Recent Comments

Prev  920  921  922  923  924  925  926  927  928  929  930  931  932  933  934  935  Next

Comments 46351 to 46400:

46351. scaddenp at 07:48 AM on 12 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Hmm, I wonder if Tamino simply confused you with Tim Curtin (definitely persona not grata there)?

46352. chris at 07:44 AM on 12 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Regarding the 8.2 kYr event: This isn’t necessarily a fair test of the sort of analysis that Tamino has done. That’s not to say that the issue settled and I personally think it’s a shame that this interesting study has become factionalised.

       The astonishing thing about the 8.2 kYr event as captured in Greenland cores is how fast it was. Temperatures dropped and rose so fast that there was only a 70 year period in which isotope ratios were below the Holocene average.

       The event is captured in high resolution Greenland cores and is also seen in N. Atlantic proxies. However a detailed analysis of these indicates that the amplitude of the event in proxies drops quite rapidly away from the main event. There isn’t much evidence that the 8.2 kYr event had much of a temperature impact further afield. Modelling of the event suggests that the cooling is expected to be localised mostly in the N. Atlantic with a warming in the Southern Oceans (as less heat is transported by the AMOC). The Kilimanjaro paper Tom  linked to has an indirect proxy for the climate event around (fluoride levels in dust arising from partial lake drying). This doesn’t necessarily arise from a local temperature change but might involve changes in hydrology arising from the event further afield. However if one wanted a more direct local temperature measure (e.g. delta 18O) the Kilimanjaro cores actually have a “warming” spike (or series of spikes) around the 8.2 kYr period.

       The Antarctic cores don’t help to pin things down very much. The dome C core shows a very long slow cooling that starts around 10,000 years ago and continues through the 8.2 kYr event with no particular change in rate (the temperature in the starts to rise slowly soon after). I don’t see how this can be taken as evidence of Antarctic cooling associated specifically with the 8.2 kYr event in Greenland. Interestingly the Vostock core has a very marked positive temperature spike right at the time of the 8.2 kYr event. Not sure if this is considered to be an artefact but it is represented by 3 or 4 points in the core time series that rise and then fall (I was going to plot this but someone has already done so ).

       I would conclude:

       i) If the Marcott proxy set is a representative selection of global temperatures captured in proxies then (a) the large N. Atlantic signal is likely to be diluted (or negated) by the relative smaller cooling elsewhere (or warming contributions from the S. hemisphere) so that the nett global signal is small (e.g. relative to the globally averaged warming that has accrued over the last ~ century). The fact that it hardly exists in the Marcott composite may simply reflect the fact that globally-averaged there wasn’t much of a temperature change (need to inspect each of the Marcott proxies to assess this).

       (ii) The extremely rapid signal in the ice cores approximates to around 70 years in total up and down. Such rapid temperature excursions (much faster than current warming) might be poorly captured in the proxies and/or smeared by the Marcott/Tamino methods (again would be helpful to inspect the individual proxies).

       What this boils down to is that the 8.2 kYr event isn’t a particularly fair test of the ability of the Marcott/Tamino methodologies to preserve a contemporary-style temperature excursion since (a) the 8.2 kYr event may not have involved much of a temperature change globally averaged and (b) it was much faster up and down compared to our (pretty fast) temperature rise.

46353. bouke at 06:52 AM on 12 April 2013
       The anthropogenic global warming rate: Is it steady for the last 100 years?
       

       Two points regarding Tung and Zhou:

       1) If you add a factor to your multiple linear regression, even if it's just random noise, that factor is going to explain some of the trend. If you then put that factor into the non-anthropogenic group, you reduce the anthropogenic part. If the factor correlates with the trend, this effect becomes much stronger.  A look at the AMO graph shows that the AMO was at a minimum in 1910, and at a maximum in  2010, which means it is correlating with the trend.

       2) Lets take the following model:

       T(t) = a * distractor₁(t) + b * distractor₂(t) + c * distractor₃(t) + d * T_detrended(t) + e * trend(t) + residual(t)

       T_detrended is equal to T(t) with the linear trend removed. trend(t) is the linear trend of T(t). I can already spell out what the best model is: a, b and c are 0, d and e are 1. Taken together, they perfectly reproduce T(t).

       This is, in essence, the model of Tung and Zhou.  T_detrended is the AMO, which is defined as the detrended North Atlantic SST. Not quite the detrended world temperature record, but almost.  trend(t) is their anthropogenic factor, which they make a linear trend. Because these two factors can explain the temperatures so well, all the other factors become mere distractors.

       Note that it does not matter in linear regression which actual trend you use, as long as it is regular. If you would halve trend(t), the factor e would double, and you end up with the same model.

       To the degree that NA SST and world temperature correlates, the Tung and Zhou approach can only find linear anthropogenic forcings.

