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Philippe Chantreau at 01:56 AM on 1 May 2010Common graphical tricks and the Medieval Warm Period
Thingadonta @ post 27. The "skeptic" position as you define it seems to be total nonsense. Why would the climate be more sensitive to a radiative forcing than another? How could the Earth/atmosphere system react differently to an energy imbalance according to the origin of that imbalance? How does the Earth "know" to react little from the extra w/sq.m coming from GHG but lots to that of solar irradiance? It makes no sense. What possioble physical processes could be at work in such discrimination? Where does the extra energy go for "low sensitivity" forcings? Are you sure that this is what "skeptics" argue? Is that what you believe? -
Philippe Chantreau at 01:41 AM on 1 May 2010Skeptical Science talk at University of Qld on May 7
Portland, OR being a rather distant suburb of Brisbane, I won't be able to attend but I wish you the best John. Thanks for walking the talk :-) -
HumanityRules at 01:33 AM on 1 May 2010Common graphical tricks and the Medieval Warm Period
40.MarkR Mann in 2009 produced a paper that purported to show that the MWP was a regional occurence (essentially NH). You can read John's post about it here. Was there a Medieval Warm Period? That paper uses 6 SH series that stretch back to the MWP that show a lack of warming in the SH. The papers I link to in #28 include 5 SH series that show greater temperature variability than Mann and show the MWP as warm as the present. The Mann 2009 paper was uncritically presented on this website as proof of a regional MWP. So is 6 a "significant #s of proxies" while 5 is insignificant? -
suibhne at 01:30 AM on 1 May 2010Where is global warming going?
KR ......G&T, on the other hand, seem to claim that radiative heating doesn't exist at all, which would overturn ~220 years of scientific consensus, contradicts _all_ the experimental evidence and measurements, and is certainly not proven by their collection of errors, logical fallacies, and outright junk........ What makes you think that G&T "claim that radiative heating doesn't exist at all" Quote a page number or such like. -
suibhne at 01:25 AM on 1 May 2010Where is global warming going?
KR I think you must have missed recent post in which Kevin Trenberth frankly admitted that he couldn't account for what he called the "missing heat" and further worried that unless it is found "it could come back and haunt us". I on the other hand like Richard Lindzen do not believe in radiative equilibrium hence the post above. The very simple model excluded geothermal and gravitational effects such as tidal flows etc which would only detract from the focus on these points. I have exaggerated many physical effects to make radiative equilibrium as big a problem as I can make it. If you can think of any further reasonable inflation of the problem please let me know and I will include it. Including non related phenomena only make the case for human induced CO2 as a major problem much weaker. Reasonable conductivity given the time scale of 1000 years should enable the one degree rise in temperature. -
shdwsnlite at 01:03 AM on 1 May 2010Skeptical Science talk at University of Qld on May 7
Any chance of the event being recorded for those of us not in that part of the world?Response: I haven't discussed it with the UQCfC. Honestly, I'm not a big fan of the idea as I don't particularly like the sound of my own voice but I'll ask. At the very least, I can always post the slideshow on the webesite. -
KR at 00:14 AM on 1 May 2010Where is global warming going?
