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HumanityRules at 01:01 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
18.skywatcher Why would clouds respond the same to CO2 variation in the industrial period as they might have to solar variation in the pre-industrial period? While you can measure the direct affect from increasing levels of CO2 or changes in solar irradiance (assuming accurate measurements) you can't really calculate what the feedback responses are. Maybe I'm wrong but these sorts of calculations that John are describing seem to assume simple fedback mechanisms shared by all forcings. -
Ken Lambert at 00:38 AM on 20 October 2010It's the sun
KR #692 and kdkd #696 Two points: Firstly - KR seems to still not get the fact that a forcing component does not have to be rising to be adding energy to the system. A steady or roughly constant forcing such as F.Solar (say S) will add energy over time as St - a linear increase. Lets say that F.CO2 is linearly rising wrt time (over a short period of say 25 years). Therefore F.CO2 = Kt where K is a constant. F.CO2 will add energy over time as Kt^2/2 - a squared function increase. Both are adding energy. Secondly, the F.CO2 and other component forcings are theoretical and not directly measured - only the combined imbalance is directly measured at TOA. This is supposed to be +0.9W/sq.m. In fact the CERES satellites are measuring +6.4W/sq.m. So this is 'corrected' down by -5.5W/sq.m to the theoretical imbalance. The problem is that not even the 0.9 is being observed in OHC. The wide error bars on aerosol cooling, and other forcing components mean that the mix of components is not really known accurately. I would like to see a combined forcing chart including S-B cooling over time to see what the energy balance is as well. Anyway - I think my point is made - the Solar forcing component 1950 - now is about 0.4W/sq.m - not 0.12W/sq.m as the IPCC chart implies. -
Doug Bostrom at 00:36 AM on 20 October 2010Throwing Stones at the Greenhouse Effect
You appear to be missing some key concepts, RSVP. Baffling, considering how much time you spend arguing here.
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Alexandre at 00:26 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
skywatcher #16 I thought I had said that too on my third paragraph... anyway, if I did not make it clear, I'll rectify it by endorsing what you said now. -
skywatcher at 00:25 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
chriscanaris - why would clouds operate differently in the present day compared to the past? If clouds are a strong negative feedback, we would see far less natural variation than we do in the palaeoclimatic record, be it last 1000 years, or ice ages. There simply haven't been large enough positive natural forcings to allow clouds to operate as a big negative feedback. You'd end up with a palaeoclimate flatter than a Mann et al (1999 vintage) hockey stick shaft... -
robert way at 00:25 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
Philip64, You are correct. Sea level was higher than today during the MWP by between 12 and 21 cm. This is because of the prolonged length of the MWP allowed for losses of ice and thermal expansion to occur over a long period of time. Grinsted et al (2010) conclude that if we saw no increase in temperatures from the year 2008 to 2100 we would see a sea level rise greater than during the MWP as the thermal inertia of the oceans and the ice caps catch up. The article I am citing is here: http://www.springerlink.com/content/527178062596k202/ -
Doug Bostrom at 00:23 AM on 20 October 2010Explaining Arctic sea ice loss
Hi, garethman. There are numerous "periods of recovery" visible in the graph since it began showing an extended decline ca 1970. These have all swiftly ended, to be overwhelmed by subsequent declines. The graph in this article ends in 2009; a look at a graph including 2010's melt season shows another "period of recovery" appearing to draw to a close. This particular article is more about attribution. Peter Hogarth has done a fine job of covering "recovery" here on Skeptical Science. -
skywatcher at 00:20 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
Good post - a topic on which I've had a number of debates with irrational skeptics. A minor text quibble - maybe change the opening "The" in the 3rd sentence to "Their" - the logical leap is only logical if you're a skeptic! Alexandre - it does change the sensitivity to CO2, because if the world's climate responded significantly to the ~ +0.3W/sq m of the MWP, it will respond correspondingly more significantly to the >1W/sq m of anthropogenic CO2 forcing. Few parts of the climate system are particular about from where they get their extra W/sq m. Larger natural variability must result in larger climate forcing from anthropogenic CO2. Unless you can argue that the CO2 forcing is a much lower value in W/sq m, then the latter must follow the former. And there is relatively little uncertainty about the CO2 forcing value, as Ned's posted figure shows. RSVP - the Sun has as much impact now as it did in the past, but the forcing is rather small in comparison to that of CO2. The papers linked in this NASA article are well worth a read: CO2: The Thermostat that Controls Earth's Temperature, particularly two new ones, as they are quite relevant to this post. -
