Since Hansen’s article in September, we’re starting to hear the phrase “warmest in 12000 years”- google “warmest 12000 years” and you’ll see recent coverage. This immediately raises the question of the Holocene Optimum – a period from about 8000 to 5200 BP in which there is undisputed evidence of significant NH warmth. The Team has taken a preditable position on the Holocene Optimum: that it’s a regional and restricted event. realclimate:
The [Holocene Optimum] is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today. We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere. This summer warming appears to have been due to astronomical factors that favoured warmer Northern summers, but colder Northern winters and colder tropics, than today (see Hewitt and Mitchell, 1998; Ganopolski et al, 1998). The best available evidence from recent peer-reviewed studies suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).
realclimate links in turn to a NOAA website which thanks “Dr. Keith R. Briffa, Dr. Phil D. Jones, Dr. Michael E. Mann, and Dr. Henry N. Pollack” for their contributions, and which takes a similar position to realclimate as follows:
In summary, the mid-Holocene, roughly 6,000 years ago, was generally warmer than today, but only in summer and only in the northern hemisphere.
The question that I’m wondering about: do we know that mid-Holocene warmth was only in summer and only in the northern hemisphere, and, if so, how do we know it? I’m not going to consider high-latitude NH evidence, as that does not appear to be in issue. At some point I might re-visit the question of whether we know that it was only in summer, but for now, I’m going to focus on the topics and the SH. A recent survey of NH northern sites from 0-180W (Kaufman et al 2004) – and results would be similar for 0-180E – stated:
The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0–180W; north of ~60N). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.6 +- 0.8 deg C higher than present (approximate average of the 20th century), but the warming was time-transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12–10 ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9 ka, about 4000 yr prior to the HTM in northeast Canada
The proxy evidence for the Holocene is different than millenium proxies – ring width chronologies decline dramatically in relevance, while ocean sediment dO18 and Mg/Ca, ice core dO18 and stalagmite dO18 all increase dramatically in importance. On a million-year scale, there is a quite decent and interesting similarity between the pattern of ocean sediment Mg/Ca and O18 and Antarctic ice core dO18 and dD values. So one does get a sense that the data rises above cherry-picked red noise.Here’s some of the sites that I want to look at: Stott’s ocean sediment sites in the West Pacific Warm Pool; tropical ice cores (Thompson and others); southern ocean sediments; Antarctic ice cores. There is some surprisingly strong evidence of high-latitude warming in the Holocene Optimum – evidence which seems to be just ignored by the Team and by NOAA. In the face of this evidence, Lorenz et al 2006 (and predecessor article Kim et al QSR 2004) have proposed a newish theory that is gaining sway in Team-world – that there was Holocene Optimum warming in the extratropics, but there was tropical cooling in the Holocene Optimum. So I’ll probably start with some southern extratropic sites – oncluded some of the Lorenz et al concessions and then get to the tropic sites.
I’ve made a new category “Holocene Optimum” to index the posts. Past this, there is the interesting question of the Holocene interglacial as compared to other interglacials during what has been generally a very cold past million years (the Pleistocene).
Climate Audit 
42 Comments
Well, this paper, which seems pretty thorough on first look, seems to show a pronounced southern Holocene warming and cooling events during the general Holocene deglaciation.
Bianchi, C & Gersonde, R (2004) “Climate evolution at the last deglaciation: The role of the Southern Ocean” Earth and Planetary Science Letters 228,407-424
Abstract: Two sediment sequences recovered close to, and south of, the present Polar Front (50 degrees , 53 degrees S) in the Atlantic sector of the Southern Ocean were analysed in order to evaluate the environmental evolution of the Southern Ocean surface over the last deglaciation and the Holocene. Our reconstruction is based on radiocarbon-dated records of diatom-based sea surface temperature and sea-ice proxies and planktic foraminiferal stable isotopes. The onset of the deglacial warming and gradual southward retreat of the winter sea-ice field between 18 and 17 cal kyr BP, occurrence of a thermal reversal centered at ca. 13 cal kyr BP (Antarctic Cold Reversal, or ACR), and early Holocene occurrence of the “climatic optimum” well correlate with climatic reconstructions available from the Indian Southern Ocean and from Antarctic ice cores. Time correspondence of Southern Ocean warming and Heinrich event 1 in the North Atlantic is compatible with the transmission of the climate signal from the Northern to the Southern Hemisphere through the “bipolar seesaw”. Our data support modeling results suggesting that the Northern Hemisphere Bolling warming and turn-on of the North Atlantic Deep Water formation are triggered by gradual warming and sea-ice retreat in the Southern Ocean. Meltwater shedding into the Southern Ocean associated with the ACR may maintain Northern Hemisphere warming during the Allerod. The development of sea surface warming and sea-ice retreat is compatible with a Southern Ocean control on the atmospheric CO2 increase during the deglaciation. During the early Holocene (9-7 cal kyr BP), our southern core records renewed surface ocean cooling and northward readvance of the winter sea-ice field. Such early Holocene cooling is common to cores from the high-latitude Atlantic sector, and might be brought about by expansion of the Weddell Gyre circulation at that time.