        

46354. KR at 06:26 AM on 12 April 2013
       The anthropogenic global warming rate: Is it steady for the last 100 years?
       

       Also of note in regards to the AMO definition is Emanuel and Mann 2006, along with a discussion by M. Mann and G. Schmidt at RealClimate, concluding in part that:

       The linear detrending is intended to remove any potential forced signal, under the assumption that it is linear in time. However, if the forced signal is not linear, then this procedure can produce a false apparent ‘oscillation’ purely as an artifact of the aliasing of the non-linear secular trend (Trenberth and Shea, 2006). In fact, we have very strong indications for the 20th Century that the forcings over that period have not varied in a smooth, linear fashion.

       Because of the procedural difficulties in isolating the AMO signal in the instrumental record, the estimated attributes of the signal are quite sensitive to how it is defined. [...] It is therefore likely that the non-linear temporal history of anthropogenic tropical Atlantic warming has masquaraded as the ‘AMO’ in some studies.

       [Emphasis added]

       Again, subtracting signal from signal is going to give incorrect regression results for other components, and linear detrending is not a good match to the actual forcing history. 

46355. scaddenp at 06:24 AM on 12 April 2013
       Antarctica is gaining ice
       

       "Is he correct in his statement that models predicted this increase in ice?" What he says is that models predict an increase in snowfall, and yes they do (going back to TAR I think). Warming in the southern ocean inevitably means more humid air moving into the interior of the Antarctica where it will fall as snow. The prediction was that this would increase the ice thickness in the interior (GRACE shows this happening). However, ice loss from the margins is so far outpacing that gain. These predictions were not about sea ice.

46356. KR at 05:47 AM on 12 April 2013
       The anthropogenic global warming rate: Is it steady for the last 100 years?
       

       I would agree with dana1981 that the standard AMO index, being a linearly detrended set of sea surface temperatures, is quite tied to global warming and incorporates some of that warming signal - subtracting signal from signal, and reducing the identified anthropogenic component. 

       Any regression against the AMO requires, of course, defining which AMO index you are discussing - the linearly detrended version, or one as suggested by Trenberth and Shea 2006 Atlantic hurricanes and natural variability in 2005, who recognized the incorporation of a global warming signal into the traditional definition:

       In particular, the recent warming of North Atlantic SSTs is known to be part of a global (taken here to be 60
       N to 60
       S) mean SST increase. While detrending the AMO series helps remove part of this signal, the SST changes are not simply linear and a linear trend has no physical meaning. To deal with purely Atlantic variability, it is highly desirable to remove the larger-scale global signal that is associated with global processes, and is thus related to global warming in recent decades. Accordingly, the global mean SST has been subtracted to derive a revised AMO index.

       Also of interest is Anderson et al 2012, Testing for the Possible Influence of Unknown Climate Forcings upon Global Temperature Increases from 1950 to 2000, which analyzes ocean heat content (OHC), sea surface temperatures, and forcings, and indicates from an energy conservation point of view that:

       ...less than 10% of the long-term historical increase in global-mean near-surface temperatures over the last half of the twentieth century could have been the result of internal climate variability.

       According to that work, there is insufficient energy available within the constraints of OHC to cause observed warming via natural variability and maintain observed OHC. 

46357. Paul Magnus at 05:43 AM on 12 April 2013
       The anthropogenic global warming rate: Is it steady for the last 100 years?
       

       Some people are just blinded by science....

       Just love the dynamic definition function....

46358. Bob Lacatena at 05:19 AM on 12 April 2013
       Models are unreliable
       

       bouke,

       First, for reference, readers can look at the two figures that you reference. In each figure, the black line/square represents the NSIDC observed value, while the colored lines/squares represent the values resulting from various model ensembles. The first graph is of 5-year running mean September sea ice extent, while the second cross references the1979-2010 mean and trend (the observed value is in the center of the 2-sigma black box, and the average of all of the models is shown as an orange cross).

       Note that these figures focus on the September mean. They show nothing concerning the September minimum or the overall flux of ice of the course of the year.  They also show extent, not area or volume.  As such, the main question one must ask is "how does this short lived model discrepency affect overall global mean temperature within the model."  In particular, it should be noted that most models overestimate the ice extent, especially in relation to the recent plummet, and so most models are most likely underestimating the expected feedback (with respect to Arctic ice extent) in recent years.

       Figure 1:
       
       Figure 2:
       
       Your question conflates any number of false assumptions.

       First, let me point out that the existence of this flaw in the models is first and foremost excellent evidence against the silly denier's misunderstanding that models are "tweaked" and "parameterized" to produce a particular result. This is not the case. The models are based on physics, and the only valid way (in most cases) to adjust the model is to refine the physics to bring the final result more in line with observations.

