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Shakun et al. Clarify the CO2-Temperature Lag

Posted on 10 April 2012 by dana1981

A popular myth amongst climate 'skeptics' is that historically atmospheric CO2 levels have risen after temperature increases began, and therefore it's actually temperature increases that cause CO2 increases, and not vice-versa as basic climate science and physics would have us believe.  To this point, the standard response to this myth has been that initial temperature increases have historically been caused by the Earth's orbital (Milankovitch) cycles, which in turn warm the oceans, causing them to release CO2, which in turn amplify the global warming.  Thus while the initial warming hasn't historically been caused by CO2, CO2 has amplified the warming for thousands of subsequent years, and thus is still the principal control knob governing Earth's temperature.

An intriguing new paper by Shakun et al. (2012) takes a more in-depth look at this particular myth.  Many headlines have declared that Shakun et al. have demonstrated that CO2 has historically led (rather than lagged) global warming - the reality is a little more nuanced than that, but that is the basic take-home message.  In Figure 1, the red line (Antarctic temperature) and yellow dots (atmospheric CO2) illustrate our previous unerstanding, while the blue line (global temperature) is the nuance added by Shakun et al.

Shakun Fig 2a 

Figure 1: The global proxy temperature stack (blue) as deviations from the early Holocene (11.5–6.5 kyr ago) mean, an Antarctic ice-core composite temperature record (red), and atmospheric CO2 concentration (yellow dots). The Holocene, Younger Dryas (YD), Bølling–Allerød (B–A), Oldest Dryas (OD) and Last Glacial Maximum (LGM) intervals are indicated. Error bars, 1-sigma; p.p.m.v. = parts per million by volume.  Shakun et al. Figure 2a.

What did Shakun et al. Do?

The key to this myth is that it's based on Antarctic ice core records, which are not necessarily an accurate representation of global temperatures.  In recent years there have been many studies collecting data from ice cores in Greenland, sediments drilled from the ocean floor and from continental lakes, and so forth.  Most of these proxies don't extend as far back in time as the Antarctic ice cores, but many do extend back to the last glacial-interglacial transition which began approximately 18,000 years ago, as Figure 1 shows.

Shakun et al. examined 80 such proxy records from around the globe (Figure 2), recording sea surface temperatures for the marine records and surface air temperatures.

Shakun Fig 1

Figure 2: Proxy temperature records. a) Location map. CBT = cyclization ratio of branched tetraethers; MBT = methylation index of branched tetraethers; TEX86 = tetraether index of tetraethers consisting of 86 carbon atoms; Uk37 = 37, alkenone unsaturation index. b) Distribution of the records by latitude (grey histogram) and areal fraction of the planet in 5° steps (blue line).  Shakun et al. Figure 1.

By comparing the atmospheric CO2 increase (note that since CO2 is well-mixed in the atmosphere, a single ice core record can be used as an accurate representation for CO2 - Shakun et al. used the Antarctic EPICA Dome C ice core for CO2 data) to these many different temperature records, Shakun et al. are able to discern whether the CO2 increase led or lagged temperature changes in various different geographic locations, and for the planet as a whole.

Does CO2 Lag or Lead?

This is where it really gets interesting, because the answer is yes - CO2 lags and leads.  In the Southern Hemisphere, Shakun et al. found that the temperature rise happened first, whereas in the Northern Hemisphere, the CO2 increase was first (Figures 3 and 4).

Shakun Fig 2b 

Figure 3:  The phasing of CO2 concentration and temperature for the global (grey), Northern Hemisphere (NH; blue) and Southern Hemisphere (SH; red) proxy stacks based on lag correlations from 20–10 kyr ago in 1,000 Monte Carlo simulations. The mean and 1-sigma of the histograms are given. CO2 concentration leads the global temperature stack in 90% of the simulations and lags it in 6%.  Shakun et al. Figure 2b.

Shakun Fig 5b

Figure 4:  Proxy temperature stacks for 30° latitude bands with 1-sigma uncertainties. The stacks have been normalized by the glacial–interglacial (G–IG) range in each time series to facilitate comparison.  Shakun et al. Figure 5b.

What's Going On?

What appears to have happened, based on global climate model simulations run by Shakun et al., is not all that different from our previous explanation of the supposed CO2 lag - just a bit more nuanced. 

  • As we already knew, the Earth's orbital cycles trigger the initial warming (starting approximately 19,000 years ago), which is first reflected at the highest latitudes (i.e. Greenland and the Arctic - see "Onset of seesaw" in Figure 4). 
  • This Arctic warming melted large quantities of ice, causing fresh water to flood into the oceans.
  • This influx of fresh water then disrupted the Atlantic meridional overturning circulation (AMOC), in turn causing a seesawing of heat between the hemispheres.  The Southern Hemisphere and its oceans warmed first, starting about 18,000 years ago.
  • The warming Southern Ocean then released CO2 into the atmosphere starting around 17,500 years ago, which in turn caused the entire planet to warm via the increased greenhouse effect.

In short, the initial warming was indeed triggered by the Milankovitch cycles, and that small amount of orbital cycle-caused warming eventually triggered the CO2 release, which caused most of the glacial-interglacial warming.  So while CO2 did lag behind a small initial temperature change (which mostly occurred in the Southern Hemisphere), it led and was the primary driver behind most of the glacial-interglacial warming.

According to the Shakun et al. data, approximately 7% of the overall glacial-interglacial global temperature increase occurred before the CO2 rise, whereas 93% of the global warming followed the CO2 increase.

What Does Shakun Say About Climate Sensitivity?

Shakun et al. did not address the question of climate sensitivity in their paper.  Readers may recall a paper by Schmittner et al. which used the glacial-interglacial transition to estimate climate sensitivity, and came up with an estimate (1.7–2.6°C with a best estimate of 2.3°C global surface warming in response to doubled CO2) towards the lower end of the IPCC range (2.0–4.5°C with a best estimate of 3°C).  However, this lower estimate could mostly be attributed to Schmittner et al.'s low estimate of the glacial-interglacial temperature change, of just 2.6°C globally (most previous estimates put the value at around 5°C).

Shakun et al. estimate the global surface temperature change at approximately 4°C during the transition.  A similar paper by many of the same authors recently published in the Proceedings of the National Academy of Science (Clark et al. 2012) estimates the greenhouse gas radiative forcing during the transition at approximately 2.5 Watts per square meter (W/m2), but neither Shakun nor Clark et al. estimated the total radiative forcing (including surface reflectivity changes, for example).  Overall, the estimated temperature changes and radiative forcings are both slightly lower than in Hansen and Sato (2011) (Figure 5).

Fig 2

Figure 5: Climate forcings during the ice age 20,000 years ago relative to the pre-industrial Holocene from Hansen and Sato (2011)

Similar to the implied sensitivity in Hansen and Sato, a ~4°C global temperature change caused by a ~6 W/m2 forcing corresponds to a ~2.5°C sensitivity to doubled CO2.  Note that this is a very rough estimate based on the Shakun and Clark results, but is within the IPCC climate sensitivity range.

