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Comments 125651 to 125700:

  1. Why does CO2 lag temperature?
    According to the graph presented here and in a previous article: http://www.skepticalscience.com/The-correlation-between-CO2-and-temperature.html (figure 2) a 10 degree change in Earths temperature causes a change of 90 ppm CO2, while a change of 60 ppm CO2 could possibly have partially effected 1 degree of change in the Earths temperature. This data indicates that temperature drives CO2 much stronger than CO2 drivers temperature.
  2. Why does CO2 lag temperature?
    Boba, interesting comments. I've always felt that CO2 coming from warming oceans didn't seem quite right from a simple chemistry view point (it seemed to me that it was unlikely that the oceans would be saturated because of various cycles). Have you considered that the increase in CO2 during deglaciation periods could be from methane released by the retreating ice and permafrost? The methane will then be oxidized both biologically and photochemically to CO2.
  3. Why does CO2 lag temperature?
    First I’d like to commend John for a great blog. This is a fabulous resource and your careful, thorough, and prompt explanations of new science papers is very impressive. Thanks! Temperature’s lead over CO2 in Antarctic ice core records keeps getting mentioned as proof against human impacts on climate, so it’s good to have an objective discussion of the issue. Here I present some additional perspective from the paleoclimate community I’m sorry this comment is so long, but it’s a complex issue. John - It seems that the link to Shemesh et al., 2002 is still broken. At least I get a damaged file. Presumably this is: Shemesh, A., Hodell, D., Crosta, X., Kanfoush, S., Charles, C. and Guilderson, T., 2002. Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores. Paleoceanography, 17(4): 10.1029/2000PA000599. Turboblocke - Henry’s law absolutely applies to CO2, as it does to all gases. The CO2SYS document from the CDIAC web site doesn’t support that claim. The main difference between CO2 and other gases is that once CO2 dissolves from air into seawater it undergoes further reactions, dissociating into bicarbonate and carbonate ions. This makes the chemistry of carbon dissolved in seawater complex, but CO2 gas still obeys Henry’s Law. Dennis, Riccardo - Yes, the uncertainty in the overall age model for an ice core gets larger further back in time, as does the uncertainty in the difference between the ages of gas and of ice at any given depth. For those who aren’t familiar, at any given depth in an ice core the ice is at least a few hundred years, and sometimes a few thousand years, older than the gas. This is because gases diffuse through firn (packed snow) before it is sealed off as ice. The age offset between gas and ice increases as the accumulation rate of snow decreases. Therefore, the ice-gas age difference is much greater during ice ages, when there is less snow accumulation, than during interglacials. Uncertainty in the ice-gas age difference has been a big problem in establishing reliable lead-lag relationships between temperature and CO2. People have done statistical analyses of gas-ice age differences, but the best statistics still produce meaningless results if the age models for ice and/or gas are inaccurate. This applies to the data set cited by Ari Jokimäki. Age models for ice cores are constantly being revised. See: Bénédicte et al., Consistent dating for Antarctic and Greenland ice cores. In Press, Quaternary Science Reviews, Available online 3 December 2009 The uncertainty between gas age and ice age can be virtually eliminated at glacial terminations (i.e., at the end of an ice age) when the initial warming is recorded by the isotopic composition of argon gas, which can then be compared directly against CO2 concentration. Since both temperature and CO2 come from the gas phase, there is no age offset in need of correction. This is how Caillon et al. 2003 (cited by John) was able to show that temperature started to rise in Antarctica before CO2 began to increase. This direct evidence is more robust in my opinion than the statistical comparison of CO2 and temperature on different age models, each with their own uncertainty. I think Caillon et al convinced paleoclimate scientists that the initial increase in temperature in Antarctica leads the initial rise in atmospheric CO2 at the end of an ice age by several hundred years. This leads to the main point that I wanted to make, namely: Why did temperature start to rise in Antarctica before concentrations of CO2 began to increase at the end of an ice age? Does this mean that CO2 does not have an impact on climate? Two hypotheses have already been described. I will summarize those and add a third. The first hypothesis invokes changes in earth’s orbit (Milankovitch) and its effect on spring insolation around Antarctica. Increasing insolation in spring is suggested to cause sea ice to melt back earlier in the year, which allows more CO2 to escape from the ocean to the atmosphere. A scenario like this was invoked by Shemesh et al. (2002) and would follow from the conclusions of Huybers and Denton (2008; cited by Chris). The general principles are described in a paper by Stephens and Keeling: (Stephens, B.B. and Keeling, R.F., 2000. The influence of Antarctic sea ice on glacial-interglacial CO2 variations. Nature, 404(6774): 171-174.). However, if you read the papers that comment on Stephens and Keeling, you will find skepticism in the paleoclimate community about whether or not sea ice can truly serve as a “lid” holding CO2 in the ocean. Second, Chris described a hypothesis that is commonly invoked for the sequence of events at the end of an ice age, namely: 1) Changes in Earth’s orbit (Milankovitch again) led to warmer summers in the Northern Hemisphere. 2) Warmer summers started melting the large northern ice sheets that built up during the ice age. 3) Freshwater from melting ice flowed into the North Atlantic. Because of its lower density, the freshwater slowed or stopped the overturning circulation that transports heat northward. 