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Comments 93651 to 93700:

  1. Climate Sensitivity: The Skeptic Endgame
    90 Eric:
    when I see a probability distribution I immediately look around for the data it was based on.
    well yes. but now you have seen that that is not the only sort of probability distribution, and really - as a remark on the general technique, rather than the objective/subjective side issue - it is a perfectly proper technique which lots of science uses (e.g. CERN wouldn't work without it). In my limited experience of them, however, they are rarely used to determine The Truth, but to bound understanding and projections... as, IMHO, they are being used here. As for policy, it's also an issue with lots of obfuscating ideas, like intergalactic cosmic ray flux, and the demand that things are more absolute that is ever the case in reality, put about by people who probably actually know better... which is definitely off topic.
  2. HumanityRules at 00:28 AM on 5 March 2011
    Climate Sensitivity: The Skeptic Endgame
    "If the IPCC climate sensitivity range is correct, if we were to stabilize atmospheric CO2 concentrations at today's levels, once the planet reached equilibrium, the radiative forcing would have caused between 0.96 and 2.2°C of surface warming with a most likely value of 1.4°C. Given that the Earth's average surface temperature has only warmed 0.8°C over the past century" Dana how much of the 0.8oC would you attribute to anthropogenic GHGs?
  3. Arkadiusz Semczyszak at 00:01 AM on 5 March 2011
    Putting a new finger on climate change
    @Marcus CO2 poorer in 14C and 13C - may have come from fossil fuels, but also from the soil, or deep ocean. Nowinski et al., 2010.: “Radiocarbon ages of heterotrophically respired C ranged from <50 to 235 years BP in July mineral soil samples and from 1,525 to 8,300 years BP [!] in August samples, suggesting that old soil C in permafrost soils may be metabolized upon thawing.” Upper-ocean-to-atmosphere radiocarbon offsets imply fast deglacial carbon dioxide release, Rose et al., 2010. : “The atmospheric decrease in the radiocarbon signal coincides with regionally intensified upwelling and marine biological productivity ... ..., suggesting that CO2 released by means of deep water upwelling in the Southern Ocean lost most of its original depleted-14C imprint as a result of exchange and isotopic equilibration with the atmosphere.” Oxygen ... - we can not be attributed strictly decrease atmospheric O2 of A. CO2. A conceptual model for the temporal spectrum of oceanic oxygen, Ito and Deutsch, 2010.: “Observed across the world oceans in recent decades have been interpreted as a response of marine biogeochemistry to climate change. Little is known however about the spectrum of oceanic O2 variability [...].” “We find a statistically significant spectral peak at a 15–20 year timescale in the subpolar North Pacific [background], but the mechanisms connecting to climate variability remain uncertain.” On evaluating ocean models with atmospheric potential oxygen, Naegler et al., 2006.: “We used observed and simulated atmospheric potential oxygen (APO) to evaluate simulated air-sea flux fields from 11 ocean global carbon cycle models. APO is defined in terms of atmospheric CO2 , O2 and N 2 so as not to depend on terrestrial photosynthesis and respiration. Hence, it is in principal suited to evaluate simulated air-sea fluxes of these gases.” “The simulated amplitude of the seasonal APO variability was generally less than observed. We conclude that it is difficult to validate ocean models based on APO because shortcomings in atmospheric transport models and problems with data representativity cannot be distinguished from ocean model deficiencies.”
  4. Roy Spencer’s Great Blunder, Part 3
    Alexandre@14: I think the point now is that it doesn't matter. Based on Barry's post, it might have been valid as a test of predictive power. Indeed, the question of whether Spencer's model had any predictive power should have been tested by Spencer in the first place. However, after Arthur's analysis it is kind of irrelevant. All the model consists of is a target temperature, an initial transient from which temperature decays exponentially towards the target temperature, and a forcing which also has an effect which decays exponentially. In fact, you can preconvolute the forcing to get Arthur's Q(t), and you just have a linear combination of the transient and Q. The transient is clearly meaningless - it's an arbitrary parameter and it's effect depends totally on when you start your simulation. And yet without it, Spencer's model can't even produce the rising temperature from 1910-1940.
  5. Roy Spencer’s Great Blunder, Part 3
    How robust is the MacDonald and Case (2006)PDO reconstruction? To what extent can we rely on that as an accurate series?