Predictable Denial Reactions

Not surprisingly, since the 'CO2 lags temperature' myth is a climate denialist favorite (coming in at #12 on the most-used climate myths list), the reaction has predictably been one of, well, denial.  WattsUpWithThat in particular has devoted several posts denying the results in the Shakun et al. paper.  One such post quoting Don Easterbrook (of failed global cooling prediction fame) began with the following objection:

"1. They assume that CO2 is capable of causing climate changes..."

Need we continue?  We could devote an entire post to the glaring errors from Easterbrook in this WUWT post, but let's not. 

In the same post, Willis Eschenbach criticized the paper saying "My rule of thumb about these kinds of things is, no error bars … no science."  However, Shakun et al. were quite explicit about the associated uncertainties throughout the paper (for example, see the uncertainty ranges depicted in Figures 1 and 4 above).  Upon actually reading the paper, Eschenbach's criticism rings quite hollow.

Speaking of apparently not reading the paper before attacking it, a second WUWT post on Shakun et al. (also from Eschenbach) argued that their results are not valid because the glacial-interglacial warming occurred at different times in the different temperature proxies.  But that is of course the point - the Southern Hemisphere warmed before the CO2 increase, while the Northern Hemisphere warmed after (as Figures 3 and 4 show).  In looking for an excuse to reject this research, the denialists manage to miss the entire point of the paper.

In yet a third post, this one by Watts himself, Watts objects that Shakun et al. refuse to call orbital cycles the warming "trigger."  This is a little bit silly, since the authors titled an entire section of their paper The trigger for deglacial warming, discussing that the first warming (of the Arctic 19,000 years ago) was indeed triggered by orbital cycles.

An Intriguing Result

The knee-jerk denial rejections of the Shakun et al. results reflect the inconvenience of their results for the climate "skeptics."  The authors summarize their intriguing results, which expand upon our understanding of glacial-interglacial transitions.

"Lag correlations from 20–10 kyr ago suggest that the modelled global temperature lags CO2 concentration by 120 yr, which is within the uncertainty range of the proxy-based lag."


"Our global temperature stack and transient modelling point to CO2 as a key mechanism of global warming during the last deglaciation. Furthermore, our results support an interhemispheric seesawing of heat related to AMOC variability and suggest that these internal heat redistributions explain the lead of Antarctic temperature over CO2 while global temperature was in phase with or slightly lagged CO2."

Also see good coverage of this study by Climate Crocks, The Washington Post, and BBC.

Note: the Shakun et al. results have been incorporated into the CO2 lags temperature myth rebuttals.

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Comments 101 to 150 out of 161:

  1. I wonder why Shakun et al. 2012 did not use all the proxy data that was utilized in the Clark et al. 2012 paper. I understand that some of the proxy's used in the Clark et al. 2012 were for precipitation data, but it still looks like there was a lot more temperature records used compared to Shakun et al. 2012. Below is a comparison of the two papers with Shakun et al. 2012 on top and Clark et al. 2012 on the bottom, the blue dots on the Clark et al. 2012 graph are precipitation proxy's and I am not sure if these could also be used as temperature records.
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    Moderator Response: [RH] Fixed image width.
  2. lurgee, it is hardly skeptical to view things in terms of "Sides" (or "Tribes", as some put it). This "Side" discusses climate science in view of what the actual science has to say, viewed through the lens of the scientific method. The other "Side" you refer to prefers to employ insinuation, false balance, character assassination, misrepresentation and cognitive/confirmation bias in lieu of the science and scientific method. Unless you have a fascination for train wrecks. Then carry on.
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  3. I was inspired by the estimable Albatross, in another discussion: "The last thing I want is to be responsible for sending someone to the 'dark side'." Some people seem to be drinking too much coffee.
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  4. Sorry for being behind in my comments. I may get caught up eventually. 78 Tom Curtis. Thank you for the good work. According to you the change in CO2 forcing from LGM to the year 2000 was 3.7 watts per square meter. The change in the GHE you say from LGM to the Holocene is somewhere between 50 and 100 watts per square meter. Since H2O is the domanant green house gas then it must be the driver. The effects of H2O really overwhelm that of CO2. This is according to the data that you have presented. We are talking about cimate here and not weather. H2O is in many ways the big weather maker with relative humidity varying quite a bit from day to day. As water precipitates out more is added through vaporazation and or sublimation. What matters is the average amount of H20 in the atmosphere and as average temperatures increase so does the average amount of water vapor. This is commonly used in modeling an increase in retained heat caused by more water vapor that is in turn caused by a warmer atmosphere that in turn is caused by an increase in CO2. It is modeled as a CO2 related feedback mechanism. We live in a water world which was especially true during the first 2,500 years after the LGM. H2O will not only evaporate from liquid water exposed to the atmosphere but it will sublime directly from ice. I assume that, for temperatures less than -22 degrees f, water vapour content will drop to zero but even at the LGM it was not less than -22 degrees f over the entire earth's surface. So far I have been talking about the first 2,500 years after the LGM when according to the article the CO2 levels did not change so there was no CO2 change to effect average temperatures. We are talking about climate change that occoured gradually over a period of 2,500 years. Remember that 2,500 years ago was before the rise of the Roman empire. It is a very long time, and a long enough time for local varinng weather effects to average out.
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  5. William - reiterating earlier commentators: H2O is important feedback - it cannot be a driver. A driver (forcing) is something changes the energy flow independent of temperature. You cannot vary H2O independently of temperature so is feedback only. CO2 is both.
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    Moderator Response: TC: html tags fixed.
  6. 79 danieic 82 Skywatcher most likely answered your question but let me add something. At lower temperatures the amount of CO2 in the atmosphere relative to H2O will be higher so according to green house gas theory the relative contribution to heat trapping of CO2 compared to H2O will be much higher. At temperatures less than -22 degrees f, H2O vapor disappears from the atmosphere but the level of CO2 does not change. I do not believe that changes in green house gasses are considerd to be the trigger that started the climate change at the LGM but they may have added to the effect.
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  7. William Haas @104, I made a major error in my post 73, which I corrected in my post 87. The effect of the error was to overestimate the difference in the GHE between the LGM and the late 20th century by 60-70 W/m^2. In consequence, the unexplained change in GHE is around 30 W/m^2. As noted in my post 73, even that is an over estimate because it does not allow for the effect changes in albedo, nor from minor Greenhouse gases like methane, nor the effect of the increased temperature difference between equator and pole, which allows larger IR emissions from the surface for a given global temperature. Consequently the increase in contribution to the total GHE from water vapour is almost certainly less than 30 W/m^2, but also very likely to be greater than 15 W/m^2.
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  8. William Haas #107, you're making no sense at all. I fear I'll just have to repeat scaddenp in reminding you that water vapour is a feedback, not a forcing. This is a crucially important concept that you're failing to grasp, and it is not something that there is the least bit of doubt about. It is (and physically must be) that way, even though water vapour is the largest single component of the greenhouse effect. It does not matter how wet our planet is (it is very wet!), we need the stabilising effect of long-lived CO2 to provide a warming 'base' for the WV feedback to be propped up on, or else the combination of precipitation, freezing and albedo increase would turn our planet quickly into the ice house it would be at this distance from the Sun, were there not long-lived greeenhouse gases (dominantly CO2) in our atmosphere. CO2 does not precipitate out of the atmosphere, so when you change the CO2 level it stays changed for a century or more until slow carbon cycle processes, if favoured, remove it. It lasts long enough to impact ice volume (albedo) and ocean currents (CO2 ventilation), which operate on the decade-to-century scale. That makes it the most important control knob on climate. Thus long-lived greenhouse gases regulate the water vapour, which precipitates out at the drop of a hat (less if you are in Glasgow...).
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  9. @William Haas The initial warming was caused by the extra amount of sunlight hitting the planet in the far north. This started around 20 kry as shown on the graph below and CO2 had "nothing" to do with it. This warming caused the (AMOC) to stop which forced the north to cool and the south to warm, which is marked on the graph below as the seesaw. This process also had "nothing" to do with CO2. With all the extra water vapor being produced in the south, it did "nothing" to global temperatures. Look at the graph below, its all local warming as would be expected from water vapor. Global warming did not start until CO2 was released, which is clearly shown.
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  10. Again sorry for the slow response. I see that I am getting responses to my posts but I am trying to comment on them in order. I thank you for the effort that you are all putting in. 81 Danieic You wanted me to state a "plausible mechanism". A plausible mechanism is that orbital forcing drove up tempertures enough to release H2O that then amplified the forcing signal. We are talking about the first 2,500 years since the last LGM where the article says that 7% of the warming took place and CO2 levels did not increase. H2O is a green house gas. There is plenty of H2O in both solid and liquid form to evaporate or sublime and enter the atmosphere. As long as the air is above -22 degrees f, there will be H2O in the atmosphere. If the temperature of the atmosphere increases the average amount of H2O will increase. According to the green house gas effect, more green house gases in the atmosphere will cause more heat to be trapped which will cause the temperature of the atmosphere to increase even further. It is often modeled as a feed back mechanism as I have stated before. In the first 2,500 years since the LGM H2O could not possible be a CO2 feedback mecaanism because according to the article, CO2 did not increase. Yet the temperature increased so H2O had to increase. One could probably write a recursion relation to compute what is happening. I think of it, myself, as a low pass filter with a well damped step response. The system is fundamentally stable so there is no chance of runaway heating. Rising temperatures causes the atmosphere to increase its capacity to hold water vapor. Relative humidity varies with time as a function of weather but what we are concerned about are averaged values of atmospheric H2O capacity because we are talking about changes in climate and not weather.
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  11. I think this information from Clark et al. 2012 might point to the reason why Shakun et al. paper did not use all the Antarctic ice core proxy data. "whereas in Antarctica, East Antarctic ice cores and two West Antarctic ice cores have similar patterns that broadly follow the classic seesaw pattern, whereas two other West Antarctic ice cores (Siple Dome and Taylor Dome) suggest a more complicated deglacial record (58, 59). It remains unclear, however, as to whether these latter differences are due to uncertainties in chronology, elevation changes, stratigraphic disturbances, or spatially variable climate changes (59–61)." (clark et al. 2012)