4) This had a global impact, but here some hypotheses diverge (denoted A and B below). According to the ocean bi-polar seesaw hypothesis described by Chris: A5) Reduced northward flow in the Atlantic allowed heat to build up in the Southern Hemisphere, a phenomenon known as the bipolar seesaw. A6) Warming of the Southern Ocean caused CO2 to be released from the ocean due to the lower solubility of gases in warmer water. Rising CO2 followed the initial warming of the Southern Ocean and of Antarctica, and also contributed to warming of the Earth as a positive feedback. (See Chris - Post 6, point 2c) A problem with this hypothesis is that the temperature dependence of CO2 solubility in seawater is well known, and the rise in ocean temperatures during deglaciation is not nearly large enough to have caused the observed rise in CO2. This was pointed out long ago by Broecker and others. The principle is firmly established in the scientific literature. Broecker, W.S., 1982. Glacial to interglacial changes in ocean chemistry. Progress in Oceanography, 2: 151-197. Something other than warming must have caused CO2 to be released from the oceans. This is why some people invoke the melting of sea ice to allow more CO2 to escape (see above). However, (a) as noted above, others have argued that sea ice is not sufficiently effective as a barrier to gas exchange and (b) changes in sea ice driven by orbital forcing cannot explain the tight correlation between CO2 and Antarctic temperatures on the millennial time scales that are shown in Figure 1 of: Ahn, J. and Brook, E.J., 2008. Atmospheric CO2 and climate on millennial time scales during the last glacial period. Science, 322(5898): 83-85. A third hypothesis not yet described in this thread of comments involves a reorganization of global wind systems toward conditions more favorable for mixing in the Southern Ocean that drives CO2 from the ocean to the atmosphere. The process begins as above, with changes in Earth’s orbit melting northern ice sheets and slowing Atlantic overturning circulation (Points 1 - 4). Then the emphasis switches from the ocean to the atmosphere: B5) When freshwater shuts down Atlantic overturning circulation, winter sea ice expands over the North Atlantic, causing severely cold winter conditions. B6) Cold winters cause changes in atmospheric circulation, which are well documented for the Intertropical Convergence Zone and for the Asian Monsoons (see Cheng et al., 2009, cited by Chris, and references therein). B7) Reorganization of the winds extends all the way to Antarctica, strengthening the Southern Hemisphere westerlies so that they are more effective at driving CO2 out of the ocean. According to this hypothesis, intense cooling in the northern hemisphere causes warming in the southern hemisphere by changing wind patterns. The initial warming in Antarctica is caused more by a redistribution of heat from north to south than by a global rise in temperature. The winds then drive CO2 out of the ocean so that the observed rise in CO2 lags slightly the initial warming detected in Antarctic ice cores. It takes a few thousand years to melt the northern ice sheets. During this time when meltwater is being dumped onto the North Atlantic, the winds are shifted and CO2 is being driven out of the Southern Ocean. These conditions can experience brief reversals, as happened 14,500 years ago during the Bolling period. After the Bolling warm period, the conditions resumed during the Younger Dryas period. Increased atmospheric CO2 together with reduced albedo following the meltback of the northern hemisphere ice sheets provided the feedbacks to Milankovitch forcing that brought the earth out of the last ice age into a warmer interglacial period. The principles underlying the forcing of CO2 by shifting winds over the Southern Ocean are described by Toggweiler (2006). Evidence to support the principles, but modifying the timing, are described by Anderson (2009). See also comment by Toggweiler (2009). Toggweiler, J.R., Russell, J.L. and Carson, S.R., 2006. Midlatitude westerlies, atmospheric CO2, and climate change during the ice ages. Paleoceanography, 21(2): doi10.1029/2005PA001154. Anderson, R.F., Ali, S., Bradtmiller, L.I., Nielsen, S.H.H., Fleisher, M.Q., Anderson, B.E. and Burckle, L.H., 2009. Wind-driven upwelling in the Southern Ocean and the deglacial rise in atmospheric CO2. Science, 323(5920): 1443-1448. Toggweiler, J.R., 2009. Shifting Westerlies. Science, 323(5920): 1434-1435. These hypotheses all need to be investigated further. Each has strengths and weaknesses. Given the complexity of Earth’s climate system and its connection to the global carbon cycle, the correct answer is likely to be “all of the above”.
  4. What happened to the evidence for man-made global warming?
    - Satellites measure less infrared radiation escaping out to space at the wavelengths that CO2 absorb energy (Harries 2001, Griggs 2004, Chen 2007) - Surface measurements find more infrared radiation returning back to the Earth's surface (Philipona 2004), specifically at the wavelengths that CO2 absorb energy (Evans 2006) I think these two arguments are very strong. What would be the clincher, however, is if the radiation loss going outward and radiation increase going back onto the surface where mathematically equivalent to the energy increase in the athmosphere. Are you aware of any such calculation? The argument would be problematic if, for instance, the increased radiation back would be much less than the increase in temperature.
  5. Can you make a hockey stick without tree rings?
    The only link that worked for me here was Oerlemans'. Is it just me or have the links indeed been moved? Another question: why does the Mann graph show a 0.8+ degree warming after de mid-century pause? Shouldn't it be some 0.5ºC?
  6. What ended the Little Ice Age?
    Thank you for an excellent post Chris. John your site is a wonderful model of how knowledgeable lay people and scientists should interact with ordinary inquisitive folk such as myself whose initial approach to the subject is skeptical.
