal variability." Evidently they would not agree with Luning and Varenholt's summary of the temperature history shown in that graph over the last one thousand years.
The second point is that it amounts to special pleading for you to accept the IPCC global temperature reconstruction that you showed, which is actually that of Mann et al (2008), but to not then also accept the reconstruction of spatial variation on MWP warmth from Mann (2009) which uses the same data as Mann (2008):
Apparently the data counts as good when it appears to support a position you agree with, but as bad when it does not. If you wish to reject Mann (2009), you need also to reject the reconstuction in 2008 and conclude that we have not reliable global temperature reconstruction for the MWP (unless you want to use the PAGES 2000 data). If, on the other hand, you accept Mann (2008), end your special pleading and accept Mann (2009) as our best current indication of the spatial variation of MWP warmth.
Answering here, as requested by the moderators, rather than the other thread that Tom points to (Angusmac elsewhere).
Angusmac's argument that the MWP was global seems to be akin to using past southern hemisphere summer temperatures as a direct comparison to current global mean temperatures, under the argument that "summer happens everywhere, so it's global"
...all while ignoring that it's pretty hard to find a time when both the southern and northern hemisphere had summer at exactly the same time.
You"re kidding with the heat maps, right? Way to cherry pick a nine-year period and compare it with a 300 year period as evidence of increased global temperatures. The irony is, you can make the same argument at any time in history: Some locales are warmer, and some locales colder, just like today. While the western and southern U.S. can enjoy higher than normal temperatures, the northeast can be much colder and snowier. More than anything, it's a matter of time and location. Next thing you will tell me is, CO2 levels were not higher more than 30,000 years ago.
scarletrogue @237 refers to this map from the intermediate post:
He claims the period to have been cherry picked, even though it merely shows the most recent decade at the time of publication of the paper discussed above. Moreover, it shows a period that excludes the El Nino of 1997/98 and that of 2010, but includes the La Nina of 1999/2000, and that of 2008, thereby being biased cold relative to trend in that period. The claim that it was cherry picked is therefore just empty rhetoric.
Of course, 1999-2008 is no longer the last decade, so here is 2006-2015 (again chosen because it is the last decade):
scarletrogue goes on to say, "Some locales are warmer, and some locales colder, just like today." Well yes. Some places are warmer in the MWP than other places in the MWP; and some places today are warmer than other places today. But I think scarlet rogue is trying to imply that some places in the MWP are warmer than the same places today. Comparing to either 1999-2008 or 2006-2015, I can find no such place. If scarletrogue wishes to claim otherwise, let them specify approximate latitude and longitude of the location so we can compare.
Northern Hemisphere vs 2016:
[PS] While your image is pretty self-explanatory, please note that image only/link only posts can be confusing. An extra sentence to explain the point you are making is good.
This report below is certainly more believable than what Skeptical Science puts forth when they claim that: "The Medieval Warm Period was not a global phenomenon. Warmer conditions were concentrated in certain regions."
"The 2485-year temperature data used in this study are taken from reference [13]. This temperature series is not only representative of the central-eastern Tibetan Plateau, but also the vast area of central-northern China. It is also significantly correlated with seven other temperature series of the Northern Hemisphere [13]. It even has a teleconnection with series for middle-low latitudes in the Southern Hemisphere [15]. Therefore, the spatial representative of this temperature series is quite clear. Since a conservative negative exponential or linear regression is employed in the detrending process, most low-frequency signals are preserved in the chronology and can be used to detect the low-frequency components of climate change."
http://www.agbjarn.blog.is/users/fa/agbjarn/files/tibet-2485_years.pdf
[DB] One would think that in the 5 years since your last participation here that you'd have learned to comport your comments better with this venue's Comments Policy. Simply copy/pasting up a paper from years ago selected at seeming random with no cogent context of your own added is just sloganeering (snipped).
This report below is certainly more believable than what Skeptical Science puts forth when they claim that: "The Medieval Warm Period was not a global phenomenon. Warmer conditions were concentrated in certain regions."
Earth and Planetary Science Letters
Volumes 325–326, 1 April 2012, Pages 108–115
An ikaite record of late Holocene climate at the Antarctic Peninsula
This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.
Highlights
► Ikaite forms in a narrow and shallow zone. ► Natural crystal (in modern porewater) validates the fractionation factor from lab. ► Trends in ikaite δ18Ohydra and δ18OCaCO3 are comparable with other records. ► Ikaite record indicates that the influence of LIA and MWP reached the AP.