  6. gallopingcamel at 23:33 PM on 4 March 2011
    Icing the Medieval Warm Period
    [ -Edit: Complaints about moderation removed- ] However this post speaks directly to the relation between historic events and climate, a special interest for me. I applaud the author for providing several interesting links. After reading everything that was not behind a pay wall, I was encouraged to find that the Martín-Chivelet et al abstract claims clear correlations with ice core data and historical events such as the Roman and Medieval Warm Periods. Thank you for an excellent post Daniel Bailey although it does pretty much the opposite of what the title suggests. As Willam of Baskerville says this is not an argument against the MWP. For example, here is the concluding paragraph from Matin-Chivelet et. al: "Spectral analysis of the time series shows consistent climatic cycles of ~ 400, ~ 900 and ~ 1300 yr, comparable with those recognized in the North Atlantic marine record, the Greenland ice cores, and other terrestrial records for the middle – late Holocene, suggesting common climate forcing mechanisms related to changes in solar irradiance and North Atlantic circulation patterns."
    Moderator Response: [DB] Actually, all the data we have shows that the MWP to not be an analog for modern warming in both scope and degree. In addition, the available data shows the MWP to be a heterogeneous mix of cooling, warming and drought over similarly varied geographic and temporal areas. And what warming data there is for the MWP shows it to fall short of the warming of the last 30 years, which is now comparable to levels last achieved in the Holocene Altithermal.
  7. Arkadiusz Semczyszak at 23:27 PM on 4 March 2011
    Icing the Medieval Warm Period
    @Robert Way I do not know all the work of J. Zasadni, perhaps this applies only to the Zillertal
  8. Arkadiusz Semczyszak at 23:20 PM on 4 March 2011
    Icing the Medieval Warm Period
    I think that this publication speaks in a way that best condensed - all: Climatic fluctuations in the Central Region of Argentina in the last 1000 years, Cioccale, 1999.: “The Medieval Warm Period was characterized by a humid and warm climate in the plains and recession of the Andean glaciers. In contrast, during the Little Ice Age the plains had temperate, semi-arid to arid climates, and Andean glaciers advanced.” The “fall” of civilization that (so far) is always cool - never warming.
  9. Eric (skeptic) at 23:19 PM on 4 March 2011
    Climate Sensitivity: The Skeptic Endgame
    les, my advice to poptech is Choose One (objective or subjective). I have always had an objectivist philosophy (although not perfectly matched to Randianism), so when I see a probability distribution I immediately look around for the data it was based on. Often there is literally none. As for your policy argument, we are not facing unknowns like one or more typhoid Marys or a human-based decision to go to war. It is simply a complex natural process with some true unknowables like intergalactic cosmic ray flux, future volcanic activity, future solar activity (known to some extent), etc. A lot of these are ambiguous or more likely to cool, so not really worth debating. Everything else is knowable. There is no reason to apply subjectivity to the issue of sensitivity, just better models, validated against real world measurements. The bottom line is that 5C warming (or choose your favorite number) has a zero or a 100% probability of happening within time X (choose 100 years but not 1000), under specific conditions such as BAU. That statement contains no room for any subjectivity other than BAU being made as a human choice which is really only a marginal issue.
  10. Icing the Medieval Warm Period
    There are a few advancing glaciers, but most of the advances are quite limited and hence not overrunning developed forest vegetation. The evidence uncovered here is pretty systematic for the time periods noted in Table 1. The difference between a glacier advancing and disappearing like Helm Glacier, one of the sample sites is vast.
    Moderator Response: [DB] Thanks, Mauri!
  11. williambaskerville at 22:49 PM on 4 March 2011
    Icing the Medieval Warm Period
    Hi, I don't think this is a argument against the MWP. Don't we actually have increasing glaciers in Norway, New Zealand and the Karakorum? Don't we have regions in the world, not getting warmer? I am writing about this on my post "Nicht alle Gletscher schrumpf(t)en" (Not all glaciers we/a-re melting) http://tinyurl.com/64kmfuj If you want to read more, take a look on my German blog: http://mittelalterlichewarmperiode.blogspot.com Feel free to post comments!! Best Willam of Baskerville Ps. I've made interviews on this topic - MWP - with scientists like Dr. Heinz Wanner, Dr. Ulf Büntgen, Frederic Ljungqvist and others.