  7. Why does CO2 lag temperature?
    Dennis, you are correct that there is large uncertainty in measurements, and there is additionally the fact that datapoints for carbon dioxide are typically separated by thousands of years which adds to the measurement uncertainty. This leads to the situation where you can't usually say on individual moments for sure that there's temperature leading. However, the lead/lag situation has been determined statistically from the whole datasets, not from individual events. So, I would say that the temperature leading is real phenomenon but we can't rule out that there might be some individual events where CO2 leads. Here's an example data for carbon dioxide (from Vostok ice core) where you can get the feel of the thing yourself: http://cdiac.ornl.gov/ftp/trends/co2/vostok.icecore.co2
  8. Hockey sticks, 'unprecedented warming' and past climate change
    I have a few relevant points to add here. On my reading of Jared Diamond's book "Collapse" (highly recommended read I might add), there are 3 civilizations whose collapse is consistent with a warming period between the 7th & 14th C AD. The Khmer Empire, the Mayans & the Anasazi all declined/collapsed around the same time, & all the Paleo-climatic data from the respective areas (especially sediment cores from lake beds & coastal regions) show that there was definitely a warming event which triggered/accelerated the decline of these civilizations. So we do have fairly reasonable evidence of warming-induced collapses of civilizations from the low N. Hemisphere & Tropical S. Hemisphere. What is interesting, though, is this-the warming events are believed to have been on the order of +0.5 to +0.8 degrees, but occurred over a period of almost *seven hundred years*. Secondly, solar activity proxies for that time period (Be-10 & C-14) suggest a surge in solar activity not unlike what we saw during the 19th & early 20th centuries. So this again leaves us with the fact that the current warming period is *faster* than any other in the last 2000 years (at least), & is the only one not underpinned by changes in the heliosphere.
  9. Is the airborne fraction of anthropogenic CO2 emissions increasing?
    I'm not sure if I'm witnessing the conception of a new misconception or just a "rebunking" (hat tip to Hank Roberts) but ralphiegm's constant repetition of problems with C02 measurements sure sounds like a launch to me. ralphiegm, all of the measurement sites you worry over show a steady increase in C02 content. How would the poor mixing you imagine comport with that? Is each site measuring a hermetic local atmospheric cell with its own C02 sources? For instance, what about the grandpa site, Mauna Loa? Is Hawaii stuck in a persistent gyre, with the atmosphere isolated from the rest of the world? Does the C02 measured at that site originate just within Hawaii? Or does the imaginary bubble extend to Midway? Japan? San Francisco? Where does the C02 in the contrail of a jet flying to Hawaii make the transition from one magical domain to another? Is there a mysterious atmospheric atomic and molecular sieve at play here, unknown until now but identified via proxy only by you? Remember Chernoybl? Remember how it was detected outside of the Ukraine? How about those radionuclides, hmm? Did the the sieve remove Ukrainian C02 prior to crossing the border? Speaking of isotopes, how about the C02 isotope distribution? Does each mysterious atmospheric bubble include a special synchronizing system so that even while mixing does not take place, isotope ratios are kept at the proper proportion across domains? Wait a minute. Maybe it's more reasonable to accept that the atmosphere is mixed. I dunno. What do you think?
  10. Is the airborne fraction of anthropogenic CO2 emissions increasing?
    I concur Ned. Ralph's comments about CO2 varying by +/- 200ppm sound very reminiscent of the results of the Beck "paper". Ralph's coyness about his knowledge of Beck actually *confirms* that this is his primary source (methinks he doth protest too much). Beck's collection of historical CO2 samplings ignores the poor quality of both the sampling sites, the measurement methods & the sensitivity of the measurement tools-all of which are suspect. For a very good analysis of Beck's data-I suggest going here: http://www.realclimate.org/index.php/archives/2007/05/beck-to-the-future/ Oh, & before Ralph accuses me of merely trying to "squeeze out skeptics"-that claim is simply *not true*. I just want to squeeze out BAD SCIENCE! That's as true of Beck as it is of Manne (he of the awful Hockey-stick. I mean, seriously, what kind of *scientist* uses a single, dubious source of paleo-climatic information & builds a paper round it?) By contrast, though it has still to be independently verified, Lindzen's hypothesis regarding "The Iris Effect" is based on quite sound scientific principles (yes, I have read the paper, & understand enough of it to make this judgment)-even though Lindzen is a noted Skeptic.
  11. Why does CO2 lag temperature?
    Dennis, the uncertainty on lag of CO2 is of the order of some centuries, not thousands of years. The precision in the absolute dating of the air bubles depends on many factors, including accumulation rate and temperature, so it strongly depends on the geographic location of the ice core. Whenever possible the dating of the ice core (or part of it) is calibrated using known and well defined events.
  12. Why does CO2 lag temperature?
    Henry's Law is not appropriate for the solubility of CO2 in sea water. See here for more details: http://cdiac.ornl.gov/oceans/co2rprt.html
  13. Why does CO2 lag temperature?
    Non-scientist asking a scientific question here. The chart showing CO2 and temperature changes for the past 400,000 years shows CO2 lagging. I would assume that the level of uncertainty in our measurement of the number of years increases as we increase the number of years we go back in time. For example, we can confidently compare data that's measured decades back, but I would suspect that thousands of years back (as we see above) have a much greater margin of error. This would suggest to me that CO2 may not lag temperature and may even be a driver in the increase. What data disproves that and why can we be confident with that? My thinking is that, e.g., while we may say that a particular ice core sample used to measure CO2 is 400,000 years old -- perhaps that plus or minus 10,000 years?