Hmm... I'm reminded of a joke about a farmer (with milk production problems) asking a physicist for ideas, leading to a discussion of "spherical cows". The Earth's core is already pretty warm (think lava) from radioactivity and residual heat; it would be interesting although irrelevant to calculate how long before we melted once we stopped losing radiative energy to space. It was my understanding that Trenberth has refined his data and estimates, based on temperature variation and a fourth-power rule for heat radiation (to use the Max Planck term). That's science - always improving your results with further study. G&T, on the other hand, seem to claim that radiative heating doesn't exist at all, which would overturn ~220 years of scientific consensus, contradicts _all_ the experimental evidence and measurements, and is certainly not proven by their collection of errors, logical fallacies, and outright junk. It reminds me somewhat of the Transformative Hermeneutics of Quantum Gravity paper, 'tho with less overall humor. And once again, short term variations are quite large - that doesn't change the facts about long term temperature shifts of the center-point around which those variations are based. -
Jonathan E Markham at 23:37 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
I don't think it's valid to compare the 10yr average now with the 50yr average from 800yrs ago, you need to plot the 10yr averages for the whole graph or, inconvenient as it may be, stick with the current 50yr average. -
John Russell at 23:04 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
RSVP: The question John asks -- " (if) ...there's any empirical evidence that humans are causing global warming?" -- is perfectly valid. That question does not exclude the possibility that there are underlying natural variations of temperature that would have occurred anyway. Any human causes of warming clearly modify natural events, either worsening or mitigating their effects. If you read the relevant sections of this site you'll find that a critically-important point is that the human-induced element of the current global warming is resulting in change at an unprecedented rate -- too fast for most plants and animals to move, adapt or evolve to accommodate (and I include humans). And THAT'S the rub. -
JMurphy at 22:35 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
Just how many studies would be enough to satisfy the so-called skeptics ? NOAA have published the data for nearly 100 reconstructions, and shown them individually here, along with visualisations, using lots of proxy data types Will any number of studies satisfy those who want to keep believing in a 'broken' hockey-stick or a 'lying, cheating, etc.' Mann ? I don't think so. -
sleepership at 20:44 PM on 30 April 2010It's cooling
April has been record breaking in Connecticut for warm temperatures. Today it will be 77 degrees- after a month that has been 6.7 degrees above normal. Tomorrow 85 degrees, and Sunday 90. Of course this is day to day weather- however, warming of this magnitude after years of milder winters and earlier springs is troubling to say the least. The climate models always predicted that after 2010 we would begin to see record warming-is this 'that' beginning? -
Alexandre at 20:39 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
It's great to hear that, John. Let us know if the slideshow or video or audio is available afterwards. -
ktam at 20:03 PM on 30 April 2010Why are there fewer weather stations and what's the effect?
Another issue is the claim that the temperature adjustments at various weather stations are the reason for the warming trend, once again this is based on anecdotal evidence. What demonstrates this claim to be false is a different graph from the Zeke Hausfather page already referred to in this piece. In that plot they compare the warming trend various forms of the raw data against GISS Temp. GISS Temp shows the weakest warming trend of them all demonstrating that the adjustments are reducing the measured trend not increasing it.
From Zeke Hausfather at rankexploits
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ktam at 19:16 PM on 30 April 2010Why are there fewer weather stations and what's the effect?
I think an important bit that you have missed out is the analysis of the surfacestations.org data by Menne et al. I refer to it in a rather provocatively titled blog post here: Nasa underestimates global warming" -
MarkR at 18:56 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
#28 HumanityRules: My main criticisms of using graphs like that (there were many examples on CO2science, I might put them up in another post) are that they often concentrate on one region or that they cut off post 1950. Now, that isn't necessarily a problem with the science. Sometimes proxies don't go after 1950 for whatever reason. But to claim that this shows the MWP was warmer is just wrong. You need alternative evidence to do that & so far I'm not aware of any reconstructions of hemispheric or global means from significant #s of proxies that show that. -
Argus at 18:45 PM on 30 April 2010A visual depiction of how much ice Greenland is losing