Because of the ‘polar see-saw’ of Earth climate, which sees warming and cooling oscillate between the hemispheres during any overall global glaciation or deglaciation trend, to insist that some regional warming or cooling during a larger-scale global trend either obviates that global trend locally or restricts it to some locality, seems merely tendentious.
Here’s another southern ocean proxy that ought to *really* put a seal on the question of global Holocene warmth:
B. L. Hall, ea (2006) “Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea” PNAS 103(27) 10213-10217
Abstract: “We show that southern elephant seal (Mirounga leonina) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting grounds. We propose that this was due to warming (including a previously unrecognized period from approximate to 1,100 to 2,300 C-14 yr B.P.) that decreased coastal sea ice and allowed penetration of warmer-than-present climate conditions into the Ross Embayment. If, as proposed in the literature, the ice shelf survived this period, it would have been exposed to environments substantially warmer than present.“
I am not sure why they would say the “Holocene Optimum” is an outdated term. I suppose they want to get rid of the Holocene (most recent) Optimum (HO) with its implications of it being the warmest in the post glacial part of the Pleistocene just as Deming tells us they saw the MWP as a problem to be eliminated.
The HO has variously been called the Post Glacial Climatic Optimum and the Climatic Optimum. The latter became problematic when the MWP was called the Little Climatic Optimum. The HO was also called the Altithermal or Hypsithermal, but that didn’t stay around very long. The latter two terms were mostly used in the American literature.
Names of different periods and agreement on their dates of onset and termination have always been problematic in most areas of historic reconstructions of the environment. For example, the identification of different glacial periods and application of different terms created confusion that led to an attempt to standardize terminology. The WMO has made some efforts but more are needed.
The terms used by by Hansen et al., relate to temperature, but there are other definitions using different measures. For example, a similar period is also defined as the Atlantic period using vegetation as the measure. This was generally a period of mixed hard wood forests (mostly oak) in western Europe and spans from 6000 to 3000 B.C.
I cannot comment immediately on the argument about it being a period of warmer summers and colder winters. The general evidence from vegetation types and changes as indicated in pollen studies (palynology) is a period of warmer winters, indeed some argue the warmest in post glacial times. I suspect that there are rarely times when seasonal changes are going in the same direction. I don’t know where they get the evidence that it was warmer summers. I would like to know because I think this point is very important. In the public campaign only global annual averages are considered with the implications that the changes are uniform and annual. I believe the record shows that most of the warming of the last 200+ years has been in winter temperatures (Increasing UHI efect?) One of the criteria for understanding the Milankovitch Effect’s on temperature is to determine what combination of juxtapositions leads to what effects for different latitudes. For example, Milankovitch understood that tilt had a greater effect at high latitude and calculated accordingly. In other words a look at seasonal differences provides a very different picture, which requires very different explanations. Isn’t it likely that if CO2 was the cause the temperature change would be occurring in all seasons and at all times? As another example, I understand much of the recent measured warming has been in night time temperatures (UHI again?).
Steve,
It may be that the HT is admitting that many of their proxies only represent mean summer termperatures, not mean annual temperatures. They may therefore be extrapolating that the HO data is likewise representative only of summer temperatures.
There is a huge amount of evidence from a variety of independent proxies (pollen and plant macrofossil data on land, diatoms, forams and alkenones in the ocean) that high-latitude northern summers were warmer in the early Holocene. The case for northern winters temperatures is less clear, as most biological proxies are not that sensitive to dormant season temperatures. There is some evidence that winters were colder (eg pollen reconstructions in Davis et al. QSR 2004) in Northern Europe.