    Moderator Response: [DB] No one is suggesting that the warming of the globe will be a uniform or linear process. But it is indeed a global process, as you can see here:
  12. Icing the Medieval Warm Period
    The LIA in the alps did not end in 1950. That's a complete fallacy and is not supported by the literature at all. You might find one paper where a small portion advanced during that period but the fast majority of glaciers in the alps had their LIA between 1750 and 1850.
  13. Roy Spencer’s Great Blunder, Part 3
    Here's a graph of the 1000 year PDO forcing used to drive the 1000 year simulation in figure 10. I just took the Macdonald and Case data and applied a 19 year moving average. Comparing this with figure 10, it is now obvious that Spencer's model starts from an initial temperature set by the ΔTo value (off the bottom of the graph in this case) and constantly heads towards towards a temperature set by the equilibrium temperature and the current value of the forcing term.
  14. Arkadiusz Semczyszak at 22:32 PM on 4 March 2011
    Icing the Medieval Warm Period
    #The Inconvenient Skeptic ... a propos China I would add: Characteristics of cold–warm variation in the Hetao region and its surrounding areas in China during the past 5000 years, Li et al., 2010.: “1450 - 1000 cal yr BP: The climate was relatively warm compare with the temperature of its adjacent periods but less so than the degree of warmth at 5000 cal yr BP. This period corresponded to the Medieval Warm Period.”
  15. Arkadiusz Semczyszak at 22:20 PM on 4 March 2011
    Icing the Medieval Warm Period
    @Marcus Not so long ago in my TV - Professor L. Thompson - explaining the length of the Maya (more than 5 thousand. years) - his last end, he showed how in the Andean glaciers have advanced so quickly - it now - going back - glaciers reveal - frozen, “of unimpaired quality” plants ... Droughts - in this period of strong cooling (Neo-glacial) - covered most of the two continents of America. The same drought (cooling effect) destroyed the civilizations of the Sahara and Middle East. Stable isotopes of a subfossil Tamarix tree from the Dead Sea region, Israel, and their implications for the Intermediate Bronze Age, Frumkin, 2009.: “The Sedom Tamarix demonstrates a few hundred years of 13 C and 15 N isotopic enrichment, culminating in extremely high δ 13 C and δ 15 N values. Calibration using modern Tamarix stable isotopes in various climatic settings in Israel shows direct relationship between isotopic enrichment and climate deterioration, particularly rainfall decrease.” “This was apparently the most severe long-term historical drought that affected the region in the mid-late Holocene.” Lonie Thompson explained that the Atacama desert in the Quaternary, only once was inhabited by people - during MWA ... During the Roman maximum - period; around Masada was warmer and wetter - growing bushes Tamarix at the point where today it is a desert. Climatic effects on the δ 18 O and δ 13 C of cellulose in the desert tree Tamarix jordanis, Lipp et al., 1996.: “Since the Roman period, RH at Masada decreased by about 17% [!], while the δ 18 O value of local groundwater remained similar to present-day values, suggesting that changing atmospheric circulation has played a role in climate change in the Middle East over the past two millennia.” Polish scientist J. Zasadni, from the Institute of Geological Sciences, Jagiellonian University, who is preparing a doctoral thesis about shifting of glaciers in the Alps - Zillertal, after many years (and very precise) research - argues strongly that: in the days of ancient Rome and later - warming in the Middle Ages - expiring on the late fourteenth century, frequented alpine glaciers coverage certainly considerably smaller than today. LIA in the Alps ended only in 1950 ... Anasazi - “During the Pueblo II period, from 900-1100 CE, these designs were made even more bold, and the Anasazi (Hisatsinom) began to build kivas, or communal rooms for ceremonial purposes in their villages. Their population increased, and during this period small Anasazi villages began to spread throughout the southwest.” “During the Pueblo III period from 1100-1300 CE, the Anasazi (Hisatsinom) began to build the cliff dwellings for which they are most well-known. Many buildings in these villages under the cliffs were several stories tall.” „For unknown reasons, near the end of this period the western Anasazi (Hisatsinom) sites were completely abandoned, while the eastern sites continued to flourish and expand.” ... circa 1270-1300 - the beginning of the LIA in America ...