chris1204 at 00:17 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
Ned @ 8 PS: Just take a look at what I presume are the uncertainty bars for CO2 and clouds respectively in your diagram from AR4. -
chris1204 at 00:12 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
Ned @ 8 'Cloud feedbacks remain the largest source of uncertainty.' For example, see: Cloud Feedbacks in the Climate System: A Critical Review (Stephens 2005). Googling 'cloud feedbacks in the climate system' yields 289,000 results - this just happens to be a reference on the first page. I think we can be too quick to dismiss the role of clouds. -
HumanityRules at 00:12 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
...the 0.8oC from the past 1500years isn't natural? should read 150 years. -
Doug Bostrom at 00:10 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
RSVP, just as an exercise, look up the definition of the Watt as a unit of power, eh? Once you've got the notion of a Watt under your belt, you can then begin relating it to mass, specific heat, conversion into sensible versus latent heat, etc. -
HumanityRules at 00:09 AM on 20 October 2010Do critics of the hockey stick realise what they're arguing for?
John, Roy Spencer in his recent post about the recent Lacis paper has suggested that the past variation in temperature could, in part, be driven by internal mechanisms. for example cyclical changes in the oceans could have an affect on the hydrological cycle and cryosphere thus affecting albedo. This would make the whole process of trying to calculate sensitivity from past climate flawed. It seems like a difficult one to disprove. Also generally on the overall idea you show here, does your analysis depend on the idea that feedbacks are roughly similar depending on the different forcing. Are you saying that if the relatively small changes in TSI have larger affects on surface temperature then this means that doubling Co2 will also have a similar larger affect? The changes in solar irradiance have a complicated affect on different parts of the climate system, take for example the stratospheric effects from UV in the discussion about the Haigh paper and all the possible knock on effects that has. This will be totally absent in forcing from CO2. How can you confidently say that because you deduce great climate sensitivity from solar variance means greater sensitivity from CO2? The same could be said for forcing from volcanos superficially they seem the same by changing the net energy budget but they do it in very different ways that will lead to very different feedback mechanisms. Finally there also seems to be something missing if we accept that solar variance has had a greater effect in pre-industrial times. It must also mean that solar is having a greater affect in industrial times, unless you think solar variance has switched itself off for the past 100years. It must mean that solar is implicated in some of the cyclical features of the 20th century temperature record. The idea that the 1940-1970 'cooling' and recent warming are all about aerosols and CO2 respectively seems flawed. If as Moberg and other say that natural processes can change temp by up to 0.7oC in 5-600years then what's to say some (or much) of the 0.8oC from the past 1500years isn't natural? There seem to be more implications from greater natural variability in the past 1000 years than the one you present (climate sensitivity). (small point Hergel et al is 2006 not 2000) -
Ken Lambert at 00:08 AM on 20 October 2010It's the sun
archiesteel #695 As the planet warms from a forcing imbalance, it emits black body radiation in proportion to the fourth power of the absolute temperature (degK) via the Stefan-Boltzman equation. The forcing imbalance gap then closes and a new equilibrium temperature is approached. The 'emitting temperature' is quoted as about 255degK which is the temperature that space sees the Earth. The average surface temperature is about 15 degC or 288degK. The difference of 33degK is the 'greenhouse effect' of the atmosphere which slows down the heat transfer like an insulating blanket. -
Alexandre at 22:50 PM on 19 October 2010Climate Change Impacts on California Water Resources
