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Eric (skeptic) at 23:19 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
les, my advice to poptech is Choose One (objective or subjective). I have always had an objectivist philosophy (although not perfectly matched to Randianism), so when I see a probability distribution I immediately look around for the data it was based on. Often there is literally none. As for your policy argument, we are not facing unknowns like one or more typhoid Marys or a human-based decision to go to war. It is simply a complex natural process with some true unknowables like intergalactic cosmic ray flux, future volcanic activity, future solar activity (known to some extent), etc. A lot of these are ambiguous or more likely to cool, so not really worth debating. Everything else is knowable. There is no reason to apply subjectivity to the issue of sensitivity, just better models, validated against real world measurements. The bottom line is that 5C warming (or choose your favorite number) has a zero or a 100% probability of happening within time X (choose 100 years but not 1000), under specific conditions such as BAU. That statement contains no room for any subjectivity other than BAU being made as a human choice which is really only a marginal issue. -
mspelto at 23:18 PM on 4 March 2011Icing the Medieval Warm Period
There are a few advancing glaciers, but most of the advances are quite limited and hence not overrunning developed forest vegetation. The evidence uncovered here is pretty systematic for the time periods noted in Table 1. The difference between a glacier advancing and disappearing like Helm Glacier, one of the sample sites is vast.Moderator Response: [DB] Thanks, Mauri! -
williambaskerville at 22:49 PM on 4 March 2011Icing the Medieval Warm Period
Hi, I don't think this is a argument against the MWP. Don't we actually have increasing glaciers in Norway, New Zealand and the Karakorum? Don't we have regions in the world, not getting warmer? I am writing about this on my post "Nicht alle Gletscher schrumpf(t)en" (Not all glaciers we/a-re melting) http://tinyurl.com/64kmfuj If you want to read more, take a look on my German blog: http://mittelalterlichewarmperiode.blogspot.com Feel free to post comments!! Best Willam of Baskerville Ps. I've made interviews on this topic - MWP - with scientists like Dr. Heinz Wanner, Dr. Ulf Büntgen, Frederic Ljungqvist and others.Moderator Response: [DB] No one is suggesting that the warming of the globe will be a uniform or linear process. But it is indeed a global process, as you can see here:
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robert way at 22:44 PM on 4 March 2011Icing the Medieval Warm Period
The LIA in the alps did not end in 1950. That's a complete fallacy and is not supported by the literature at all. You might find one paper where a small portion advanced during that period but the fast majority of glaciers in the alps had their LIA between 1750 and 1850. -
Kevin C at 22:39 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 3
Here's a graph of the 1000 year PDO forcing used to drive the 1000 year simulation in figure 10. I just took the Macdonald and Case data and applied a 19 year moving average.
Comparing this with figure 10, it is now obvious that Spencer's model starts from an initial temperature set by the ΔTo value (off the bottom of the graph in this case) and constantly heads towards towards a temperature set by the equilibrium temperature and the current value of the forcing term.