  14. Why does CO2 lag temperature?
    One of the papers in the link above to papers on Milankovitch cycles (link at end of article) argues that the relationship between ice ages and the Milankovitch cycles is very weak and doesn't really explain anything. "Quantitative estimate of the Milankovitch forced contribution to observed Quaternary climate change", Wunsch 2004
  15. Why does CO2 lag temperature?
    chris: Thank you, that was interesting. So that will imply a local negative feedback mechanism related to warming in the NH, but which on the global scale just rearranges heat so that the SH warms even more. I have heard elsewhere about the see-saw NH/SH pattern, the explanation you provide seems quite plausible. What you are arguing, I take it, is that the insolation at 65N is the most interesting in order to predict milankovitch-related warming even at the SH, due to circulatory mechanisms such as the AMOC. That is also what I after some doubt assumed in my post, so I do appreciate that argument. (although I'm not sure how the milankovitch-related insolation varies depending on latitude, or if it does it in a way that is at all significant on the timescales in question here. This might even be a non-issue?). However, do you suggest that differences in how the AMOC responds to insolation changes may explain why we see different phase patterns (between insolation and warming) at the different warming periods present in the vostok ice core data? Or are we still clueless on that account?
  16. It's cooling
    selti, i'm afraid you didn't even bother to look at how a cycle is define and identified from the links i gave you. Indeed, statistics is no joke, just looking at a couple of up and downs does not define a cycle. It looks like you are following a pre-defined idea and do not care of contrast it with science. Do you have any physical _and_ statistical reason to claim that there is a cycle, other than looking at a couple of up and downs?
  17. It's cooling
    #21 Tom Dayton. Sooner than later, it will be established that CO2 driven global warming is the greatest scientific stuff up of all times. The stuff up is caused by assuming the temperature rise from 1970 to 2000 was unprecedented. Actually, as shown in this oscillating anomaly, this rise in temperature is similar to those at the end of 1880s and 1940s. Once the oscillating anomaly reaches its maximum it reverses and the cooling phase starts.
  18. Why does CO2 lag temperature?
    Andreas, the answers to your good questions haven’t been worked out yet, but recent research provides some very plausible (in my opinion!) scenarios. One of the most powerful hypotheses for providing insight into climate variation on centennial, millennial, and the longer timescales relevant to Milankovitch cycles is the variations in the Atlantic Meridonial Overturning Circulation (AMOC), the most well know aspect of which being the Gulf Stream, that transports heat from the equator to the high Northern latitudes. There is evidence that changes in the intensity of the AMOC made contributions to the Little Ice Age and the Medieval Warm period, both episodes (especially the MWP) having indications of a “focus” in the high N. latitudes. It’s easy to see that if the AMOC is strengthened (weakened), heat transfer to the high N latitudes in enhanced (reduced). The evidence indicates that variations in the AMOC may have been very dramatic in the past, and recent studies support a role for this in ice age terminations and the anomalous differences in the N and S hemisphere responses to Milankovitch insolation variations that you refer to in your post. The idea is as follows: 1. The AMOC [*] can (in principle) be completely “switched off” by large scale melt of Arctic ice, which dilutes the cooling dense high salinity portion of the current as it sinks in the high Atlantic regions between ~ Greenland-Iceland - after having left some of its heat to the grateful occupants of the Western European fringes! [*]http://en.wikipedia.org/wiki/Thermohaline_circulation Weakening, or cessation of the AMOC results in cooling of the high Northern latitudes, but warming of the S. hemisphere, since less heat is transferred northwards – it remains in the S hemisphere and low latitudes. This is a likely explanation for a large amount of data that supports a northern, southern hemisphere bipolar “see-saw”, where evidence from ice cores, for example, shows an asynchronicity in temperature variations between Greenland and Antarctica. Likewise, temperature reconstructions from ice cores, shows (in Greenland cores) some extremely abrupt large scale temperature rises and falls (due likely to switching on and off of the AMOC), which are barely visible or highly damped in Antarctic cores. 2. The “see-saw” is apparent in glacial terminations, and a detailed examination was recently published in Nature [**] (a good commentary accompanies the article [***]). The progression of events is proposed to be: a. The gradual Milankovitch-induced change in summer insolation at 65 oN resulted in retreat of the N. ice sheets, lowered albedo and enhanced high NH warming, which is observed in Greenland (but not really in Antarctic) cores between around 21000-19000 years ago. b.The meltwater from this ice sheet retreat is proposed to have switched off the AMOC (as in 1. above) about 18000 years ago, switching the bipolar “see-saw” to its “warm-south” mode, resulting in significant Antarctic and Southern ocean warming (observed in Antarctic cores). c. The warming of the Southern oceans resulted in a lagged release of CO2, which produced slow warming on a global scale, which promoted N. hemisphere ice retreat, the melt-water from which kept the AMOC in its “warm-south” mode, increasing CO2 further, and driving the termination towards completion. d. It’s thought that the AMOC switched on again around 14700 years ago where there is an abrupt rise in temperatures in the Greenland cores, and a slower cooling in the Antarctic cores, and the termination was effectively brought to completion by as combination of high insolation, high CO2, reduced albedo and the resumption of massive heat transfer to the high N. latitudes by the resumption of the AMOC. That scenario (there are other possible explanations [****]) provides an explanation of how Milankovitch insolation changes manifest largely in the high Northern latitudes can result in glacial terminations that seem to be led by events in the Southern hemisphere. [**] Barker S et al. (2009) Interhemispheric Atlantic seesaw response during the last deglaciation Nature 457, 1097-0111 http://www.nature.com/nature/journal/v457/n7233/abs/nature07770.html [***] Severinghaus, JP (2009) Southern hemisphere see-saw Nature 457, 1092-1094 [****] Stott et al. (2007) Southern hemisphere and deep-sea warming led deglacial atmospheric CO2 rise and tropical warming Science 318, 435-438 linked in John Cook’s top article [****] e.g. H. Cheng et al. (2009) Ice Age Terminations Science 326, 248 – 252 http://www.sciencemag.org/cgi/content/abstract/326/5950/248 P. Huybers & G. Denton (2008) Antarctic temperature at orbital timescales controlled by local summer duration Nature Geoscience 1, 787 – 792 http://www.nature.com/ngeo/journal/v1/n11/abs/ngeo311.html E. W. Wolff et al. (2009) Glacial terminations as southern warmings without northern control Nature Geoscience 2, 206 – 209 http://www.nature.com/ngeo/journal/v2/n3/abs/ngeo442.html
  19. It's cooling
    selti: Look at the forest, not the individual trees.
