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Comments 64501 to 64550:

64501. Norman at 16:02 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       KR @25 From the article you linked to. "Gornitz (2001) compiled estimates of mining rates for specific countries from various sources; those explicitly reported rates totaled about 61 km3/year (or 0.17 mm/year sea-level rise) both for recent years and for the last half-century. Gornitz extrapolated that value by assuming that the ratio of mining to total groundwater withdrawal was similar globally to what it was in the studied regions. Depending on the details of the extrapolation, this approach led to a wide range of estimates of 0.17–0.77 mm/year for the gross effect of groundwater mining on sea-level rise." The problem is the report I linked to (which does not seem to work now) states the deep ground water use for irrigation is 545 cubic kilometers of water a year (and rising) Try it here again. Groundwater use in irrigation -a global inventory. In your link it states that 61 km^3 is equivalent to a 0.17 mm/year sea rise. If the more correct figure for the acutal global amount of deep water being used for irrigation is 545 km^3 (and much of this irrigation is in arid regions with slow recharge rates for the aquifiers which is described in the link), that comes out to 8.93 times more than 61. If 61 is responsible for a 0.17 mm sea level rise per year, 8.93 times this amount would be equal to a sea level rise of 1.52 mm/year. Multiply this by 7,for the GRACE study years that gave melting ice as responsible for 12 mm rise in sea level and the deep water withdrawal (with very slow recharge rates), and you have an equivalent of 10.63 mm of total sea level rise from pulling water from aquifiers.
64502. KR at 15:59 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       muoncounter - The chapter from Milly et al 2010 notes that "water content of the global atmosphere (≈25 mm water equivalent) is tightly constrained thermodynamically", and therefore they consider the remaining water to either be on/in the land surfaces or in the ocean. Norman - My initial comment on this thread was in response to your mistaken statement that "...the water added to the system via irrigation is fairly close to the amount of water added by melting ice. Meaning the sea water will continue to rise regardless if the ice melting stops and the problems of the future will still remain." I believe I have referenced sufficient data to indicate that is incorrect - that our water usage (despite climate effects on local water availability) is not having any significant effect on SLR, that you are only looking at one side of the equation. Unless you have relevant comments and references indicating that Milly, Chao, and others, and their data, are somehow wrong, unless you can demonstrate that we have increased net flow to the oceans and hence affected SLR, I fail to see the point of chasing that particular red herring. And that includes external constraints on our net water flow - the contributions from thermal, haline, and ice melt to SLR severely limit the range of any additional anthro contribution. I believe the remainder of the discussion on aquifers versus physical impoundment versus redistribution of terrestrial water supplies is off topic in this thread. Perhaps you can take this to one of the discussions on climate change related droughts?
64503. PrezMulkeyUnity at 15:54 PM on 11 February 2012
       Book review of Michael Mann's The Hockey Stick and the Climate Wars
       I have been directly involved in the hockey stick war. I have been been an active research ecologist for over 20 years, and during the last 10 years I have focused on climate change and its effects on living systems. During part of my recent career, I was employed as science advisor to the Century Commission for a Sustainable Florida, a legislatively mandated commission. In March of 2007, while giving an invited report on climate change to a select committee of the Florida legislature, a conservative legislator rose from his seat and declared me to be a liar and demanded that I be dismissed. Indeed, I was asked to step from the podium. Only one newspaper in the state carried the story, and my employers did not so much as apologize for my treatment. Democracy in action, right? My sin? I had shown the hockey stick. When I approached the legislator who had objected, I discovered that he did not know that the National Academy and reviewed Michael Mann's work and found it to be fundamentally sound. Indeed, it was not apparent that he even knew of the existence of the US National Academy. After the climate gate emails were released, the prestigious journal Nature referred to the push back from the oil soaked Irrational Right as a "street fight." I could not agree more. I have carefully read and evaluated Mann's work and I find it to be of the highest standards of scientific integrity. He has been vindicated by numerous reviews. Despite continued harassment, he continues to find time to do excellent research. I have the greatest respect for him as a colleague and role model. To date 32 national academies have endorsed the fundamental reality of human caused climate change. Numerous professional organizations have also made clear statements to support the mainstream science. 