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  12. @William Haas: You cannot trap the extra heat unless there is a heat-trapping gas already present. That is CO2, not H2O(v). You cannot warm the planet unless you trap extra heat. You have to have a mechanism in place already in order to trap the extra heat (in the north, due to orbital cycling). The heat trapping mechanism that was already in place and available instantaneously was... CO2. H2O(v) is a strong feedback, but not a driver, because without the trapping mechanism to keep that heat, there will be no warming. Without warming, no extra H2O(v) will enter the atmosphere. It will not do so until the atmosphere warms up. The atmosphere warms up only is more heat is trapped. You are getting into a very circular argument in your attempts to downplay the importance of the basic step in the warming cycle... heat trapping due to CO2. That is the important factor, the one that drives and controls the H2O effect.
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  13. 82 skywatcher We are talking about the first 2,500 years after the LGM. The article states that during that time 7% of the warm up that ended the ice age occoured but that atmospheric levels of CO2 did not increase. During that time water surfaces dominated the earth much as they do today and as they have for billions of years. During the ice age, ice sheets developed where there are none today but they did not cover the entire earth. Ice is also a water surface. Water molecules can pass directly from an ice surface into the atmosphere through sublimation. So plenty of water was available 19,000 years ago to pass into the atmosphere just as there is plenty of water available today. We are talking about climate. So the day to day levels do not matter, it is the average amount of water vapor in the atmosphere that matters. As average temperatures increase so will the average amount of water vapor. Water vapor is a green house gas and in fact it is the domanant green house gas. Just how dominiate water vapor is, is a matter debate, but from my reading, all who believe in the green house gas theory agree that water vapor is the green house gas that accounts for the most warming. The primary reason for this is that during at least modern times there is usually 100 times more water vapor in the atmosphere than there is CO2. The average amount of water vapor depends on temperature. If the average temperature increases so does the average amount of water vapor in the atmosphere. This idea is used in modern models of how CO2 contributes to global warming. Increased levels of CO2 traps more heat which raises temperatures. The rises in temperatures causes more water vapor to enter the atmosphere because higher temperatures increase the atmosphere's ability to hold more water vapor. The additional water vapor causes the atmosphere to trap even more heat. Because of this, water vapor is considered to be a positive feedback to the effect of adding more CO2 to the atmosphere. As such H2O amplifies the effect of increased levels of CO2 on global warming. I would think that most people on this site would understand that and for that matter even defend it. During the first 2,500 years since the LGM, CO2 levels did not rise but temperatures did rise. This is all according to the article. I am not desputing it nor am I making this up. The feeling is that Milankovitch forcing was the cause. To raise CO2 levels it takes more than just surface heating of the oceans to have any significant effect. Apparently it took 2,500 years for the Milankovitch forcing to heat a large enough volume of ocean water to effect global CO2 levels. But to increase average H2O levels in the atmosphere all that is needed is for the temperature of the atmosphere to increase. The article says that temperatures did increase during this period of time so that H2O levels must have increased and the increased levels of H2O must have added to the warming. If this is not the case then current models that predict that increased CO2 levels are warming the globe and that incorporate H2O related feedback and or amplification, must be all wrong. Water vapor amounts in the atmosphere vary from day to day and water leaves the atmosphere through condensation but it is quickly replaced through vaporization or sublimation. Water takes up additional heat when it melts, vaporizes, or sublimes, but then it releases that heat when it condenses or freezes. During the time I am talking about there was CO2 in the atmosphere but because it did not increase, its increase could not have contributed to global warming.
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  14. William, multiple people have engaged you multiple times in an attempt to correct your errors. You display no indication that you have read and understood their efforts. You are simply, fundamentally, wrong on the ability of water vapor to be a temperature forcing of climate in any capacity. Until you grasp the difference between the forcings and the feedbacks, you will not be able to overcome your block in this matter.
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  15. William, I superficially read your posts so far. Can you clarify for me the following: are you making the argument that water vapor acts as a forcing when it is somehow injected in the atmosphere (whatever the mechanism)?
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  16. It is a sensible idea that water vapor increases can cause global warming. Water vapor increases from initial warming cannot possibly trigger runaway warming because water vapor is lighter than air. It rises, easily saturates, and condenses. There is no requirement that CO2 rise, although it rose later as an amplifier. Another thing to remember is that water vapor is very uneven during glacial periods with very dry continental interiors except for mountain ranges and glacier sources. See for example. When the water vapor starts to even out due to Milankovitch forcing, then there is net global warming.
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  17. If water vapor could magically increase as a volume percentage of the atmosphere, and stay at those elevated levels over centuries... then it could be a forcing factor. As it stands, it is not a forcing factor... it is an amplifier, because it cannot and does not go into the atmosphere and stay there on its own. It must have "something" that acts to heat the atmosphere and keep it heated. The only thing that can do that is the interaction between increased insolation (the initial trigger) and subsequent enhancement and maintenance of increased CO2 levels. CO2 mixes and stays mixed for centuries. CO2 concentrations can be reduced via silicate weathering and photosynthesis + rapid burial of dead organic matter... but that process is much, much slower than the introduction and mixing of CO2 due to increased temperatures. Increased levels of H2O cannot cause global warming because they require the warming to exist beforehand. Once warming has started, the warmer atmosphere can then hold more H2O(v), and more H2O(v) is available due to enhanced evaporation, then it can begin to amplify already existing warming trends. Hence, H2O(v) is a feedback, not a driving force.
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  18. William Haas's comment at 113 is correct in every detail. It is also correct that thetotal increase in contribution to the Green House Effect from water vapour between the Last Glacial Maximum and the Holocene is greater than the equivalent increase for CO2, or indeed for all well mixed Green House Gases. It is important that we recognize where William is right, even though we think he takes those correct premises and goes of to a completely wrong conclusion. To be clear, what Haas has stated at 113 is that Water Vapour was a significant short term feedback on the milankovitch cycle effects at the initiation glacial to interglacial transition, and that that feedback strengthened the response. Indeed, the WV feedback strengthened the original response by a factor between 2 and 4. Unfortunately, Haas has been arguing that "...starting with an ice aged earth, H2O would dominate any green house gas triggering effects." However, as he states in 113:
    "Water vapor amounts in the atmosphere vary from day to day and water leaves the atmosphere through condensation but it is quickly replaced through vaporization or sublimation. Water takes up additional heat when it melts, vaporizes, or sublimes, but then it releases that heat when it condenses or freezes."
    What he needs to recognize is that the same thing applies on the other side of the equation as well. If the WV content of the atmosphere exceeds the equilibrium level for temperature, it quickly precipitates out, so for time scales of a year or more it can be always assumed to be in equilibrium for the temperature and conditions. Consequently, the initial and significant response of the WV feedback could not have led to ongoing warming by itself. Its full effect, if no other factors were brought into play, would have been worked out within a century or so at most. Consequently, without the intervention of other factors, the WV feedback alone could not have lead to continuing warming centuries after the initial trigger. IMO, Haas needs to clearly state whether he agrees with, or disagrees with the last (and bolded) sentence. If he agrees, we have then just simply misunderstood what he has been trying to say. If he disagrees, he needs to clearly state why a factor which equilibriates over mere days can still be driving ongoing warming thousands of years later. Certainly nothing he has said in 113 suggests that it would. Of course, from the basis of the consensus on climate science, there is no issue here. WV is a strong short term feedback, but the long term increase in temperature from LGM to Holocene was driven by the far more stable factors of ice sheet melt and increased CO2 and CH4 concentrations. Because CO2 and ice sheets take thousands of years to equilibriate with temperature, there is no issue as to why they are able to drive warming over the long term. And because they are the long term drivers, they explain the transition in a way that WV cannot, even though WV contributed more to the change in the total GHE.