       With that said, one of the first issues with comparing models to observations is the quality of the observations. In the case of sea ice extent, there is a lot of wiggle room for how one computes the extent... how much of a "pixel" of sea area do you count as ice or open water? You can use this page to view some of the various methods all at once. There is a fair spread in the values of the various methods within observations. Why then would you not expect a spread in the model estimates?

       Secondly, and this is the more important point, the number of factors in the models is huge. You've picked one and said it doesn't work, so throw out the models and substitute the most unphysical thing you can imagine, a linear trend -- which in turn is the ultimate in parameterization. Such a false dichotomy is absurd. This is rather like complaining that some people die in car crashes, so until no one dies in a car crash, cars are too unsafe to drive and everyone should walk everywhere.

       Thirdly, you are missing the point of the climate models, and you present a strawman before your question ("it may be wiser to look at the linear trend"). Look at the linear trend for what? Sea ice prediction? Global mean temperature? For what reason? To evaluate the climate system, or to address policy issues?

       The climate models exist first and foremost to study the climate. Scientists will know they have Arctic sea ice modeled very well when they start to fall within that 10% range you discuss, but honestly, I don't think that will ever happen, because at the current rate the ice will be completely gone before they've figured out what is innaccurate within the models. Then they can just cut sea ice out of the picture.

       Climate models have another value in being one predictor of climate sensitivity. The linear trend that you suggest would need to be based on something. Observations? The flaw there is that we only have a very short time span to use as a basis. Paleo-studies? Very valuable, but also very constrained by the inference of "observations" through indirect means.

       In the end, however, what we do see is that the estimates for climate sensitivity from a very wide variety of models, observations, paleostudies and other methods all converge in the same 2˚C to 4.5˚C range. This tells us that, despite individual flaws within the models, the overall answers are pretty darn good.

       Lastly, I would point out that people have long been pointing to the plunge in Arctic ice, and the discrepency in the models, in that the Arctic ice is failing far faster than anyone ever imagined possible. I do wish that the modelers would redirect their attentions to that sphere, and figure out whe the models are so far off in that respect.

       But, as I've already said, there may be little value in that. It might be that heat transport under the ice is far greater than expected. It may be that additional factors such as black soot and altered weather patterns have a greater influence than expected. It may be that summer water runoff from North America and Siberia has a far greater influence on sea surface temperatures and salinity. It may be that the polar amplification of warming is even worse than expected (something that is difficult to perfectly measure, since most global mean temperature analyses are sparse in the polar regions).

       But whatever the reason... I'm pretty sure that the Arctic is going to be ice free for large parts of the summer and fall long before the modelers get around to understanding all of the physics behind the particular details of Arctic ocean currents and ice, and the Arctic will have become such an alien environment that that entire part of the models will more easily be replaced with a very, very simple linear trend... a flat line centered on zero.

        

46359. KR at 05:14 AM on 12 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Ray - While Clive Best has some interesting work there, it isn't (IMO) complete.

       He presents data binned into 50-year blocks, rather than with 20-year linear interpolations (meaning a larger smoothing at 1/4 the spike length, reducing/spreading the hypothetic spikes). That is not directly comparable to either Marcott or Tamino - the difference in processing may make a considerable difference in results, and I don't see any evaluation of its effect. 

       In addition he has (as far as I can see) only presented two realizations of the data; one with nominal dates and one with a randomization of 20% of proxy resolution (not the age uncertainties described in the supplemental data). Given the high variability of individual realizations, a fairly large number of runs will have to be evaluated - which is why Marcott et al did 1000 perturbations - to see the signal common to all realizations. Running a 5-point smoothing (as Best did on his first realization) is not equivalent to a Monte Carlo permutation of the uncertainties. 

       There are other differences in approach that I suspect don't matter much, such as date-shifting an entire proxy rather than random-walking the radiocarbon age control points, and the Marcott modeling of time uncertainty as a first-order autoregressive process. But those first two (additional smoothing and only two realizations) may account for much of the difference in results between Best and Tamino. 

       ---

       Again, though, since current warming will not be a 200-year spike, but rather take thousands of years to reverse, well covered by the Marcott resolution, such hypothetic arguments about Marcott et al processing are irrelevant to current conditions - there is zero evidence for, and considerable evidence against, warming akin to current conditions during the pre-Industrial Holocene, including in the Marcott data. 

46360. dana1981 at 05:04 AM on 12 April 2013
       The anthropogenic global warming rate: Is it steady for the last 100 years?
       

       I have two major issues with this response.

       My issue with point #1 is that although not all radiative forcing estimates are equal, they do all show an accelerated anthropogenic forcing sometime after 1950, so we should expect to see accelerated anthropogenic warming since, say, the 1970s.  If you don't, you have to explain why not, and saying 'the forcing is uncertain' isn't sufficient if all anthropogenic forcing estimates include an acceleration.