Influx of seawater in aquifers is a problem in the Orange County wherabouts for a long time. Sea level rise would certainly worsen this. The problem and -mainly- the efforts in litigation and rule making to solve it have been subject of extensive research, including the Nobel Prize Elinor Ostrom. Her work about common-pool resource management should have more attention than it has had in these times of natural resource overuse. Two recommended books: - Rules, Games and common-pool resources (very academic and technical. Lots of math) - Governing the commons (a still academic but more readable text) Both have these Californa aquifers as one of their case studies. -
CBDunkerson at 22:41 PM on 19 October 2010Explaining Arctic sea ice loss
garethman #56: "The problem with this is that when year after year it does not happen, the warning begin to look like one of these chaps walking around with a billboard saying "the end is nigh" and it has the opposite effect on peoples perceptions." To my knowledge NO ONE has predicted an ice free Arctic ocean in the Summer prior to 2012 at the earliest. Most projections are closer to 2050... or 2100 if you go back about four years. Thus, I can't agree with the 'year after year' bit... it hasn't been projected to happen YET. So the fact that it actually hasn't in several years when no one thought it would doesn't seem particularly 'damaging'. "The other issue is that although the long term trend is obviously down, the short term trend is up from the 97 low. If this continues for another year or two the graph will start to look curiously like a hockey stick." Since we are now far below 1997 ice levels I assume you mean the 2007 low in ice extent... which was only a tiny amount lower than the 2008 and 2010 values. Claiming an 'upward' (barely) trend of three years is like claiming that Summer is going to be below zero because June 2-4 were one degree cooler than June 1. In any case, that's ice extent... which is largely determined by how spread out the ice is. The ice volume, the actual AMOUNT of ice, hit new all time lows of 5800 km^3 in 2009 and 4000 km^3 in 2010. If that trend continues nearly all the Arctic sea ice will be gone within a few years. -
Alexandre at 22:39 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
Lars #1 This does not change the sensitivity argument from John's post. If the MWP was even warmer (as "skeptics" like to believe), that means the climate is even more sensitive to those rather mild forcings that occurred then. And this means climate would be more sensitive than expected to those CO2 W/m2 as well. Moberg points out (as far as I understand it) that natural forcings and natural variability seem to be more present than previously thought, and therefore projections should account for them too - as far as we can predict them, of course. But again, this does not change the sensitivy to CO2. -
Daniel Bailey at 22:22 PM on 19 October 2010An underwater hockey stick
Re: HumanityRules (97) Why on Earth would anyone be happy about that? Unless the increase was less than expected (that I would have been happy about)? You cannot imagine the joy I would feel if I could wave a magic wand and undo what we as a species have done with our injection of the bolus of fossil-fuel-derived carbon into our environment... ...a joy to be un-experienced and un-felt. The Yooper -
Ned at 22:09 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
RSVP writes: Should'nt sensitivity be related in some way to units of time? Yes, it is, in that ultimately climate sensitivity is the product of all feedbacks each of which has its own time scale. Some are very fast (water vapor), some intermediate (carbon cycle) and some are slower (ice albedo and tundra-taiga albedo). Often CS is referred to in terms of its equilibrium value once all of these feedbacks have taken effect. But the time evolution of global mean temperature from T0 to Teq will be nonlinear. -
Ned at 22:01 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
chriscanaris, I'm afraid I'm not following you. The IPCC AR4 section you link to doesn't seem to suggest that CO2 is not the driver of anthropogenic climate change. It merely states the probable range of uncertainty around the best estimate for climate sensitivity, and lists some of the major feedbacks that contribute to climate sensitivity. CO2 is the largest anthropogenic forcing, unless you have something to suggest that everybody's been missing:
Anthropogenic and natural radiative forcings (IPCC AR4 Section 2.1)
The feedbacks mentioned in the IPCC text you link to are not independent actors. They are in fact the mechanism by which the forcings (shown in John Cook's figs 2 and 3 above) translate into temperatures (shown in JC's fig 1).
The point of this thread is that we know pretty well what the forcings have been for the past millennium. If it turned out that the amplitude of the MWP-LIA difference was larger than expected, that would necessarily imply that climate sensitivity is also larger than expected. Nothing in the IPCC section that you cite contradicts this (or even particularly relates to it).