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  19. #116 - William, you really, really need to re-read Michael Whittmore's post at #109, and mine at #108. You might note I said at #108 that we live on a wet planet, and that WV was the largest component of the GH effect, we agree on that, and a surprising amount of correct (if obvious statements in your post). Your conclusions are still miles wide of the mark though. The first crucial phrase is this, used by you: "The average amount of water vapor depends on temperature." The second crucial point is that the average amount of water vapour in the atmosphere responds very quickly to temperature change, through evaporation and precipitation, also elucidated by you. Therefore something else must force the temperature in order to keep the water vapour in the air. Water vapour alone does not do it as, alone, eventually it finds a place to freeze and increase albedo (Lacis et al 2010). Orbital forcing can change temperatures locally, thus changing water vapour locally, much as excellently described by Michael Whittmore in #109. But this is still not enough forcing to get us out of an ice age. CO2 can change WV levels globally as it is non-precipitable and well-mixed. Michael Whittmore's excellent #109 (as well as the OP of course) describes succinctly the pattern of events leading to global warming at the end of the ice age. Perhaps you would care to explain where he is wrong, and how a variable that is locally effective on timescales of a week or two can be globally effective for century-scale warming (deglaciation or current)?
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  20. How much of an effect does the latent heat of melting ice have? Take the present day, for example: if we are losing ~100 km^3 per year of ice (Howatt et al., 2008, PDF), that works out to 9x10^12 kg of ice melted, which would XXXXXXX absorb 334 kJ/kg, or 3x10^15 kJ per year (focused on areas where melting is most prominent). That seems like a lot to me...
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    Moderator Response: TC: post edited at authors request. 1:34pm 18/4
  21. LOL... grrr... I went backwards: absorb 334kJ/kg on melting, release 334 kJ/kg on freezing - any chance of correcting that last post? 3x10^15 kJ absorbed per year just to melt the ice we are losing - does that heat absorbtion have a significant masking effect on what we measure with thermometers?
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  22. Let me take a little break here. I again want to thank you for all of the effort that has been put into this. There seems to be more than one person responding to my posts so that there are all that many more posts that I have to respond to. I guess my post 113 did not go all that badly. I do agree with quite a bit that has been said. Some of you seem to be jumping the gun on what conclusions I am going to come up with. I am not trying to espose anything that is revolutionary or sinister. I am just trying to find the truth as I am sure that your are too. I plan to continue to respond to posts in order. Some of them take additional effort on my part to consider and I am sure that, like you, I have a lot more going on in my life then just responding to posts on this site.
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  23. I cant believe we are even wasting our time on William Haas. He clearly thinks that the 7% warming seen during LGM was global, and that it was caused by H2O. Just look at his comments below “To enhance or continue global warming is atmospheric CO2 really necessary to explain it? What about H20?” Comment can be seen here “There is no imperical data uncovered by this article to show that in the first 2,500 years since LGM that the green house gas, an increase in average atmospheric H2O did not have some roll in global warming” Comment can be seen here From the very start we have all been trying to disprove these statements. We all know that the initial forcing was the change in Earth’s orbit, H2O was not the forcing just the feedback. Even when the (AMOC) stopped, there was no added forcing that warmed the South it was just an energy imbalance with less warm water going north and more staying in the south. Even in William Haas resent comment he clearly tries to attribute H2O to global warming, even though we all know that the 7% warming seen during the LGM was nowhere near global. Just read the comment below “During the time I am talking about there was CO2 in the atmosphere but because it did not increase, its increase could not have contributed to global warming.” Comment can be seen here @Tom Curtis you say that “William Haas's comment at 113 is correct in every detail.”. You really think that William’s saying “Apparently it took 2,500 years for the Milankovitch forcing to heat a large enough volume of ocean water to effect global CO2 levels.” Is true?
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  24. Michael Whittemore @123, If you look at figure 4 in the original post, you will see the following sequence: 20 kyr: temperatures start to rise from 60 to 90 degrees north, presumably due to Milankovich forcing, temperatures start falling from 30 to 60 degrees north; 19 kyr: temperatures start falling from 60 to 90 degrees north, and continue falling from 30 to 60 degrees north. Temperatures from 30 degrees north to 60 degrees south start rising; 18 kyr: temperatures start rising from 60 to 90 degrees south; 17.5 kyr: CO2 levels start rising, temperatures cease falling from 30 to 90 degrees north. That makes it 2,500 years from the onset of the Milankovitch forcing until tropical and southern hemisphere waters were warm enough to start a steady rise in CO2 levels. The Milankovitch forcing heated that water indirectly by shutting down the AMOC, an important subtlety Haas does not mention, but his statement that it took 2,500 years for the Milankovitch forcing to trigger the rise of CO2 levels is correct. Haas may in fact just be very confused on certain points, or he may be very subtle. He may have adopted the approach of making egregiously wrong statements and then defending a reasonable position which can be mistaken for the false position he originally stated. If that is his game, by not acknowledging where he is correct, but clearly distinguishing it from his initial statements you fall for a rhetorical trap and find yourself arguing against true beliefs in the mistaken opinion that you are arguing against false beliefs. In doing so, you hand victory to the rhetorician how laid the trap. I am not saying that is what Haas is doing. As I said, he may just be confused, or even just have stated a reasonable position in a very confused way. Regardless, he has persistently made claims which are false, even absurdly false as you have highlighted; but defended the reasonable position that H2O was a significant positive feedback during the first 2,500 years of the glacial/interglacial transition. To avoid continuing the confusion, Haas needs to clearly answer my questions in 118. But to avoid continuing the confusion we need to recognize when he is right, but clearly state why what he is saying that is correct is not the same thing as, and does not support those things which he has said which are wrong.
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  25. So what we're quibbling about here on the basics is the definition of "forcing" where H20 is concerned. William may be insisting, if he is actually insisting, that WV is a forcing post LGM because it is the largest contributor in GHG warming. If so, no -- orbital changes are the forcing. WV is a feedback, and it is always the dominant element in GHG-based warming (but not the controlling factor -- like a bad mob film, WV is the "muscle" that does the bidding of the little guy in the shadows--Joe "CO2" Maguire--but doesn't do much on its own, unless the big big boss (orbital) needs some long-term project done -- ooo, I see a climate-as-film-noir project). Sublimation rate does not change of its own accord. WV will not increase of its own accord on the climate scale. It is always a feedback to whatever forcing. CO2, likewise, does not increase of its own accord. We don't speak of AGW-concurrent permafrost CH4 mass release as a forcing. We shouldn't speak of post-LGM WV increase as a forcing or as a trigger. I don't think that is William's intent in 113. If he clings to the idea that WV is a trigger, a forcing, then we need to question his ability to honestly engage. If, instead, he means that WV played a more crucial role than CO2 in early post-LGM warming, then that's a good, debatable position.
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  26. Part of the confusion may be that Milankovitch forcing is not a earth-averaged W/m2 forcing. There is a component of W/m2 forcing for part of the earth, specifically longer NH winters. As those winters shorten towards the end of the glacial period, there will be weather and climate changes including localized water vapor increases. But William Haas talked about global average water vapor as if Milankovitch were a simple global average W/m2 forcing which it is not.