<http://www.sciencedirect.com/science/article/pii/S0012821X12000659>
[DB] Again, one would think that in the 5 years since your last participation here that you'd have learned to comport your comments better with this venue's Comments Policy. Simply copy/pasting up a paper from years ago selected at seeming random with no cogent context of your own added is just sloganeering (snipped).
"[DB] One would think that in the 5 years since your last participation here that you'd have learned to comport your comments better with this venue's Comments Policy. Simply copy/pasting up a paper from years ago selected at seeming random with no cogent context of your own added is just sloganeering (snipped)."
I became aware 5 years ago that unless a comment comported without a doubt with the message that you were trying to push, it would end up like this one that I sent your way.
This is what I have found and if it doesn't meet your standards that is because you have no interest in discovering what the truth is if it contradicts your forgone, unsubstituted conclusions. It appears from your uninformative reason why my comment didn't "comport" to your very dodgy Comments Policy, that in your mind, when you say; "a paper from years ago", that you are now saying that valid scientific evidence backed up by the Earth Sciences department at Syracuse University, Syracuse, NY, The American Geophysical Union & Harvard University has a shelf life and if it exceeds a certain time frame it is deemed invalid.
After going over more of the comments I now see what type of comment "comports" to your rigorous standards.
MrN9 at 00:23 AM on 26 April, 2015 "Glenn Tamblyn and DSL. What my point is that what is being discussed here is the wrong "myth". It's not about people thinking: "The Medieval Warm Period was warmer than current conditions. This means recent warming is not unusual and hence must be natural, not man-made." ... People think something more like... "Oh look, people who talk about global warming pick and choose the data which they tell us about, and omit that which does not support their view so as to make their own view sound more convincing". Exactly how warm or not the MWP may or may not have been is irrelevant. Most will never understand the complexities of the issues, this is about trust…"
The wealth of information to be derived from the above comment is truly astounding, wouldn't you say, [DB]?
Now for one of my comments that did not comport.
SAO/NASA ADS Physics Abstract Service
An ikaite record of late Holocene climate at the Antarctic Peninsula
Lu, Z.; Rickaby, R. E.; Kennedy, H.; Pancost, R. D.; Shaw, S.; Lennie, A. R.; Wellner, J. S.; Anderson, J. B.
That this report has Affiliation with (I will not show the long list of scientific organizations affiliated with this study, Skeptical Science, for obvious reasons, is not mentioned)
Publication Date: 12/2011
"Our interpretation, based on ikaite isotopes, provides additional qualitative evidence that both the Medieval Warm Period and Little Ice Age were extended to the Southern Ocean and the Antarctic Peninsula."
http://adsabs.harvard.edu/abs/2011AGUFMPP51A1819L
This ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.
<http://adsabs.harvard.edu/abs/2012E%26PSL.325..108L>
I'm not sure if in this case who [DB] is. I am guessing that it is doug_bostrom. I like it in these kinds of discussions when people have enough confidence in their believes to use their real names.
[JH] Moderation complaint & sloaganeering snipped.
Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.
Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive or off-topic posts. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
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Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter.
From recent experience on this site and dealing with this topic "How does the Medieval Warm Period compare to current global temperatures?" I'm sure that neither Daniel Bailey & doug_bostrom will believe that this information below pertains to the Medieval Warm Period and, if not, they should tell me why it does not.
Since Michael Mann felt that he could get away with using falsified tree ring observations from two trees in Siberia to make his hockey stick graph when pollen records show something very different.
Widespread evidence of 1500 yr climate variability in North America during the past 14 000 yr
Abstract: "Times of major transitions identified in pollen records occurred at 600, 1650, 2850, 4030, 6700, 8100, 10 190, 12 900, and 13 800 cal yr B.P., consistent with ice and marine records. We suggest that North Atlantic millennial-scale climate variability is associated with rearrangements of the atmospheric circulation with far-reaching influences on the climate."
<http://geology.geoscienceworld.org/cgi/content/abstract/30/5/455>
Climate Change Froze the Vikings Out of Greenland, Say Scientists
''What’s the News: Climate change may have sparked the demise of early Viking settlements in Greenland, according to a new study published online in the Proceedings of the National Academy of Sciences, when temperatures cooled rapidly over several decades. Around the time the Vikings disappear from the island’s archaeological record, temperature appears to have plunged. Nor were the Vikings the only people in Greenland whose fortunes rose and fell with the average temperature, the study suggests. Earlier cold spells may have played a role in the collapse of two previous groups on the island.''