97% of all climate scientists agree. NSF, NASA, NOAA, USDA, the NPS, and the CDC have active research programs predicated on the reality of human-caused climate change. The clarity of the climate change threat could not be greater. It is most sobering to realize that our present emissions trajectory will result in a global average warming of over 5 degrees C by 2100. Such a planet will not sustain civilization in any recognizable form. The excess CO2 that is pumped into the air today will affect our planet for thousands of years into the future. I am not an alarmist, but I am alarmed. You should be too. I urge everyone to read Mann's book. It is well written and compelling. Any publishing scientist who reads it will likely be chilled to the bone. I have contributed to the climate scientist legal defense fund, and urge all of you to do the same. http://climatesciencedefensefund.org/ Stephen Mulkey, PhD President, Unity College Unity, ME 04988
64504. KR at 15:43 PM on 11 February 2012
       Monckton Myth #17: Debate vs. Denniss, Part 1
       And to continue that quote: "In sum, a strategy must recognise what is possible. In climate research and modelling, we should recognise that we are dealing with a coupled non-linear chaotic system, and therefore that the long-term prediction of future climate states is not possible. The most we can expect to achieve is the prediction of the probability distribution of the systems future possible states by the generation of ensembles of model solutions. This reduces climate change to the discernment of significant differences in the statistics of such ensembles." (emphasis added) And hence the use of model ensembles, each running a non-linear coupled system with slightly different initial conditions and modeling - marking out the probability distribution that we can expect from the climate. We can (in climate) make probabilistic predictions that it might (in average) be rainier or dryer in a particular region. But we'll never be able to predict exactly what the weather on a particular Tuesday a decade from now will be... Monckton's out of context quote is deceptive. And he's an experienced enough writer and speaker to understand that.
64505. Norman at 15:42 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Tom Curtis @26 The rate of replacement of underground water storage depends upon location. In wet areas the groundwater removed it easily replaced. In dry areas this is not the case and the drier areas are the ones pumping up most of the the deep ground water (that is not being replaced). In wet areas irrigation is not a highly needed activity. Here is a short article that describes the situation. In Texas a chart in this document Ogallala Aquifier. it shows the rate of pumping out of the large aquifier is 6.22, while the recharge rate is 0.3. The rate of pumping water out of the Ogallala is 21 times greater than the recharge rate. This means that the water pumped out of this aquifier will indeed add to the surface water amount. Yes it will add to the surface storage, the atmosphere and yes the ocean as well.
64506. Jim Eager at 15:20 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Bob, I didn't say anything at all about irrigation or sea level, I just pointed out that the nice neat divisions are not so nice and neat, as you just did as well.
64507. jmsully at 15:15 PM on 11 February 2012
       Book review of Michael Mann's The Hockey Stick and the Climate Wars
       Owl905, you forgot the Chinese sailing over the ice free north pole and discovering America (albeit a couple hundred years after the Vikings).
64508. IanC at 15:14 PM on 11 February 2012
       Monckton Myth #17: Debate vs. Denniss, Part 1
       What also needs to be emphasized is that the quote regarding predictability is that the phrase is quoted out of context by Monckton from the IPCC TAR. The section this quote appears in section 14.2.2.2 Balancing the need for finer scales and the need for ensembles

       In sum, a strategy must recognise what is possible. In climate research and modelling, we should recognise that we are dealing with a coupled non-linear chaotic system, and therefore that the long-term prediction of future climate states is not possible. The most we can expect to achieve is the prediction of the probability distribution of the system's future possible states by the generation of ensembles of model solutions.

       If the sentence after the quoted text is included, it completely changes the meaning of the text quoted by Monckton. Ever since Lorenz discovered chaos, it is recognized that we can't forecast climate the way we approach weather forecasting, and what we are after is the probability distribution of global surface temperature in Jun 2100, not the precise temperature.
