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Global warming since 1997 more than twice as fast as previously estimated, new study shows

Posted on 13 November 2013 by dana1981, Kevin C, robert way

A new paper published in The Quarterly Journal of the Royal Meteorological Society fills in the gaps in the UK Met Office HadCRUT4 surface temperature data set, and finds that the global surface warming since 1997 has happened more than twice as fast as the HadCRUT4 estimate. This short video abstract summarizes the study's approach and results.

The study, authored by Kevin Cowtan from the University of York and Robert Way from the University of Ottawa (who both also contribute to Skeptical Science), notes that the Met Office data set only covers about 84 percent of the Earth's surface. There are large gaps in its coverage, mainly in the Arctic, Antarctica, and Africa, where temperature monitoring stations are relatively scarce. These are shown in white in the Met Office figure below. Note the rapid warming trend (red) in the Arctic in the Cowtan & Way version, missing from the Met Office data set.

Met Office vs. Cowtan & Way (2013) surface temperature coverage and trends 
Met Office vs. Cowtan & Way (2013) surface temperature coverage and trends

NASA's GISTEMP surface temperature record tries to address the coverage gap by extrapolating temperatures in unmeasured regions based on the nearest measurements. However, the NASA data fails to include corrections for a change in the way sea surface temperatures are measured - a challenging problem that has so far only been addressed by the Met Office.

The Berkeley Earth Surface Temperature (BEST) project used a similar approach as NASA, but with a statistical method known as "kriging" to fill in the gaps by interpolating and extrapolating with existing measurements. However, BEST only applied this method to temperatures over land, not oceans.

Dr. Cowtan is an interdisciplinary computational scientist who recognized some potential solutions to this temperature coverage gap problem.

"Like many scientists, I'm an obsessive problem solver. Sometimes you see a problem and think 'That's mine, I can make a contribution here'"

In their paper, Cowtan & Way apply a kriging approach to fill in the gaps between surface measurements, but they do so for both land and oceans. In a second approach, they also take advantage of the near-global coverage of satellite observations, combining the University of Alabama at Huntsville (UAH) satellite temperature measurements with the available surface data to fill in the gaps with a 'hybrid' temperature data set. They found that the kriging method works best to estimate temperatures over the oceans, while the hybrid method works best over land and most importantly sea ice, which accounts for much of the unobserved region.

Both of their new surface temperature data sets show significantly more warming over the past 16 years than HadCRUT4. This is mainly due to HadCRUT4 missing accelerated Arctic warming, especially since 1997.

Cowtan & Way investigate the claim of a global surface warming 'pause' over the past 16 years by examining the trends from 1997 through 2012. While HadCRUT4 only estimates the surface warming trend at 0.046°C per decade during that time, and NASA puts it at 0.080°C per decade, the new kriging and hybrid data sets estimate the trend during this time at 0.11 and 0.12°C per decade, respectively.

These results indicate that the slowed warming of average global surface temperature is not as significant as previously believed. Surface warming has slowed somewhat, in large part due to more overall global warming being transferred to the oceans over the past decade. However, these sorts of temporary surface warming slowdowns (and speed-ups) occur on a regular basis due to short-term natural influences.

The results of this study also have bearing on some recent research. For example, correcting for the recent cool bias indicates that global surface temperatures are not as far from the average of climate model projections as we previously thought, and certainly fall within the range of individual climate model temperature simulations. Recent studies that concluded the global climate is a bit less sensitive to the increased greenhouse effect than previously believed may also have somewhat underestimated the actual climate sensitivity.

This is of course just one study, as Dr. Cowtan is quick to note.

"No difficult scientific problem is ever solved in a single paper. I don't expect our paper to be the last word on this, but I hope we have advanced the discussion."

The perceived recent slowdown of global surface temperatures remains an interesting scientific question. It appears to be due to some combination of internal factors (more global warming going into the oceans), external factors (relatively low solar activity and high volcanic activity), and an underestimate of the actual global surface warming.

How much each factor is contributing is being investigated by extensive scientific research, but the Cowtan & Way paper suggests the latter explanation is a significant contributor. The temporary slowing of global surface warming appears to be smaller than we currently believe.

Note: these results have been incorporated into the rebuttal to the myth It hasn't warmed since 1998

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Comments 51 to 83 out of 83:

  1. Dhogaza  Perhaps it didn't take decades for plate tectonics to become accepted but as it took about 50 years for mainstream science to "properly reject" continental drift, it seems an extraordinarily long time for scientists to recognise that the continental drift hypothesis was physically impossible

    Thank you Victor Venema, your comment is the epitome of scientific restraint which is as it should be given the "newness"  of the paper.  I mentioned Judith Curry in response to this challenge from "Bert" who wrote "Show me a reputable site that refutes this refereed paper that is not run by the scientific illliterati". So I did.

