|Oct21-09, 06:30 AM||#1|
The methane mystery
I have been searching internet for a legitimate source for this graph (I made one like that myself orginally):
But this one was found by Skyhunter, so there can be little doubt about it's legimaticy.
It shows the comparison of the delta 18O records of the ice cores, which is supposed to be a proxy for temperature. Note that the red greenland graph was here first, followed later by the Antarctic results.
Although it puzzled the researchers, it was nevertheless accepted that the different hemispheres seemed to have undergo big temperature differences of about 10 degrees C even within a decade or so, looking at the onset of the warming after the last glacial maximum (19-18 thusand years ago versus 14.5 thousand years ago) and the Bolling Allerod (~14,500-12,700 years ago) - Younger Dryas Oscilations (~12,700-11,600 years ago). See for instance the Two-Mile-Time-Machine of Richard Alley.
But it had to be temperature, right? because the Methane concentrations correlated very closely with the Greenland isotopes:
One could also be puzzled already, why the atmospheric (and hence global) signal of the CO2 concentration corrolated (lagged) the local Antarctic Ice core isotopes while the atmospheric (and hence global) signal of the CH4 concentration corrolated with the local Greenland Isotopes. A warming mystery or a methane mystery?
But then suddenly there was this publication as introduced by Sylas:
Clark 2009 Ice sheet retreat and sea level rise during the last deglaciation, PAGES News, Vol.17, No 2, June 2009
which shows that the glacial retreat in the Nothern Hemisphere followed the warming schedule of the southern hemisphere. Apart from that I was attempting to demonstrate here that something was wrong with the warming assumptions of the Northern Hemisphere.
So what is the real story of the warming and the story of the CH4 concentrations?
|Oct21-09, 01:29 PM||#2|
Anyway, of course, when I suggested, backed by substantial evidence that the northern hemisphere warming was much earlier than the isotopes in the greenland Ice cores (as well as the isotopers in several other proxies - speleothems, laminated lake sediments, etc), we had an interesting discussion about that here; which is good of course, since counter-intuitive conclusions like that better have to be backed up by convincing evidence. But the bottom line seems to be that other evidence, except for the isotopes, do not support the late post glacial warming as shown in the ice cores. A s said it indicates a much earlier warming.
I also made a few posts in this thread, like here and here and here that there were similar considerations for the Younger Dryas, the 'isotopic cold' - not being supported by other geological records.
Therefore, I have proposed here that the isotopes in Greenland have something else to tell. They registrate most dominantly the "cloud temperature", which is actually known as 'dew point', a value that is directly related to moist - arid changes. This is fully supported by the strong correlation of snow/ice accumulation rates and (however, not yet demonstrated) the deuterium excess records.
Therefore, overlooking all the factors, it could be argued that the Greenland Isotopes are not a major indication of temperature, but instead it appears to registrate aridity and perhaps changing seasonality of precipitation.
However, as said, the records of methane concentrations in the atmosphere correlate closely with the Greenland Isotopes. But if that is not temperature, then the atmospheric methane concentration changes are not evidence of greenhouse effect during the last glacial transition.
|Oct21-09, 07:12 PM||#4|
The methane mystery
Ruddiman wrote a paper in 2003 (sorry no link), where he presented the concentration of methane over the past 350,000 years. Along with this, the July insolation at 30 degree North was presented on the same graph with scales adjusted. The peaks and valleys line up reasonably well over this period. About 15 peaks and 15 valleys, with only 1 valley missing the mark over that period.
He also presents a graph of Methane over the past 15,000 years. There is a pronounced dip around 13000 to 11000 year BP. It's labeled "YD" presumably for the Younger Dryas period.
In the text, he mentions the orbital forced monsoon theory about Methane. Not sure how the Younger Dryas may have impacted the monsoons, but presumably they dried up during the time.
So, I take it that a leading theory for methane is that it follows the monsoons. In other words, methane levels are influenced by the amount of precipitation which in turn control the amount of swampy land that is cooking up methane.
Of course, according to Ruddiman, this was until humans started to grow rice 5000 years ago at which time methane levels started to rise from 600 ppb.
|Oct21-09, 07:24 PM||#5|
Also, understand that while methane levels were relatively stable from 1998 to 2006, they increased in 2007 and 2008.
It's also not uniformly distributed around the earth:
|Oct21-09, 10:47 PM||#6|
Blog Entries: 9
Hi all... I'm back from a brief holiday.
This is an honest question. I'd really like to know. So far you are the only person I know of who suggests this as an alternative to the normal deuterium temperature; but that's just an indication of what I've heard on the subject. I've asked about this several times; you've said it's not a private notion but I still have no idea who else proposes it or whether there's any actual work investigating such a notion by working researchers.
If you are proposing this as an argument yourself, then it would be worth taking a bit of time to put together a clear exposition of this proposal for the Independent Research Forum. It would be an interesting exercise to look at it more thoroughly; and if it isn't actually part of any existing published research then that would be the place to discuss it.