64509. Jose_X at 14:19 PM on 11 February 2012
       Monckton Myth #17: Debate vs. Denniss, Part 1
       Fitz1309, the original context should have been preserved but wasn't. For example, the first reply is Monckton literally pointing out how the IPCC says that (long-term) prediction is impossible. He is correct. The IPCC also says that while we cannot know with 100% certainty, we can manage how much confidence we have with various predictions. So Monckton pointed out an obvious point implied already in current climate papers and the majority of scientific work (managing levels of confidence and error). Monckton's failure was in suggesting that this lack of 100% certainty means we have almost no clue. Now, Monckton never said the we have no clue, but his speech was such to possibly create the impression in the minds of many. Unless you want to get into a silly war of semantics, it's best simply to ask Monckton to clarify his position. Does he believe, as his speech sounded to "me", that the IPCC does not make a projection/prediction of x or y with fairly high certainty. Getting angry doesn't help. The goal is for people to understand. If they feel they misunderstood Monckton, some will over time simply learn not to trust Monckton without first getting clarification and may get used to waiting for the summary version by others who do chase down the details. They may even start seeing Monckton as a clever speaker whose words suggest one thing different than what he will put on paper with his signature.
64510. Steve L at 13:14 PM on 11 February 2012
       Still Going Down the Up Escalator
       DM @ 132 -- Thanks. It's all about finding the time. Probably I spend too much time reading and commenting to do much learning of how to actually do (& therefore better understand) stuff. I'll endeavor to re-prioritize; I suspect there are many of us who would benefit from this effort. Thanks again for your good example.
64511. Bob Loblaw at 12:33 PM on 11 February 2012
       Still Going Down the Up Escalator
       RobertS @ :for some unobservable, unverifiable parameter like "slope" under the assumption that your straight line model is correct (and several other similar comments) You keep putting terms like "slope", "average", etc. in scare quotes, as if they have no meaning. You seem unwilling to agree that such an entity can be a property of the underlying process itself, rather than the analysis of the data. Let's look at calculus. Let's take the function Y=x^2. Not linear. Yet calculus says that we can calculate the slope at any value of X by taking the derivative of Y with respect to X. Numerical methods also tell us that we can get a pretty close approximation to that slope by taking pairs of (X,Y) values close to that point and calculating the slope of the linear segment between the points. Is that slope a property of the function Y=X^2, or a property of the analysis? Can the results of the analysis tell us anything about the function? Can you give a straight answer without resorting to an argument that tries to pretend that words don't mean anything?
64512. Eric (skeptic) at 12:30 PM on 11 February 2012
       Still Going Down the Up Escalator
       EliRabett, Thanks for the example. Are observations are uniformly spaced? I assume that daily or seasonal cycles are already averaged out in some way? I don't think those are difficult problems but the methods can sometimes be controversial. Once the cycles are removed is there any other role for spectral analysis? Are there any a priori statistical tests for the residuals or trends in the residuals? By what method are nonlinear trends in the residuals measured? How do we know that we have sufficient data for that method?
64513. Bob Loblaw at 12:17 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       and, Jim, some won't. Some will fall on land. And some of that will run off into streams and eventually reach the sea, and some will soak into the soil, and some will eventually make back into deep aquifers... ...so you can't look at this by pretending that one small portion of the water cycle is everything. Taking the number that represents the removal for irrigation and expecting that it all ends up raising sea level is wrong.
64514. Jim Eager at 12:03 PM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       But muoncounter, what goes up by evaporation comes down as precipitation, and depending on the location, some of that will end up in the ocean.
64515. muoncounter at 11:55 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Norman#24: "water is being added to the surface system. Some will be impounded, some will end in the sea." And some will end in the atmosphere. Per the USGS, ... of the water used for irrigation, only about one-half is reusable. The rest is lost by evaporation into the air, evapotranspiration from plants, or is lost in transit, by a leaking pipe, for example. Sounds like there is a high level of uncertainty in the fraction of groundwater that reaches the ocean. You neglect, as well, the fact that groundwater depletion is a major factor in land subsidence, exacerbating coastal sea level rise. This is an argument so thin as to be transparent.