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Arkadiusz Semczyszak at 22:32 PM on 4 March 2011Icing the Medieval Warm Period
#The Inconvenient Skeptic ... a propos China I would add: Characteristics of cold–warm variation in the Hetao region and its surrounding areas in China during the past 5000 years, Li et al., 2010.: “1450 - 1000 cal yr BP: The climate was relatively warm compare with the temperature of its adjacent periods but less so than the degree of warmth at 5000 cal yr BP. This period corresponded to the Medieval Warm Period.” -
Arkadiusz Semczyszak at 22:20 PM on 4 March 2011Icing the Medieval Warm Period
@Marcus Not so long ago in my TV - Professor L. Thompson - explaining the length of the Maya (more than 5 thousand. years) - his last end, he showed how in the Andean glaciers have advanced so quickly - it now - going back - glaciers reveal - frozen, “of unimpaired quality” plants ... Droughts - in this period of strong cooling (Neo-glacial) - covered most of the two continents of America. The same drought (cooling effect) destroyed the civilizations of the Sahara and Middle East. Stable isotopes of a subfossil Tamarix tree from the Dead Sea region, Israel, and their implications for the Intermediate Bronze Age, Frumkin, 2009.: “The Sedom Tamarix demonstrates a few hundred years of 13 C and 15 N isotopic enrichment, culminating in extremely high δ 13 C and δ 15 N values. Calibration using modern Tamarix stable isotopes in various climatic settings in Israel shows direct relationship between isotopic enrichment and climate deterioration, particularly rainfall decrease.” “This was apparently the most severe long-term historical drought that affected the region in the mid-late Holocene.” Lonie Thompson explained that the Atacama desert in the Quaternary, only once was inhabited by people - during MWA ... During the Roman maximum - period; around Masada was warmer and wetter - growing bushes Tamarix at the point where today it is a desert. Climatic effects on the δ 18 O and δ 13 C of cellulose in the desert tree Tamarix jordanis, Lipp et al., 1996.: “Since the Roman period, RH at Masada decreased by about 17% [!], while the δ 18 O value of local groundwater remained similar to present-day values, suggesting that changing atmospheric circulation has played a role in climate change in the Middle East over the past two millennia.” Polish scientist J. Zasadni, from the Institute of Geological Sciences, Jagiellonian University, who is preparing a doctoral thesis about shifting of glaciers in the Alps - Zillertal, after many years (and very precise) research - argues strongly that: in the days of ancient Rome and later - warming in the Middle Ages - expiring on the late fourteenth century, frequented alpine glaciers coverage certainly considerably smaller than today. LIA in the Alps ended only in 1950 ... Anasazi - “During the Pueblo II period, from 900-1100 CE, these designs were made even more bold, and the Anasazi (Hisatsinom) began to build kivas, or communal rooms for ceremonial purposes in their villages. Their population increased, and during this period small Anasazi villages began to spread throughout the southwest.” “During the Pueblo III period from 1100-1300 CE, the Anasazi (Hisatsinom) began to build the cliff dwellings for which they are most well-known. Many buildings in these villages under the cliffs were several stories tall.” „For unknown reasons, near the end of this period the western Anasazi (Hisatsinom) sites were completely abandoned, while the eastern sites continued to flourish and expand.” ... circa 1270-1300 - the beginning of the LIA in America ... -
RSVP at 22:05 PM on 4 March 2011Icing the Medieval Warm Period
"It's cold out!"... and I am suppose to believe it should be colder on average, and that the world would be better off if this were the case. As long as the price of fossil fuels is rising faster than the temperature, it's hard to imagine how winters of the future are going to be more confortable. -
les at 22:03 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
83 Eric objective/subjective?!?! now you sound like Poppy Tech!! ;) ;) < big wink > sure, though. of course for scientists that's fine. Governments rarely have the luxury - as I pointed out to someone: armies have to be maintained without knowing the exact probability of war or invasion, hospitals and school have to be build with out knowing exactly the population in 20 years, vaccines have to be stockpiled without knowing the exact epidemiology or the next flu outbreak etc. etc. Power security has to be maintained, the environmental resources managed, healthy environment preserved (or restored)... better to understand the proper meaning of likelihood rather than stuffing it in quotes and pretending it's meaningless. -