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  2. Sorry, Poster, but using Curry as an exhibit to cast doubts on Cowtan and Way is still using the scientific illiterati. She has no cogent response to their work, has used nothing that can even come close to being called a rigorous look at their paper, and is just doing her usual heming and hawing, and using the old tactic she's perfected, of parroting something about "uncertainty." Will Cowtan and Way stand the test of time? I don't know, for I am not an expert, but, having read in excess of 1200 various articles, essays, and papers concerning this subject, one thing I can say, with good reliability, is Curry hasn't done anything except her usual non-rigorous trashing of a paper I sincerely doubt she understands.

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  3. I have two questions, and I am surprised no one else has asked them.

    1) Why not just use UAH or RSS satellite data in the first place? My perception is that the satellites are pretty accurate (once they are calibrated) and they have almost worldwide coverage. They also do not have any issues with alleged poor siting and/or urban heat island affects. Why supplement the relatively sporadic land/sea based measurements of HADCRUT4 with UAH data? UAH data shows the warmest year as 1998 and the temps have been flat since then.

    2) Has anyone noticed that all of the heat has accumulated in the Artic? Antarctica has actually cooled over this time period. This seems very curious to me and I cannot think of a way this highly asymmetrical heating could be caused by a well-mixed gas like CO2.

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  4. SASM (1) The satellites don't measure surface temperature, but temperature in vertical sections of the atmosphere, so if you want to know surface temperatures, the satellite data cannot help you.  While they don't have UHI problems, they do have other issues, hence the many adjustments to the dataset that have been made over the years.  Note also that the trophospheric temperatures are considerably more sensitive to ENSO than surface temperatures (hence bigger spike in 1998).

    (2) The assymetry might be caused by the fact that Antarctica is land and the Arctic is ocean.  I suspect the oceans buffer Arctic temperatures which prevents them from getting as cold as the Antarctic.  Also the circumpolar currents in the southern ocean isolates the Antarctic a fair bit.

    CO2 is not the only thing that causes temperatures to change.  If it were, we wouldn't need climate models.

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  5. "Antarctica has actually cooled". Well that is what models predicted in 1992 (Manabe) but I am not so sure how well that prediction is holding out.

    Here is Antarctica temperature chance 1981 to 2007. What is the basis of your claim of cooling?

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  6. Dikran @54: What are the “other issues” with UAH and RSS? I’ve researched the difference between UAH, RSS, GIS, HADCRUT, and for the most part the plots are all very similar. While satellites have a wider swing up and down, they all tend to match fairly close. I would not expect a perfect match because each measurement system is measuring different things and locations and at different times.

    You mention surface temperatures versus lower troposphere air temps, but what about ocean temperatures (surface and deep) -- which one is most important or the most meaning with respect to AGW?

    Since air has such low heat content, I wouldn’t think air temps would be all that important and shouldn’t be the driver of much of anything. Just look at air temperatures in California – on the coast the cool Pacific ocean brings cool air across the land in the sea breeze, but the air doesn’t have to go very far before it gets very hot. The solar energy hitting the ocean and the land is the same. The ocean doesn’t warm quickly, so the cool water from Alaska remains cool for a long time, and cools the air. But the land warms quickly, and hence warms the air in just a few miles. The air temps in Los Angeles on the coast are 60 degrees F and 20 miles inland the air rapidly warms to 100 degrees F. Clearly, in this case, the ocean or land surface temperatures completely control the air temperatures. Since air temperatures can change a lot and quickly based on surface temperatures, I would think measuring lower troposphere with satellites would be the most accurate since it measures more points more frequently.

    scaddenp @55:” What is the basis of your claim of cooling?” All the blue and darker green area in Cowtan and Way’s map posted in this article. I just eye-balled the data -- I didn’t integrate it and I understand that there are some odd map projections issues; this is just a vague observation on my part. But clearly, the Artic has warmed way more than the Antarctica region. I just find that very curious. I wouldn’t expect CO2 to cause such asymmetrical warming, so it seems to me that something natural phenomenon is occurring. Perhaps this is support for Judith Curry’s Stadium Wave theory?