64516. scaddenp at 11:48 AM on 11 February 2012
       Newcomers, Start Here
       "only have data running back to a 100 years" This is highly inaccurate. We only have instrumental data going back a little over 100 years but we have data in various forms covering millions of years. This also seeks to avoid the issue that climate theory is based on physics and validated daily in countless data sets. Do we not send a rocket to Mars because we only have data on gravity going back 200 years?
64517. Tom Curtis at 11:48 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Norman @21, you make the assumption that extracted groundwater is not being replaced. That is not correct. Although groundwater is not being replaced at the rate at which it is being extracted in many aquifers, surface water is still making its way underground. Therefore simply taking the figure of the consumptive use of ground water as being the net addition to surface waters is inaccurate.
64518. Bruce at 11:36 AM on 11 February 2012
       Major Study of Ocean Acidification Helps Scientists Evaluate Effects of Atmospheric Carbon Dioxide on Marine Life
       With available instrumentation both pCO2 and pH can be measured with enough accuracy to determine aragonite saturation . We know that here along the Calif. coast we seasonally flirt with undersaturated water . Putting long term biological data sets together with carbonate chemistry requires bringing pH sensors to existing biological sites. Getting funding to maintain weekly or biweekly larval settlement studies has always been very difficult . Industry has funded a 20 year by weekly study on sea urchin recruitment in calif. and the oyster industry maintains a along term dataset for oyster recruitment in washington . Other than those two baselines we don't have have much to go on. At some point the public will demand real world evidence and maintaining a long term record will be more convincing than lab studies. Bruce
64519. EliRabett at 10:56 AM on 11 February 2012
       Still Going Down the Up Escalator
       It might become even a teensy bit clearer if one considers a series of measurements of something unknown made in a black box with only a digital readout on the cover. Eric doesn’t know what the instrument is. Eric doesn’t know how accurate or precise the instrument is. Eric doesn’t know what the instrument is measuring. Eric doesn’t know if what the instrument is measuring is changing in time. All Eric knows is the numerical (digital) representation of what he reads on the indicator. Eric diligently records the numbers and then arranges them in a table as a function of time. We know that Eric never gives up so he gives us a long series or maybe not. Eric can now use statistical analysis to estimate the probability of there being a trend or not and to estimate the trend and the uncertainty in the trend. The residuals and trends in the residuals can be used to estimate the probability of the trend being linear or higher order (since everything reduces to a power series we don’t have to directly deal with anything but polynomials. From that point of view accepting or rejecting the hypothesis that the behavior of whatever is being measured is unchanging is simply checking if the zeroth order term in the series is the only significant one). From this POV, the residuals tell us of the summed variability of the what is being measured and the measurement device. We would, of course, have to break into the box and calibrate the instrument against a well characterized source to separate accuracy and precision.
64520. KR at 09:27 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Norman - It does matter in terms of sea level rise (SLR). Groundwater depletion is a serious ecological issue, reducing the carrying capacity of many regions. But the total amount of water making it's way to the oceans is what matters in terms of SLR. You have to add up all the sources and sinks of terrestrial water to see what's going on. A more recent (and complete than Chao) reference is Milly et al 2010 - Terrestrial Water-Storage Contributions to Sea-Level Rise and Variability. Considering groundwater depletion, irrigation, impoundment, etc., they state: "When we consider only those processes ... in which we place medium to high confidence, we obtain a zero net trend in sea level. This is consistent with the most likely range of ≈0 to 0.3 mm/year deduced [from external constraints] ... for the past two decades ..." (emphasis added)
64521. Norman at 09:01 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       KR @23 I think we are not on the same page. Water impoundment is not the same concept as adding water to the surface water system from groundwater sources. The number you give is for the total amount of water that has been impounded by mankind to date. The number I gave is a yearly extraction of groundwater sources and a lot of that is depleting the ground water supply at a much faster rate than entering it. This means the water is being added to the surface system. Some will be impounded, some will end in the sea. The impounded water is a static amount that will change only if new lakes are made. The irrigation is a every increasing amount. Also irrigation rates are going up so more water is being extracted. Groundwater use for irrigation - a global inventory.