  20. It's cooling
    #18 Tom Dayton What I am comparing is the data after 2005. For all the data points after 2005, the actual anomaly measured observations are BELOW the anomaly projections with CO2 restricted at the 2000 level:
    Year Measured (deg C) Projections (deg C)
    2005 0.47 0.45 2006 0.42 0.47 2007 0.40 0.48 2008 0.33 0.52
    As a result, the IPCC projections are utterly wrong. Are you asking you me to believe you and deny my own lying eyes?
  21. It's cooling
    #18 Tom Dayton What I am comparing is the data after 2005. For all the data points after 2005, the actual anomaly measured observations are BELOW the anomaly projections with CO2 restricted at the 2000 level: Year Measured (deg C) Projections (deg C) 2005 0.47 0.45 2006 0.42 0.47 2007 0.40 0.48 2008 0.33 0.52 As a result, the IPCC projections are utterly wrong.
  22. It's cooling
    selti, your link "The IPCC projections are deadly wrong" is to an IPCC chart whose ranges of model runs (the shaded areas) and the observed data (the black dots and line) go up only to 2005. The black line for HADCRUT3 observed temperatures smoothed has been extended beyond that not by the IPCC, but by someone who modified (doctored, faked, falsified, as in Elvis with Bigfoot) the graph but adding an unsmoothed line! Perhaps the added black dots after 2005 really are the observed anomalies, but the line's extension is not smoothed across the dots! The resulting and false impression is that the smoothed line dove after 2005. The actual smoothed line makes a much shallower dip after 2005, especially if you add 2009 data. If you want to look at smoothed data then you must smooth it all the way from 1990 through 2008. If you want to look at unsmoothed data then you must look at unsmoothed data across all years, by ignoring the black line and just looking at all the black dots starting in 1990 and going up through 2008. If you want to draw a line from dot to dot you must do so for all the dots starting in 1990, not just starting in 2006. You must also look at either the line or the dots within the range of projections (the shaded areas) beyond 2005. That is shown on RealClimate in the post Updates to Model-Data Comparisons. Guess what? Observations are within the bounds of the projections!
  23. Why does CO2 lag temperature?
    Is it possible to know in detail how the Milankovitch cycle affected temperature in the past? Analogously to comparing the phases of the temperature and CO2 cycles, it should be possible to do the same involving the milankovitch cycles. This picture from wikipedia show the milankovitch-related insolation at 65 deg north superpositioned on proxy temperaures from the vostok (Antarctica) ice core: http://en.wikipedia.org/wiki/File:Vostok_420ky_4curves_insolation.jpg 65 deg north is far from Antarctica, but assuming that it is globaly relevant (lowest-albedo latitude?) I tried a comparision of the cycles based on the picture. In the picture we see four major temperature/CO2 peaks, at roughly 320k, 230k, 120k and 1k years from now. Looking on the lowest temperature dips before these peaks (the points where the respective warmings starts) I read that two oldest dips (at -340k and -245k years) actually coincides with peaks in insolation, each followed by a period where the insolation (at 65N) declines but the temperature (in the antarctic) rises. In these cases the temperature trends does not start to decline until we have reached the insolation's next local minimum. This would possibly indicate that the milankovitch cycle can only explain the onset of the warming, leaving the rest to be explained by CO2 only. However, this does only hold for two of four warming periods that we can see in the core (the others being more in phase with the milankovitch cycles), Antarctica is not near the 65N latitude, and I do not know how the milankovitch-related insolation varies globally (apart from 65N). Are there better models on how the fluctuations in insolation due to the milankovitch cycles affects the southern hemisphere, and antarctica in particular, more specifically? In that case such models would be a better starting point.