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  7. SASM, since Manabe models in 1992 were predicting cooling, then isnt that a hint that there is more going on in climate than just CO2? As Dikran said, that's why we build models.  I frankly dont expect a plateau at 2000m to respond the same way as seaice at sealevel,  but other factors in Antarctica is the circumpolar circulation which isolates the continent (whereas arctic amplification is in part due to circulation); and ozone depletion.

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  8. It is astonishing that people persist in vaunting the accuracy of satellites temperature data relative to surface temperature data.  Satellite temperature data does not suffer from urban heat island effects, for example, but it does suffer from instrument heat island effects.  It needs numerous corrections for change of instruments having gone through multiple satellites over the years.  It also requires a set of very difficult calculations to convert instrument readings of microwave radiation from O2 into temperatures.  There are no a priori reasons to assume that satellite temperature data is more accurate than surface data.  Indeed, as it involves more corrections, and more processing than does the instrument record, the opposite is true.

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  9. "Issues" /wrt satellites:

    A good starting point to explore issues with satellite data is provided right here on SkS:

    Satellite measurements of warming in the troposphere (last update 24 March 2011 by Glenn Tamblyn)

    The sections named "Further reading" should be noted.

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  10. SASM wrote "Dikran @54: What are the “other issues” with UAH and RSS?" Thes issues are well documented, for example see the ReadMe file provided with the dataset.  If you look at the Wikipedia page for the UAH dataset you will find a section on the corrections that have been made.  There comes a point where you need to take some time to investigate these issues for yourself after they have been pointed out to you (as I did here), Google is a useful research tool (especially Google Scholar).

    SASM then goes on to write "...I’ve researched the difference between UAH, RSS, GIS, HADCRUT, and for the most part the plots are all very similar..." in which case why should C&W just use satellite data? 

    SASM wrote "You mention surface temperatures versus lower troposphere air temps, but what about ocean temperatures (surface and deep) -- which one is most important or the most meaning with respect to AGW?"

    This is evasion.  You asked why satellite data is not used, and I answered your question, yet rather than acknowledge your question had been answered you change the topic.  This is trolling.

    As to why near surface air temperatures are important, well that is where most of us tend to live, and our crops etc.  Again this is just another example of goal-post shifting that we have seen rather too much of from you.

    Lastly SASM writes " But clearly, the Artic has warmed way more than the Antarctica region. I just find that very curious. I wouldn’t expect CO2 to cause such asymmetrical warming, so it seems to me that something natural phenomenon is occurring. Perhaps this is support for Judith Curry’s Stadium Wave theory?"

    So you completely ignored the reason for the assymetry that I explained in my posts.  Frankly that is pretty shabby behaviour on your part, and I will continue the discussion no further and I suggest others do likewise.

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  11. Why do you all keep deleting my questions?  Do you think you've answered them, or do you not like them?

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    Moderator Response:

    [DB] Comments not adhering to the Comments Policy were removed due to sloganeering and trolling on your part.

  12. SASM. Suggest you stick to one point at a time. Acknowledge responses and stick to the science. Above all moderators here apparently can stand only so much comment policy violation. Trolls are two a penny and totally unwelcome. If you want to discuss the science fine. If you are mostly interested in trolling and no data or argument could change your mind then perhaps another forum is more suited to you. (eg WUWT or CA).

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  13. Maybe against my better judgement, but I will answer why C&W use satellite despite the issues.(which of course SASM could have found by reading the paper).

    They use satellite only to fill the gaps - they are proposing a way to avoid the problems with coverage bias. They dont use the satellite temperature directly (how would combine an average over 4000m with surface temp?) but instead posit that the temperatures are related. The infill temperature is an estimate of surface temperature. They avoid the many problems with stability and drift in the satellite trends by recomputing the relationship monthly. ie no stability in satellite measurements is assumed.

    As to north/south assymetry, spot the big geographical differences between north and south. To substantiate a claim of "unexplained" assymetry, then you would need to show that such assymetry is not present in the models.

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  14. Arrhenius predicted over 100 years ago that the high latitude Arctic would warm faster than the Antarctic. Models and explainations of this asymmetry are not post hoc explainations after it was observed, they are 100+ years old.  It seems to me that people who claim to be reading the science should be aware of this basic fact.  Arrhenius also predicted winter warming faster than summer, night warming faster than day, land warming faster than ocean and Northern Hemisphere warming faster than Southern.  For those who did not notice, all of these are falsifiable predictions, made long ago and confirmed by observation.  Arrhenius missed the stratosphere cooling as the troposphere warms.  That was because the stratosphere had not been  discovered yet.