Phila (#71), your comment to #61-gallopingcamel : How could sea levels continue to rise if the amount of CO2 in the atmosphere was hypothetically reduced by a factor of 2 (to 194 ppm). If the CO2 content in the atmosphere is so essential for the increasing temperatures we observe (and the rising sea levels), I would rather expect the earth to rapidly cool off, and the sea levels to decrease as a consequence. -
Marcel Bökstedt at 18:42 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
thingadonta> OK, so according to you, the (a?) skeptic position is that there is some external forcing that caused both the medieval warm period and the present warm period. Can this be made more precise? I would like to know what mechanism is supposed to be responsible. The linearity probably comes from the assumption that effects are differentiable functions of causes. This is a very common assumption, and by definition it means that if the cause is "sufficiently small", then the effect depends linearily on the cause. Your example with the volcanoes is not relevant here, because you are talking about large effects. There is a catch of course, namely whether the causes really are "sufficiently small". As for climate sensitivity varying with the forcing, I think that we first have to agree on the definition on "climate sensitivity". The IPCC is guilty of confusing this issue, as discussed in the first 15 lines of wikipedia's article on climate sensitivity . But lets go with their latest definition. According to this, climate sensitivity is the reaction of the system of an increase in temperature. That is, suppose that a forcing would cause a temperature rise of RF if there were no feedbacks. We would like to know how big the increase would be if we include the feedbacks. The climate sensitivity provided by the feedbacks would conspire to give a temnperature rise of l * RF, where the number l is the climate sensitivity. So in this definition of climate sensitivity, it does not depend on any particular forcing. It is determined by the reaction of the system to an increase in temperature. Maybe I'm missing some point here. -
Riccardo at 18:22 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
ESVP, if you want to anticipate John's answers to your questions take a quick tour of this site, you'll find them and a lot more. -
Riccardo at 18:18 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
Semczyszak, even if Professor Boryczka is right it would not be smart to lower our chances of a safe landing after the pending climate crises. I mean, if there will be a natural trend of, say, 2 °C for the next century it surely won't help to add 3 more degrees ourselves. Or should we be so nihilist to say we're doomed anyways and we should not even try to fight? -
Arkadiusz Semczyszak at 17:23 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
"... like cherry picking 100 Chinese companies that are having bad results to "prove" that Chinese economy is not growing. ..." - Is sophistry The existence of these "100 Chinese companies" however, proves that the "Chinese economy ..." not everything" is in order ... Incorrect interpretation - the use of cherry picking theory; is "a nightmare" discussion about climate ... "... the *rate* of change & the presence or absence of forcings to explain the previous warming events ..." Small "* rate * of change" in the earlier research (MWP) showed (in large part) of using a wavelet "old style" - excessive "smoothing" reconstructions (especially multi-proxies). About this repeatedly, even by Tamino. "... forcings ..." Polish climatologist of the our greatest University (Cracow), Professor Boryczka, forecasting solar activity and the NAO, believes that awaits us, in the XXI century (circa 2070-2100), a strong natural warming (the imposition of the cycles of 100 and 180 years - I would add Millennium x 3) - greater than in the MWP - MWA and CWP-CWA. -
RSVP at 17:16 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
Are humans causing global warming? (I contend that this is a very loaded question. Here's why...) In order to answer that question, you need to break it down a little. What would climate be doing right now if there were no humans at all? would there be... A: warming anyway? B: a static condition? (and if so, for how long?) C: a cooling trend? To ask if humans are "causing" global warming only makes sense when you know what the trend would be for Nature alone without a human presence. For case A, humans would only therefore be contributing to warming. (And then the question would be "to what extent?".) If case C, humans could actually be detaining an impending iceage, or may have even reversed the trend. And a little more... The question is not, "Have humans caused global warming?", or "have humans touched off global warming?" When you ask if "humans are causing global warming" it seem to imply that the moment they stop activities, things will turn back to "normal". -
nautilus_mr at 16:45 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