Kevin C at 21:50 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 3
APSmith@11: That's a beautifully clear analysis and probably the definitive one, at least for anyone who can (still) solve a differential equation. It leaves me banging my head asking 'why didn't I see that straight away'? To many computers are bad for the brain. We've forgotten the power of algebra! -
The Inconvenient Skeptic at 21:23 PM on 4 March 2011Icing the Medieval Warm Period
Here are some paleoclimate studies from China. http://epic.awi.de/Publications/And2005g.pdf http://www.sciencedirect.com/science?_ob=ArticleURL... http://hol.sagepub.com/cgi/content/abstract/13/6/933 ftp://ftp.ncdc.noaa.gov/pub/data/paleo/historical/china/china_winter_temp.txt None of these are records from Chinese history, but nodern (non tree-ring) reconstructions. -
invicta at 21:12 PM on 4 March 2011Icing the Medieval Warm Period
invicta It occurs to me that an area of the world that has a well documented dynastic cycle for at least two thousand years is China. I have never seen any references to any records from this area being used to support or deny claims for the MWP or similar globa v regional discussions. Are there people with knowledge of the cycles of dynastic rise and decline which do seem to have at least some links to natural disasters (famine Drought etc)? I have no specialist knowledge myself but would be fascinated to see some discussion of the subject in the appropriate place -
Gilles at 20:18 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
sorry for some misprints and disappearing signs. You should read : e : you're wrong, if you take a random gaussian distribution of the "f" amplication factor, with an average value f0, the average value of the "1/1-f" (and hence sensitivity) factor will be larger than the 1/(1-f0)) This is a high bias. and If tau is small (with respect to the characteristic timescale for S(t)), T(t) follows closely S. F(t). -
Tom Curtis at 20:10 PM on 4 March 2011Putting a new finger on climate change
Philippe Chantreau @11 With regard to C14 and the ocean: yes, you are correct. The ocean contains much more CO2 than does the atmosphere, but in equilibrium, an equal number of CO2 molecules flow each way at the surface. That means residence times in the ocean are much larger than residence times in the atmosphere. So for a given molecule in the ocean, it is probably a long time since it was in the atmosphere, and hence had a chance to form with a C14 atom. In contrast, a molecule in the atmosphere has (obviously) been very recently in the atmosphere, and has therefore a higher chance of having formed with a C14 atom. (I'm not sure that this is clear either, but I'm not sure I can make it clearer in a short space.) Regarding the C13/C12, you are tecnically correct, but I'm not sure your phrasing avoids any likely misunderstanding. -
Arkadiusz Semczyszak at 20:05 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 2
@Shoyemore As quoted by you (perfectly known to me), Mike Lockwood's paper, is also an important sentence: "... the current [solar] grand maximum has already lasted for an unusually long time ..." Lockwood (in this paper) will not close a road to prove that the Sun has a more significant impact on the climate than we thought previously. However, imposes a condition: “Thus advocates of the huge solar amplification (positive feedback) factor [that is, for example, I] must also explain why the feedback to greenhouse forcing is at the same time negative. The issue is not ‘can the GMAST curve be fitted with combinations of solar variations’—with enough free variables the answer will be ‘yes’ (but such fits would have very low or no statistical significance): the challenge for attempts to show such a phenomenon could be real is to give credible explanations of feedback amplifications of more than 13 within the constraints set by observations and their uncertainties (and yet still give negative feedbacks to GHG forcings).” As cited above, this paper presents but too little potential direct and indirect influences of the Sun, which completes Lockwood (as a co-author) in a later work: Solar Influences on Climate, L.J. Gray, J. Beer, M. Geller, J.D. Haigh, M. Lockwood, K. Matthes ,U. Cubasch, D. Fleitmann, G. Harrison, L. Hood, J. Luterbacher, G. A. Meehl, D. Shindell, B. van Geel, W. White (Reviews in Geophysics, 2010). In this work - with many "types" of direct and indirect sun (especially the impact of changes in solar UV - for example, ozone, ozone in the stratosphere, water vapor, etc..) is a record that they require “urgent” research - because we know about them too enough - to assess (even initially) the actual impact on climate. -
scaddenp at 19:33 PM on 4 March 2011Putting a new finger on climate change
There is continued fractionation going on so that different sources having different degrees of C13 depletion. -