  24. What ended the Little Ice Age?
    My feeling is that the LIA and its ending are more straightforward. Some points: 1. Meehl et al don’t really address the end of the LIA. They address attributions to global warming since the mid-19th century, and the evidence indicates that the LIA had pretty much ended by then (see 5). 2. In relation to Meehl et al., since their paper was submitted, there’s been a pretty substantial re-evaluation of the solar contribution to temperature variation of the last several hundred years. The scientists that study solar outputs and its proxies (Lean, Foukal, Solanki), indicate that the contribution of enhanced solar output since the Maunder Minimum (MM; bottom of the LIA) to the mid-20th century is around 1-1.4 W/m2, equivalent to a warming at equilibrium of up to 0.2 oC [*]. This is a bit more than the Svalgaard estimated that DeNihilist refers to in post #3 above, but I find it hard to believe that a pretty well established surface warming/cooling contribution of ~ 0.1 oC through the solar cycle, doesn’t indicate that the complete absence of sunspot activity through a few cycles at the time of the MM wouldn’t have been associated with a cooling effect of at least 0.1 oC. 3. Referring to Meehl et al again, a more recent attribution study of natural and anthropogenic contributions to global temperature since the mid 19th century, indicates that all natural contributions (solar included) have produced essentially zero nett contribution since the mid-19th century. This study (Ammann et al. (2007) [**], is very similar to Meehl et al in its methodologies, but uses the more up to date solar parameterizations. 4. If one examines CO2 levels through this period [***], the atmospheric CO2 levels rose from around 276 ppm at the bottom of the LIA to 300 ppm by 1900 to 310 ppm by 1940. It’s likely that the small reduction of CO2 from the pre-LIA values near 280 ppm to 276 ppm was the atmospheric response to reduced temperatures (as discussed on the “Why does CO2 lag temperature” current thread). But the 280-310 ppm rise is anthropogenic and should give a global equilibrium temperature rise of 0.3 oC by 1900 and 0.45 at 1940 values (assuming the medium value of the climate sensitivity of around 3 oC of surface warming per doubling of atmospheric [CO2]. Since this occurred over a long time, we’d expect quite a lot of this to have been “realized” by the mid 20th century (say 0.35 oC). 5. So what ended the LIA? If you look at the most variable temperature reconstruction (Moberg et al, 2005 [****]; a N. hemisphere one, remember), the temperature anomaly was around -0.4 oC (relative to mid 20th century values) for several hundred years before the Medieval Warm Period (MWP), rose to around 0.0 oC at the height of the MWP, and then dropped to near -0.7 oC between around 1100 AD and 1600 AD at the bottom of the LIA. So recovery from the LIA really constitutes recovery from an anomaly of -0.7 oC back to the pre-industrial -0.4 oC (it helps to look at Moberg’s reconstruction!). This was largely a recovery of the solar irradiance (say 0.2 oC, and from the enhanced volcanic activity that likely made a small contribution to LIA cooling – say 0.1 oC). 6. So there are really two questions: What caused the recovery from the LIA? …. and What has caused the marked warming during the last 150 years. Considering the total (NH) temperature rise from the bottom of the LIA to the mid 20th century (~ 0.7 oC, and to now (~ 1.2 oC), I’d say the evidence is consistent with around 0.3-0.4 oC of natural “recovery” which was largely realised by the mid 19th century, and ~0.3-0.4 oC of anthropogenic contribution up to the mid 20th century, and more like 0.7-0.9 oC anthropogenic contribution to the present, with some of the natural and anthropogenic contribution “offset” by anthropogenic aerosols. [*] Y.-M. Wang, J. L. Lean and N. R. Sheeley, Jr. (2005) Modeling the Sun's Magnetic Field and Irradiance since 1713 Astrophysical J. 625 522-538 P. Foukal, G. North, Tom Wigley (2004) A Stellar View on Solar Variations and Climate Science 306, 68-69 Lean, J. L., and D. H. Rind (2008), How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett., 35, L18701 http://www.atmosp.physics.utoronto.ca/~jclub/journalclub_files/LeanGRL2008.pdf [**] C. M. Ammann et al. (2007) Solar influence on climate during the past millennium: Results from transient simulations with the NCAR Climate System Model Proc. Natl. Acad. Sci. USA 104, 3713-3718 http://www.pnas.org/content/104/10/3713.abstract (open access – so should be downloadable from this link) [***][ D. M. Etheridge et al (1996) "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn J. Geophys Res. 101, 4115 -4128 [****] A. Moberg et al. (2005) Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data Nature 433, 613-617 coast.gkss.de/staff/storch/pdf/moberg.nature.0502.pdf
  25. 1998 DIY Statistics
    #11 SLRTX: thanks for the heads up on the book. Through the wonder of the internet I now have a second hand copy of 'How to lie with statistics' - looking forwards to it! #20 Marcus: Is it this data? In which case first column is yr, 2nd column is month and 3rd+ columns are anomalies. You want the third column data because that's as close as it gets to global (the numbers are latitudes). It's not as easy to handle in excel as hadCRUT and GIStemp, but the data is all there :)
  26. Why does CO2 lag temperature?
    Marcus: afaik the solution of CO2 should, in principle, be governed by Henry's Law: http://en.wikipedia.org/wiki/Henry%27s_Law For the constant you get your typical Boltzmann exp(-A/T) form, and if 5C of global warming does occur then that's something like a 0.7% increase in the ratio. Meanwhile the partial pressure should be increasing linearly with atmospheric concentration, which will probably increase by at least 100% (and for 5C warming would likely need to go up by ~300%). So oceans should continue to absorb CO2, hence the fears about ocean acidification. Time for me to go look more in the literature I guess, but quick calcs suggest that airborne fraction will increase, but not by a huge amount?
  27. It's cooling
    #16 Riccardo There is a cycle! The cycle is approximate 30 years of warming followed by 30 years of cooling. Cooling phase from 1880s to 1910s. Warming phase from 1910s to 1940s. Cooling phase from 1940s to 1970s. Warming phase from 1970s to 2000s. And the current cooling phase from 2000s to 2030s. No more spin please. The data is cyclic.
  28. It's cooling
    selti, the only thing your graph shows is that a linear trend from 1880 is not adequate to describe the actual temperature trend, let alone prove the existence of a periodic oscillation. Indeed, there's no cycle. Although in some (rare) cases it is possible to do a statistical-only analysis of physical phenomena, it needs to be done appropiately.