64522. KR at 08:27 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Norman - Looking at the amount of water used is not very informative without also looking at the amount of water retained, the input to irrigation. From Chao et al 2008 - "By reconstructing the history of water impoundment in the world's artificial reservoirs, we show that a total of ∼10,800 cubic kilometers of water has been impounded on land to date, reducing the magnitude of global sea level (GSL) rise by –30.0 millimeters, at an average rate of –0.55 millimeters per year during the past half century." (emphasis added) Your assertion that there is significant sea level rise from irrigation is, in fact, incorrect.
64523. Tristan at 08:19 AM on 11 February 2012
       Hockey stick is broken
       KR and DB You guys are champs. Thanks a lot.
64524. DMCarey at 07:56 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       @michael sweet, I may be mistaken, but I believe Camburn was, in this case, referring solely to people living on Greenland. Those occupying coastal areas over the rest of the world are a different, and altogether more serious, concern. Absolutely incredible, and terrifying, the sheer scale of the ice loss per year
64525. Norman at 07:42 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       From the article "The total global ice mass lost from Greenland, Antarctica and Earth's glaciers and ice caps during the study period was about 4.3 trillion tons (1,000 cubic miles), adding about 0.5 inches (12 millimeters) to global sea level. That's enough ice to cover the United States 1.5 feet (0.5 meters) deep." One problem is that even if the ice melting halted the oceans would continue to rise at about the same rate. The result of irrigation pulling water from aquifiers that had the water locked away and now going into the surface water balance. "Of the total irrigated area worldwide 38% is equipped for irrigation with groundwater, especially in India (39 million ha), China (19 million ha) and the United States of America (17 million ha).[9] Total consumptive groundwater use for irrigation is estimated as 545 km3/year. Groundwater use in irrigation leads in places to exploitation of groundwater at rates above groundwater recharge and depletion of groundwater reservoirs." source of quote. 545 km3/year equals 5.35 x 10^11 tons of water a year. cubic kilometers to tons conversion calculator. In the 7 year period of the Grace study you would have extracted 3.745 trillion tons of water from groundwater sources that are not being recharged by surface water so this basically will add this much water to the surface (at least for many years). So the water added to the system via irrigation is fairly close to the amount of water added by melting ice. Meaning the sea water will continue to rise regardless if the ice melting stops and the problems of the future will still remain.
64526. Dikran Marsupial at 07:13 AM on 11 February 2012
       Has Global Warming Stopped?
       Eric (skeptic) "Why would linear models be exempt from that?" They are not really, if they are intended to be a model of the data generating process. However they can also be used as a method of estimating the local gradient of the data generating process, in which case they need only be locally congruent. The choice of model depends on the nature and purpose of the analysis. For the graph in 63, I would say it is not a reasonable model for "recovery from the LIA" as GMST is already higher than the temperatures prior to the LIA. See also my comments in post 64. However please do not discuss the LIA any further on this thread as it is clearly off-topic.
64527. Eric (skeptic) at 06:58 AM on 11 February 2012
       Has Global Warming Stopped?
       Dikran, I didn't see this thread with comments when I posted on the staircase thread, only the print version. One of my questions is answered in the comments, that complex models should be congruent with some underlying physics. Why would linear models be exempt from that? Second, there is a linear trend shown in post 63 that is labeled "recovery from the LIA", which appears to be an estimate of an average natural warming trend. Is that a valid model of the "recovery" or is it invalid? (IMO, not really valid). There are a variety of arguments about the LIA and recovery from http://climate.envsci.rutgers.edu/pdf/FreeRobock1999JD900233.pdf (a heavier emphasis on volcanic activity and other natural factors) to http://www.arp.harvard.edu/sci/climate/journalclub/Ruddiman2003.pdf (natural factors are mostly cooling and warming including post-LIA is anthropogenic). I don't believe the science is settled on that topic.