<http://blogs.discovermagazine.com/80beats/2011/05/31/climate-change-froze-the-vikings-out-of-greenland-say-scientists/>
While we are dealing with the Vikings, may be either Daniel Bailey & doug_bostrom can inform me of how this information is off topic.
The farm under the sand
Researcher challenges conventional thinking on disappearance of Viking community
"The Norse arrived in Greenland 1,000 years ago and became very well established," says Schweger, describing the Viking farms and settlements that crowded the southeast and southwest coasts of Greenland for almost 400 years.
"The Greenland settlements were the most distant of all European medieval sites in the world," said Schweger. "Then the Norse disappear, and the question has always been: what happened?"
Cross-sections of the GUS soil show the Vikings began their settlement by burning off Birch brush to form a meadow. Over the next 300 to 400 years, the meadow soil steadily improved its nutritional qualities, showing that the Greenland Vikings weren't poor farmers, as McGovern and others have suggested. "At GUS, the amount of organic matter and the quality of soil increased and sustained farming for 400 years," says Schweger. "If they were poor farmers, then virtually all the farming in North America is poor farming."
<https://sites.ualberta.ca/~publicas/folio/38/16/03.html>
''We find that major temperature changes in the past 4,500 y occurred abruptly (within decades), and were coeval in timing with the archaeological records of settlement and abandonment of the Saqqaq, Dorset, and Norse cultures, which suggests that abrupt temperature changes profoundly impacted human civilization in the region. Temperature variations in West Greenland display an antiphased relationship to temperature changes in Ireland over centennial to millennial timescales, resembling the interannual to multidecadal temperature seesaw associated with the North Atlantic Oscillation. ''
<http://www.pnas.org/content/early/2011/05/23/1101708108.abstract>
[JH] Antogonisitc sloganeering snipped.
Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.
Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive, off-topic posts or intentionally misleading comments and graphics or simply make things up. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
Finally, please understand that moderation policies are not open for discussion. If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.
Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter, as no further warnings shall be given.
[PS] Just for further clarity, simply repeating long-debunked myths, especially those dealt with in the main article, without providing supporting new evidence is sloganeering. At the moment, it seems you have simply skimmed (at best) the article rather than studying the arguments and source material, then launched in with already debunked arguments. If you are going to make any sensible contribution here, then spend some time understanding the evidence and science.
It might be worth pointing out to commenter J Doug Swallow that while he may feel he is justified @243 in accusing Mann of falsifying work, the authors he cites in support of an such egregious accusation are not in any way supportive of the J Doug Swallow position. Four of the five authors of the paper he cites Viau et al (2002) are also the authors of Viau et al (2006) which considers the Mann 'hockey-stick' compatable with its own findings, stating "The results are remarkably similar, in spite of the different methods and proxies employed in these studies (Figure 6). This provides further evidence that our North American temperature reconstruction is reasonable and also representative of a large region of the Northern Hemisphere."
More recently two of the authors published Viau et al (2012) which surely supports the contention of this SkS OP as it kicks off its conclusions stating "The pollen-based paleoclimate reconstructions show that warmer conditions during the MWP and cooler in the LIA were all nevertheless cooler than the 1961–1990 base period, and this result emerges even without comparing the results to the instrumental record."
The other two papers cited by commenter J Doug Swallow are similarly inappropriate as support for his contentions.
[PS] I strongly doubt Swallow is reading the material he is citing - more likely just repeating something from a denier site somewhere. I'd guess Co2Science.org given the sites perchance for claiming papers says opposite to what they really do, confident that their readership will not check. They have misrepresented Viau in the past.
NorrisM asked on a different thread:
"But it does raise questions. If it is accepted that there was a MWP and a Little Ice Age, then unless these are explained using natural causes there is a natural inference that the existing warming may consist of more than just CO2 concentrations. "
And lo an behold, as explained here or in even a cursory glance at IPCC reports 3,4, or 5, there are indeed natural causes that produce model results consistant with forcings. You seem to leaping to assumptions without making an effort to be informed first (again).
michael sweet and eclectic
Thanks for the information.