Gilles at 19:17 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
e : your wrong, if you take a random gaussian distribution of the "f" amplication factor, with an average value, the average value of the "1/1-f" (and hence sensitivity) factor will be larger than the 1/(1- )) This is a high bias. I don't want to prove that climate models and measurements are wrong. I'm just saying that the kind of line you adopt (reasoning on a large sample of different valuers) is not very convincing from a scientific point of view., if the issue is whether the whole model is correct or not. It relies on the implicit assumption that the models have been proved to be true - which is precisely the point. This is kind of a circular justification. concerning the point of relaxation timescales : in the simplest approximation, there is a single timescale, and the relevant equation is dT/dt + T/tau = S.F(t)/tau where tau is the relaxation timescale and S the sensitivity. The exact solution of this equation is T =S. ∫ F(t')exp(t-t'/tau) dt'. Mathematically, T(t) tries to follow the variations of F(t), but with some delay of the order of tau, and smoothes all variations of the order of tau. Basically, it responds to the average of F(t) over a past period tau. If tau is small (with respect to the characteristic timescale for S(t)), T(t) follows closely S(t). If it is large , the T/tau term is negligible and one has rather dT/dt = S F(t)/tau , so T(t) = S ∫ F(t) dt'/tau. The "response" is the the integral of F(t) (the system "accumulates heat") but it is curtailed by a factor tau. Now there are interesting questions around tau. If tau is small, S should be just the ration of T(t) to F(t), so it should be precisely determined by current variations, which is obviously not the case. So we are rather in a "long" tau, longer than or comparable with 30 years. This allows some "flexibility " between S and tau, because constant ratio S/tau will give the same signal T(t) - I think this is the main reason for the scattering of S (and tau) , they are not well constrained by the data. However, if tau is large, the response of a linearly increasing forcing should be quadratic (this is obvious because the temperature has to increase faster in the future to exceed the 2°C thershold for instance), so an acceleration should be measurable. Is it the case? not really. Temperature are less or equally increasing than 30 years ago - you can discuss whether they're still increasing or not, but they're not accelerating.That's kind of puzzling in my sense (leading to the obvious observation that if they aren't accelrating, a warming rate of 0.15 °C will only produce 1.5 °C after 100 years). So there is a small window for which the sensitivity is high but not too much, and the timescale high but not too much, and the "curvature" will be significative in the near future , but not yet just now. Outside this window, the curve T(t) is essentially linear with a linearly increasing forcing (as the forcing is is logarithmic with the concentration and the production of GHG is supposed to increase more or less exponentially with a constant growth rate, the forcing should be close to linear). This is only possible for tau between 30 and 100 years, Say (which is essentially what is found in current models). But again this raises other interesting questions. 30 to 100 years is SHORT with respect to paleoclimatic times , and astronomical (Milankovitch) changes of forcings. So IF it were in this range, temperatures should follow rather closely teh forcings, and change only very slowly with them. But we hear here also on a lot of "variations " of climate at the centennal time scale (medieval "anomaly" whatever happened then, D-O events, and so on) which should NOT happen if the forcing is not changing at this time scale. But why is the forcing changing? aerosols, volcanoes, do they have a reason to statistically change when averaged over 100 years or so (remember that the temperature changes by averaging over this time scale?) -
Tom Curtis at 18:23 PM on 4 March 2011Crux of a Core, Part 1b
Here is a detail of Rob Honeycutt's image @25 so that the extent to which temperature fluctuations in northern and southern polar regions are antiphased during the Holocence can be clearly seen:
And for completeness, ice cores over the Holocene for a Greenland, a Northern Chinese (Northern Hemisphere), two Andian (Tropcical), and two Antarctic (Southern Hemisphere)to give some idea as to the extent of regional variability involved:
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Hockey Stick Own Goal
angusmac> Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998. Considering that Ljungqvist used decadal averages (as Tom pointed out), it would indeed be unreasonable and quite inaccurate to draw this conclusion. -