64528. Mammal_E at 06:54 AM on 11 February 2012
       The Year After McLean - A Review of 2011 Global Temperatures
       Under "Short-Term Natural Temperature Influences", "aggression" should be replaced by "regression".
       Moderator Response: [DB] fixed, thanks!
64529. KR at 06:37 AM on 11 February 2012
       Still Going Down the Up Escalator
       Addendum to previous post - The model used also depends on whether that model makes physical sense. One of the primary arguments against 'step' models, even though they can fit the data with considerable statistical significance, is that physically they just don't make sense in terms of thermal inertia and the mechanics of heat transport.
64530. KR at 06:34 AM on 11 February 2012
       Still Going Down the Up Escalator
       Eric (skeptic) - The use of a linear model in the figure you reference is entirely appropriate for the question asked, which is in determining that recent warming does not fit a linear trend to the last 150 years of data. Without the linear fit in that figure, you wouldn't be able to evaluate the question. Linear fits are a minimal model, perhaps the easiest to evaluate based upon limited data - and almost always an excellent first pass. Fitting a 2nd or higher order polynomial requires fitting additional parameters, meaning more information is required to fit such a model with statistic significance. As Dikran has pointed out in several conversations, the model used when looking at any data set is dependent on the question asked, and whether the data statistically supports such a model over alternatives.
64531. jimspy at 06:16 AM on 11 February 2012
       Volcanoes emit more CO2 than humans
       The link to "Morner 2002" is broken. Can I get a good one? Sadly, I need it.
64532. Dikran Marsupial at 06:13 AM on 11 February 2012
       Still Going Down the Up Escalator
       Eric (skeptic) models can describe, explain or predict; how well they perfoem any of these tasks depends on the appropriateness of the model. If you are not sure what a model represents, why not ask on the appropriate thread (I?
64533. Eric (skeptic) at 06:06 AM on 11 February 2012
       Still Going Down the Up Escalator
       I am sorry about the LIA digression, I was obviously not clear on what I meant by bringing it up in this thread. For an example, see Figure 4 here The linear trend shown there encompasses some natural warming and cooling transitioning to manmade warming with natural variations. IMO, it is not a suitable use for a linear model. According to Dikran above a model describes and explains. The use in that link explicitly predicts but is not explicit about what it is predicting (natural?, anthro plus natural? anthro exceeding natural?)
64534. KR at 05:32 AM on 11 February 2012
       Hockey stick is broken
       DB - Thanks for the links. Tristan - From that discussion: "It appears [Jolliffe] now discredits decentering, and he's entitled to his opinion. But the hockey stick remains when using centered PCA, and when using no PCA at all. The claim that it's nothing but "utterly bogus artifacts" is what's really bogus." - Tamino For those who are interested in the subject, Tamino has a fairly extensive discussion of Principal Component Analysis (PCA) which is still on the intertubes here: Part 1 and Part 2
       Response:

       [DB] Tamino also deals with the PCA/non-PCA kerfluffle in this post at RealClimate:

       http://www.realclimate.org/index.php/archives/2010/07/the-montford-delusion/

64535. Dikran Marsupial at 05:29 AM on 11 February 2012
       The Year After McLean - A Review of 2011 Global Temperatures
       McLean should be praised for having made a testable prediction, that at least is good science (Popper would have approved) even if the basis for the prediction wasn't.
64536. Jim Eager at 05:16 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       Thanks, Yvan. I agree, if that is a real measure of aquifer drawdown then it is very worrying indeed.
64537. Tristan at 04:56 AM on 11 February 2012
       Hockey stick is broken
       Sorry JH Principal Component Analysis.