Basically, what you are saying is that although there were these blips both up (MWP) and down (LIA) they in no way compare to the rise since 1800 or the more extreme rise since 1950. It is hard to tell looking at these small graphs how much the rate has increased since 1950. Is there a large graph that provides this? I have to admit that I have not first searched all the IPCC reports to locate one.
[JH] NorrisM: You would benefit greatly by reading the Intermediate version of this article and by watching the Denial 101x video appended to it.
Moderator
Thanks. I have read the above material and watched the video. I think the best summary of things is the National Academy of Sciences 2006 report which you have quoted above.
I think the full paragraph makes it clear that although they generally agree with the Mann representation they clearly disagree with some of his statements regarding the 1990's being the hottest on record:
"Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods and because not all of the available proxies record temperature information on such short timescales."
My take on all of this is that no one is denying that there clearly was a MWP which, given the droughts in the SW US and the recent Chinese Academy of Sciences report on a MWP in China, suggests that this was probably prevalent in most of the Northern Hemisphere. It was not caused by humans so there had to be natural explanations for it. Those explanations have been provided which suggests higher solar activity and less volcanoes. But the evidence seems to be clear that these temperatures did not reach today's world levels. The "global temperature" at that time did not reach what we are experiencing globally today. At this same time, the sea levels did rise and drop matching the MWP and Little Ice Age but again not as significant as the sea level rise in the last 100 years or so. I also note that the Michael Mann 2008 EIV proxy data temperatures (which I believe he thinks are the best) no longer look like a hockey stick.
But the bottom line is that without some other explanation, given the significant increases in CO2 since the beginning of the Industrial era, most of the present temperature rise since 1800 has to be attributed to man.
Interesting, in my summary, I think you would have agreed with my analysis until I said 1800 and not 1950 as per the IPCC. Perhaps there is some other explanation for that part of the temperature rise that occurred from 1900 to 1950?
I am happy to move on to considering what the predictions are for the future and how best to deal with those predictions and the consequences.
Norris M @247: You state,
Your tentative conclusion about the MWP being prevelant in the Northen Hemisphere is not supported by the research documented in the following articles:
So-Called Medieval Warm Period Not So Warm After All by Michael D Lemonick, Climate Central, Oct 1, 2012
Study undercuts idea that 'Medieval Warm Period' was global: Vikings may not have colonized Greenland in nice weather, Science Daily, Dec 4, 2015
Recommended supplemental reading:
How A Viking Swimming With A Sheep Led To Climate Change Denial by Matthew Gabriele, Forbes, Oct 14, 2018
Wow, a hundred answers, but I think most of them missed the obvious. Everyone keeps focusing on the mythic global mean temperature that they say they can measure into the decimals (BS). They have been talking about sea level rise for the past 30 years almost within every sentence that contains the words global warming. So take a look at sea levels during the Medievil Warm Period then. Historical sea level charts show sea levels almost a foot higher than today and better yet actual History and living proof confirms historic Sea Ports miles inland from current sea shores. Actual physical empirical EVIDENCE that establishes sea levels much higher than today in the Medieval Warm Period, no science, no theory, no BS, just ABSOLUTE PROOF. The same goes for the the Mini Ice Age Cooling, sea level was down almost a foot from what it is today, again no BS, just Absolute Proof. Surely to God the Scientists are not now disputing the link between warming and sea level rise? What does it take to accept actual physical empirical evidence over scientific theory? Why go back tens of thousands of prehistoric years ago to predict what’s going to happen in the next hundred years, when you have historical evidence from the last 2000 years. Obvious cycles of warming and cooling are there in the sea level charts, a $10 tide gauge proves we have been warming for the last 250 years with another foot to go before we reach the levels of 450 years ago. Man (and the Polar Bears) have already survived a much warmer Earth, it’s a fact not a theory.
[DB] "So take a look at sea levels during the Medievil Warm Period then"
Sea levels are extremely likely (95%) higher know than at any point in the past 2,700 years.
Thank you for taking the time to share with us. Skeptical Science is a user forum wherein the science of climate change can be discussed from the standpoint of the science itself. Ideology and politics get checked at the keyboard. As this venue is based on credible evidence for claims and using the scientific method at all times, the onus is on each participant to be able to cite credible sources for claims made. Your above claims about past sea levels with respect to those in the modern era are without merit and demonstrably false.
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Off-topic snipped.