The Medieval Warm Period was just as warm as today

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


Objection:

It was just as warm in the Medieval Warm Period (MWP) as today, in fact Greenland was green and they were growing grapes in England.

Answer:

There is actually no good evidence that the MWP was indeed a globally warm period comparable to today. Regionally, there may have been places that did exhibit notable warmth, Europe for example, but all of the various global proxy reconstructions agree that it is warmer now and the temperature is rising faster than at any time in the last one or even two thousand years. Anecdotal evidence like wineries in England and Norse farmers in Greenland can never tell you a global story.

NOAA presents a whole selection of proxy studies together with the data they are based on and these can be found here. Specifically, they have this to say about the MWP:

"The idea of a global or hemispheric "Medieval Warm Period" that was warmer than today however, has turned out to be incorrect."

In specific answer to the "grapes used to grow in England" bit, I like to point people here as fairly solid evidence that grapes are in fact growing there now, denialist talking points aside.. If that is not enough, Real Climate did a remarkably in depth review of the history of wine in Great Britain and how reliable it is as a proxy for global temperatures.


This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.


“The Medieval Warm Period was just as warm as today” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

184 thoughts on “The Medieval Warm Period was just as warm as today

  1. Lighten up, Crakar. No one’s called you a fucker–sad, old or otherwise.

    You have got to be kidding me, many posts ago i asked if the models are out by so much what are the ramifications of this. But none of you morons wanted to discuss this instead you launched a smear campaign in an attempt to reduce my credibility whilst simultaneously over exaggerating your own as if to suggest a wildlife scientist a whatever the hell you are Skip are the worlds experts on the subject of all things important.

    And now the same cast of dodgy believers are at it again, you are not interested in discussing what these two studies my suggest you are simply defending the faith. In fact Skip i would suggest that you have no right to sling shit at other people because you have no opinion of your own. Your only contribution to this site is about narratives and the statement “I agree with what he said”.

    In other words you make no meaningful contribution at all. Mandas you simply ooze ignorance and arrogance you are of the belief that you are right about everything even though you know about as much as anyone else here and no dont come back with “but….but…but i am a scientist”. Dont forget to let the dog now and again so he can take a piss.

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  2. crakar

    Skip said it best – lighten the fuck up!

    You want to discuss these two studies? Ok, let’s discuss them. Your first task is to go away and read them for the first time. And don’t bluster and rant and rave about me smearing your credibility, everyone here knows that you have NOT read the studies yet. That is not unusual – we all know that your contributions to this blog rest solely on your ability to cut and paste the opinions of others from various websites. So stop acting as if we somehow besmirched your good character. It is not skip or I that have no credibility or that our opinions are not supported by evidence – that is your job.

    In the meantime, my views on both studies are clear. I have posted them a number of times, and if you are too damn rude to actually read what I had to say, then my supposition about you having no credibility has been amply demonstrated. But just to refresh it for you, in regard to the McShane and Wyner paper, have a look at post #141. I think that’s pretty clear. The paper changes nothing except that it suggests that the proxy data sets for the northern hemisphere are inadequate to provide statistically significant, accurate temperature reconstructions over the past 1,000 years. It does not say that the reconstructions are wrong (just that the data sets are statistically insignificant, and it does say that the instrumental record clearly shows recent, unexplained temperature increases. When you have read the paper, come back and tell us what YOU think.

    With regard to the McKitrick and McIntyre paper, I will continue to state that I do not understand it, and will reserve judgement on it. IF it is accurate – and that will only be determined following review by experts (ie not me and certainly not you, peer review is only the FIRST step in that process (which you would know if you had the slightest understanding of the scientific process), it may well be that some of the prediction models will require modification. Once that is done, we will have a clearer indication of any revised forecasts. But we will not know what the paper means until, a) the paper has been verified, and b) any verified findings of the paper have been incorporated in the appropriate models. You never know, it may indicate that climate will warm slower than predicted by some models, or, because of the complexity if the system, there may be other consequences we haven’t considered.

    Particularly with regard to the M&M paper, both skip and I have refused to accept it or reject it, because we have insufficient knowledge to do so. And I have asked you repeatedly why you have apparently accepted it as accurate. If you want to demonstrate that you have the slightest degree of credibility, you would answer that question openly and without evasion. So far you have consistently refused to do so.

    How’s that for discussing the issue? How about you now contribute to the debate by telling us all what you think?

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  3. whatever the hell you are Skip are the worlds experts on the subject of all things important.

    I can’t claim that, sadly.