It is a challenge to stay clear-eyed about the Hockey Stick, because it has been such an iconic image and therefore of tremendous political importance. It has been used by the IPCC, Al Gore and others, precisely because it is so much more effective a communication tool than virtually any other illustration. It is certainly the image that got me tuned into the global warming problem -and I bet that is also true of many readers of this site. It is also no accident that the earliest attacks from AGW deniers were against the hockey stick and often Manne personally. The focus of AGW deniers is to score political wins; they use the language of science, because in this culture it adds gravitas, but their main targets are always the stuff laypeople can easily understand. People reasonably acquainted with the science know the various studies that comprise the hockey stick are only a small part of our overall understanding of climate change. Politically, however, it would be a massive coup for the deniers' camp if they could tear it down. The hockey stick has been given a political importance far beyond its scientific importance. So far as I can humbly tell, it has also yet to be proven wrong. But that could change, and we must always take care not to argue for a scientific theory because of the political consequences of it being incorrect-leave that to the Moncktons and Plimers of this world. -
James Wight at 15:24 PM on 30 April 2010Skeptical Science Housekeeping: flags, printable versions, icons and links... lots of links
For some reason, neutral links aren't showing up on the resource pages.Response: The reason was because I hadn't programmed it to show neutral links yet. I've just remedied that and while I was in there tinkering with the code, I added a feature I've been wanting myself for a while - a "peer-reviewed" link so while you're in there looking at links for a particular argument, you can select to narrow it down to purely peer-reviewed papers. -
HumanityRules at 15:23 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
34.Marcus Would "the contrarians" include Phil Jones (of CRU fame) who co-authored two of the papers I linked to in #28? 31.Jeff Freymueller I agree with what you say except I still think you can't ignore the political interference in this subject on both sides of the argument. It's what takes it from an interesting scientific problem to a controversy. Given you recognise the limitations and problems with the science why do you think Mann et al are so defensive about critisism? I'm aware of egos but a drive should be to improve the science and that partly comes through critical analysis. -
Bern at 14:48 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
@MattJ: heh... no, it's purely descriptive, because it's a knoll which is, well, grassy... (i.e. nowhere to hide) There's also a Conifer Knoll on the other side of the uni, which may be well lit these days with the multi-storey car park right next to it, but back in the early 90s it was a pretty dark & spooky place at night, despite being in the middle of a well-lit campus. Unfortunately my calendar for next Friday is already rather full - not sure how I'm going to fit in work, let alone a trip to UQ at lunchtime... :-( -
Jeff Freymueller at 14:46 PM on 30 April 2010Skeptical Science talk at University of Qld on May 7
As long as John is not being shot at from the "Grassy Knoll", that will be OK. -
Marcus at 14:46 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
Even if the contrarians could prove-definitively-that the absolute temperature anomaly was higher in the MWP than today, there are still other issues to consider-namely the *rate* of change & the presence or absence of forcings to explain the previous warming events. Take a look at all the MWP reconstructions-even those produced by contrarians-& you see that it was a multi-century event (300-600 years from trough to peak, depending on which graph you look at). By contrast, we're seeing an almost identical magnitude of warming in the 20th century in the space of merely 50 years-a massive difference! The other point is that a look at proxies for Total Solar Irradiance during the MWP show a strong upward trend during that period, wheras the TSI for the last 30 years has been on a slight downward trend. So over the last 60 years we've seen an unprecedented *rate* of warming, without the forcings that characterised past warming events! -
barry1487 at 14:38 PM on 30 April 2010Why are there fewer weather stations and what's the effect?
Seems to me that data collection of this type would be the perfect next step for surfacestations.org. It would be good outreach from NOAA to skeptics and make a fine and logical contribution for critics of the temperature record, obviating post-hoc auditing. Thinking about it, it's a pretty obvious marriage. -
Bernard Leikind at 14:19 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
I believe that you are missing the word "not" in this sentence. They are showing you that the last decade was warmer than any 50 year period on the graph including the MWP. You need not post my comment, after correcting your sentence. Excellent, clear, informative post. -
Jeff Freymueller at 13:40 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