If the temperature differences involved in the ice ages are smaller than what is described by scientists working on the matter, that would have implications for sensitivity estimates; but the greenhouse effect from CO2 and CH4 is determined by the concentrations of the gases, not by the temperature.
As I understand it, there IS significant uncertainty about all the processes by which CH4 and CO2 concentrations change. The greenhouse effect of these gases, however, is pretty straightforward.
Cheers -- sylas
|Oct22-09, 06:00 AM||#7|
But anyhow, closest that anyone came to the notion that accumulating isotopes on ice sheets may not always represent average global temperatures accurately, is Michel Helsen in his PhD thesis, which makes it not a private notion. Much work is done on Antarctica this way, but mind that it is not comparable with Greenland because of the much lower temperatures, where the difference between specific humidity and relative/absolute humidity diminishes.
We see methane fluctating between some 450 and 700 ppbv (0.47-0.7 ppm) during the Bolling-Allerod-Younger Dryas-Preboreal oscilations. When we run that in Modtran with CO2 on a mid glacial transit value (230 ppm in between 180 and 280 ppm) then we are looking at outradiation values of 291.109 and 290.827 W/m2, a variation of a mere 0.3 W/m2, compare that to the 3.7 W/m2 for doubling CO2 and the associated temperature difference allegdly of a few degrees. Yet, if these CH4 spikes are associated with the isotopes spikes, allegdly in the 10-15 degrees celsius range, then I think it is legitimate to raise an eyebrow and do some independent thinking.
|Oct23-09, 01:56 PM||#8|
Blog Entries: 9
The details of what you are proposing are still not clear to me. It seems to be rather different to anything in the literature; well beyond the conventional scientific work on all the open questions of calibrating and refining the estimates of temperature from isotope ratios -- such as in the thesis you have cited, or other literature that has been mentioned.
There are of course various well known issues with calibration of the deuterium temperature relation, and this is still an open research question. Ongoing work continues to recognize the large swings in isotope ratios in ice cores as resulting from large swings in temperature; but the calibration of deuterium temperature can vary from location to location and changes over time.
There's negligible association with "global warming" in the modern era. I am looking at this paleoclimate topic as accurately and fairly as I possibly can on its own merits and nothing else. You can address my posts on their own merits as well, please. I think we can all stick to the paleoclimate topic and data for this thread, without prejudging on the basis of other periods. Agreed?
The link to Kuhn is baffling. If you are not proposing some revolutionary new Kuhnian "paradigm shift" for paleoclimate reconstruction from ice core data, then Kuhn is just a distraction. If you are speaking of a paradigm shift in the interpretation of deuterium temperature, then you are proposing new theory development, and something quite different from any of the references given. There's nothing wrong with that, of course, but if it is different from what is in the references, then it belongs in the independent research subforum, please.
The work of mainstream scientists like Mike Helsen, and others before him, has been cited in the forum previously. See my msg #3 of thread "climate scepticism and ice cores", which lists some references on the matter of temperature inferences from icecores. I singled out this one:
But before you do that, I think you need to follow the conventional thinking better. CH4 is generally considered to be a relatively minor contribution to the temperature changes. It's pretty standard in this whole field that the CH4 spike is driven by rising temperatures, and that the associated methane greenhouse effect works as a positive feedback, accounting for a only small part of the whole temperature rise. Your basis for thinking some independent thinking is needed at all appears to be a simple misunderstanding of the thinking already being done in paleoclimatology.
You are also giving unusual high values for the temperature change! Deuterium temperature relations tend to be in the range of roughly 0.5 to 0.9 ‰ C-1. This is seen in Helsen's thesis, and in the review article I've cited. The jump at the end of the Younger Dryas in your cited graph is from about -41 to -37 ‰ in the GRIP δ18O value, which is around 5 to 8 degrees. Note that this jump shows up much better in the Northern Hemisphere; Antarctic cores suggest a smaller shift in the South. So the global temperature change is smaller again. In my view there is significant uncertainty in the actual temperature difference to the last glacial maximum. The differences vary by region and by season; but 10 to 15 degrees is far too high for a global temperature change at in these times.
For what it is worth, a direct answer to your question on the greenhouse forcing from a conventional perspective is available in
In Joos and Spahni, the methane forcing contribution to the end of the Younger Dryas is a bit less than 0.2 W/m2. I've done a rough calculation myself using the formulae for estimating forcing from the IPCC third assessment report (equations in table 6.2, section 6.3.5) and obtained 0.17; using 450 to 700 ppb CH4 and 235 to 260 ppb N2O (which has a small impact on the CH4 forcing due to overlap in the absorption bands).
There's also an additional contribution from N2O of about 0.09. The CO2 change after the Younger Dryas is about 240 to 260, for another 0.43 W/m2 or so. These numbers also fit well with figure 1 of Joos and Spahni (2008). Hence the greenhouse forcing contribution to the end of the Younger Dryas should be roughly 0.7 W/m2, by these standard estimates. Sensitivity is around 0.5 to 1.2 degrees per W/m2, so even with high sensitivity this forcing accounts for less than one degree. This all pretty standard stuff; conventionally the warming at the end of the Younger Dryas is not thought to be driven by greenhouse effects.