       My other issue is that the main point of Dumb Scientist's post doesn't seem to be addressed.  That's the criticism that AMO is associated with Atlantic sea surface temps, which themselves are warmed by the anthropogenic forcing.  So if you remove the AMO influence in your linear regression, you're removing some of the anthropogenic warming, and that may explain why it's apparently underestimated.  As far as I can tell, that main point isn't addressed in this response, unless I'm missing it.

46361. Kevin8233 at 04:33 AM on 12 April 2013
       Antarctica is gaining ice
       

       Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate warming, consistent with model predictions, may be offsetting increased dynamic losses.

       The above was tail end of the conclusion of Zwally's presentation (I believe it was his presentation and not his paper), but anyway, my question is this; Is he correct in his statement that models predicted this increase in ice?  I believe "Barry" even suggested that AR4 had similar predictions.

       I'm not asking if his paper or his observations are correct, just the above statement.  If it is correct, does this debunking need to be re-done?

46362. CBDunkerson at 22:19 PM on 11 April 2013
       Models are unreliable
       

       The 'intermediate' article for this topic notes that Arctic Sea ice decline and global sea level rise models have proven to be very conservative in comparison to actual results.

       The reasons for this are also generally known... scientists have only recently begun to get a handle on the rate of ice loss from Greenland and Antarctica and thus these were excluded from sea level rise models. Now that we know that there is significant ice loss going on that will be factored in to the models and they will move closer to the observed values. Similarly, recent findings have shown that mechanical effects (i.e. ice breaking up under wind), bottom melt due to unexpected circulation patterns, ice export, and other significant factors were not included in the Arctic ice loss models.

       This does not mean that all climate models are similarly lacking important factors. The atmospheric temperature models have been largely on target. The PIOMAS Arctic ice volume model has been confirmed by recent sattelite measurements. Et cetera.

       No model includes the wing flaps of every butterfly on the planet, but we have a pretty good idea of which models include major uncertainties and which do not. Also, contrary to what you say, it is very common for linear (and other) trends to be used when looking at various climate factors. Indeed, a linear trend is a model... just a very simple one. Search on Maslowski or Neven for examples of this pertaining specifically to Arctic sea ice. Their trend projections show sea ice extent dropping to near zero in the next few years.

46363. Dikran Marsupial at 22:12 PM on 11 April 2013
       Models are unreliable
       

       @bouke The fact that the models are obviously missing some physics that is important for regional (i.e. Arctic) climate does not imply that they are not useful for global climate projection, for the simple reason that the missing physics is only relevant to a particular region, and hence this doesn't substantially affect the global climate.

       Scientists are perfectly happy to discuss the flaws in the models, however the reason they don't often explicitly say that "the models aren't good enough" is because it isn't an all-or-nothing issue.  There are some things the models predict well, and others that they don't.

       The main reason they use models rather than linear trends on the other hand has nothing to do with predictive power.  A physical model allows you to test the consequences of a set of assumptions of how the physics of climate works.  A linear trend is just a statistical model based on correlations and does not allow you to draw any causal conclusions.

       I doubt there is a fundamental discussion on the relative merits of the two approaches for the simple reason that they are two tools with different jobs.  Secondly a linear model is only appropriate for a situation where the (rate of change) of the forcings are approximately constant, which is unlikely to be true of centennial scale projections for which physical models are more appropriate.

46364. bouke at 21:33 PM on 11 April 2013
       Models are unreliable
       

       I have a question on model reliability in predicting arctic sea ice. I just read (parts of) "Constraining projections of summer Arctic sea ice" by Massonnet et al. Looking at their figure 1, it is clear that most CMIP5 models do not accurately model
       past september sea ice extent (SSIE). This is even more visible in their figure 2, which shows that 90% of the models either simulate an average SSIE in
       1979-2010 outside of 2 sigma of the actual average, or a trend in SSIE outside of 2 sigma of the actual trend. If the physics of the models were perfect, only 10% of model runs would be expected to fall outside this window.

       To my mind, this shows that the models still miss essential physics, and it would be unwise to attribute too much predictive power to them. A linear trend may be a better predictor. Yet, I never hear a scientist say 'The models aren't good enough at the moment, so it may be wiser to look at the linear trend.'

       Why is that?

       Is there a fundamental discussion somewhere on the relative merits of a linear trend versus a model as a predictor of the future?

46365. Tom Curtis at 21:08 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       michael sweet @36, when I first raised issues regarding Tamino's argument, I raised them at Open Mind.  They never got past the "awaiting moderation stage".  I reposted the comment to be sure, with the same result.  I have drawn the conclusion that Tamino does not want my comments, for whatever reason, and given that, would not deign to comment at Open Mind again if future.

       Since you asked ...