Daniel Bailey at 17:09 PM on 4 March 2011Twice as much Canada, same warming climate
muoncounter Yeah, not yet so blind as to have missed that. Nice segue from Arctic Amplification to Spinal Tap! Dunno if you follow Arctic ice developments much, but Patrick Lockerby over at Neven's Sea Ice blog just linked to his March Arctic Ice post here. Patrick is explaining his rationale as to "...why I expect the central Arctic to be essentially ice-free by the end of this Arctic summer 2011". Also says the 2011 melt season has already begun... (Gonna have to find amps that go to 12) The Yooper -
Marcus at 16:12 PM on 4 March 2011Icing the Medieval Warm Period
OK, so maybe I overstated the whole "destruction" thing in regards to the Maya, but it was used as an example of societal collapse in Jared Diamond's book of the same name-specifically where societies failed to adapt to changing environmental conditions & so hastened their own demise. Sorry if that's off-topic. -
Riduna at 15:54 PM on 4 March 2011Putting a new finger on climate change
CH4 emitted from coalmining and decaying organic matter has residence of ~10 years during which it oxidizes to produce CO2. Am I right to assume that CO2 so produced is predominantly carbon isotope 12? -
apsmith at 15:41 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 3
A bit of further analysis on this from me here: http://arthur.shumwaysmith.com/life/content/mathematical_analysis_of_roy_spencers_climate_model (using Barry's figures, thanks!) Spencer really should be ashamed of this. And turning it into a book! -
bbickmore at 15:38 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 3
Hi Albatross @9, I sent him the links after I posted Part 3, but I haven't heard from him. Hopefully, he's combing goofing around with his model to see if I'm right. -
KR at 15:33 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
Sorry, the start date should be 1800, not 1850, in my last post, for the start of anthropogenic CO2 - typing too fast... Incidentally, although I suspect most of the usual suspects will have seen this already, the YouTube video from CarbonTracker is worth showing to everyone. -
Tom Curtis at 15:30 PM on 4 March 2011Hockey Stick Own Goal
angusmac @135, the data may include 1998, but Lundquvist reports decadal averages. The early 1990's was quite cool compared to 1998, so there is still a sharp difference in temperature. The difference between the decadal average of GISStemp for 1990-1999 and 2000-2009 is 0.18 degrees, sufficient to lift recent tempertures well above the peak decadal average for the MWP (0.15 degrees greater than 1990's). Of course, that is the difference in global temperatures. The difference in NH extra tropical temperatures is likely to be far greater, and would show a correspondingly greater increase. -
KR at 15:22 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
Berényi - I'll admit to having some trouble following that last posting. The last I heard you were claiming that the relaxation time was essentially zero, so that there was no heating left in the pipeline. Now you are arguing that relaxation times are long enough to slow warming to a manageable level??? You're contradicting yourself. Second, 1934 is not the start of anthropogenic carbon forcing - that's somewhere around the beginning of the industrial revolution, circa 1850 or so. Third, relaxation times are relative to multiple time frames - from the several week H2O forcing to the multi-century ice response. Your simple formula is therefore inappropriate. And, since rate of change is dependent on scale of forcing, your 1.8C/century limit is, in my opinion, nonsense. I'll leave it at that for now - you have posted completely contradictory arguments in just the last few days, I'm certain there are issues others might raise. -
ribwoods at 15:13 PM on 4 March 2011Putting a new finger on climate change
Rather than a new, 11th fingerprint, isn't this really just another example, as in Fingerprint 4, of measurement of the C-13/C-12 ratio incorporated into living things? It's independent of coral C-13/C-12 ratio measurements, but not so different an indicator of fossil-fuel origin as to deserve separate listing, I think. I'd just add it to Fingerprint 4. -
angusmac at 15:08 PM on 4 March 2011Hockey Stick Own Goal
Moderator @132, new data is always welcome. However, the purpose of my post was to show that you could use the data presented in Dana's post and come to a completely different conclusion. Tom @133 and Anonymous @134, I agree that we need more up to date proxies. This should be a high priority in the paleo community. Nevertheless, Table 1 of Ljungqvist (2010) shows that 10 of the 24 proxies used by him extend to 1999 thus including the very hot year of 1998. Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998. -