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  15. If you see here, other people keen to have C&W available have stumped up the funds to make it freely available. However, the points I made above were outlined in the Realclimate article which you claimed to have read.

    Most of the energy imbalance created by CO2 goes into heating the ocean which has complex mechanisms for distributing heat vertically and horizontally, with decadal level effects on surface temperature. Want to describe that without models? Noone is claiming  that climate is solely a function of GHG. Currents, cloud cover are all part of this but they are responses not forcings.

    If you are aiming at solely nitpicking anything at all that you can, without also making some effort to understand the explanations given to you and to read the references supplied for understanding, then frankly that counts for trolling. Writers and commentators here are not here to pass some test you want to put, but are certainly interested in helping someone understand the science. You come across as trolling when you dont acknowledge responses, apparently ignore links and instead jump to some new denier talking point.

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  16. Frankly it is hard to someone seriously if they are reading WUWT. You are happy with being misinformed? Why would that be?

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  17. I have not looked at ocean circulation and climate in any detail at all,  however, this little fact sheet on the thermohaline circulation does talk qualitatively on the effects on climate.

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  18. SASM If you want to avoid the impression of trolling, when someone answers your question, explicitly state those parts of the answer that you accept, and explain why you reject those parts of the answer that you do not accept.  Do not just raise another objection without dealing correctly with the answer you have already been given.  A common tactic of trolls is not to give a hostage to fortune by explicitly agreeing to anything as it means that they cannot then go back to that topic later and say the opposite.  Also if someone asks you a direct question, give a direct answer.

    Now as to the assymetry.  The Arctic is an ocean and it has currents floating into and out of it all the time.  As the Arctic ocean is colder than the Atlantic or Pacific, that suggests that these ocean currents are on balance transporting heat into the Arctic, causing it to be warmer than would otherwise be the case.  This doesn't happen for the Antarctic, becase it is a land mass, so the ocean currents can't bring heat to the pole (note the Anarctic peninula is warming).  Secondly if sea water gets much colder than 0C it freezes, rather than getting colder.  This means that the ocean under the ice is much warmer than the air above it in the Arctic.  There is no similar phenomenon that stops the rock under the ice in Antarctica from getting colder until there is an equilibrium with the air temperature above the ice.  I am not a physicist, but my intuition suggests that the formation of ice is slightly exothermic (i.e. gives out heat) as otherwise you wouldn't need heat to melt it.  That explains why the oceans don't get much colder than a few degrees below zero C (depending on salinity).  I suspect someone here who is a physicist can explain the details.

    P.S. I was going more for an English civil war look ;o})>

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  19. Dikran,

    Freezing of sea ice releases a lot of heat into the atmosphere.  This accounts for much of the increase in temperature in the Arctic in fall.  Then the ice insulates the ocean from the coldest part of the winter.  In the summer, that heat is absorbed again from the sun to melt the ice.

    The melting and refreezing of sea ice does not contribute to the net heat budget of Earth since it is returned later.  Melting ice caps uses some heat, but it is a small fraction of what the Earth absorbs from AGW.

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  20. Thanks Michael, glad to hear my intuition wasn't too far out!  Hopefully this fully addresses SASM's question.

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  21. You are only considering SST. How about looking at basin wide OHC? Looking at THC, you have northward movement of warm water into arctic, where it indeed cools, and sinks.

    Have you found things on this site by the way that arent backed by peer-reviewed published science (something you certainly cant say about Watts)? Do you think authors here delibrately mischaracterize science to support an idealogical position? It is good to be skeptical about science but there is a big difference between skepticism and delibrately pushing misinformation.

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  22. PS. My evidence of ideological bias. In an interview with Watts on PBS.

    "SPENCER MICHELS: What’s the thing that bothers you the most about people who say there’s lots of global warming?

    ANTHONY WATTS: They want to change policy. They want to apply taxes and these kinds of things may not be the actual solution for making a change to our society."

    To me that sounds pretty much like the wonderful "skeptic" logic of "The only solution I can see to AGW involves things contrary to my political ideology, therefore AGW must be wrong". A better approach would be think up a solution that it is compatiable with your ideology.

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  23. Further PS on SST change. What period on time are you looking at? Decadal level cycles like PDO and AMO affect SSTs. If you are only looking at <20 years, then that data doesnt tell you much about climate change.

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  24. StealthAircraftSoftwareModeler: Your three most recent posts have been deleted for violating the Comments Policy prohibition against sloganeering. Your proposensity to pratter on about anything and everything is indeed tiresome to Moderators and readers alike.