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CBDunkerson at 22:01 PM on 19 October 2010Despite uncertainty, CO2 drives the climate
Joel #28: "IPCC projections are no better than the economic models they use for inputs. The science can be perfect, but with a bad economic model it is GIGO." All of which is smoke since the IPCC projections span a range of emissions scenarios that extends both above and below what you consider likely. They covered everything from impossibly high (i.e. continuous population and economic growth) to impossibly low (i.e. immediate cessation of all fossil fuel use). In short, it's covered. -
RSVP at 21:54 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
John Cook "Technically, climate sensitivity is defined as the change in global temperature if the planet experiences a climate forcing of 3.7 Watts/m2" Should'nt sensitivity be related in some way to units of time? If something responds slowly, it is described as being less sensitive. If something responds faster, more sensitive, etc. -
chris1204 at 21:19 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
Always assuming that you believe anthropogenic climate change as originating *overwhelmingly* with CO2. If some of the uncertainties acknowledged in at least one authoritative source are taken seriously, the picture may be somewhat more complicated and hence close scrutiny of the palaeoclimate record and climate sensitivity and its sources may still be warranted. CO2 is *very* important but it may not be the whole story. I do not buy arguments that suggest that a robust MWP would justify 'business as usual' on an indefinite basis. However, ”The last temptation is the greatest treason/ To do the right deed for the wrong reason.” Pedantry aside, doing the right deed for the wrong reason may cause us to overlook vital elements in planning for an uneratin future. Philip64 @ 4: Interesting that you mention Venice, which has been subsiding because of exploitation of aquifers. Tidal factors seem to be of lesser signhifcance than is commonly supposed. -
JMurphy at 21:09 PM on 19 October 2010It's the sun
I wouldn't waste your time with Howard's site. An example of its 'thinking' : "Ever so Clever Alarmist Tricks of Trade There seems no end to the assemblage of clever tricks and blockades which the bretheren of the alarmist church can dream up. And since they hold pretty much all the top jobs all over their global diocese they for the most part go undetected and unreported." Hm, nice... -
Ned at 20:59 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
John, this is a really clear and well-written post. Just the kind of thing that SkS is known for. Nice work. Philip64's point is a good one. With the MWP being a long, slow rise rather than the steep increase in temperatures from AGW, more of the slow responding components of the climate system should have had time to adjust. That means sea levels, alpine glaciers, alpine/arctic tree lines, etc. -
Philip64 at 20:51 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
Excellent piece with a clear enough message, I think, even if the explanation behind it is (inevitably) complex. I don't know the answer to this, but if the MWP really was longer and warmer than the climate today, shouldn't it have seen a significantly larger rise in sea level than ours to date? Are there any reliable measures of sea level back then? (Anecdotally, I note that Venice was mainly built between the 12th and 15th Centuries, at sea level. No evidence that it was sitting high in the water during the subsequent little ice age, when Canaletto was endlessly painting it!) -
JMurphy at 20:43 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
I don't think the so-called skeptics are actually bothered about any of this because they hold those two propositions in totally separate compartments in their heads. I.E. the MWP was warmer than today, because, well, just because. That's what they are being told by their blog scientists and that is what they believe. Separate from that, climate sensitivity is lower (almost zero, in fact) because Lindzen says it is, and they believe him above all other scientists. To a so-called skeptic, the above can be held and believed at the same time without contradiction - well, to them, at least. -
macoles at 20:03 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
Whoa John, you might want to further add that the MWP was local to the northern hemisphere and had little to do with global climate forcing. While as a thought exercise it is an interesting idea that an increased Global MWP would infer greater climate sensitivity, you wouldn't want to inadvertently confuse people about the actual relationship to a Local MWP. -
Lars Rosenberg at 19:36 PM on 19 October 2010Do critics of the hockey stick realise what they're arguing for?