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  27. Eric (skeptic) @126, the changes in albedo from ice sheet melt in the transition from glacial to interglacial are strictly regional phenomenon, not global. Yet they are treated as a globally averaged effect in any discussion of the issue, and in any model except full Global Circulation Models. Even the Green House Effect from increasing CO2, and come to that the Water Vapour feedback are not everywhere the same because of differences in temperature between the equator and poles (among other reasons), and are treated as globally averaged effect. Choosing the WV feedback from the Milankovitch signal, and only that feedback to not be treated as a globally averaged effect is pedantry, and an inconsistent pedantry to boot. It adds nothing to the discussion.
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  28. @ Tom Curtis 124 You say “20 kyr: temperatures start to rise from 60 to 90 degrees north, presumably due to Milankovich forcing, temperatures start falling from 30 to 60 degrees north” I personal think that the 30-60N cooling is completely natural, you can even see that it starts to warm before the seesaw event takes place. The Milankovich cycle only warms the far north, and if the AMOC is working, it would be the main driver of climate in the 30-60N region. 30-90N only started cooling when the AMOC stops. You say “The Milankovitch forcing heated that water indirectly by shutting down the AMOC, an important subtlety Haas does not mention, but his statement that it took 2,500 years for the Milankovitch forcing to trigger the rise of CO2 levels is correct.” Haas does not say that the Milankovitch forcing triggered the CO2 rise, he says that it warmed a large body of ocean which released CO2. The forcing from the Milankovitch cycle could not have warmed a large body of ocean and forced it to release CO2. It is the trigger not the forcing. There was no forcing that warmed the southern ocean, the Earth just had an energy imbalance caused by the AMOC stopping. @ Tom Curtis 127 We are talking about forcing, the only forcing other then CO2 during the last glaciations was the Milankovitch cycle. I don’t even think it can be called a forcing, it is an energy imbalance caused by the orbit of the Earth redirecting sunlight. The only considerable forcing taking place is the release of CO2. Other GHG are short lived. To be clear, you could have everything taking place during the LGM but without the release of CO2, there really should be no added warming to the system. I know the Shakun paper says 7% of the warming took place before the rise in CO2 but I personal think that with more proxy records the global average temperature should not rise until there is a release of CO2.
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  29. Tom, I believe the things you mention are treated globally when models are not readily available to evaluate them regionally. One of the main points of the OP is that regional differences matter. I agree that the WV should not be exclusively treated globally the way I implied in 116, but I did not mean to exclude other forcings and feedbacks.
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  30. Michael Whittemore @128: 1) Every change in temperature either globally or by latitude band prior to the Holocene (10 kyr) is natural, almost by definition. Certainly the large increases in CO2 levels and the large decreases in albedo over the period 20-10 kyr was not anthropogenic, so of course the increase in temperature from 60-90 north starting 20 kya was natural. As it happens, it was both natural and driven by the Milankovitch cycle. 2) The only forcing in the transition from glacial to interglacial was the Milankovitch Cycle. In addition to that, you had slow feedbacks (CO2 increase, CH4 increase, ice sheet reduction, changes in vegetation patterns, changes in ocean currents) and fast feedbacks (Water Vapour feedback, lapse rate feedback, changes in atmospheric dust content, changes in snow extent, changes in sea ice extent, and changes in cloud cover). The lists are not exhaustive. In order to calculate the fast feedback climate sensitivity, you can treat the changes in the Earth's energy balance due to increased GHG and reduced ice sheets as forcings, but that is merely a convenience for calculation. You should not make the mistake of thinking that they were forcings. 3) Even among slow feedbacks, CO2 or well mixed GHG generally were not the dominant players. By all accounts, the change in albedo from the change in ice sheet extent was a larger player. It is probable that for the first thousand years or so of the transition it was the dominant player, with changes in CO2 concentration not being relevant until after significant warming. Of course, changes in vegetation patterns may also have been significant players as well, with a switch from savannah to rainforest significantly decreasing albedo (although also increasing cloud cover). 4) The Milankovitch cycle did warm a large body of water. It just did it indirectly by shutting down the AMOC rather than directly by increased insolation on the body of water.
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  31. Eric (skeptic) @129, I certainly agree that regional and even seasonal forcings are very important in understanding the transition from glacial to interglacial. In fact, that is one of the two hard lessons from that transition which are not given sufficient attention. The other is that there are without doubt tipping points in the climate system. What that transition shows us is that a seasonally strong regional forcing can under the right circumstances push the entire globe into a new stable state whose mean global temperature differs by several degrees (4-6 C) from the initial stable state. It is probable that had the seasonal regional forcing in the high NH been equally strong globally and throughout the year, the same tipping point would have been crossed, but in centuries rather than millenia. Currently we are applying such a strong global forcing. We know that tipping points exist, but we don't know how strong the push has to be to push us past any given tipping point. Further, we don't know whether there are any regionally specific factors which will amplify the risk of crossing a tipping point as the NH summer insolation amplified the very weak global forcing of the Milankovitch cycle. We are gambling at very high stakes without yet knowing the rules of the game. That, however, is not strictly relevant to this discussion. What is relevant is that the WV feedback would also have been seasonal and regional in response to the seasonal and regionally strong Milankovitch forcing. As a result it would have amplified that forcing significantly even though the global Milankovitch forcing (and hence WV feedback) was weak. However, that is not particularly relevant to the debate with William Haas. That focuses on two questions: 1) Does the WV feedback contribute more to the change in the total greenhouse effect in W/m^2? To which the answer is yes! 2) Is the WV feedback sufficient without slow feedbacks to account for the 4-6 degree increase in Mean Global Temperatures from glacial to interglacial? Haas appears to say yes to this, but the answer is clearly no! In discussing these questions, we can treat the WV feedback as global, thus gaining simplicity for our treatment, without loosing clarity.
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  32. I'm not sure what William Haas' position is exactly. It seems he would like to shift the "control knob" role to water vapor. That would be hard to square with pretty much everything known about paleoclimate. In addition, it wouldn't exactly make anything easier, as burning fossil fuels releases massive quantities of water vapor along with the CO2.
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  33. @Tom Curtis It would seem I have to make myself clear, I was talking about the Milankovitch cycle affection the 30-60N region and that I don’t think the cooling you pointed out was caused by it. I also disagree that what Hass said is correct. The Milankovitch cycle did not warm a body of ocean that released CO2, there was no forcing involved that warmed the southern ocean which caused the release of CO2. The Milankovitch cycle was a trigger, a very small one at that. I stand by my point regarding CO2 being the only real forcing occurring. The orbit change and the stop of the AMOC did not add in substantial forcing, it really only caused an energy imbalance that would have corrected itself over time. I think Haas is wrong when saying H2O played any major part in a global forcing. H2O did not add anything to the energy system. I know that when there was a build up of warm ocean water in the south due to the AMOC stopping, water vapor would have played a part in the warming process, which eventually released CO2, but regarding the actual forcing that caused an actual global warming, CO2 is the only major added forcing. I understand that everything you have said is correct Tom, I just don’t give Haas the benefit of the doubt when it comes to his misguided comments.