  29. It's cooling
    There is no global warming that is taking place at the moment. Here is a chart for the mean global temperature anomaly from the Hadley center. The above graph shows a linear warming of 0.44 deg C/ Century, and superimposed on this linear warming there is an oscillating component that moves up and down about the linear trend line. The linear warming of 0.44 deg C/ Century is only 0.004 deg C/ year. As a result, this linear warming is insignificant when looking at mean global temperature trends at the moment. To look at mean global temperature trends, this linear warming of 0.004 deg C/ year can be removed by de-trending the anomaly, which gives the oscillating global temperature anomaly pattern. This pattern shows global cooling and warming phases of about 30 year duration, and the current trend is global cooling until 2030. There is no global warming that is taking place at the moment.
  30. It's cooling
    #13 Tom Dayton How could I be wrong as I used the data without any spin. Here are the data for the mean global temperature anomaly for the Hadley center. Year=>anomaly (deg C) 2005=>0.47 2006=>0.42 2007=>0.40 2008=>0.33 And the chart itself is from IPCC 2007 WG1-AR4. I am not wrong. The IPCC projections are deadly wrong.
  31. Why does CO2 lag temperature?
    What causes me added concern is this-at the moment around 40% of all man-made emissions are being absorbed by the Oceans. Yet if increased warming causes the oceans to become net *emitters* of CO2-as it has in the past-then what impact will that have on the future global warming?
  32. Why does CO2 lag temperature?
    The first link to "Shemesh 2002" is broken, at least for me..
    Response: Fixed the link, thanks for pointing that out. I've linked to the AGU site which is the safest option. There was another PDF online found in google scholar but it also had loading problems.
  33. Why does CO2 lag temperature?
    Well that's certainly how I've always understood it, but it still leaves us with the question the skeptics have failed to answer-why are CO2 levels rising this time around, & why do they appear to *precede* the warming trend this time around? It can't be due to the Milankovitch Cycle, because the next one isn't due for around another 70,000 years (&, anyway, will generate cooling, not warming). It could be due to the warming from the 19th & early 20th century-except that ice core data shows that CO2 levels remained largely at around 280ppm throughout that entire period (unless you believe the "data" compiled by Beck-which shows CO2 levels of around 300ppm (+/-200ppm) throughout the 19th century). This 2nd theory is further debunked by the change in the C-13/C-12 ratio of the CO2 which has entered the atmosphere, post-1950. Either way, there is little doubt that CO2 levels started rising a good 20 years *prior* to the much more accelerated warming trend we've seen since 1979. Indeed, if you look at the post-1950 warming trend in 20-year intervals, you see a very slow warming in the first interval (barely +0.02 degrees per decade), followed by a rise to +0.15 degrees per decade for the second interval, & a rise of +0.18 degrees for the final interval-suggesting an acceleration in the warming trend which *trails* the measured rise in CO2.
  34. 1998 DIY Statistics
    Oh, here's another thing-Nofreeewind-try reading here about glacial retreat: http://www.nichols.edu/departments/Glacier/glacier_retreat.htm or here: http://glacierchange.wordpress.com/ As to the Arctic, perhaps you are unfamiliar about the stories, in 2008 & 2009, which highlighted how conventional merchant ships were able to navigate the length of the North-West & North-East passage, in *late Autumn*! Doesn't sound like much of a recovery to me.
  35. Sea level rise is exaggerated
    Riccardo, I'm not sure I really want to see where he got the argument and suspect it's not an argument based on any numbers; rather, it's an argument that appeals to something that sounds credible only as long as numbers are absent. Which is why I'd like to see some.
  36. CO2 is not the only driver of climate
    Your site is excellent! But it took me eons to find you. I just want to add that deforestation creates an enormous carbon source, which I suspect, would more than cancel out any advantage in cooling the planet due to albedo effect. Do you have any idea exactly by how much?
  37. High CO2 in the past, Part 2
    Got time to add Breecker? All I have seen is Hrynshyn's blog mention http://scienceblogs.com/islandofdoubt/2010/01/is_the_earth_even_more_sensiti.php Hrynshyn's good, but can only give a pointer to the abstract, as the paper is paywalled, so he's getting lots of questions that need the paper to answer.
  38. It's freaking cold!
    @rader5 Okay, so the Meehl paper is more robust. I get that. But my question was more about the charge of "cherry picking" data from 1950 on, as opposed to including the 1930's and earlier. Is there a reason the Meehl paper starts in the 1950's?
    Response: The 1950 to 2006 period was chosen because of the decision to use continuous station records. They chose this period to avoid any effect that would be introduced by a mix of shorter and longer records. The final result (the increasing ratio of record high versus record lows) isn't dependent on the start date of 1950.
  39. 1998 DIY Statistics
    "Here is the IPCC projections, circa 2001. They were wrong. " Why IPCC 2001 rather than AR4? Another form of cherry picking? The temperature record falls within the two-sigma error bars of the ensemble projections in AR4. I imagine a similar exercise performed on the earlier projections would show a similar result, but Real Science tends to look at recent results rather than focus on the past ...
  40. 1998 DIY Statistics
    nofreewind: I'm not convinced by your politics argument. If something is wrong mathematically then it's wrong regardless of whether you believe in communism, free markets or pastafarianism. As far as I can tell, when a function has periodic components in it (eg assume that temperature is affected by the Sun's output), looking at a single trend over periods similar to the periods of those components and making absolute conclusions about longer trends is simply wrong. Not bad, or communist, just plain wrong.
  41. What ended the Little Ice Age?
    Re 3 and 4 - I had tried to read Svalgaard too or at least his comments on his work on another blog. If he is right (little solar variation in the last 165 years)and Riccardo is right that climate cannot be so very highly sensitive it leaves me still scratching my head as to what ended the LIA. I note John has said on on a different thread that he was working on a post on ice age/inter-glacial mechanisms.