    I can claim I’ve never plagiarized incorrect scientific argumentation. Is that a start?

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  4. Oh – and crakar. You are fond of criticising the fact that I am a wildlife scientist, and am therefore not qualified to comment on climate issues etc. I want to know if you stand by that criticism.

    That should not be a hard question to answer. Do you stand by your view that I should not comment on climate issues because I am not qualified in that field?

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  5. Mandas,

    The papers have been peer reviewed. Both the MMH 2010 and MW 2010. I also have not seen any place where a statistician has pointed out any flaws with these works.

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  6. 154,

    From what i have read of the MWP paper it appears that it is saying that from the available data you cannot accurately reproduce the past 1000 year temps.

    As i said in a round about way in post 140 (you know the post where you read what you wanted to read and then went nuts) we have a study claiming that there was not enough available data for Mann to create the stick, but yet just enough data for them to say they dont know what shape it should be. Eventually a new method of statistical torture will be invented and the past 1000 years will look like a tennis racket.

    As for the other study, my beef with you on this is not that your opinion is “i can neither accept or reject it” but it is with your opinion that everyone else should think just like you. I do understand the scientific process of which you speak regardless of how stupid you think i am.

    156,

    Mandas i only critise you about being a wild life scientist because it pisses you off much the same way you say things to me. Wildlife scientists play a vital role in understanding the environment and the more we have the merrier and i am sure you are very good at what you do. I acknowledge that what i said was intended to piss you off and this was not the right thing to do.

    In regards to what you can and what you cannot comment on, if you want to comment on something then fill yer boots Mandas. Thats the whole point of being here, if we were to take the attitude of “you cant comment on such and such because your just a (insert skill set here)” then it would be a bloody boring place.

    My attitude here is let everyone comment when they want on what they want, if i want to say this study shows the models to be wrong then you can say “not yet it needs to be verified etc” Ok fine lets wait but in the mean time lets talk about what it means if it is verified or something along those lines.

    Dont take everything i say as an affront to AGW, maybe i could have worded my posts better i will grant you that. One study will never convict or clear CO2 we all know that.

    One last thing I have one question that i have asked before which must have got lost in the process which i would like both you and Skip to try and answer and if i have left a question unanswered then let me know.

    You state the paper must be verified which i accept but let me ask you again have the models been verified in the same way and how was this done?

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  7. crakar

    Thank you for your reasoned and thoughtful comments. It would all probably be a lot better if we were all a little more civil at time, and I will accept my share of the blame in that regard.

    I don’t believe everyone should think the same as I do – but my ongoing beef is that people should refrain from criticising things that they both do not understand, and which they haven’t even read. I also believe strongly in a rational and logical approach to understanding things, and that when the evidence suggests that an opinion is wrong, then you (anyone – not you in particular) should be open minded enough to accept that you may have been mistaken. Its hard to do this – which I know from personal experience – but it is also the right thing to do. I hate it when people who do not know anything about my particular subject of interest think they know better than me – and I project that same concern into areas such as climate change. Why is it that 97% of experts in the field accept climate change, but half the population thinks they know better? Imagine if people who had no background in what you do for a living told you that you were wrong or involved in a conspiracy etc. You would be rightly pissed off – so why should you (or anyone) think your opinion on climate change is right and the experts who have spent decades working in the field are wrong?

    Anyway, as far as these studies go, we both agree that the ‘hockey stick’ study actually does not really change anything, but it does suggest that the data may not be significant enough to draw definitive conclusions. I know that many people dispute that, and that is something they can argue between themselves. To be frank, I have always had concerns about some proxy reconstructions (ask dhogoza, we had a very frank exchange of views on the subject some time ago), but in the end I don’t think it changes much. The real issue is current warming and what is causing it, not what may or may not have happened a thousand years ago.

    The other study is more problematic. You may not be aware that neither study author has any expertise in climate science. McKitrick is an economist and McIntyre is a geologist, so if you have concerns about my qualifications to comment, you would have to have the same concerns about them. Nothwithstanding that, the real issue is if the findings are valid. Peer review is just a first step – it essentially means that a study is fit to be published (there is more to it than that, but that will do as a lay explanation). The real validation of a study comes after it is published, when everyone – not just the peer reviewers – can check the work to see if it can be reproduced, and to check whether it is accurate. Science can be a cruel game in that regard, as I am sure most here will attest.