  16. Icing the Medieval Warm Period
    "It's cold out!"... and I am suppose to believe it should be colder on average, and that the world would be better off if this were the case. As long as the price of fossil fuels is rising faster than the temperature, it's hard to imagine how winters of the future are going to be more confortable.
  17. Climate Sensitivity: The Skeptic Endgame
    83 Eric objective/subjective?!?! now you sound like Poppy Tech!! ;) ;) < big wink > sure, though. of course for scientists that's fine. Governments rarely have the luxury - as I pointed out to someone: armies have to be maintained without knowing the exact probability of war or invasion, hospitals and school have to be build with out knowing exactly the population in 20 years, vaccines have to be stockpiled without knowing the exact epidemiology or the next flu outbreak etc. etc. Power security has to be maintained, the environmental resources managed, healthy environment preserved (or restored)... better to understand the proper meaning of likelihood rather than stuffing it in quotes and pretending it's meaningless.
  18. Roy Spencer’s Great Blunder, Part 3
    APSmith@11: That's a beautifully clear analysis and probably the definitive one, at least for anyone who can (still) solve a differential equation. It leaves me banging my head asking 'why didn't I see that straight away'? To many computers are bad for the brain. We've forgotten the power of algebra!
  19. The Inconvenient Skeptic at 21:23 PM on 4 March 2011
    Icing the Medieval Warm Period
    Here are some paleoclimate studies from China. http://epic.awi.de/Publications/And2005g.pdf http://www.sciencedirect.com/science?_ob=ArticleURL... http://hol.sagepub.com/cgi/content/abstract/13/6/933 ftp://ftp.ncdc.noaa.gov/pub/data/paleo/historical/china/china_winter_temp.txt None of these are records from Chinese history, but nodern (non tree-ring) reconstructions.
  20. Icing the Medieval Warm Period
    invicta It occurs to me that an area of the world that has a well documented dynastic cycle for at least two thousand years is China. I have never seen any references to any records from this area being used to support or deny claims for the MWP or similar globa v regional discussions. Are there people with knowledge of the cycles of dynastic rise and decline which do seem to have at least some links to natural disasters (famine Drought etc)? I have no specialist knowledge myself but would be fascinated to see some discussion of the subject in the appropriate place
  21. Climate Sensitivity: The Skeptic Endgame
    sorry for some misprints and disappearing signs. You should read : e : you're wrong, if you take a random gaussian distribution of the "f" amplication factor, with an average value f0, the average value of the "1/1-f" (and hence sensitivity) factor will be larger than the 1/(1-f0)) This is a high bias. and If tau is small (with respect to the characteristic timescale for S(t)), T(t) follows closely S. F(t).
  22. Putting a new finger on climate change
    Philippe Chantreau @11 With regard to C14 and the ocean: yes, you are correct. The ocean contains much more CO2 than does the atmosphere, but in equilibrium, an equal number of CO2 molecules flow each way at the surface. That means residence times in the ocean are much larger than residence times in the atmosphere. So for a given molecule in the ocean, it is probably a long time since it was in the atmosphere, and hence had a chance to form with a C14 atom. In contrast, a molecule in the atmosphere has (obviously) been very recently in the atmosphere, and has therefore a higher chance of having formed with a C14 atom. (I'm not sure that this is clear either, but I'm not sure I can make it clearer in a short space.) Regarding the C13/C12, you are tecnically correct, but I'm not sure your phrasing avoids any likely misunderstanding.