Riduna at 15:01 PM on 4 March 2011Icing the Medieval Warm Period
Tikal, Copan and other great Mayan city-states in the south did succumb to a combination of internecine warfare, over-population and drought induced crop failures in the 8-9th centuries, bringing the Classic Period to an end. That is a long way from destruction of Mayan civilization which survived in northern areas, notably Yucatan, where city-states such as Uxmal, Mayapan and Chechen Itza flourished into the 17th century. Their demise was at the hands of the Spanish, not climate change. Can prolonged droughts in Guatemala, Belize and Honduras in the 8-9th centuries be regarded as synonymous with the European MWP? -
Albatross at 14:33 PM on 4 March 2011Roy Spencer’s Great Blunder, Part 3
Dr. Bickmore, Has Roy responded to your critique? I'm a little surprised that he has not bothered to drop by and discuss this. I would not be surprised if he tried to frame this as an "attack" on skeptics over at his blog. We'll see. -
mspelto at 14:22 PM on 4 March 2011Icing the Medieval Warm Period
To get a better sense of the field sites and work by Koch and Clague take a look at Koch's research pages . Nice maps and photographs. -
muoncounter at 14:05 PM on 4 March 2011Twice as much Canada, same warming climate
Yooper: Didja notice that appears to be 5 degrees in approx 20 years? One of them natural cycles we hear so much about, I guess. Or maybe the Arctic Amplifiers are turned up to 11? -
Berényi Péter at 13:55 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
#59 Sarah at 14:09 PM on 3 March, 2011 Hansen and Sato recently determined that climate sensitivity is about 3 °C for doubled CO2 based on paleoclimate records.[...]Moderator Response: [Daniel Bailey] Thanks, Sarah. The preprint is here.I don't see it was a peer reviewed paper. Dr. Hansen says it's a "Draft paper for Milankovic volume", whatever that may be. However, it is still interesting, because it is based on empirical data and has definite numbers to work with. Its biases and omissions are also telling. The first thing to note they assume a 4 W/m2 forcing for doubling of atmospheric CO2 concentration, which is slightly above the IPCC AR4 WG1 2.3.1 (2007) estimate of 3.7 W/m2, with no explanation whatsoever. The figure seems to come from IPCC FAR WG1 3.3.1 (1990). Anyway, if we accept their value, using CO2 concentration measurements at the Mauna Loa Observatory we get the annual rate of change in forcing due to CO2 as α = 0.024 W/m2/year for the last 54 years. The paper calculates an equilibrium climate sensitivity of λ = 0.75°Cm2/W using paleoclimate data. As temperature variability is much smaller under current warm interglacial regime than for the bulk of the last 3 million years, climate sensitivity obviously decreases sharply with increasing temperatures, but let's go with their figure anyway, at least for the time being.
Greenland temperatures during the last 100 kyears -- click for larger version
If we assume a scenario under which atmospheric CO2 concentration was constant for a long time (presumably at pre-industrial level, let's say at 280 ppmv) then started to increase exponentially at the rate observed, we get an excitation that is 0 for dates before 1934 and is α(t-1934) for t > 1934. The artificial sharp transition introduced in 1934 this way does not have much effect on temperature response at later dates.
If global climate responds to an excitation as a first order linear system with relaxation time τ, rate of global average temperature change is αλ(1-e-(t-1934)/τ) for a date t after 1934. As the expression in parentheses is smaller than 1, this rate can't possibly exceed αλ = 0.018°C/year. It means global average temperature can't increase at a rate more than 1.8°C/century even in 2100, which means less than 1.6°C increase relative to current global average temperature, no matter how small τ is supposed to be.
However, a short relaxation time is unlikely, because it takes (much) time to heat up the oceans due to their huge thermal inertia.
For example if τ = 500, current rate of change due to CO2 forcing is 0.26°C/century while in 2100 it is 0.51°C/century (according to Hansen & Sato, of course). However, ocean turnover time being several millennia, we have probably overestimated the actual rates. It means that most of the warming observed during the last few decades is due to internal noise of the climate system, not CO2.
Anyway, the exponential increase of CO2 itself can't go on forever simply because technology is changing all the time on its own, even with no government intervention whatsoever. Therefore it should follow a logistic curve. If the epoch of CO2 increase is substantially shorter than the relaxation time of the climate system, the peak rate of change due to CO2 becomes negligible.