    But – if the study proves to be valid, then the findings can be used as accepted science. Current models are verified by hindcasting – checking them against what has been known to have occurred to see if they can predict past events. Unfortunately, a LOT of models can do that, and they all contain different parameters and have different forecasts of the future. That is why the IPCC uses a range of models – because no ONE model can be said to be the only answer. As the data is refined, the models are also refined and the less accurate models fall by the wayside.

    If this study is verified, it should be included as part of the model calculations. But what that actually means cannot be determined by a simple reading of the paper. The calculations would need to be incorporated, and then the models run to see what happens. That is why I – and I assume skip as well – are reserving judgement. We are a long way from knowing an outcome, and any decent scientist would hold back on forming too definite opinion until some more of these issues are resolved.

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  8. Vernon, reading that McShane and Wymer paper was indeed hard yakka, hard to stay awake that is. Given my knowledge of statistics is very limited, and some of the technical jargon requires quite some translating on my part, some thoughts:

    – What’s with all the political posturing at the beginning of the paper?, a major turn off for me, and a declaration of the authors motivations it would seem.

    -Edward Wegman excoriated Michael Mann?, That plagiarist guy, Edward Wegman?, the same guy who claimed CO2 lagged temperature? What’s that sort of junk doing in a peer reviewed paper?.

    – So using the authors model they end up with virtually the same “hockey stick” shape as earlier reconstructions, but with greater uncertainty due to their choice of methodologies.

    – Could it be that that is a reflection of their approach rather than the proxies themselves?

    – Why do they calibrate against the Northern Hemisphere mean temperature rather than screen for proxies which reflect local temperature, such as the CSP used in Mann 2008?.

    I’m working my way through it, but it seems the authors have attempted to discredit earlier reconstructions by using a tweaked approach that, not surprisingly, yields a rather different conclusion.

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  9. Vernon said:

    I also have not seen any place where a statistician has pointed out any flaws with these works.

    Try here Vernon, Deep climate shows many of the flaws in this paper.

    http://deepclimate.org/2010/08/19/mcshane-and-wyner-2010/

    Is this journal to be taken seriously when it accepts such editorializing and political posturing? It seems that it may be vying with E & E as the most discredited so called “science journal”.

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  10. Ian,

    You have yet to point out where a statistician has pointed out any flaws. Please present a CV of Deep Climate that shows he is a qualified statistician. All I see in your link to his blog is that he recycled his talking point without addressing the paper at all.

    And yes, Annals of Applied Statistics is one of the leading journals which publish articles in statistics. Your opinion not with standing.

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  11. I have to agree with Vernon.

    AAS is ranked in the top 10 in terms of impact factor, so my guess is it does not routinely traffic in rank quackery. The question remains how the work will be received by the body of statistical expertise. This is really interesting at this point, I have to say.

    But I would ask you this, Vernon: Are *you* in a position to evaluate the merits of this paper? If not, I’d advise remaining noncommittal for the nonce.

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  12. dapple/Ian

    I agree with both of you about the ‘political posturing’ in M&W, and that is has no place in a science paper. But I also have some concerns about some of the other criticisms levelled in the Deepclimate critique. A lot of it appears – to me at least – to be ‘defending the faith’, and while the paper should be critiqued for any flaws in its methodology, those criticisms should also be free of any political motivation. And unfortunately, I don’t think they are. Whilst the critique is right to point out the posturing in the paper, I believe it focussed to much on this and not enough on the underlying thesis of the paper – that the proxy datasets are inadequate to provide a significant reconstruction of past temperatures.

    The point should be – is this a fair thesis? To be frank, all that I have read seems to suggest that M&W may have a reasonable point. I am not suggesting they are perfect or that the paper could not do with some work, but nothing I have read demonstrates that they are fundamentally off base with what they are saying.

    However, and this is the big however, I go back to the point I raised in post #159. In the context of climate change and the current warming, does it matter? M&W are critiquing northern hemisphere proxy reconstructions, and there is this small issue of the southern hemisphere that has to be considered to understand global temperatures. We know there was not a temporally synchronous global MWP – all the proxy measurements from the SH do not line up with the NH (scroll up for the evidence). And no-one, not even M&W, are disputing that the instrumental record shows an unusual increase in temperatures right now. That is the real issue.

    People can argue all they like about what the proxy measurements show, but even if they were able to demonstrate past global climate variability (which they haven’t), to make the case that the current climate variability was just another example of this they would have to show the conditions were the same. And we all know they are not. So…. so what?