The conventional existence of a greenhouse effect and the normal calculations for estimating greenhouse forcings remain entirely consistent with all this data, of course. But they are evidently not the primary cause of the temperature changes we are looking at.
Felicitations -- Sylas
|Oct23-09, 02:21 PM||#9|
Sylas, before looking at any application of isotope variation and before going into the complications of all research anywhere, it may help that we have a clear understanding about the meteorological / Hydorgrafical processes as described in this thread. I know that I'm a lousy explainer so that may not be the case.
Can we agree that isotopes predominantly indicate "cloud temperature" and that cloud temperature - dewpoint - is a matter of aridity?
With that in mind, we could run a detailed comparising of the two hypotheses for isotopes in the ice cores, temperature or humidity, checking all the relevant studies. At least that's why I did.
Again, that doesn't look like theory devellopment, the physics for isotopes and aridity for moderate lattitudes has been studied before, no theory devellopment here.
I think that we start talking about theory development on the moment when we would start suppositions about why these sudden large aridity swings occured and whether or not (and how) they could be related to the 100,000 years cycle, then we're talking about real independent research. But that has no meaning as long as the isotope - temperature notion is deeply rooted.
|Oct23-09, 03:16 PM||#10|
Perhaps allow me to illustrate such a research of the relevant studies whether we see temperature variation or moisture variation.
The Younger Dryas is probably the most intensly researched oscilation interval during the last transition and if there is any consensus at all in paleoclimatology, it is that the Younger Dryas was some 10-15 degrees colder at least in the northern hemisphere, than in the following Preboreal period. So why challenge it?
This is one of the most detailed pollen diagrams covering the Younger Dryas, thanks to the annual lamination of the facies and sediment it has been dated very accurately
source: Lücke, A. Brauer A., 2004. Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany). Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 211, Issues 1- 2, 19 August.
The Meerfelder maar is an old crater lake in the Volcanic Eifel in Germany. The Eifel area has been active during the last glacial transition like many other areas. Due to the moist soils, volcanism here is thought to be explosive due to the water explosive evaporating, leaving deep craters, which fill up with water, the "maars". There are dozen of them, containing a marvellous record of geologic history in their muddy sediments.
In those static waters sediments accumulate slowly. In dry periods, wind- blown dust settles on the bottom (facies). In spring there usually a short bloom period of algae and other micro-organisms (diatoms), the remains of which show a tiny white layer on the bottom. But on top of that there are pollen in summer, which don’t decay for some reason. So you get separate layers accumulating for each season and as long as nothing disturbs this annual “stratification”, you can count each individual year just like the ice
cores. Here is such a sediment core with the annual layers (varves)
So if you start analysing this diagram with the preprogrammed notion that the Younger Dryas was cold, then you find evidence (right side) in the total pollen count which reduced strongly during the Younger Dryas and also the decline of the trees in favor of grasses (graminineae) could suggest the same.
However if you looked at the polen variation without knowing the period, the outcome of the reseach may be different. Why would the warm prefering water flora (Potamogeton - pondweed, Botrychium - fern and Pediastrum -algeae ) florish during the cold Younger Dryas?
We also see the moderate winter hardy great burnet (Sanguisorba officinalis), which we have already seen in the guts of the Yukagir Mammoth in some other thread and we also see the genus Helianthemum appearing in the Younger Dryas and disappearing afterwards. But this genus is generally confined to arid/warmer conditions mainly around the mediterrain but also in Germany nowadays. Coming to think of it, the pollen cocktail represents the meadows that we still see in the same area today. Also what we don't see are typical species abundant in the arctic, like for instance the Crowberry (Empetrum) or the name giving dryas (Dryas octopetala) for the period.
Moreover, steppes, grassland prefers aridness and hence the decline of trees in favor of grasses and the decline of pollen is also consistent with aridness.
So it has all the likes that the Meerfelder maar biotope change during the Younger Dryas was all about aridity not as much as temperature.
|Oct23-09, 05:26 PM||#11|
Aridity and temperature; they do tend to be linked.
Cold tends to be dry, warm tends to be moist.
So, this is why methane rises as does moisture levels which create the swamps for gas production.
|Oct24-09, 06:00 AM||#12|
Please check the global forum guidelines:
"It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion. Personal theories/Independent Research may be submitted to our Independent Research Forum, provided they meet our Independent Research Guidelines; Personal theories posted elsewhere will be deleted."
This is not the place to develop new ideas out of existing data. The goal of PF is to help students learn the current status of the different fields of science, as practiced by the scientific community.
|Similar Threads for: The methane mystery|
|Methane-air combustion||Biology, Chemistry & Other Homework||10|
|methane, bonding, and more...||Biology, Chemistry & Other Homework||5|
|Energy from methane||Chemistry||3|
|Methane Everywhere (I Told You All!)||General Astronomy||24|