46366. michael sweet at 20:07 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Tom,

       Instead of debating yourself here, have you tried going to Tamino's blog and asking him what he thinks of the 8.2 ka event?  What did he say?   Tamino frequently replies to informed questions.

       As I read Tamino, he does not claim the analysis proves that no sudden spikes could occur.  He claims Marcott is strong evidence that such spikes did not occur.  This seems reasonable to me.

       How could all the proxies have missed such a spike?  As you point out, there is evidence of a drop in proxies at 8.2 ka.  Others challenge that as a global event.  Marcott may be correct that it was mostly a North Atlantic event, like the midieval warm period.  Manns' data shows that if you cherry pick your proxies you can find a lot of spurious, local trends.  KR lists several known local events. Where are the proxies for a sudden, global spike?  I do not see skeptics here providing a list of proxies showing a spike. They must have searched for such proxies without being able to find them.

       In addition to showing that Marcott might have missed a sudden spike, a physical mechanism for such a spike is required.  

46367. scaddenp at 18:29 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       KR - if you applied Marcott method to only the altantic proxies and failed to find a 8.2ka cooling spike, then this would suggest problems with the method in resolving spikes. The magnitude of the 8.2ka event on global temperature being definitely debatable. The mechanism for sudden cooling in that region is there.

       However, I have little time for the argument that could be 0.9 warming spikes in the absence of any physical mechanism for creating one. I just share Tom's doubts the Marcott (and Tamino's) work conclusively provide observational evidence to show that they didn't occur. I am also of the opinion that it is a side-show from the significance of the paper.

46368. Lars Karlsson at 17:07 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Steve, KR and others,

       To the convinced "skeptic", <a href="http://www.skepticalscience.com/marcott-hockey-stick-real-skepticism.html#93376">all those "might" would turn into "must"</a>, and the alternatives hiding behind them would be invisible.

        

        

46369. Ray at 14:32 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       scaddenp  There are some calculations and comments by Clive Best on the Tamino generated peaks that reach somewhat (but not entirely) different conclusions that you might find interesting.  

46370. KR at 14:27 PM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       scaddenp - There's a good set of information on the 8.2 Ka event from NOAA, which lists various paleotemperature proxies from Minnesota, Germany, Costa Rica, Greenland, and the North Atlantic as supporting evidence. 

       They also list paleo evidence for the end of the African Humid Period, drought during the Akkadian Empire, and the drought leading to the collapse of the Mayan Empire. Those were all regional events of only a few hundred years, but multiple sets of relevant paleo evidence is available for each. 

       I would therefore consider a larger scale global warming event to be something for which we would see paleo evidence - and we do not.

       Just to clarify - Is anyone actually claiming both that the Marcott data might miss such a spike (which I'm willing to postulate for the sake of the discussion), and that we wouldn't see such a global event in the rest of the data? There really is no evidence for such a spike, let alone a physical mechanism. 

       WRT Tamino's work, I have yet to see anyone put forth a convincing counter to his work regarding a hypothetic Holocene 0.9 C global warming event, and his conclusion that it would be visible in the Marcott data. There has been a lot of discussion and/or complaints with regards to sampling effects and averaging, but - IMO there needs to be math, or it didn't happen. 

46371. dana1981 at 12:40 PM on 11 April 2013
       It's not bad
       

       Mark @344 - first off, almost all of the estimates in the Tol paper you reference are from the most conservative economists doing climate research (Nordhaus, Tol, Mendelsohn, etc.), so the paper almost certainly underestimates the economic damage from climate change (probably by a very large amount, in my opinion).  It's really interesting that it references Chris Hope, who now says that the social cost of carbon is in the ballpark of $150 per tonne of CO2, which is 1-2 orders of magnitude higher than Tol believes.

       Despite these underestimates, the paper still concludes that the net impact on GDP at 2.5°C will be negative, and we're already committed to about 1.5°C warming and still rising fast.  So I'm not really sure what your point is.

46372. dana1981 at 12:26 PM on 11 April 2013
       Climate's changed before
       

       Mark @345 - there's nothing directly wrong with 'the skeptic argument' as articulated by Lindzen here.  It's the implication of the statement where the problem lies.  Saying 'climate has changed naturally in the past' is like saying 'humans breathe oxygen'.  No duh.  Everybody knows that.  So what's the point in saying it?  The answer to that question is pretty clear.

46373. Mark Bahner at 12:19 PM on 11 April 2013
       It's not bad
       

       Oops. I forgot to include the link:

       The Economic Effects of Climate Change

46374. Mark Bahner at 12:16 PM on 11 April 2013
       It's not bad
       

       The economic impacts of climate change may be catastrophic, while there have been very few benefits projected at all.

       What about Figure 1 of this paper?