    Please read the SkS Comments Policy and adhere to it. If you do not, you will forfeit your privalege to post comments on this site. 

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  25. On an other track completely, I found this paper ("Interhemispheric asymmetry in transient global warming: The role of Drake Passage") on why models end up with interhemispheric assymetry in warming. The writers note the attribution to land-ocean differences between the hemispheres and Arctic sea ice melt, but also point out the role of the Antarctica Circumpolar Current in isolating Antarctica by running the models with and without a landbridge across the Drake Passage.

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  26. John Hartz @74: I am really trying hard to get this.  I’ve gone and read several different Comment Policies in SkS, one from John Cook back in Nov 10, 2009 and one that I found in the article about the Dunning-Kruger effect.  For the record, I don’t see a link to the Comment Policy from the main menu links and one must search for it.  Between reading these policies, and examining my posts, I think I may have figured out the secret decoder ring of what you call sloganeering. I’ll try harder in the future to avoid it.

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    Moderator Response:

    [JH] Repeated text deleted per author's request.

  27. Opps. Cut and paste error. Delete the redundant second paragraph in 76.

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  28. Scaddenp @75. I took a quick look at the abstract (all I can read) and this looks interesting and seems to support what you and Dikran were saying. Thanks for digging it up for me. I’ve done some searching and found this: LINK. This proposes a different mechanism than the paper you found.

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    Moderator Response:

    [RH] Hotlinked URL that was breaking page format.

  29. StealthAircraftSoftwareModeler: 

    The curent and operative SkS Comments Policy can be accessed by clicking on the "Updated Comments Policy" link found immediately above the Comment edit box and below the "Post a Comment" header.  

    You will be better able to interact with SkS authors and readers on this comment thread if you focus your comment on specific issue and do not engage in polemics. Having said that, dialoguing on comment threads  on SkS and other websites may not be the best way for you to learn about climate science. There are other options such as signing up for an oline course or reading a textbook on the subject. 

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  30. SASM - your paper is complimentary. It looks at why Antarctica is colder than the Arctic. You will find similar papers over in the "Antarctica is gaining ice", No 10 of popular myths. The paper I stumbled on  at looks at the  role of the ACC in why SSTs are different between hemispheres under the same forcings which I thought was closer to your question. 

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  31. SASM, note section 2.2 of that paper investigates ocean circulation, which is the main difference between the Arctic and Antarctic that I mentioned.  Even if the greenhouse effect has the same direct effect on both poles, you still need to consider the transport of heat around the globe.  If there was no transport of heat by ocean and atmospheric circulation there would be no need to make climate models (GCM stands for General Circulation Model). 

    As I also pointed out, CO2 is not the only forcing that affects global and regional temperatures, so to expect a simple relationship between CO2 and temperature (especially over short timescales less than 30 years or so) is unreasonable.

    The really big point that was missing from my answer to your question was of course ice-albedo feedback.  Any summer melting of sea ice in the Arctic exposes dark ocean water, which absorbs far more sunlight than the bright ice that is now gone, so any warming there tends to be amplified.

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  32. VictorVenema #1 "those adjustments are huge". Hang on, those adjustments are huge for that region and obviously of great interest in knowing who is computing best, but offhand I think they look negligible as a global adjustment (the underlying topic). My assessment is only based on my eyeballing GISTEMP-Cowtan & Way graphic and estimating ranges of differences and areas but it's a low order of magnitude. I have 0.8Mk2 @ -1C<=>-2C, 1.0Mk2 @ 0C<=>-1C, 8.5Mk2 @ 0C<=>-0.3C and 8.5Mk2 @ 0C<=>+0.8C (GISTEMP a warmer anomaly for this one). I compute -0.0025C, -0.0010C, -0.0025C and +0.0066C as global equivalents for a net effect on GMST of +0.0006C (Cowtan & Way showing this much less global warming than GISTEMP) but my final quantity detail is not significant and might be incorrectly signed because I used the graphic, not data, and minimal effort so what it indicates is only that it's negligible as a global adjustment.

    Per 2013-11-13 post, the Cowtan & Way paper regarding HadCRUT4 (on which this post is an interesting aside) noted HadCRUT4 at +0.046°C per decade GMST anomaly, NASA at +0.080°C per decade, the C&W kriging and hybrid data sets at +0.11C and +0.12°C per decade. That's the one with global adjustments are huge .

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  33. Me @ #82 I meant to comment this for 25 April 2014 post, not here.

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