64538. Tristan at 04:54 AM on 11 February 2012
       Hockey stick is broken
       KR I completely agree with your comment. That said, I'm still interested in the whole MM03 vs MBH debacle. I can't find the original reference, I think it may be one of Tamino's vaporised posts, but here's the context from everyone's favourite website.
       Response:

       [DB] Links to the once-lost Tamino/Open Mind posts can be found in this post here:
       http://www.skepticalscience.com/Open_Mind_Archive_Index.html
       
       The post you seek is located here:
       http://web.archive.org/web/20080911215131/http://tamino.wordpress.com/2008/08/10/open-thread-5-2/
       
       The specific portion of the thread in question begins here:
       http://web.archive.org/web/20080911215131/http://tamino.wordpress.com/2008/08/10/open-thread-5-2/#comment-21873

64539. KR at 04:43 AM on 11 February 2012
       Hockey stick is broken
       Tristan - Do you have a reference to what Joliffe wrote? Decentered means are frequently used in Principle Component Analysis (PCA), and have been for a number of different analysis areas. See a quick look at Google Scholar. The various arguments I have seen about decentering have failed to show that use of decentered means invalidates MBH98, or even significantly changes the results. See Wahl 2007 as linked in the original post. While McIntyre 2004 was able to generate some 'hockey-sticks' from red noise, analysis of the eigenvalues for those shows that McIntyre was looking at noise (low correlation, lots of fairly low value components), while the MBH98 data components have only a couple of very large eigenvalues. That's how you determine whether you are looking at actual correlations (MBH98) or just noise (McIntyre). I will note that MBH98 was a pioneering paper in terms of the reconstructions - much work has followed on in both reconstruction techniques, additional and improved proxies, etc. See Mann 2007 for a partial review. All of the work supports the late 20th century being as warm or warmer than anything in the last 1200 years, and warming faster than anything we have data for. There may well be statistical arguments for/against decentered means in this field, but again - none of them invalidate the multiply confirmed results. --- What's really stunning (IMO) about this entire discussion is the 'skeptic' focus on a paper published over a decade ago, while a dozen later works using several different methods (with what should be refined techniques), are getting the same results. It's the equivalent of someone in an active field of professional research criticizing what somebody did in grade school - even though all work done since then agrees...
64540. muoncounter at 04:13 AM on 11 February 2012
       Still Going Down the Up Escalator
       "when will we know when we have finally recovered from that LIA...?" Here's a chronology of sorts, putting the end of LIA in the 1850s. That looks similar to the pattern of this graph, which shows flattened temperatures in the mid 19th century: --source And then the modern warming began. So LIA over, we're not just 'recovering,' whatever that actually means.
64541. Tristan at 04:05 AM on 11 February 2012
       Hockey stick is broken
       Ian Joliffe considers MBH98 to contain 'dubious statistics' and says of the use of decentred PCA: It is possible that there are good reasons for decentred PCA to be the technique of choice for some types of analyses and that it has some virtues that I have so far failed to grasp, but I remain sceptical. Is using a decentred PCA the norm in paleo reconstructions or was it just MBH98?
       Moderator Response: [JH] Please define "PCA". Thank you. [Sph] John, PCA is Principle Components Analysis, a statistical technique whereby components are isolated and prioritized.
64542. KR at 03:29 AM on 11 February 2012
       Still Going Down the Up Escalator
       Sphaerica - Very interesting references. While the exact causes of the LIA are not entirely fleshed out, it's clear that anthropogenic greenhouse gases are the overwhelming cause of current warming - not natural forcings, which we have a fairly good identification of. If, on the other hand, we have to placate some great Sky God, I definitely want to be on the committee selecting who gets tossed into the volcanoes...