    The instrumental record shows increasing GLOBAL temperature right now. The instrumental record shows an increasing level of anthropogenic CO2 in the atmosphere. We know about the link between CO2 and LWR absorption. You can carry on all you like about the accuracy of proxy data set reconstructions over the past thousand or even million years if you like. But it is a red herring. It changes nothing. Climate change is real, and we are causing it.

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  13. Skip,

    I am not a statistician either. To the extent I can follow it, the arguments and methodology seems logical. I too am waiting to see what is said once this is published by other statisticians.

    mandas,

    your arguments that they only did the NH and the past does not matter are not logical.

    a. If they are right, and we should know in a few months, then it does not matter if it is a NH proxy or a SH proxy, neither will be good enough reconstruct past temperatures to the degree needed.

    b. If we do not know the past temperatures, then there is no way to determine if the current warming is outside of normal variability.

    That is why this paper is fairly important and is about time the statistical community became involved.

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  14. Mandas 159,

    Just a few points

    I thought geology was one of a few fields related to the climate? Also they use statistical methods used in economics circles. Is this the right way to develop a 1000 year temp data set? I do not know.

    (remember what i said about not everything being an affront to AGW)In regards to model verification your explanation is the way i understood it. I see it this way, if we know all there is to know about the climate then we can tweak the models to accurately hindcast and therefore we will be able to accurately predict the future.

    If we do not fully understand the climate but tweak our models to match the past then there is a good chance we will not accuartely predict the future. This study or future studies like it, if verified, will show shortcommings in the models and hence our understanding of the climate. The key words here are “if verified” i accept and understand that. I suggest we now take a wait and see approach in regards to this issue, agreed?

    In regards to the M&W paper i must admit when i read the preamble i thought it was something from Monkton or Watts and it does make one question the neutrality of the authors. Having said that i dont get the stats side of it so by the mere fact it has cleared peer review and will be published i must assume it has some merit. Once again only time will tell i suppose.

    165,

    I agree with Vernon in b, in order for us to understand the present and indeed the future we must first understand the past. If the MWP was global or merely of the Nth Hem or even just a local event then what caused it, did the LIA exist, was it global or just in Europe then what caused it. Why have temps swung up and down every 30 years or so in the 20th century?

    If we dont know these things plus many others then how could we possibly predict the future with any certainty?

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  15. “The point should be – is this a fair thesis? To be frank, all that I have read seems to suggest that M&W may have a reasonable point. I am not suggesting they are perfect or that the paper could not do with some work, but nothing I have read demonstrates that they are fundamentally off base with what they are saying.” – Mandas

    Hmmmm, they claim that the proxies in general are too weak to detect a climate signal, then in the very next paragraph talk about the warmth of the MWP?, and that warmth would be known from?, climate proxies perhaps?. Sounds a bit off base to me, but I’m still trying to figure out the fundamental differences in their approach and that of Mann 2008, that statistical jargonese is sooooo tedious.

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  16. Vernon

    “…..If we do not know the past temperatures, then there is no way to determine if the current warming is outside of normal variability…..”

    This statement could not be more wrong. Unfortunately, it has become a mantra of many who oppose the concept of AGW that the climate has always varied, and always will. The change is just ‘natural variability’.

    But then, no-one denies that. Of course the climate always varies and always will. But what deniers leave of this mantra is that the climate varies in response to something happening – it does not just vary for no reason.

    Climate is a complex system and is influenced by many drivers and feedback mechanisms. The sun, orbital and rotational factors, atmospheric particulates, albedo, oceanic currents, and the chemical composition of the atmosphere all play a part. We try to understand the past so we can understand the system better, but in the end when there is a change in the climate it is because something has changed to make it change.

    When we look around right now, every one of these known primary influences is absent – except for one: a change in the chemical composition of the atmosphere caused by anthropogenic gas emmissions. We know this will cause the climate to change, so we can be confident with a very high level of probability that it is the culprit. And unless there is some other factor that we are not currently aware of, then we have to accept the very simple fact that the current unusual global climatic warming is as a result of GHG emmissions.

    If you want to look around and find something else that is the cause, go ahead. In fact, I encourage you to do so. But until and unless you can come up with something, I am going to stick to the science we know – not the science that hasn’t been discovered yet (and which may not even exist).

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  17. crakar

    A few points:

    “….I thought geology was one of a few fields related to the climate?…”

    Not really. Geology is as close to climatology as oceanography or biology is. Paeloclimatology is the study of past climate – but it uses information from sources such as geology (and others) to reconstruct past climate.

    “… Also they use statistical methods used in economics circles….”