Orbital parameters in the early Holocene gave a different latitudinal and season distribution of insolation, but no real difference in the global total, so temperature anomalies should largely cancel, unless there are global changes in e.g albedo or greenhouse gases.
Had a similar discussion thread on another (weather/climate) website recently. It takes a while, but looking at a range of papers for NH & SH warming/optima appears to show that the two hemispheric periods of optimum warming are at different times – the SH having warming both before and after the NH, but not at the same time as. Given that what is being discussed here is global temperature – for better or worse – then at the very least the term ‘HCO’ needs modification, to take this into account, perhaps by making reference to the hemispheric context of whichever proxy is being used. Personally, I’m with the NAS/BASC on this; the uncertainty levels are high enough (and unlikely to greatly improve)about the temperature prior to about 400 years ago as render comparisons with the present meaningless. Where paleo evidence (sic) is significant is in calculating, for example, climate sensitivity, rather than in establishing or ‘proving’ that the current (or future) climate is being modified by WMGHGs. And, yes, this does rather beg the question…
Go here
for a conprehensive collection of recent papers showing a global Holocene Thermal Optimum.
One way to look at this question might be to ask how a paleoclimate researcher 4000 years in the future might be able to characterize the current period. given that ice cores etc. have limited time and temperature resolution, and given that the current warming is much more pronounced at the higher lattitudes of the NH, with some net cooling in the SH, could one not conclude that the 20th century warming was mostly a local event? And how would one discriminate between winter and summer warming, and/or night-time and daytime warming or cooling?
Another Team-World link: http://www.realclimate.org/index.php?p=65
The seemingly unremitting need to point to past warming periods as local and seasonal events while maintaining the global average of the current warming period as greater than those periods becomes more and more curious to me and more in line with a climate policy requirement than a scientific one. Maybe it’s because of my skeptical view, but that need to state that point seems way overdone.
Re #5: “Orbital parameters in the early Holocene gave a different latitudinal and season distribution of insolation, but no real difference in the global total, so temperature anomalies should largely cancel, unless there are global changes in e.g albedo or greenhouse gases.” My understanding is that differences in this distribution (in both latitude and timing) are key to the changes. After all, annual total insolation does not chnage significantly over such periods of time.
Re #s 13/4/5: Self-cancelling criticism.
Stupid question. Where did the polar bears disappear to during the Holocene Optimum?
Re #12: If the transition was slow enough and the warming did not affect all of the habitat simultaneously, it doesn’t seem unreasonable that they would be able to survive without acquiring a genetic marker indicating a population “bottleneck” (which I assume they must not have since none has been reported). Also, even with a more uniform warming, the geography looks as if it would allow a small but entirely viable population to survive around the northern tip of Greenland even after all the existing habitat had disappeared. All speculation, BTW.
RE: #12 – It is not unthinkable that even as recently as a few thousand years ago, there was more of a continuum, including widespread interbreeding, between the Kodiak-Grizzly subspecies and the Polar Bear one. If so, then during past extreme warm events, Polar Bears might have seemed to become “extinct” (in reality, subsumed within Kodiak-Griz) only to “reappear” as an adaptive branching when conditions cooled again.
On the question of Polar Bears and their habitat, is it established that the Arctic was free of sea ice during the Holocene optimum? Or is there not enough information?
Steve S,
The way I understand it, the farther north a mammal goes, the more likely they are to become white furred/blue eyed. This is due to the amount of solar radiation they are absorbing. I am no expert, but heard this on science channel recently. They said it takes like 10,000 to 20,000 years to change things like hair color and eye color in large mammals. It is related to how fast and how far humans migrated out of Africa many years ago. Maybe someone else can find links either supporting or denying this info? Heard it like 3 weeks ago, and have read simlilar articles going back some time.
Any thoughts?
There has always been sea ice and glaciers. See Greenland, see 6 months of darkness at the poles. Alaska, Hudson Bay and Siberia may not have been a good place for polar bears during the Holocene Optimum, but the northern Canadian arctic islands and Greenland would have had sea ice for long periods of the year.