64543. Bob Lacatena at 03:00 AM on 11 February 2012
       Still Going Down the Up Escalator
       140, KR, A brief digression... another theory for an influence (far from sole cause) on the LIA is the recovery of forest land, which drew down CO₂ levels by about 4 ppm, from the combination of population first lost in Europe due to the Black Death and 150 years later in Native American populations due to the introduction of European diseases like smallpox. In effect, we had two major population losses which allowed land that had been cleared to be reclaimed by forests, taking CO₂ out of the atmosphere. Forest re-growth on medieval farmland after the Black Death pandemic—Implications for atmospheric CO2 levels (Thomas B. van Hoof et al, 2006) Effects of syn-pandemic fire reduction and reforestation in the tropical Americas on atmospheric CO2 during European conquest (Nevlea and Bird, 2008) I have no idea how viable the theories are... but it's another example of trying to understand the system and the "natural variations," rather than just saying "Sky God angry... find virgin sacrifice, make Sky God happy... ugh!"
64544. Yvan Dutil at 02:52 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       From the paper this is aquifer withdrawal. Scary enough for me.
64545. JMurphy at 02:13 AM on 11 February 2012
       Still Going Down the Up Escalator
       And when will we know when we have finally recovered from that LIA...?
64546. KR at 01:49 AM on 11 February 2012
       Still Going Down the Up Escalator
       Eric (skeptic) - "...since then there is a mixture of AGW and recovery from the LIA." (emphasis added) This is a meme I've been seeing more often recently. I will simply note that this is discussed in some detail on the We're coming out of an ice age threads. The LIA was (as far as can be determined at the moment) a combination of solar minimum and possibly (recent evidence) a triggering tipping event of high volcanic activity. While the climate warmed from that low point, that does not explain recent warming. Only AGW can account for the magnitude of climate change over the last 50 years or so.
64547. Jim Eager at 01:39 AM on 11 February 2012
       NASA Mission Takes Stock of Earth's Melting Land Ice
       What's with the large area of mass loss south of the Himalaya? Soil moisture loss? Top soil loss?
64548. muoncounter at 01:09 AM on 11 February 2012
       Still Going Down the Up Escalator
       Eric#137: "The single number for the trend is inadequate and oversimplified." All curves (including sine curves) can be linearly approximated on a local basis; that's one of the things that makes calculus work. Fitting a linear trend is an essential first step because it forces you to justify the cause of the linear trend and it alerts you to look for departures from linearity. If those are merely residuals, you look for sources of 'noise,' as in FR2011. If those are changes in slope, you suspect acceleration (+ or -) and again go looking for causes. You seem to be suggesting a variant of the 'we don't know nuthin' myth' because we can see a linear trend and use it as a descriptor. Rather than address what is underlying the trend, imposing these arbitrary jumps doesn't seem like a valuable exercise to me.
64549. Bob Lacatena at 01:01 AM on 11 February 2012
       Still Going Down the Up Escalator
       137, Eric, I'm not exactly certain what you're saying... are you saying that there is no trend that is reliable? But you are right in that simply looking at the numbers and trying to tease things out without an underlying understanding is climatology climastrology [oops -- Sph]. The solution is to study and tease out the mechanics of the system, like the physics (e.g. radiative emission and absorption) and the component systems (e.g. ENSO and aerosol sources) and then to put it all together, rather than looking at any one piece of information in isolation. The wrong thing to do is to attribute great power to unknown acronyms, like a savage giving homage to the Sun God and the Wind Spirit, and then to just throw up your hands and say that no one could possibly know anything, and anyone who says they do is a nutter.
64550. Eric (skeptic) at 00:36 AM on 11 February 2012
       Still Going Down the Up Escalator
       As a purely hypothetical example, if we had a time series with some underlying physical properties that suggested a sinusoid, it would be possible to do a linear regression on a small portion of the sinusoid (e.g. from below the origin to above). But the slope from that section would only "make sense" in the context of the sinusoid and the underlying physical causes. In the same sense a linear trend of some portion of the global average temperature should be considered as part of a bigger picture. A shorter interval (e.g. the 80's and 90's or the 2000's) would involve some natural GW and GC, AGW and possibly some counteracting aerosols. The single number for the trend is inadequate and oversimplified. Looking at longer intervals is even more problematic since then there is a mixture of AGW and recovery from the LIA. This does not seem like a valuable exercise in analysis to me.

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