    They use statistical methods in all sciences. I use them in my studies. My point about M&M being an economist and a geologist was to highlight the fact that they are no more qualified to comment on climate than me, or skip, or dapple, or you. I am not saying they are wrong – I was making comparisons to a concern you had previously expressed about qualifications.

    “….. I see it this way, if we know all there is to know about the climate then we can tweak the models to accurately hindcast and therefore we will be able to accurately predict the future….”

    We will never know all there is to know about climate, and our models will never be 100% accurate. The climate is just too complex. But we will improve over time as we gather more information.

    “…. I suggest we now take a wait and see approach in regards to this issue, agreed?…”

    If you are asking that we stop arguing about it and wait and see if the paper is accurate and what effect it may have on models, then I do agree. But if you are suggesting that we should hold off on taking any action on climate change until our models are perfect, then I do not agree, for the reason I expressed above.

    The probability that the current climate change is being caused by humans is so high as to make no difference (but the answer will never be 100%). And while we can argue about the extent of future changes, the probability of further temperature increases and associated consequences if we do nothing is also so high as to make no difference.

    Wouldn’t be better to move off the track as soon as we see the train coming, rather than waiting until it hits us?

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  18. “If you are asking that we stop arguing about it and wait and see if the paper is accurate and what effect it may have on models, then I do agree.”

    Thats what i meant.

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  19. Very interesting discussion. My view on this subject is that it’s impossible to measure exactly how much human beings affect the climate, and the climate is changing a lot without human beings anyway. In my opinion we should focus on stopping pollution of oceans before spending all the time on discussing whether the global warming is happening or not.

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  20. If your prime concern is the oceans, I would have thought that ocean acidification would be top of your agenda.

    The only way to reverse that is to reduce CO2 concentration in the atmosphere.

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  21. Hi Ann,

    Yes, it is impossible to know exactly how much we will influence the climate, but the range has been identified as somewhere close to 3oC for doubled CO2 levels with a very high degree of confidence, and the likely range extends further towards the higher side than the lower. Climate has changed alot in geological history from natural causes, but none of these causes are active right now, so it is clear that, as expected and predicted, hman influences have now overwhelmed natural ones.

    I am curious as to how you feel about having a view that is directly at odds with the view of 97% of experts in this subject? Are all opinions equal when it comes to scientific questions? I tend to think not and with the exception of politically hot topics, I think most of us trust experts, especially when first, second, third and fourth opinions are all the same, and for very good reasons.

    How much research and energy do you devote to a topic before you are confident that you have it right where the experts in the field have it wrong?

    Thanks for the visit, and I am happy to provide some online resources if you do want to test your knowledge of the issue agaist the experts!

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  22. Ann,

    “….My view on this subject is that it’s impossible to measure exactly how much human beings affect the climate…”

    While that’s strictly true, we are affecting it to some degree.

    “…the climate is changing a lot without human beings anyway….”

    The climate does change for reasons other than human influence, but none of those factors are evident at the moment. Therefore, we can be very confident that the current climate changes are because of anthropogenic factors.

    “… In my opinion we should focus on stopping pollution of oceans …”

    An admirable goal!

    “….before spending all the time on discussing whether the global warming is happening or not…”

    We shouldn’t be discussing this at all. We know its happening. What we should be discussing is what to do about it. But why can’t we do both – reduce both ocean pollution and anthropogenic CO2 emissions? They are not mutually exclusive, and we can multi-task.

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  23. There are too many studies to link to with strong evidence that the MWP was global and possibly the LIA as well.
    Anyone who writes those studies off completely, is an alarmist in the true sense of the word.
    Science works in all directions and scepticism rules in just as many directions.
    No one, scientist or layman, should accept any one train of thought or evidence as read, there’s a lot still to be learned about the Earth we inhabit and climate science especially, is still in it’s infancy, yet to take its first baby steps.

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  24. “There are too many studies to link to with strong evidence that the MWP was global and possibly the LIA as well.”

    Too may? Give us one at least. Can’t be too hard with so many to choose from.

    “climate science especially, is still in it’s infancy, yet to take its first baby steps.”

    Older than genetics, rocket science, several other branches of physics…

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  25. Earthling, we’ve seen all that before. The problem is that all of those studies look at individual regions, there are no global reconstructions that indicate a pronounced MWP.

    I am closing this thread and refer you and any future would be commenters to this more recent thread:
    http://scienceblogs.com/illconsidered/2010/04/great_resource_on_various_mwp.php

    To any and all who are going to claim “countless studues” showing a MWP, please read that post and deal with its contents over there.

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