It may be of some interest to quote the conclusion of Moberg et al. (2005), whose graph You reproduce: ”We find no evidence for any earlier periods in the last two millennia with warmer conditions than the post-1990 period—in agreement with previous similar studies. The main implication of our study, however, is that natural multicentennial climate variability may be larger than commonly thought, and that much of this variability could result from a response to natural changes in radiative forcings. This does not imply that the global warming in the last few decades has been caused by natural forcing factors alone, as model experiments that use natural-only forcings fail to reproduce this warming. Nevertheless, our findings underscore a need to improve scenarios for future climate change by also including forced natural variability—which could either amplify or attenuate anthropogenic climate change significantly.” -
Howard at 19:24 PM on 19 October 2010It's the sun
If you want to know the answer to sun spot production and the link to global temperature variation, then see this site, the answer will surprise you!! http://www.solarchords.com -
HumanityRules at 19:07 PM on 19 October 2010An underwater hockey stick
Jumping around linksd brought me back to this page. I'm just curious if people are happy with the >1.5oC increase in temperature since 1900 seen in this underwater hockeystick? -
garethman at 18:22 PM on 19 October 2010Explaining Arctic sea ice loss
THe difficulty I find is that there are lots of predictions of tipping points such an ice free Arctic in the summer which will be the thing that convinces everyone that the models of climate change are correct. The problem with this is that when year after year it does not happen, the warning begin to look like one of these chaps walking around with a billboard saying "the end is nigh" and it has the opposite effect on peoples perceptions. The other issue is that although the long term trend is obviously down, the short term trend is up from the 97 low. If this continues for another year or two the graph will start to look curiously like a hockey stick. -
RSVP at 18:11 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
gpwayne "Some climate change skeptics dispute the so-called ‘greenhouse effect’, which keeps the surface temperature of the Earth approximately 30 degrees C warmer than it would be if there were no greenhouse gases in the atmosphere." Hmmm. No water vapor means no clouds. So with an open sky consisting only of N2 and O2 after millions of years of steady sunshine, you are saying that the oceans would remain frozen? No water vapor also means no snow or rain, so the land is now a dry powder as on the Moon. The dry air in contact with the dry land would receive heat via convection and rise and mix. This air has no GHG, so it cannot radiate heat... only accumulate it via convection with the surface, or release it back via convection to cooler locations on the surface. But this convection is limited to only the cooler air that has circulated downward. The hot air would rise and the stratosphere would get warmer and warmer. All this may sound like nonsense, yet it is no better than the picture you have painted. -
archiesteel at 16:31 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
@HR: do you have figures that would justify this change in terminology to show us? After all, "Very Few" is more precise than "Some", so you must be basing this on some kind of empirical evidence, right? -
HumanityRules at 16:24 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
Shouldn't "Some climate change skeptics..." be "Very few climate change skeptics..." -
Phila at 16:21 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
TIS: However, this article is inaccurate as I am not aware of anyone claiming that the atmosphere doesn't have an effect. Logically speaking, your (admitted) ignorance does not and cannot make this article "inaccurate." -
Chris G at 14:36 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
Roger A. Wehage, The relationship between the amount of CO2 in the atmosphere and the effect it has in terms of direct retention of energy is logarithmic. A fair number of 'skeptics' become aware of this and try to argue that it means that the effects will be minimal. However, it's no secret to anyone who knows anything about the science. Remember, the central prediction is that, with feedbacks included, there will be a roughly 1% change in the earth's absolute temperature with doubling of CO2. That's 3 Kelvin / ~300 Kelvin which in about 1%. -
David Horton at 12:54 PM on 19 October 2010Throwing Stones at the Greenhouse Effect
Bibliovermis "she has over a decade of peer-reviewed field research under her belt" eh? Care to elaborate? -
kdkd at 11:29 AM on 19 October 2010It's the sun
KL #693 The multiple regression on the climate karaoke confirms your analysis rather nicely - after the mid-20th century, co2 is the main driver of warming (as expressed in that case by temperature anomaly as the dependent variable). I can't remember offhand what the precision of the prediction is, but it was reasonable, although regression assumptions were violated somewhat. Who'd have thought - convergent evidence. I can't see this supporting your 'sceptic' argument at all though. It more confirms the opposite. -
Joe Blog at 11:01 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
AHHH 12C or 20C -
Joe Blog at 11:01 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