But during the ice ages, all of the arctic was covered in ice year round, miles high glaciers on land, sea ice that was too thick on the ocean. Where did they go during the long ice age? Oregon and New York?
Well, according to the writers of LOST, the answer is mysterious tropical Pacific islands. Glad I could help.
FYI:
http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA024587
http://www.fathom.com/feature/122557/
The tilt of the Earth was at a maximum at the time of the Holocene optimum, more direct sunlight at high latitudes combined with extended summers almost certainly meant that sea ice all melted. Remember that at this time mile thick NH glaciers melted away to nothing and sea level rose enough to submerge the Bering Land Bridge. Yet somehow, polar bears remain with us. Look at the GRIP ice core and remember that at the time of the HO in that record, fluctuations have been lost, so it is inevitable true that it was both warmer and cooler than the average which gets recorded in the borehole.
The movement of peak insolation north and south has to affect ocean and atmospheric currents. It defies logic otherwise.
The polar bears have survived many interglacials in the past. Alarmists in love with the sea ice story can explain perhaps why this time is going to be any different.
Re: #23,
Well,no they haven’t. Ursus Maritimus only split off from the brown bear, Ursus Arctus, about 200,000 years ago. It’s not actually a completely separate species because polar bears and brown bears can interbreed and have produced fertile offspring in the wild. So they have survived only one interglacial as a separate breed.
DWP, yes, pizzlies, thanks, do you have a reference? If the split was 200ky ago then they are batting 1 for 1. Not bad. I change my “many” to “all”.
🙂
Re: #25,
Wikipedia. Yes, I know, not definitive. The article cites a number of primary sources that I didn’t bother to try to find. I checked the discussion and history tabs and there doesn’t appear to be any controversy over the article. Apparently there was a larger earlier version that did become extinct in the Pleistocene.
12 (bender): maybe the polar bears went to live with Al Gore’s penguins…
From The Evolution of Arctic Marine Mammals
Re: #28,
Reading the full review article makes the suggestion of 1 to 1.5 Ma origin appear suspect to me. I have my doubts about the accuracy of mitochondrial DNA species dating anyway, but I’m not an expert and my opinion doesn’t count for much. It’s certainly not worth starting a food fight on an OT subject. It does confirm that the oldest fossil remains found for polar bears are less than 100,000 year old and that there is at least one clade of brown bears that are genetically closer to polar bears than other brown bears. So polar bears have indeed survived at least one and possibly more interglacial periods as well as the Holocene Optimum where temperatures were comparable to and possibly higher than the present.
Looks we’ve got ourselves an argument!
Cancel that food platter. Time for some reading.
bender,
One last OT post vaguely related to polar bears. I’d bet a lot of quatloos that the statistics used to determine when species separated by analyzing mitochondrial DNA is at least as big a can of worms as tree ring climate reconstructions. But since nobody outside the field, including myself, really cares, we may never know.
Re: #32
Because no one really needs to care because the science is not being used to justify trillion dollar public policy decisions. I have been frequently frustrated by warmers who don’t seem to understand that “the way science is always done” is not good enough when huge sums of money depend on the science being right.
Contrast the statistical robustness of pattern matching exercises when it comes to DNA fingerprintsing vs. tests of GCM fit to reality. No contest. The level of mathematical formalism and scale of collaboration with real statisticians in the bioinformatic world is astounding ny comparison. [Yes, yes, Big Pharma. But I though NASA was big too?]
Re: #34,
DNA fingerprinting has to survive challenges in courts of law so it’s not surprising that the analysis has been rigorous. It’s far better tested than actual fingerprint identification, from what I’ve read.
Dewitt, having done the experiments myself and taught aspects of mitochondrial dna variation I’m fairly confident that the findings will hold up. For there to be a major error in the dating of the divergence of species would require there to be a markedly slower rate of mutation in Polar bear mitochondria than in the many other species which have been investigated which seems unlikely.
See here for example:
Mol Phylogenet Evol. 2000 May;15(2):319-26.
Phylogeography of mitochondrial DNA variation in brown bears and polar bears.
Shields GF, Adams D, Garner G, Labelle M, Pietsch J, Ramsay M, Schwartz C, Titus K, Williamson S.
Institute of Arctic Biology, University of Alaska at Fairbanks, Fairbanks, Alaska 99775-7000, USA.