#26 chriscanaris, in your comment you seem to be mixing up a couple of very different things. The data may permit a wide range of reconstructions, but that does not mean "anything goes", and does not mean that picking the average or most likely reconstruction is "cherry-picking". Maybe you need to look up the term! In any case, if you look at the reconstructions in scientific papers (and the recent IPCC reports) they come with error bars or shaded error regions, which show you how precise the estimates are. Presenting the best estimate, with a description of how you got it and its error bars, is very, very far from cherry-picking. -
Jeff Freymueller at 13:34 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
#28, HumanityRules, it is a bit misleading to say the main criticism is that they end the graphs too early. Ending the graphs too early in order to make a misleading or false impression using those graphs seems more like it. What you describe as a "political statement" can be rephrased slightly as a legitimate scientific question: "Is today’s global average temperature, averaged over a few decades, higher than any such time period in the past 2000 years?" Once you specify the averaging time and the total time span, that is a question that has a yes/no answer. Our best estimate of the answer may or may not be yes/no at this time, but the question is objective and not political. Mann made the claim in 1998 that it was, with an averaging time of a decade, and this was the only scientific conclusion of his 1998 paper that has not stood up. He was wrong not because of any error specifically in his work, but because the uncertainty in radiometric dating is more than a decade, so you can't connect records from different parts of the world to a single decade in time. His error was in failing to recognize this uncertainty in time. So the test for "unprecedentedness" has to be done over a longer timescale, like perhaps 50 years, and the total interval might need to be only 1000 or 1500 years rather than 2000 because of limitations in the older data. But in the end this is only one small part of the story, and in the end what matters far more than the size of past temperature changes is the ability to explain them based on fundamental physics. -
scaddenp at 12:33 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
"The issue remains - are our reconstructions valid? If not, no hypotheses can flow from them. If they are, then AGW is a prime suspect and our world faces major decisions with very wide ranging impacts." But hypotheses about AGW DONT come out of paleoclimate. This is the important point. AGW is byproduct of a theory of climate which comes out of physics. In turn, if it is valid, then it should be able to reproduce past climate given past forcing, (obviously within the uncertainties to which you can measure both past global climate and forcings). Its a test of a model, not the progenitor of a model. -
angliss at 12:23 PM on 30 April 2010Common graphical tricks and the Medieval Warm Period
thingadonta - ultimately, climate sensitivity is not really a "per doubling of CO2," even though it's usually described that way. Instead, climate sensitivity is really a measurement of temperature rise per unit of energy imbalance. In electrical engineering/feedback terms (my profession), climate sensitivity is the gain in the system. By definition, the gain term operates equally on positive feedbacks, negative feedbacks, and inputs. And that means that the climate sensitivity/gain must respond to a change in energy imbalance caused by solar energy input equally to a change in energy imbalance caused by CO2 to a change in energy imbalance caused by volcanic sulfur dioxide to a change in energy imbalance caused by clouds. The mechanisms of each of them may be different, but the mathematical equations require that the gain affect each identically. This is true even if the different aspects of climate operate on different time scales. The only difference is that climate sensitivity/gain becomes a function of time (or frequency), but every forcing that operates over the scale of 1 year must be treated identically just as every forcing that operates over the scale of 10 years must, and so on. -
Tom Dayton at 12:21 PM on 30 April 2010A visual depiction of how much ice Greenland is losing
gallopingcamel, you have veered off topic. Several commenters have pointed you to other threads on which your comments are relevant. -
Zardoz at 11:59 AM on 30 April 2010Skeptical Science talk at University of Qld on May 7
No chance of a national tour, I take it? You'd be welcome in the other states too - I'm sure there would be somebody who'd like to organize your visit at just about all the Oz universities. -
MattJ at 11:41 AM on 30 April 2010Skeptical Science talk at University of Qld on May 7
I wonder if "Grassy Knoll" has the same implication for Australians as it does for us United-Stateseans. You might want to have security make sure no one is hiding there just in case! Be that as it may, I hope the talk will be available on the Net afterwards for those of us who find the walk to Brisbane rather too challenging. -