  42. 1998 DIY Statistics
    nofreewind, oh yes, i see, but unfortunately now global warming has started again at the incredible pace of more the 20 °C/century!!! Pretty scaring, isn't it? Or maybe we (me and you) are missing something?
  43. 1998 DIY Statistics
    Nofreewind, it seems that you haven't got the main point here: In order to find _reliable_ trends as fast as possible, you have to sort out as much as possible of short time oscillations, special events like volcanoes etc. That's what this post is about. "It hasn't warmed sincce 1998" is a typical example of an unreliable trend observation. 1998 was a very special year, and when we are talking about trends, like "it has/hasn't warmed", we are making statements about what the typical situation is. I don't think you have looked very closely into the arctic ice data. That "enormous recovery" you talk about, led, for example, to Nov 2009 ice levels being lowest in several decades, practically the same as 2007, and, rank-wise, we are at about the same level right now. If we had been back to the situation around 2000, we would have been more safe in talking about "recovery" from the 2005-2008 average situation, but we aren't. Also, the September 2007 arctic ice extent is about as untypical as the 1998 global temperature anomaly, so that doesn't in any way establish an ice level to "recover" from.
  44. 1998 DIY Statistics
    This post was started with the statement "It hasn’t warmed since 1998" is still a very popular argument." Then the author began to obtusely deconstruct that statement using all type of complicated data not related to temperature over a much longer period than the past 12 years. I show a few simple graphs to prove the point. Here are all four graphs, it hasn't warmed since 1998, don't you think that is something to consider? Here is the IPCC projections, circa 2001. They were wrong. Marcus, what do sunspots have to do with the topic of this post? Where I hang out with my skeptic pals, sunspots are just another theory to consider, certainly their seems to be some correlation, (cycle length maybe, the Minimums had none etc), but there are diversions it seems. Give it 10 years! "willing dupes of the fossil fuel indusry". HILARIOUS! How many miles of driving using gasoline have you been "duped" into to. How do you heat your home? Why is your electricity so cheap(not oil but coal). Maybe that would I suggest you junk your vehicle and use wood to heat your house, and coal(on to wind), let's not get into that on this topic. Anyone here who believes that big oil has had anything but minuscule influence on this scientific debate is being deceived. Do you want to know about money, read this. , i'll show you the money! Glaciers melting - they have been melting since 1850, don't you know. Arctic Ice - The past two years there has been an enormous recovery from the 2007 September low. And I just read a warmer arctic scientist state he expects further recovery this year. Antartica, at least as far as sea ice goes, no strong trend, except maybe slightly up. Of course there are all kinds of measurements going on in Antartica.
  45. 1998 DIY Statistics
    I tend to agree Ken. Looking to use a single data point to invalidate 30-60 years worth of warming really does highlight the desperation of the Fossil Fuel Industry & its willing dupes (apparently these dupes would rather stuff an extra $1000 per year in the pockets of energy generators than just insulate their homes a bit better?!?!) Oh & I concur with you too RSVP. Temperature alone isn't the only thing that leaves me convinced of global warming, it's the massive shift in rainfall patterns, the retreat of glacial, Arctic & Antarctic ice & a host of other factors that tell me the planet has been warming the last 30 years *at least*!
  46. Sea level rise is exaggerated
    Ken in Oz, as far as i can remember, sediment deposition is historically of the order of a few GTons, or a percent of current ice sheet loss. Negligible. Also, the sedimentation rate is on the decline due to the more and more dams that are bilt. I'd like to see where your friends got the numbers that explain sea level rise with sedimentation, i never heard about it.
  47. Sea level rise is exaggerated
    I got into an argument about sea level rise as an indicator of climate change and was told that all recent rise could be attributed to increased sedimentation rates. Whilst I expressed doubts that, given the global ocean surface area, it could affect overall sea levels that much I had to concede that a lot of river mouths and bays are being affected by both silt from erosion and from deliberate infilling to create waterfront building sites. Locally both can be quite extensive. I have struggled to find quantification of human induced sedimentation and infilling; if anyone can link to something that a layperson such as myself can view and provide some perspective on rates relative to sea level rise I would appreciate it. Thanks, Ken.
  48. 1998 DIY Statistics
    I think that a hot spike in a warming trend as the foundation for arguments the world is cooling just indicates how weak the case for "cooling" is.
  49. 1998 DIY Statistics
    What is also intriguing, though, is how the RSS data shows warming (I hesitate to use the word "trend") of 0.04 degrees per year between 2000-2005 (with an R^2 of 0.434-still not great, but better than 0.0027), which is nearly identical to the GISS value of +0.037 degrees per year over that same time period. These nearly identical warming rates can even be extended as far as 2000-2007 (+0.021 degrees per year for RSS vs +0.025 degrees per year for GISS). Its only in the last two years that the RSS & GISS numbers have really split apart, with the GISS anomaly showing a fall from +0.57 to +0.44 back up to +0.58, & the RSS anomaly showing a drop from 0.308 to 0.09 to 0.26. This is intriguing when you consider what a massive effect just 2 data points can have on such a small data set, & it makes me wonder which are the *correct* data points!
  50. 1998 DIY Statistics
    RSVP, good point. I happen to comment on this problem a lot of times with friends. It appears that people more easily grasp temperature than other often more important effects. I think this is because we all are directly affected by temperature and we have a feeling of it; it's a direct measurement as opposed to indirect measurements such as sea level rise, tree line shift, etc.

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