We analyzed 286 nucleotides of the middle portion of the mitochondrial cytochrome b gene of 61 brown bears from three locations in Alaska and 55 polar bears from Arctic Canada and Arctic Siberia to test our earlier observations of paraphyly between polar bears and brown bears as well as to test the extreme uniqueness of mitochondrial DNA types of brown bears on Admiralty, Baranof, and Chichagof (ABC) islands of southeastern Alaska. We also investigated the phylogeography of brown bears of Alaska’s Kenai Peninsula in relation to other Alaskan brown bears because the former are being threatened by increased human development. We predicted that: (1) mtDNA paraphyly between brown bears and polar bears would be upheld, (2) the mtDNA uniqueness of brown bears of the ABC islands would be upheld, and (3) brown bears of the Kenai Peninsula would belong to either clade II or clade III of brown bears of our earlier studies of mtDNA. All of our predictions were upheld through the analysis of these additional samples.
#36 And that was 8 years ago, when molecular ecology was still in its infancy. I suspect they have dozens of markers now for those species – robustness of results being proportional to the number of loci studied. (The 286 nucleotides cited is for a single locus).
Re #37
Yeah, it was important to look at nuclear dna too because the close relationship with the ABC islands brown bear could have been the indication of hybridisation with polar bears (mtdna is only passed via the female line). Highly variable microsatellite markers have confirmed the mtdna conclusions.
Paetkau, D., and C. Strobeck. 1998. Ecological genetic studies of bears using microsatellite analysis. Ursus 10:299’306.
Paetkau, D., W. Calvert, I. Stirling, and C. Strobeck. 1995. Microsatellite analysis of population structure in Canadian polar bears. Molecular Ecology 4:347” 54.
Paetkau, D., L. P. Waits, P. L. Clarkson, L. Craighead, and C. Strobeck. 1997. An empirical evaluation of genetic distance statistics using microsatellite data from bear (Ursidae) populations. Genetics 147:1943’57.
Paetkau, D., S. C. Amstrup, E. W. Born, W. Calvert, A. E. Derocher, G. W. Garner, F. Messier, I. Stirling, M. K. Taylor, “. Wiig, and C. Strobeck. 1999. Genetic structure of the world’s polar bear populations. Molecular Ecology 8:1571’84.
Unfortunately, the authors once more comment upon tree ring research in support of MWP reconstructions. Nonetheless, they present some observations about Antarctic lakes which supplies further food for thought and consideration in regard to evidence of a global MWP and high sensitivity to Holocene climate changes in the Antarctic.
Some time ago, decades, I read a paper in the Geological Society of America publication, “Geology”, stating that the Sahara desert was a savanah and contained a number of lakes during the Holocene Optimum. A recent issue of National Geographic, Nov. 2009, alludes to this and further indicates that the Sahara contained a lake the size of England about 200,000 years ago. Would this not be an indication that a little global warming would’nt be all bad?
Steve and all, one interesting example that might be suggestive. Two professional geologists in Wyoming who wrote something fascinating (though cryptic) about the “Climate Optimum” 7,000 years ago. I’m not assuming one comment like this could be decisive about anything, but may suggest further research. Why did two expert geologists who had spent their lives studying an area say this, what was their evidence, what is known since? Could there be a lot more items like this in the geological literature and record, and would it matter now? Their sources seem to be pre-1960 and I don’t know how much they were relying upon published scientific literature versus personal judgments. I do not have the background to really follow up (if it merits any further attention). Of course, the info may be wrong or superceded etc., but I was very struck by the following quotation from two Wyoming geologists (J.D. Love and John C. Reed, Jr.), on an obscure page of a US govt website, which flatly asserts that the “Climatic” (Holocene) Optimum was likely “warmer and drier” 6,000 years ago than today’s climate, and that the Pinedale Glacier system in the Tetons had (they “suspect”) disappeared entirely. This surprised me because it contradicts (at least for that region perhaps) the claims that contemporary climate temps. are unprecedented etc.