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  34. 87 Tom Curtis Again thanks for yours and everyone elses efforts. What is really missing in this article is a plot of the Milankovitch forcing during the time in question in high enough resolution to make any sense. From the best that I could find, change in solar irradiance caused by orbital cycling peaked in the north roughly a thousand years before the period that we are talking about and was decreasing during this period. There are those who argue that Milankovitch forcing is not strong enough to do much of anything but I am just going to assume that Milankovitch cycling started the whole thing. Clearly the Milankovitch could have only triggered the climate change but not sustain it because the Milankovitch forcing in the north was decreaseing during the entire 2,500 years but temperatures were increasing. I understand that the orbital cycling did not change the total earth irradiance, just the balance so that Artic summers would have recieved a little more sun light and hence a better oportunity to melt some ice. During this 2.500 year period, according to the article, CO2 levels did not rise but temperatures did rise. According to green house gas theory models, if the global average temperature rose than water vapor average values rose. Water vapor is the green house gas that causes the majoriety of the green house gas heat trapping effect. Therefore during this time an increase in water vapor content would have increased heat retention in the atmosphere which would have caused temperatures to rise even further. If this did not happen then the green house gas effect models that are used today to predict global warming must be incorrect. It is not clear that this water vapor effect had any real effect on climate change. I think that what allowed climate change during this period to be triggered were varations in ocean currents. I think that albedo change and unknowns had some effect but it was ocean currents that caused the the climate to trigger. During the age of the dinasours North and South America were not connected so world ocean currents were much different especially around the equator. It was after North and South America became connected that current ice age cycles began to ocour. The oceans of the world act as a huge non-linear thermal capacitor. We could be looking at some sort of natural frequency of the oceans. Most of the analysis of this data that I have seen does not get much further then simple correlation analysis. I think that work should be done to try to detect phemonenon such as orbital cycles and to compute climate change transfer functions. Who knows what phenomena may be detectable if the appropriate analysis is performed. I do not think that transfer function analysis will be of any value to predict the weather but climate change is a whole different game. No I do not think that water vapor changes alone can cause anything beyond changes in local weather. The climate is not going to spontaneously change because of a chance riae in relative humidity. I do not believe that our climate is inhaently unstable because of green house gas positive feedback and I assume that it has not been modeled as such.
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  35. I see another post of Haas trying to suggest a little bit of warming in the north is going to cause water vapour to cover the Earth and raise global temperatures. But I guess Tom will just say he is “correct” and this warming seen in the north is part of a “global average”. The simple fact is, water vapour feedback is a local event and the warming only happened in the north, it was not a global forcing at all. Yet lets look at Haas most resent comment below. “if the global average temperature rose than water vapour average values rose […] Therefore during this time an increase in water vapour content would have increased heat retention in the atmosphere” Another fine example of Haas trying to suggest that the warming before the seesaw event was global, and it was caused by water vapour. I think skeptical science is going to have to edit some of their myths if he is “correct” again.
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  36. @ William Haas #134: The following quote from your post: "What is really missing in this article is a plot of the Milankovitch forcing during the time in question in high enough resolution to make any sense. From the best that I could find, change in solar irradiance caused by orbital cycling peaked in the north roughly a thousand years before the period that we are talking about and was decreasing during this period." Indicates that you did not actually read the article, or if you did, you completely missed the very clear, very simple chart of Milankovitch forcing and solar insolation for 65°N and 65°S from 22 kyr to 8kyr. It's figure 5f in the paper. It very clearly and obviously shows that insolation started from a N. Hemisphere minimum at about 22kyr, and steadily, continuously, and reasonably steeply increased from a value about 2.5% lower than the present insolation at the same latitude to a value nearly 10% greater than the present day at about 12 kyr. Here is another diagram from Berger and Loutre, 1991, via RealClimate... Insolation vs d18O the lowest part of the figure is the NH and SH insolation curve for the time period in question... Stop assuming, and read the paper(s).
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  37. Here is the image itself:
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  38. danielc @136, here is figure 3 from Shakun et al, 2012: The important features for this discussion are the atmospheric CO2 concentration (c), the global temperature (d), and the NH and SH insolation (f). The original caption reads:
    "Figure 3 | Global temperature and climate forcings. a, Relative sea level (diamonds). b, Northern Hemisphere ice-sheet area (line) derived from summing the extents of the Laurentide, Cordilleran and Scandinavian (R. Gyllencreutz and J. Mangerud, personal communication) ice sheets through time. c, Atmospheric CO2 concentration. d, Global proxy temperature stack. e, Modelled global temperature stacks from the ALL (blue), CO2 (red) and ORB (green) simulations. Dashed lines show global mean temperatures in the simulations, using sea surface temperatures over ocean and surface air temperatures over land. f, Insolation forcing for latitudes 65o N (purple) and 65o S (orange) at the local summer solstice, and global mean annual insolation (dashed black). Error bars, 1s"
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  39. William Haas @134: 1) As can be seen above, NH summer insolation was increasing from at least 22 kyr and continued to do so until 12 kyr. That means it was increasing over the period of 20-18.5 kyr we are discussing, as pointed out by Daniel C. 2) Global temperatures rose that period by between 0.2 (Shakun et al) degrees C and 0.4 degrees C (based on scaling the Shakun et al difference to other estimates of the total temperature difference). That is equivalent to year to year variability in temperatures resulting from large tropical volcanoes or strong ENSO events. If such a globally averaged temperature variation is sufficient to trigger so large a change in temperatures over millenium, then the Earth's temperatures would be far more unstable than they are. It is the strong regional and seasonal forcing at a particular location given a particular geographic configuration which is significant in triggering the glacial to interglacial transition - not the weak global effect from 20 kyr to 18.5 kyr. It should also be noted that that 0.2-0.4 degree C increase in temperature includes the full effect of any rapid feedbacks, including the WV feedback.
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  40. I would note in passing that Mr. Haas has yet to fully articulate his position WRT the OP and has yet to attempt an answer to questions put to him over the past several days (other than to restate in muddled fashion his understandings...which run counter to the science). Given the elapsed time and his continued posting in this thread (which reveal an unchanged level of understanding of the science not in accord at all with the science), the inescapable conclusion one must draw is that we must move beyond the possibility of Mr. Haas simply misunderstanding the OP to the point of Mr. Haas prosecuting an agenda of dissembling.
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  41. I again appoligize for my late responses. I will try to answer the posts that involve my comments but I will do that in numerical order. 88 Michael Whitmore Relatively long term average amounts of H2O in the atmosphere scales with increases in temperature. According to green house gas theory, the increase in water vapor traps more heat which also adds to warming. I am sure that the effect has a stable step response or the earth would have burned up ages ago since we are a water planet. H2O levels react to local temperatures in the short term while natural CO2 levels do not. Natural CO2 levels appear to scale primarily with the heating of large volumes of sea water. During the time period that I have been talking about, acording to the article, global temperatures increased but CO2 did not and according to the article, the situation was triggered by Milankovitch cycles. Levels of H2O always vary in the atmosphere but it is the average values that we are talking about that effect climate. Over most of the earth H2O that leaves the atmosphere is quickly replaced except for water starved locations to include deserts and very cold areas of which there were probably more water starved areas of the earth at the time I am refering to than there are now. Prevailing winds also effect the situation. I do not know what actually caused the warming in the far north. Right now I am talking only the 2,500 year period after the LGM. I was initially wrong about Milankovitch forcing during this period. I apparently had the wrong data and I apologize for that. Looking at the data, it may be that this whole period was really part of the normal ice age varation in climate and that the triggering did not occour until the end of this period. Milankovitch forcing was at a low value and not a high value just before this period. Of course if the northern summers were cooler than usual than southern winters were warmer than ususl and vis versa if we consider Milankovitch forcing to be significant. I think that the seesaw effects are primarily caused by ocean currents. The ocean is a domanant player in all of this. The oceans hold a lot more heat than the atmosphere and they hols it a lot longer. The Oceans work as a giant, nonlinear capacitors. By means of convection ceans can be soaking up heat and or be adding it to the atmosphere and it may not be obvious which is occouring where and at what time. I think that the earth in contact to the ocean's bottom may also add to the oceans's heat capacity. That is why I think that some transfer function analysis may help to increase our understanding of what is really going on. You made a comment about CO2. Considerations of its effects are a primary topic here but a full disscussion is I think beyond the scope of this thread.