  23. Arkadiusz Semczyszak at 20:05 PM on 4 March 2011
    Roy Spencer’s Great Blunder, Part 2
    @Shoyemore As quoted by you (perfectly known to me), Mike Lockwood's paper, is also an important sentence: "... the current [solar] grand maximum has already lasted for an unusually long time ..." Lockwood (in this paper) will not close a road to prove that the Sun has a more significant impact on the climate than we thought previously. However, imposes a condition: “Thus advocates of the huge solar amplification (positive feedback) factor [that is, for example, I] must also explain why the feedback to greenhouse forcing is at the same time negative. The issue is not ‘can the GMAST curve be fitted with combinations of solar variations’—with enough free variables the answer will be ‘yes’ (but such fits would have very low or no statistical significance): the challenge for attempts to show such a phenomenon could be real is to give credible explanations of feedback amplifications of more than 13 within the constraints set by observations and their uncertainties (and yet still give negative feedbacks to GHG forcings).” As cited above, this paper presents but too little potential direct and indirect influences of the Sun, which completes Lockwood (as a co-author) in a later work: Solar Influences on Climate, L.J. Gray, J. Beer, M. Geller, J.D. Haigh, M. Lockwood, K. Matthes ,U. Cubasch, D. Fleitmann, G. Harrison, L. Hood, J. Luterbacher, G. A. Meehl, D. Shindell, B. van Geel, W. White (Reviews in Geophysics, 2010). In this work - with many "types" of direct and indirect sun (especially the impact of changes in solar UV - for example, ozone, ozone in the stratosphere, water vapor, etc..) is a record that they require “urgent” research - because we know about them too enough - to assess (even initially) the actual impact on climate.
  24. Putting a new finger on climate change
    There is continued fractionation going on so that different sources having different degrees of C13 depletion.
  25. Climate Sensitivity: The Skeptic Endgame
    e : your wrong, if you take a random gaussian distribution of the "f" amplication factor, with an average value , the average value of the "1/1-f" (and hence sensitivity) factor will be larger than the 1/(1-)) This is a high bias. I don't want to prove that climate models and measurements are wrong. I'm just saying that the kind of line you adopt (reasoning on a large sample of different valuers) is not very convincing from a scientific point of view., if the issue is whether the whole model is correct or not. It relies on the implicit assumption that the models have been proved to be true - which is precisely the point. This is kind of a circular justification. concerning the point of relaxation timescales : in the simplest approximation, there is a single timescale, and the relevant equation is dT/dt + T/tau = S.F(t)/tau where tau is the relaxation timescale and S the sensitivity. The exact solution of this equation is T =S. ∫ F(t')exp(t-t'/tau) dt'. Mathematically, T(t) tries to follow the variations of F(t), but with some delay of the order of tau, and smoothes all variations of the order of tau. Basically, it responds to the average of F(t) over a past period tau. If tau is small (with respect to the characteristic timescale for S(t)), T(t) follows closely S(t). If it is large , the T/tau term is negligible and one has rather dT/dt = S F(t)/tau , so T(t) = S ∫ F(t) dt'/tau. The "response" is the the integral of F(t) (the system "accumulates heat") but it is curtailed by a factor tau. Now there are interesting questions around tau. If tau is small, S should be just the ration of T(t) to F(t), so it should be precisely determined by current variations, which is obviously not the case. So we are rather in a "long" tau, longer than or comparable with 30 years. This allows some "flexibility " between S and tau, because constant ratio S/tau will give the same signal T(t) - I think this is the main reason for the scattering of S (and tau) , they are not well constrained by the data. However, if tau is large, the response of a linearly increasing forcing should be quadratic (this is obvious because the temperature has to increase faster in the future to exceed the 2°C thershold for instance), so an acceleration should be measurable. Is it the case? not really. Temperature are less or equally increasing than 30 years ago - you can discuss whether they're still increasing or not, but they're not accelerating.That's kind of puzzling in my sense (leading to the obvious observation that if they aren't accelrating, a warming rate of 0.15 °C will only produce 1.5 °C after 100 years). So there is a small window for which the sensitivity is high but not too much, and the timescale high but not too much, and the "curvature" will be significative in the near future , but not yet just now. Outside this window, the curve T(t) is essentially linear with a linearly increasing forcing (as the forcing is is logarithmic with the concentration and the production of GHG is supposed to increase more or less exponentially with a constant growth rate, the forcing should be close to linear). This is only possible for tau between 30 and 100 years, Say (which is essentially what is found in current models). But again this raises other interesting questions. 30 to 100 years is SHORT with respect to paleoclimatic times , and astronomical (Milankovitch) changes of forcings. So IF it were in this range, temperatures should follow rather closely teh forcings, and change only very slowly with them. But we hear here also on a lot of "variations " of climate at the centennal time scale (medieval "anomaly" whatever happened then, D-O events, and so on) which should NOT happen if the forcing is not changing at this time scale. But why is the forcing changing? aerosols, volcanoes, do they have a reason to statistically change when averaged over 100 years or so (remember that the temperature changes by averaging over this time scale?)