46375. Mark Bahner at 12:02 PM on 11 April 2013
       Climate's changed before
       

       What was wrong in what Richard Lindzen wrote?

46376. engineer8516 at 11:21 AM on 11 April 2013
       Making Sense of Sensitivity … and Keeping It in Perspective
       

       "Notice that it is for all intents and purposes, in that small range, linear." You're right, but the global climate is so complex. It's still not sitting well with me so I decided to try and derive it myself. Take the following with a grain of salt. I might have done something wrong or interpreted something wrong.

       Anyway, using the energy balance...

       Power in = (1-α)πR²F₀

       Power out = 4πR²ϵσT⁴, where ϵ is the emessivity

       Thus, F = ϵσT⁴, where F = (1-α)F₀/4

       Thus, T=[F/(ϵσ)]^1/4

       The total derivative is: dT/dF = δT/δF+δT/δϵ*dϵ/dF

       substituting and simplifying:

       dT/dF = T/(4F)-T/(4ϵ)*dϵ/dF, where the term T/(4ϵ)*dϵ/dF is from feedbacks.

       Thus, the linear approximation for climate sensitivity is k ≈ 4*dT/dF ≈ T/F.

       With this linear approximation we're assuming that for small changes in temp the term T/(4ϵ)*dϵ/dF is almost constant or negligible. Feedbacks aren't negligible so we're arguing it's almost constant.Thus, we're assuming

       dϵ/dF ≈ C*ϵ/T, where C is a constant. I still don't like this approximation. I guess I have to do more reading. Again I might have done something wrong or interpreted something wrong so take the stuff above with a grain of salt. Thanks

46377. chriskoz at 11:21 AM on 11 April 2013
       Antarctic Octopus Living Testament To Global Warming
       

       When I was reading Twenty Thousand Leagues Under the Sea as a child, I thought "Interesting but completely our of reality nonsense" because Jules Verne did not know that Antarctica was a continent rather than ice shlf like arctic. BTW, Verne could have been ignorant, because even back then (mid-end of XIX century) the adventurers could have known about antarctic mountains.
       Anyway, that has now changed: Nautilus could have swam under the antarctic ice just like octopuses did, if the action have taken place in Eemian...

46378. Jeffrey Davis at 11:17 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       McIntyre's work is rhetorical rather than scientific. Hence the innuendoes and sarcasm.

46379. scaddenp at 11:15 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Tom that is a very interesting point. I asked around here and no 8.2ka event known NZ circles but dating is lousy. Suppose you just used Alantic-influence proxies. If the spike doesnt show with them using Marcott/Tamino's methods you must definitely conclude that the method isnt capable of resolving such spikes.

46380. Rob Honeycutt at 10:41 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Tom @ 21...  "Such errors provide "skeptics" an opportunity to point to a mistake..."

       You know, it seems to me, that's something that can never end.  Science is iterative.  It's never perfect.  There is always something more to understand, always a better and more accurate way to look at things.  

       I keep getting the sense that the "skeptics" prey on this essential element of the scientific process in order to try and undermine it.  Any real skeptic would look at a paper like Marcott and find ways that improve it by being skeptical.  McIntyre and his ilk do the same thing, but in order to try to tear down other scientists and their work.

46381. scaddenp at 10:38 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       The point isnt whether McIntyre is a competent statician or not. It's what he does with it. Mostly what he has done is to draw attention aware from the main points of the paper to a sideshow. However the main point of the article is that the statistics were used simply to give people a reason to dismiss the paper whereas Tamino took the criticism on board and explored the effect and what it would do for the conclusions. Tamino's stuff advances science and could be worth publishing. McIntyre? All you seem to get sniping from sidelines, innuendo about improprietary and nothing published since M&M. I'd say put up or shut up.

46382. KR at 10:25 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Ray - I've read through a number of the McIntyre discussions on Marcott, and (personal opinion only) have found them to be a mix of cherry-picks and arguments in detail while ignoring the larger picture. With language like "Marcottian uptricks upticks" and the like, McIntyre appears to be taking more an ideological approach than a scientific one. 

       I've also seen numerous statistical mistakes made by McIntyre, such as not knowing how to judge principal component weighting or deal with normalization (such as incorrectly selecting significant components, giving unsupported results), both in his attacks on Mann et al and Lewandowsky et al - I have not been impressed. 

       Your mileage may vary, but I don't find his work a useful contribution. 

46383. Ray at 09:58 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       KR

        

       There are a couple of current pieces on Climate Audit looking in some detail at the proxies used in the Marcott paper and making some comparisons between these and other similar proxcies.  The language used isn't hysterical and the conclusions drawn don't seem overly comtentious. McIntyre, whatever his shortcomings, perceived or otherwise, is a competent statistician and there are points made, which, to me at least, give a wider perspective on the pros and cons of the various proxies that used in climate science.