I shall clarify my position. During a hot house period, where the average surface T may be 20k, or a glaciation when the surface T maybe around 12k, at equilibrium, the amount of energy leaving the top of the atmosphere will be the same, and equal to the amount of energy entering the system. During transitions between these states there will be an imbalance between incoming and out going, with more leaving than entering during a decline in T, and more entering than leaving during a rise in T. The difference in the surface T is a result of the amount of energy contained in the system at their respective equilibriums, and is a result in a shift in the amount of energy in the system, but the "quantity" of energy leaving the system, on its own, is not necessarily representative of the energy contained in the system(T o the climate). -
D Kelly O at 09:40 AM on 19 October 2010Explaining Arctic sea ice loss
Peter Can you tell me how you made your detrended HADCRUT series. I looks like AMO leads HADCRUT in some cases, lags in others. I'd like to reproduce your chart and take a look at how they vary. -
Joe Blog at 09:17 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
doug_bostrom at 09:04 I dont disagree, equilibrium can and does change, its the first sentence that just reads to me as though its saying proof of the GHE is that less energy leaves than enters the system... The proof is in the amount of energy contained in the system. Im being pedantic, i admit it, but that first sentence is misleading. -
Doug Bostrom at 09:04 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
Some net amount of energy is trapped or lost over time, Joe, or the collective ocean/atmosphere system could not become warmer or cooler over time. -
Joe Blog at 08:56 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
Good to the point article, but being a bit pedantic, i would agree with alkemist in regards to this paragraph. "By comparing the Sun’s heat reaching the Earth with the heat leaving it, we can see that less long-wave radiation (heat) is leaving than arriving (and since the 1970s, that less and less radiation is leaving the Earth, as CO2 and equivalents build up). Since all radiation is measured by its wavelength, we can also see that the frequencies being trapped in the atmosphere are the same frequencies absorbed by greenhouse gases." The climate may never be in perfect equilibrium, And the instrumental record certainly does suggest a build up of energy in the system, but energy in will equal energy out approximately . Energy is not trapped, its path length out of the atmosphere is increased, increasing the amount of energy in the system... Just with the way thats written it sorta comes across as suggesting that proof of the GHE is that less energy leaves than comes in... only during transition to a higher equilibrium is this true, and in something as chaotic as climate, its more a case of on "average". -
SRJ at 08:24 AM on 19 October 2010Tai Chi Temperature Reconstructions
#69 Peter Hogarth at 08:01 AM on 19 October, 2010 Thanks for the comments- I am fully aware that your originial post isn't supposed to withstand much scrutiny. Neither are my reconstruction here. As a side note, I was able to replicate your plots to a satisfying eyeball degree. I wanted to highlight that Ljungqvist 2010 is using a much more simple approach than e.g. Mann 2009. I would like to try and redo my global reconstruction using some kind of gridding or area weighting, but to do that I need some tips on how-to-do. Even better some Matlab code. By the way, how did you use those proxies given as z-scores? I just run them through the same averaging process as the temp proxies. For baseline I use the years, 1000-1900, as Ljungqvist 2010. -
Peter Hogarth at 08:01 AM on 19 October 2010Tai Chi Temperature Reconstructions
SRJ at 22:24 PM on 14 October, 2010 Thanks for this work. On first read through the Ljungqvist 2010 paper I would have to agree with you, but I would have to spend some time checking. The 2010 work is decidedly Northern Hemisphere above 30N whereas the Ljungqvist 2009 data has a fair proportion of tropical and Southern Hemisphere data also. I suspect that gridding will make some difference, but my original post wasn't meant to be a reconstruction that would withstand too much scrutiny! Your chart above is very interesting, and in my view further supports the idea of enhanced variability of the higher latitude Northern Hemisphere temperature anomalies, compared with the global average. There is some evidence of this high relative variability in paleo data going back through the ice ages. -
Bibliovermis at 07:42 AM on 19 October 2010Throwing Stones at the Greenhouse Effect
For the benefit of those who aren't familiar with Dr. Marohasy, her PhD is in Biology from the University of Queensland and she has over a decade of peer-reviewed field research under her belt. -
SRJ at 07:09 AM on 19 October 2010New temperature reconstruction vindicates ...
# 166 See my comment another thread here elaborating on this. -
SRJ at 07:05 AM on 19 October 2010Tai Chi Temperature Reconstructions
To elaborate on myself in #67: Peter Hogarth's approach is mostly similar to Ljungqvist 2010 except that Ljungqvist matches the variance of his composite series to the variance of the instrumental record. But there is no gridding or area weighting, all proxies contribute with equal weight. I have implented Ljungqvist approach and made a reconstruction using all proxies from Ljungqvist 2009 - note since the original post was written a few more have been added, the total number is now 71. The resulting graph is below, plotted together with Ljungqvist 2010.
This graph allows one to compare the Tai Chi approach of the original post with the result of Ljungqvist, 2010.
Disclaimer:
I have also used my implementation of Ljungqvist 2010 approach on the original data from that article (data kindly provided by the author). I don't get a perfect match so there must be some small differences in the methods of me and Ljungqvist.
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