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  42. I see William has replied to a "comment" of mine, the first "one" I sent him. This is because he cant seem to be able to read all the comments put to him and formulate a response. I for one am not prepared to deal with someone with that kind of intellect. But just so we can all see how he has twisted his stance, his first comment on this thread stated "To enhance or continue global warming is atmospheric CO2 really necessary to explain it?" Link to comment. Williams mentions nothing about LGM, he is simply stating that CO2 should not be needed to explain the global warming which is seen during the end of the last glaciation. This is the bases of the study by Shakun, that it was not a temperature rise that caused a global forcing, but increased concentrations of CO2 that did it. Williams second comment in this thread clearly states that CO2 is not needed to explain any of the warming by saying "It is really the increase in sun light that triggered the whole thing. As more water vapor enters the atmosphere the warming continues [...] I do not understand how CO2 is needed to explain what happened Link to comment. Even when Tom Curtis showed the science and pointed out that " [H2O] was even less able to trigger a self fueled runaway effect as [William was] suggesting" Link to comment. William just twisted his stance by saying "It seems to me that H2O levels alone are enough to explain the GHE effect part of the triggering the end of the ice age." Link to comment. This is the point when William changed his stance from CO2 had nothing to do with warming during the last glaciation, to CO2 had nothing to do with warming during the LGM. Every comment after this time is William trying to explain that CO2 did not cause the warming during the LGM period, which we all know is true. Even in his fourth comment after the one stated above, you can see how he has twisted his stance but continues to make it sound like he has not, "CO2 may have played an important part but I do not see any evidence that it had to be CO2 that caused the ice age to end." Link to comment Of cause by this time he has seen where he was wrong and understands that his stance has changed, so he states "Where am I going with all of this? No, nothing sinister. So far we are talking about just the first 2,500 years" Link to comment My first comment to William I tried to explain that the warming seen in the north after the CO2 rise could not have been caused by H20 by saying "Due to the north's temperature increase lagging CO2 and the fact that the (AMOC) was not causing any warming up there, H2O can only really be seen as a regional short term positive feedback that could not have caused a global warming as is seen." Link to comment. Williams replay to this, "Right now I am talking only the 2,500 year period after the LGM [...] You made a comment about CO2. Considerations of its effects are a primary topic here but a full disscussion is I think beyond the scope of this thread." Link to comment. Personally I think this is the most ridicules comment so far from Williams, this thread is completely about CO2, it has absolutely nothing to do with H2O I can ensure that much.
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  43. I again apoligize for the delay in my responses. Yes I am reading all of the posts but I am responding to applicable posts in numerical order. 98 Michael Whittemore I am talking about the 2,500 years following the LGM. According to the article, CO2 did not increase during this time. I am assuming that the article is correct. During this time 7% of the warmup occoured so on a global basis temperatures increased. I am again assuming that the article is correct. I do not care what happened to specific local areas. It does not matter. If global average temperatures increased then global average water vapor levels increased. According to green house gas theory, if there is more green house gas in the atmosphere more heat will be trapped and hence temperatures will increase even further. All of this increase happened within the 7% warmup. Green house gasses did not account for more heating than was observed.
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  44. William Haas @143, the initial water vapour feedback during the glacial-interglacial transition was strictly regional in nature, and confined to the upper latitudes of the Northern Hemisphere. From 20 kyr, to the "onset of the seesaw" (19 kyr, see fig 4) absolute humidity would have risen with increasing temperatures north of 60 degrees North, but fallen from 30 to 60 degrees North (a much larger area), and remained fairly constant elsewhere. With the onset of the seesaw, absolute humidity would have risen with temperature in the tropics and Southern Hemisphere, but fallen in the extra-tropical Northern Hemisphere. The net effect is that mean global surface temperature did not rise until 18.5 kyr (see graph d in my 138). That is 1.5 thousand years after the onset of Arctic warming, and 500 years after the onset of the seesaw. Global mean water vapour feedback probably tracked temperatures fairly closely, but may have risen or fallen slightly in that period. Given the distribution of the worlds oceans, and the relative importance of the water vapour feedback in the tropics and the poles, it is more probable that it fell in the first 1.5 kya of the glacial/interglacial transition than that it rose. That is irrelevant because it was strong regionally, reinforcing the high summer insolation in the NH and triggering the transition. Therefore it is acceptable to treat the increased NH water vapour feedback as a globally averaged increase as a first approximation - but only if you recognize that it is an approximation, not a literal description. There is no evidence that you do recognize it is an approximation, and if you treat it as a literal reality it will lead you to erroneous conclusions.
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  45. Let’s just try and show how lost Williams truly is, as you can see in his 143 comment it would seem he is talking about “2,500 years following the LGM”. From figure 1 above the LGM is during 22-19 (kry), so this means that Williams must be talking about 19-16.5 (kry)? He then says “During this time 7% of the warm up occurred” but the paper says 7% of the warming happened during 22-17.5(kry) which is 4500 years? But clearly if he thinks he is talking about the 7% increase we must assume he means the time 22-17.5 (kry). The facts are when CO2 concentrations increased, the whole planet warmed. During the initial 7% warming, there was no added CO2 so the warming was simply a regional energy imbalance. The most senile thing about replying to comments in a numerical order, is you know you are wrong but continue to rant.
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  46. 141, William,
    I think that the seesaw effects are primarily caused by ocean currents. The ocean is a domanant player in all of this. ... The Oceans work as a giant, nonlinear capacitors.
    Any paragraph that begins with "I think" is a huge red flag to me, especially when the tone quickly transitions from "I think" to speaking as if your conjecture is absolute fact. Please note that your entire following statement is pure conjecture, completely unsupported by any evidence whatsoever. Even its foundation is a mere thought experiment of the overly simplistic "it seems to me" variety. You presume that because oceans are large and mysterious, and water has a high heat capacity, that therefore oceans govern climate. This further allows you in all probability to dismiss the importance of known, quantifiable factors like greenhouse gases. It is akin to stone age man believing that the sun is a god, because it is high in the sky, and hot, and man cannot touch it. Please stick to science and supportable theories which are based on evidence. Conjecture, especially when based only on "common sense," and especially when presented as firm belief or even fact, is of utterly no value whatsoever.
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  47. Note also that is has to backed by some arithmetic - warming of surface needs to be accounted for in joules leaving ocean.
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  48. @ Sphaerica 146 I would have to agree, the paper by Clark et al. 2012 explains the H2O/CO2 aspect of the warming seen in the last glaciation.
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  49. The next comments in a numerical order that William has to answer is 100# which asks if William understands that "surely the [temperature rise of] 7% proposed by Shakun et al for the initial, pre CO2 warming includes any feedback due to water vapour". Only if William had the ability to read a couple of comments ahead.
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  50. The stopping of the AMOC would have caused considerable warming, but very little of its effects would have been able to cause a global forcing as CO2 does. Without a prolonged global forcing from added CO2, the AMOC would have come back on after cooling of the north had reduced melting. This would have simply had caused the Earth to go back into the LGM as short lived GHG dissipated. Its seems so logical to see CO2 is the control knob of climate.
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