  26. Crux of a Core, Part 1b
    Here is a detail of Rob Honeycutt's image @25 so that the extent to which temperature fluctuations in northern and southern polar regions are antiphased during the Holocence can be clearly seen: And for completeness, ice cores over the Holocene for a Greenland, a Northern Chinese (Northern Hemisphere), two Andian (Tropcical), and two Antarctic (Southern Hemisphere)to give some idea as to the extent of regional variability involved:
  27. Hockey Stick Own Goal
    angusmac> Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998. Considering that Ljungqvist used decadal averages (as Tom pointed out), it would indeed be unreasonable and quite inaccurate to draw this conclusion.
  28. Daniel Bailey at 17:09 PM on 4 March 2011
    Twice as much Canada, same warming climate
    muoncounter Yeah, not yet so blind as to have missed that. Nice segue from Arctic Amplification to Spinal Tap! Dunno if you follow Arctic ice developments much, but Patrick Lockerby over at Neven's Sea Ice blog just linked to his March Arctic Ice post here. Patrick is explaining his rationale as to "...why I expect the central Arctic to be essentially ice-free by the end of this Arctic summer 2011". Also says the 2011 melt season has already begun... (Gonna have to find amps that go to 12) The Yooper
  29. Icing the Medieval Warm Period
    OK, so maybe I overstated the whole "destruction" thing in regards to the Maya, but it was used as an example of societal collapse in Jared Diamond's book of the same name-specifically where societies failed to adapt to changing environmental conditions & so hastened their own demise. Sorry if that's off-topic.
  30. Putting a new finger on climate change
    CH4 emitted from coalmining and decaying organic matter has residence of ~10 years during which it oxidizes to produce CO2. Am I right to assume that CO2 so produced is predominantly carbon isotope 12?
  31. Roy Spencer’s Great Blunder, Part 3
    A bit of further analysis on this from me here: http://arthur.shumwaysmith.com/life/content/mathematical_analysis_of_roy_spencers_climate_model (using Barry's figures, thanks!) Spencer really should be ashamed of this. And turning it into a book!
  32. Roy Spencer’s Great Blunder, Part 3
    Hi Albatross @9, I sent him the links after I posted Part 3, but I haven't heard from him. Hopefully, he's combing goofing around with his model to see if I'm right.
  33. Climate Sensitivity: The Skeptic Endgame
    Sorry, the start date should be 1800, not 1850, in my last post, for the start of anthropogenic CO2 - typing too fast... Incidentally, although I suspect most of the usual suspects will have seen this already, the YouTube video from CarbonTracker is worth showing to everyone.
  34. Hockey Stick Own Goal
    angusmac @135, the data may include 1998, but Lundquvist reports decadal averages. The early 1990's was quite cool compared to 1998, so there is still a sharp difference in temperature. The difference between the decadal average of GISStemp for 1990-1999 and 2000-2009 is 0.18 degrees, sufficient to lift recent tempertures well above the peak decadal average for the MWP (0.15 degrees greater than 1990's). Of course, that is the difference in global temperatures. The difference in NH extra tropical temperatures is likely to be far greater, and would show a correspondingly greater increase.
  35. Climate Sensitivity: The Skeptic Endgame
    Berényi - I'll admit to having some trouble following that last posting. The last I heard you were claiming that the relaxation time was essentially zero, so that there was no heating left in the pipeline. Now you are arguing that relaxation times are long enough to slow warming to a manageable level??? You're contradicting yourself. Second, 1934 is not the start of anthropogenic carbon forcing - that's somewhere around the beginning of the industrial revolution, circa 1850 or so. Third, relaxation times are relative to multiple time frames - from the several week H2O forcing to the multi-century ice response. Your simple formula is therefore inappropriate. And, since rate of change is dependent on scale of forcing, your 1.8C/century limit is, in my opinion, nonsense. I'll leave it at that for now - you have posted completely contradictory arguments in just the last few days, I'm certain there are issues others might raise.
  36. Putting a new finger on climate change
    Rather than a new, 11th fingerprint, isn't this really just another example, as in Fingerprint 4, of measurement of the C-13/C-12 ratio incorporated into living things? It's independent of coral C-13/C-12 ratio measurements, but not so different an indicator of fossil-fuel origin as to deserve separate listing, I think. I'd just add it to Fingerprint 4.