46384. Tom Curtis at 09:58 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       As has previously been discussed, the 8.2 Kya event was a very significant cooling event associated with the suden release of large volumes of melt water into the North Atlantic.  The volume of melt water released may have raised sea levels by as much as 1.2 meters.  The effect in the North Atlantic was drastic, dropping regional temperatures by as much as 3 degrees C.  The fall in temperatures is detectable in Soreq Cave (in Palestine) and in Kilamanjaro Ice cores.  It is unclear whether it is detectable further afield.  There are large negative excursions within age uncertainty in Antarctic Ice cores.  The temperature excursion is large enough to effect the global mean surfacte temperature even if regionally confined.  If, as is possible, it was a global excursion, it would have resulted in a fall, then recovery of global mean temperature of about 1 degree C.

       The significance of this is that it hardly registers on the Marcott et all reconstruction.  It barely registers even on Tamino's emulation, which is more sensitive to short term variations.  If you look at figure 2, just prior to 6000 BCE there is a sharp decline.  That is followed by a short up and down blip, followed by a general rise.  Shortly after the start of that general rise there is a very brief downward blip.  That blip is the 8.2 Kya event as it shows up in Tamino's version of the Marcott reconstruction.

       This specific example shows, again, that Tamino's test was not adequate to support his claims, as repeated in the main post above.

46385. KR at 09:37 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Incidentally, the count of 'skeptic' posts terribly upset about this paper is up to at least 26 on WUWT, and 14 at ClimateAudit. Apparently they find the outlines of Holocene temperatures, compared to where we're going now, very threatening in some fashion.

46386. KR at 09:25 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Tom Curtis - And as already discussed, we have sufficient proxy evidence (completely aside from the Marcott reconstruction and statistics) indicating the 8.2 Ka event and the drop in global temperatures then, an excursion lasting only a few centuries. As I noted here, there is no such support (nor physical mechanism) for any upward spike in temperatures during the Holocene of the nature and scale seen in current warming. 

       You certainly do have a point re: Marcott and the 8.2 Ka event - I had not carefully considered the timeline in previous remarks - but there's no evidence of 0.9 C warming spikes during the Holocene. 

       That's from the full body of evidence - completely aside from the Marcott et al time resolution, there is no indication of such a spike in proxy data that shows the 8.2 event. Hence arguments based upon "a spike might have been missed" are inconsistent with that body of evidence. And claims about such spikes are IMO the result of arguing about only one paper, when there is a great deal more data available contradicting such claims. 

       [ Not to mention that current warming will not be a short 'spike' - thousands of years will be required to draw down the CO2 we've put up in the last 150 years. And therefore claims about Holocene spikes too short to show in Marcott are irrelevant. ]

       In that regard I find the 'spike' arguments seen from Watts, McIntyre, and the like to be in essence cherry-picking and red herrings; arguing about one set of data (which has its pluses, minuses, and uncertainties, and which definitely will be discussed/elaborated upon in future work) by making hypothetic claims clearly contradicted by the rest of the information available. I'm rather appalled at the time wasted on this nonsensical side-line. 

46387. Tom Curtis at 08:21 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       KR @16, as we have already discussed, the 8.2 Kya cooling event, which was large, wide spread and possibly global, does not show up in the Marcott et al reconstruction.  Or more precisely, it shows up as a 0.01 C dip in the general rising pattern at that time (in the reconstruction).  That dip is too small to be seen in standard representations of the reconstruction.

46388. Tom Curtis at 08:16 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Paul R Price @20, much as I appreciate the effort, your graph contradicts the data in Marcot et al.  Specifically, it ignores the fact that the mean reconstruction is heavilly smoothed by Marcott et al's proceedure, and that it therefore conceals probable events with higher temperatures in the past.  For example, you say that current temperatures exceed any experienced in the last 125,000 years.  Marcott et al, in contrast say that between 18 and 28% of Holocene temperatures exceed modern temperatures.  You place a line which even crosses the 1 sigma error bar with the label, "Temperatures unknown to human civilization".  In fact, if we are to take Marcott et al's figure 3 seriously, human civilization has experienced temperatures up to 0.5 C greater than current temperatures in the interval between 6000 and 2000 BCE, albeit for less than 5% of that time.

       These may seem like quibbling errors to you.  They are not.  Such errors provide "skeptics" an opportunity to point to a mistake, for the benefit of themselves or their friends.  Having found such a mistake, it is then used as an excuse to switch their minds of and not consider the true ramifications, which apart from these errors you have admirably illustrated.

46389. BBD at 08:15 AM on 11 April 2013
       Antarctic Octopus Living Testament To Global Warming
       

       # 9 william

       One has to account for the change in MSL between the Eemian and the Holocene. Eemian GAT was ~1C above the late Holocene but mean sea level was ~5m higher.