HumanityRules at 11:36 AM on 30 April 2010A visual depiction of how much ice Greenland is losing
"Are you Brisbane based?" I wish, chilly Melbourne. Have a think about recording it and posting it here or Youtube. -
HumanityRules at 10:54 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
Given your main criticism of sceptics is they end their graphs too early I'll point you to a couple of 2010 paleoclimate reconstructions in Greenland ,Indonesia and Multiple SH sites that put the MWP as warm as present day. (The following bit is just my opinion; I have no references for it, hopefully it won’t get removed.) Whether the MWP was warmer, as warm as or cooler than the present period seems to only be of political interest. It allows the following political statement "Today’s temperature is unprecedented in the past 2000 years". I recognise that much of the rightwing opposition to AGW also takes a general anti-science, anti-rationalism stance (so you have to pick your sceptics carefully). But this, for me, is one of the issues where climate science itself seems to have strayed from a purely scientific approach into the area of politics and it’s need for certainty. There is a whole raft of data that questions the ‘hockey stick' theory and other data that supports it. It strikes me as a question that is still firmly under debate. This post seems to focus on sceptics as the villains here, clouding the issue with misleading graphs. I'd like to see some criticism of the IPCC for forcing certainty onto this issue. -
thingadonta at 10:50 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
"There appears to be plenty of evidence for some places being warmer than today in the MWP, and whilst most studies say that globally it wasn’t warmer it seems that scientists still want more data to be sure (and if it was warmer, that might suggest higher climate sensitivity). " I don't think that most pro AGW advocates really understand the skeptic position on the MWP and climate sensitivity. The skeptic position about the MWP goes somthing like this: The climate can be very sensitive to solar variation/clouds/1500 solar cycles etc to produce someything like a strong MWP, but NOT be sensitive, or act in a linear fashion, to any changes in C02. Skeptics don't see why one has to raise all variables when one raises overall climate sensitivity, or that they operate in tandem when one or the other changes. Depending on the way various climate factors interact, some climate variables (eg water vapour/clouds, c02, solar cycles) can act in a non-linear fashion-ie when one goes up the other goes down. There can be negative feedbacks. Evidence for this is eg provided in the relationship between C02 and temperature in the 20th century, and also in the early 21st. Volcanoes also act in this matter, small eruptions produce overall cooling, very extended events produce overall warming. Another common position of skeptics is that the earth buffers various climate variations/forcings, by eg absorbing radiation imbalances in the deep oceans, by microbiological changes in soils, by lesser and greater amounts of cloud cover-especially in the tropics, and so on. There is no need for climate to act in a linear fashion to all these sort of changes, and yet all the IPCC models assume such. So there is no basis in arguing that if the MWP was strong, this necassarily means climate sensitiviy is high with respect to C02, which is the common argument on this website. -
chris1204 at 10:40 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
Alexandre @ 12 Oh, and let's not forget the underlying skeptic argument here: "If the MWP was warmer for whatever reason, then the CWP is due to the same reason" Actually, this is not central to a skeptical argument. McIntyre for example eschews any position on AGW. SNRatio @ 18 puts it well" Therefore, you can produce a wide range of "reconstructions", and the main problem is, that because you always use some theories when reconstructing, you are always doing some kind of cherry-picking. The issue remains - are our reconstructions valid? If not, no hypotheses can flow from them. If they are, then AGW is a prime suspect and our world faces major decisions with very wide ranging impacts. -
scaddenp at 10:09 AM on 30 April 2010A visual depiction of how much ice Greenland is losing
"Vermeer 2009 is fine as a piece of speculation but it has little relevance to the real world." Sorry, which part of Vermeer is NOT based on real world data? What Vermeer cant do is predict what emissions we will actually produce, but as far as I can see from your postings, you are quite happy that we follow along the more unpleasant business-as-usual scenarios that is used. Since the models that predict have shown excellent predictive power so far why do you think they will suddenly stop working. -
HumanityRules at 10:01 AM on 30 April 2010A visual depiction of how much ice Greenland is losing
John you were going to post the details of the UQ talk.Response: Sheesh, I'm still going through all the emails that came in overnight! :-) Will post within the hour.