  37. Hockey Stick Own Goal
    Moderator @132, new data is always welcome. However, the purpose of my post was to show that you could use the data presented in Dana's post and come to a completely different conclusion. Tom @133 and Anonymous @134, I agree that we need more up to date proxies. This should be a high priority in the paleo community. Nevertheless, Table 1 of Ljungqvist (2010) shows that 10 of the 24 proxies used by him extend to 1999 thus including the very hot year of 1998. Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998.
  38. Icing the Medieval Warm Period
    Tikal, Copan and other great Mayan city-states in the south did succumb to a combination of internecine warfare, over-population and drought induced crop failures in the 8-9th centuries, bringing the Classic Period to an end. That is a long way from destruction of Mayan civilization which survived in northern areas, notably Yucatan, where city-states such as Uxmal, Mayapan and Chechen Itza flourished into the 17th century. Their demise was at the hands of the Spanish, not climate change. Can prolonged droughts in Guatemala, Belize and Honduras in the 8-9th centuries be regarded as synonymous with the European MWP?
  39. Roy Spencer’s Great Blunder, Part 3
    Dr. Bickmore, Has Roy responded to your critique? I'm a little surprised that he has not bothered to drop by and discuss this. I would not be surprised if he tried to frame this as an "attack" on skeptics over at his blog. We'll see.
  40. Icing the Medieval Warm Period
    To get a better sense of the field sites and work by Koch and Clague take a look at Koch's research pages . Nice maps and photographs.
  41. Twice as much Canada, same warming climate
    Yooper: Didja notice that appears to be 5 degrees in approx 20 years? One of them natural cycles we hear so much about, I guess. Or maybe the Arctic Amplifiers are turned up to 11?
  42. Berényi Péter at 13:55 PM on 4 March 2011
    Climate Sensitivity: The Skeptic Endgame
    #59 Sarah at 14:09 PM on 3 March, 2011 Hansen and Sato recently determined that climate sensitivity is about 3 °C for doubled CO2 based on paleoclimate records.[...]
    Moderator Response: [Daniel Bailey] Thanks, Sarah. The preprint is here.
     I don't see it was a peer reviewed paper. Dr. Hansen says it's a "Draft paper for Milankovic volume", whatever that may be. However, it is still interesting, because it is based on empirical data and has definite numbers to work with. Its biases and omissions are also telling. The first thing to note they assume a 4 W/m2 forcing for doubling of atmospheric CO2 concentration, which is slightly above the IPCC AR4 WG1 2.3.1 (2007) estimate of 3.7 W/m2, with no explanation whatsoever. The figure seems to come from IPCC FAR WG1 3.3.1 (1990). Anyway, if we accept their value, using CO2 concentration measurements at the Mauna Loa Observatory we get the annual rate of change in forcing due to CO2 as α = 0.024 W/m2/year for the last 54 years. The paper calculates an equilibrium climate sensitivity of λ = 0.75°Cm2/W using paleoclimate data. As temperature variability is much smaller under current warm interglacial regime than for the bulk of the last 3 million years, climate sensitivity obviously decreases sharply with increasing temperatures, but let's go with their figure anyway, at least for the time being. Greenland temperatures during the last 100 kyears -- click for larger version If we assume a scenario under which atmospheric CO2 concentration was constant for a long time (presumably at pre-industrial level, let's say at 280 ppmv) then started to increase exponentially at the rate observed, we get an excitation that is 0 for dates before 1934 and is α(t-1934) for t > 1934. The artificial sharp transition introduced in 1934 this way does not have much effect on temperature response at later dates. If global climate responds to an excitation as a first order linear system with relaxation time τ, rate of global average temperature change is αλ(1-e-(t-1934)/τ) for a date t after 1934. As the expression in parentheses is smaller than 1, this rate can't possibly exceed αλ = 0.018°C/year. It means global average temperature can't increase at a rate more than 1.8°C/century even in 2100, which means less than 1.6°C increase relative to current global average temperature, no matter how small τ is supposed to be. However, a short relaxation time is unlikely, because it takes (much) time to heat up the oceans due to their huge thermal inertia. For example if τ = 500, current rate of change due to CO2 forcing is 0.26°C/century while in 2100 it is 0.51°C/century (according to Hansen & Sato, of course). However, ocean turnover time being several millennia, we have probably overestimated the actual rates. It means that most of the warming observed during the last few decades is due to internal noise of the climate system, not CO2. Anyway, the exponential increase of CO2 itself can't go on forever simply because technology is changing all the time on its own, even with no government intervention whatsoever. Therefore it should follow a logistic curve. If the epoch of CO2 increase is substantially shorter than the relaxation time of the climate system, the peak rate of change due to CO2 becomes negligible.