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Marcus at 13:44 PM on 4 March 2011Putting a new finger on climate change
Philippe-the point I was trying to make (badly I confess) is that because fossil fuels have *zero* 14C, then changes in the ratio of C14 to C12 could serve as a useful secondary signal for the anthropogenic nature of the rising CO2 in the atmosphere. However, as scaddenp has pointed out, that might not be as easy as I first thought ;-). Hope that makes more sense. -
Marcus at 13:11 PM on 4 March 2011Icing the Medieval Warm Period
I'm guessing, Daniel, that those warmer periods you mentioned were the same as those I mentioned-the ones which wiped out the 2 big Meso-American civilizations of the day? The warming/drought that caused the end of the Egyptian Old Kingdom has been linked to a slowing of the Atlantic Conveyor (the one which causes the Gulf Stream)-which also caused Northern Europe to get cold. I wonder if something similar can explain the MWP?Moderator Response: [DB] Possibly/probably. With the teleconnections being uncovered, ENSO changes in the Pacific Ocean seem to be driving subsequent "downstream" reactions and changes throughout the world. Obviously an area being looked at further; given what we now see happening in our warming world & the potential impacts discussed in Dai et al 2010 (discussed here), it's an area of critical importance. -
scaddenp at 13:07 PM on 4 March 2011Putting a new finger on climate change
Marcus, google scholar for Etiope G and Lassey K R. Both researchers active on this. Short answer - C14 is useful but its not as easy as it sounds... (I'm trying to get no. for pre-industrial fossil methane emissions from sedimentary basins in day-job so having been looking at issue). -
Eric (skeptic) at 12:59 PM on 4 March 2011Climate Sensitivity: The Skeptic Endgame
Thanks for the link les, here's the full URL; http://journals.sfu.ca/int_assess/index.php/iaj/article/download/188/139 I looked at the section on climate sensitivity where they refer to this study http://pubs.acs.org/doi/abs/10.1021/es00010a003 titled "Subjective judgements by climate experts" to obtain a subjective probability distribution of climate sensitivity values centered aroudn 3C. In that 1995 paper they start out "When scientific uncertainty limits analytic modeling, but decision makers cannot wait for better science, expert judgment can be used in the interim to inform policy analysis and choice" I would rather wait for objective probability distribution measurements. For example, the continued rapid increases in computing power will make full weather simulation possible within global climate models (i.e the mesoscale models I referred to above). Then there will be no need for subjectivity. -
rocco at 12:53 PM on 4 March 2011Icing the Medieval Warm Period
Daniel Bailey: I think the article should mention that the Martín-Chivelet et al study is for Iberian Peninsula only. If you want to go beyond the usual 2000-year reconstructions globally you should reference the borehole studies, for example.Moderator Response: [DB] Thanks for the heads-up. I realized that after the fact, but forgot to update the text in the rush to publish. I'll fix it now. -
Philippe Chantreau at 11:35 AM on 4 March 2011Putting a new finger on climate change
Marcus, fossil fuels are millions of years old, way over a hundred millions for coal. No C14 left in there but from exterior sources. I'm not sure I understand your point in #10. -
Chemware at 11:33 AM on 4 March 2011Icing the Medieval Warm Period
Was there a MWP in northwest North America ? Or was the MWP a local, European event ?Moderator Response: [Daniel Bailey] The preponderance of evidence we have strongly suggests regional warming at various periods of time over several centuries that also coincided with regional cooling. Some areas warmed and others cooled. The area with best data for a localized, regional, warm period is in Europe. This period was also punctuated with brief colder periods where glaciers in the Alps underwent significant advancement. It was a complex climatic period. For more info, go here (both the Basic and Intermediate Versions). North America had warmer periods as well, but those were punctuated with extreme droughts. -
Marcus at 11:33 AM on 4 March 2011Icing the Medieval Warm Period
Oh, correction, 2 Civilizations (The Anasazi & The Mayans) both died out during the Middle Ages-both due to extended drought which was believed to be caused by a regionally warming climate. -
Marcus at 11:32 AM on 4 March 2011Icing the Medieval Warm Period
This is actually very interesting when you consider the fact that a civilization in South-Central America died out during the Medieval Period due to warming-as did the Khmer Empire-though several hundred years apart. I say that its interesting because the there was a similar dichotomy between Northern & Central temperatures as there was during the collapse of the Egyptian Old Kingdom. i.e. the equatorial regions of the world were gripped by an extended warm period, & attendant drought, whilst many of the northern latitudes were gripped by a relatively cold period. Of course this is yet another reason why we know that what caused these past two warming events is *not* what's causing warming now-because this time we're seeing a mostly globally homogeneous warming event. -