Are you Brisbane based? I'm picturing you devising a whopper of a question to ask me. -
Marcel Bökstedt at 09:57 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
I feel ignorant about this, as about so many other subjects. I've got three questions for those who know more. I do understand that the "other side" of the discussion cares a lot about the possibility that there was a period sometimes during the middle ages when the climate was warmer than today. The facts seem to be against this (see the argument on MWP), but there are certainly also some evidence contradicting this and suggesting a medieval global warm period. (Arkadiusz Semczyszak lists some of those). Now, suppose for the sake if the argument that this assumption is actually true, and that there was a medieval global warm period. This would make some people instantly happy, for the simple reason that it would invalidate the hockey stick. But we should look beyond the hockey stick. What is the theory about the medieval warm period over on the "other side"? One possibility is that they assume that it was caused by some particular forcing. If they do, they should explain why the same forcing is at work now. Except for AGW there seems to be only one possible alternative candidate for this contemporary forcing, some version of the solar theory. One should expect some arguments about similar but stronger solar forcing in the middle ages. (Q1) Has anyone tried to carry this out? But if the argument is that some period in the middle ages was warmer than today, the most likely theoretical underpinning would be that the climate has a huge internal variation, and that the medieval warm period, the little ice age and the present warming are all caused by this internal variation. I don't know how we can be sure that there is no internal, unforced variation which could be responsible for climate changes on the scale of centuries. (Q2) Is there a way to do rule out such internal variation? If the "other side" honestly belives in this scenario, those people should now be working hard on characterizing and describing this internal variation. Which variables (besides temperature) change, how do they influence each other etc. (Q3) Is anyone aware of such work? -
Phila at 09:56 AM on 30 April 2010A visual depiction of how much ice Greenland is losing
gallopingcamel (#74) "That NSF paper you cited recommends holding CO2 concentrations to 450 ppm, something I could cheerfully accept if it can be done without destroying wealth on a large scale." Well, that's a whole other question. We could debate whether certain forecasts of wealth-destruction are "alarmist," but I don't think that's appropriate here. As far as the topic at hand goes, I'm glad we agree that human beings are capable of influencing sea level. -
Steve L at 09:25 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
A quick and lazy google search didn't bring me anything good on Medieval sea levels. It seems if it was anomalously warm for such a long period, there should have been a rise. But this figure, at least, doesn't show much evidence of a high point at the right time. Anyone else have something better? -
suibhne at 09:06 AM on 30 April 2010Where is global warming going?
KR Sorry I didn't catch you at "Is CO2 a pollutant?" ......G&T display an appalling lack of understanding of the physics of thermodynamics, particularly radiative equilibrium..... Strangely enough Kevin Trenberth is recently finding his sums don’t work out within radiative balance. However he should relax, there is no such law in physics. A much more realistic picture was given recently by Richard Lindzen. “Evidence Suggests Man-Made Warming Greatly Exaggerated” In the article Lindzen pointed out that radiative equilibrium is seldom observed. People everyday experience temperature changes of 20 degrees or so and yet the IPCC gets alarmed at a rise of less than a degree in the past century. This prompted me to do a simple calculation based on the planet having no radiative balance whatsoever. This illustrates the sheer thermal inertia of the bulk of the planet. I have used a very simple model of the Earth made of uniform material with reasonable conductivity If the Earth absorbed all the Suns radiation that landed on it and absolutely no heat ever escaped. How long would it take for the temperature to rise by 1 degree centigrade. Formula used Pxt =cm(temperature rise) P=1367W/m2x(crosssectional area of Earth) t =time in seconds C = specific heat capacity = 1000 (you can tweak this number if you like) m = Mass of Earth =6×10power24 When calculated it turns out to be 1080 years. -
gallopingcamel at 08:57 AM on 30 April 2010A visual depiction of how much ice Greenland is losing
Phila (#61), That NSF paper you cited recommends holding CO2 concentrations to 450 ppm, something I could cheerfully accept if it can be done without destroying wealth on a large scale. Scaddenp (#73), Vermeer 2009 is fine as a piece of speculation but it has little relevance to the real world. For Vermeer's sea level rise of 1,790 mm by 2100 you would need a 6.1 degree Celsius rise in temperature as well. -
nautilus_mr at 08:50 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
By the way, the study referred to by Oxford Kevin is the second link given in #7 of this thread, in which Arkadiusz claims the paper shows "Here MWP was about 0.4°C warmer than the Current Warm Period." The study's lead author, on the other hand, says "Our figure does not lead one to conclude that past sea surface temperatures were warmer than today as is suggested on these websites." -
ktam at 07:24 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
I have recently blogged on how co2science has misrepresented a recent study of proxy data from the Indo Pacific Warm Pool. You can read about it and its implications for the medieval warm period: Misrepresentation of Climate Scientists -
johnd at 07:12 AM on 30 April 2010Common graphical tricks and the Medieval Warm Period
The MWP may be of interest to many, but the real interest should the temperatures reached during the interglacial periods, and what forcings or feedbacks turned the planets warming phase into a cooling phase.
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