  43. Putting a new finger on climate change
    Philippe-the point I was trying to make (badly I confess) is that because fossil fuels have *zero* 14C, then changes in the ratio of C14 to C12 could serve as a useful secondary signal for the anthropogenic nature of the rising CO2 in the atmosphere. However, as scaddenp has pointed out, that might not be as easy as I first thought ;-). Hope that makes more sense.
  44. Icing the Medieval Warm Period
    I'm guessing, Daniel, that those warmer periods you mentioned were the same as those I mentioned-the ones which wiped out the 2 big Meso-American civilizations of the day? The warming/drought that caused the end of the Egyptian Old Kingdom has been linked to a slowing of the Atlantic Conveyor (the one which causes the Gulf Stream)-which also caused Northern Europe to get cold. I wonder if something similar can explain the MWP?
    Moderator Response: [DB] Possibly/probably. With the teleconnections being uncovered, ENSO changes in the Pacific Ocean seem to be driving subsequent "downstream" reactions and changes throughout the world. Obviously an area being looked at further; given what we now see happening in our warming world & the potential impacts discussed in Dai et al 2010 (discussed here), it's an area of critical importance.
  45. Putting a new finger on climate change
    Marcus, google scholar for Etiope G and Lassey K R. Both researchers active on this. Short answer - C14 is useful but its not as easy as it sounds... (I'm trying to get no. for pre-industrial fossil methane emissions from sedimentary basins in day-job so having been looking at issue).
  46. Eric (skeptic) at 12:59 PM on 4 March 2011
    Climate Sensitivity: The Skeptic Endgame
    Thanks for the link les, here's the full URL; http://journals.sfu.ca/int_assess/index.php/iaj/article/download/188/139 I looked at the section on climate sensitivity where they refer to this study http://pubs.acs.org/doi/abs/10.1021/es00010a003 titled "Subjective judgements by climate experts" to obtain a subjective probability distribution of climate sensitivity values centered aroudn 3C. In that 1995 paper they start out "When scientific uncertainty limits analytic modeling, but decision makers cannot wait for better science, expert judgment can be used in the interim to inform policy analysis and choice" I would rather wait for objective probability distribution measurements. For example, the continued rapid increases in computing power will make full weather simulation possible within global climate models (i.e the mesoscale models I referred to above). Then there will be no need for subjectivity.
  47. Icing the Medieval Warm Period
    Daniel Bailey: I think the article should mention that the Martín-Chivelet et al study is for Iberian Peninsula only. If you want to go beyond the usual 2000-year reconstructions globally you should reference the borehole studies, for example.
    Moderator Response: [DB] Thanks for the heads-up. I realized that after the fact, but forgot to update the text in the rush to publish. I'll fix it now.
  48. Philippe Chantreau at 11:35 AM on 4 March 2011
    Putting a new finger on climate change
    Marcus, fossil fuels are millions of years old, way over a hundred millions for coal. No C14 left in there but from exterior sources. I'm not sure I understand your point in #10.
  49. Icing the Medieval Warm Period
    Was there a MWP in northwest North America ? Or was the MWP a local, European event ?
    Moderator Response: [Daniel Bailey] The preponderance of evidence we have strongly suggests regional warming at various periods of time over several centuries that also coincided with regional cooling. Some areas warmed and others cooled. The area with best data for a localized, regional, warm period is in Europe. This period was also punctuated with brief colder periods where glaciers in the Alps underwent significant advancement. It was a complex climatic period. For more info, go here (both the Basic and Intermediate Versions). North America had warmer periods as well, but those were punctuated with extreme droughts.
  50. Icing the Medieval Warm Period
    Oh, correction, 2 Civilizations (The Anasazi & The Mayans) both died out during the Middle Ages-both due to extended drought which was believed to be caused by a regionally warming climate.

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