Philippe Chantreau at 11:31 AM on 4 March 2011Putting a new finger on climate change
Nice summary Tom. However, this appears a little obscure to me: "Because of the production of C14 in the upper atmosphere, Carbon dissolved in the ocean has a much lower CO2 content than does the atmosphere." Did you actually mean "because C14 is produced in the upper atmoshere, CO2 dissolved in the ocean has a much lower concentration in C14 than does the atmosphere." I'm still not sure about the mechanism though. Am I understanding this totally wrong? And also on this one: "Therefore declining C13/C12 ratios show the atmosphere is receiving CO2 from organic or fossil fuel (fossilized organic) sources." That should probably go "receiving CO2 produced by combining C from organic material or fossil fuel with atmospheric O2." -
Marcus at 11:27 AM on 4 March 2011Putting a new finger on climate change
OK, according to Wikpedia, C-14 has a half-life of 5,730±40 years. So I'm still wondering if this wouldn't play at least some small part in our ability to detect CO2 from natural vs anthropogenic sources. -
Marcus at 11:24 AM on 4 March 2011Putting a new finger on climate change
Thank you for that Tom Curtis. Seems my understanding of Carbon Isotopes is less than satisfactory. Lucky my job doesn't require knowledge of that ;-). -
Tom Curtis at 11:05 AM on 4 March 2011Putting a new finger on climate change
Marcus, C14 has a fairly short half life, but is generated by the interaction of cosmic rays with nitrogen. C12 and C13 are stable isotopes which means that they do not have a half life (or perhaps that their half life is several times the age of the universe). Because of the production of C14 in the upper atmosphere, Carbon dissolved in the ocean has a much lower CO2 content than does the atmosphere. Because of its low half life, fossil fuels contain almost no C14 (some trace amounts can be found due to ground water seepage in coal). Consequently a declining C14/C12 ratio in the atmosphere shows that CO2 is being introduced to the atmosphere from either the ocean or fossil fuels. C12 preferentially absorbed by plants in photosynthesis, so plants and anything that eats them or is produced from them (ie coal and oil) have lower C13/C12 ratios. Therefore declining C13/C12 ratios show the atmosphere is receiving CO2 from organic or fossil fuel (fossilized organic) sources. Finally, O2 is consumed in combustion. Consequently declining O2 levels in the atmosphere show the source of CO2 to be combustion. By comparing the decline of O2 to the declining C13/C12 ratio, it is also possible to determine what proportion of the CO2 comes from burning fossil fuels, and what portion comes from land use changes. -
johnd at 10:41 AM on 4 March 2011It's Pacific Decadal Oscillation
johnd at 10:26 AM, it should be clear to most readers, but in case it is not, the observations about the El-Nino/La-Nina data from NR&M are mine and not part of the JAMSTEC forecast. -
johnd at 10:31 AM on 4 March 2011It's Pacific Decadal Oscillation
thepoodlebites at 07:40 AM, just to add, whilst most people seem to focus on the magnitude of El-Nino/La-Nina events, the frequency of their occurrences is more relevant when it comes to discussing ocean based cycles. -
johnd at 10:26 AM on 4 March 2011It's Pacific Decadal Oscillation
thepoodlebites at 07:40 AM, FYI, the latest JAMSTEC, SINTEX-F1 CGCM forecast(27-member ensemble) (updated February 15, 2011) ENSO forecast: The current strong La Nina condition would decay in following boreal spring and summer seasons but would rebound in fall and persist up to early 2012. The revived one would show a La Nina of Modoki nature. IO forecast: Associated with the La Nina impact, the surface temperature in the equatorial Indian Ocean has become colder than normal in January 2011. The tropical Indian Ocean surface temperature would decrease further in following seasons but with strong warming along the west coast of Australia. In the second half of 2011, a weak negative IOD might tend to occur. Regional forecast: Associated with the La Nina influence, below-normal surface air temperature and above-normal precipitation would continue in Australia, northern Brazil, and southern Africa during the austral fall-winter. Southeastern China,southwestern Japan, US and Europe would have warmer-than-normal and dry climate during spring-summer seasons. According to data from the Queensland Natural Resources and Mines, La-Nina conditions that extended over multiple year occurred in 1892-93, 1916-17, 1955-56, 1970-72 and 1973-74-75. El-Ninos that extended over multiple years occurred in 1913-1914, 1918-1919, 1940-41,and 1991-92-93-94. Note, to avoid confusion, given the NR&M classify the years as from April to March, the beginning years are as indicated, but the ending years are at the end of March in the year following that indicated above.
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