So the quote which shook me is this (from the official website of the US National Park Service, but obviously not yet cleansed by CAGW types):
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“Many bits of evidence, both from North America and Europe, indicate that there was a period called the climatic optimum about 6,000 years ago when the climate was significantly warmer and drier than at present. We suspect, though there is as yet no direct proof, that the Pinedale glaciers wasted away entirely during this interval.”
http://www.cr.nps.gov/history/online_books/grte/grte_geology/sec9.htm
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They are of a previous generation of geologists, seem to have been active 1940s to 80s, and I have no idea whether more definite assessments have been made about glaciers and temps in the Rocky Mtn. West or not. The document was first published in 1959 and went through 11 editions as of the NPS website in 2007 (when or if the most interesting statement was revised since 1959 I have no idea). Could there be more evidence about temperate zone glaciers (such as in the US Rocky Mtns.) that would help to indicate whether or not there was a high “Holocene Optimum” in those areas?
It occurs to me that the quotation points to something possibly as important (or even more so) than debates about the Medieval Warm Period, i.e., if there were such a high Holocene Optimum that could also be very imporant to understanding the climate hisotry. In case there is anything here that merits further attention (and I know this is a non-scientific website but the authors do seem to be professional geologists now or formerly in Wyoming). The senior member of the pair, Dr. J.D. Love, is said to have done the first complete geologic map of Teton County (western Wyomning where many of the mountains are) and was senior geologist for the statewide geologic map of Wyoming.
Certainly I have seen discussions of the Climatic or Holocene “Optimum” but not being in a related field I had not known that there is physical evidence that the HO might be (as they assert)”significantly warmer and drier than at present.” If there were strong evidence for that claim it would seem (just as with the MWP if that is strong and not weak) to undermine the more hysterical claims about AGW. This might be a great topic for someone who has the ability to re-assess diverse geological and climate evidence that is (possibly) ignored or suppressed by contemporary climatologists. We hear how Lonnie Thompson et al are showing peril for “tropical” glaciers at high altitudes. But the climate pressures on glaciers were obvious long before the past few decades, I think? That seems obvious in many spots in N. America and the Alps, anyway. Has anyone who can rigorously assess glaciation evidence looked at what the glaciers which greatly retreated BEFORE 1950 might have to say about climate change in the past 1, 2, and many centuries?? i.e., as a traveler and mountaineer I am well aware of areas where few or only small glaciers remain, but where the glacier retreats had been far advanced long before any possible human/CO2 influence.
For instance, Glacier Bay on the Alaskan coast was the scene of a huge retreat of glaciers between the 1780s and 1880s, with dozens of miles of the bay opening up as the ice retreated (confirmed by John Muir’s visit there). Or, to take the case of the Tetons in Wyoming, glaciers there were small to non-existent by the 1950s or 60s, but of course they had once extended all over the mountain valleys there. These might be the kinds of examples at the “margin” which could show the ways in which non-human causes have been melting the glaciers in the past 1-2 centuries (and of course for much longer).
Perhaps a more specific question might be considered by CA readers knowledgeable in these areas:
Both 6-7,000 years ago and again throughout the 19th to early 20th centuries, many glaciers may have retreated or largely disappeared: how do these “natural” changes compare to recent claims of CAGW? I’m thinking of many places I have hiked and climbed in US and Canadian Rockies, the Sierra, and the Alps, where remaining glaciers are much fewer and smaller without any possible human intervention…. although of course similar examples may exist in many other places in the years since the Little Ice Age. Indeed, rather than assume that remaining ice far from the polar regions will remain as it is, my layman’s perspective is that it would not be surprising at all if many more sub-polar glaciers would be melting from natural trends.
I don’t “know” this could develop as any scientific argument, I’m simply wondering who has really looked carefully at the data, say pre-1970s, to understand what “natural” trends were already underway, either in the past 2 centures or 7,000 years ago. My hunch is that it would require more of an explanation for why sub-polar glaciers will remain indefinitely than why they might be retreating now, but I am not a scientist.
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Here is the original web source for what seems to be a booklet written for the US National Park Service many years ago (first in 1959) but which has gone through 11 editions.
[from 2007 website of US Nationl Park Service, for the Teton National Park (Wyoming)]:
http://www.cr.nps.gov/history/online_books/grte/grte_geology/sec9.htm
[emphasis added]
also, there might be many more fascinating tidbits like this scattered around the web…. this was a US National Park Service website. I wonder how many other items are out there that do not easily fit the narrative of “The Team”?