46390. Paul R Price at 07:28 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Dana,

       Thanks for the summary of Marcott reaction, great point about what it says about real vs. false skepticism.

       Inspired the post by Jos Hagelaars here is a poster annotated version of Hagelaars' Marcott graphic I have put together with temperature bands indicating human history and with last dates to constrain warming to different temperatures from Stocker (2012). 

       If a bit cluttered but is intended as a poster to convey science to policy types as another attempt to convey the enormity of what is now occurring. Any constructive comments or corrections welcome, especially if there are other strong references in contrast to Stocker for peaking or carbon budget exhaustion dates.

       Paul

       Moderator Response:

       [TD] Thanks, Paul!  A related SkS post is The Y-Axis of Evil.

46391. colinrus at 06:59 AM on 11 April 2013
       Land Surface Warming Confirmed Independently Without Land Station Data
       

       What strikes me is how different the trends are in some parts of the globe between the two maps. Does this imply that some areas have a huge warm or cool bias in the temperature record? Seems most unlikley to me. So either there are errors in the non temperature data at the "local" level or the model is ok in aggregate but error prone at the detail level or???

46392. KR at 06:40 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Bob Loblaw - Good point.

       Lars Karlsson - You're correct, some 'skeptics' might argue those points. And as I stated, I would find such arguments rather silly. They could use roughly the same arguments from unsupported possibilities to make claims about unicorns, after all.

46393. Rob Honeycutt at 06:24 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Lars... The problem there is, what ever magical unknown forcing that might have occurred has to also square with very well known changes in forcing we see today. And those forcings have to square with climate changes seen in the deep past as well.

       The holocene is not some isolated segment of time in Earth's history that had different forcings and CS than the rest of Earth's history and the present.

       It's just odd to me how hard it is for some people to accept that the overwhelming body of scientific research is mostly likely correct.

46394. william5331 at 06:23 AM on 11 April 2013
       Antarctic Octopus Living Testament To Global Warming
       

       I wonder if the scientists have taken into account the "floating ice" consideration.  For instance, if there is a basin with a bottom is 100m below sea level filled with ice, all the ice up to sea level and approximately 10 meters above sea level will have no effect on sea level if it melts.  Only the ice above 10m above sea level will cause a rise in sea level if it melts.

46395. Bob Loblaw at 06:11 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       KR: I took Lars' comment as a prediction of what we'de hear from the fake skeptics, rather than an expression of his own beliefs, but it's hard to read tone into the printed word.

       ...and the "plausible physical mechanism" is called "pixie dust" (AKA "natural cycles").

46396. KR at 05:57 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Lars Karlsson - Just to make certain I have your points straight:

       According to your post, large scale temperature rises in the past, which we have no evidence for (despite proxy evidence showing events like the 8.2 Kya cooling, which should indicate our ability to see such changes), nor any plausible physical mechanism for such a spike, involving forcings that we somehow haven't detected over the last century (the most measured period in human history), are sufficiently possible for you to argue against known radiative physics (the CO2 contribution) and/or that because of these unseen forcings you feel the climate sensitivity might be low?

       I find myself oddly unconvinced...

46397. Rob Painting at 05:51 AM on 11 April 2013
       Antarctic Octopus Living Testament To Global Warming
       

       Yes, the last interglacial, the Eemian (about 120-130,000 years ago), was thought to be slightly warmer than present. This was due to changes in Earth's orbit and rotational tilt (obliquity) which allowed more sunlight to reach Earth's surface - especially the Northern Hemisphere. See this SkS series of posts on the last interglacial.

46398. Steve Metzler at 05:46 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       Lars, with all due respect... you're bending over so far backwards there that... well, you know :-)

46399. William Haas at 05:39 AM on 11 April 2013
       Antarctic Octopus Living Testament To Global Warming
       

       This must be evidence that past interglacials could have been warmer or of longer in duration or both then the one we are experiencing today.  The causes of these past interglacials must have all been of natural origin. 

46400. Lars Karlsson at 04:22 AM on 11 April 2013
       Real Skepticism About the New Marcott 'Hockey Stick'
       

       If some "skeptic" has actually thought about the implications of more variability in the past, he/she may have thought along the following lines.

       Larger temperature variations in the past does not necessarily imply a higher climate sensitivity. They might instead indicate some stronger natural forcings, which might in principle have gone undetected or unaccounted for during the last century, and these forcings may have then contributed singificantly to the warning in the last 100 years in which case the contribution from CO2 would be less and hence climate sensitivity might be lower.

       So this leaves a rather slim but still existing possibility that larger temperature variations in the past and a low climate sensitivity can both be true at the same time. 

Prev  920  921  922  923  924  925  926  927  928  929  930  931  932  933  934  935  Next