I’ve been running off down the rat hole of web searches of various terms, looking for some detail on the Dark Ages Cold Period (and I’ve found a fair amount).
One of the first things I realized was that it was a few hundred years long. Yes, there is a probable volcano in the middle of it, but that’s well AFTER a lot of the cold is soaking in. One of the second things I realized is that weather then was much more volatile and much colder than now. (Well, than the last 40 years. The UK is presently experimenting with something more like the weather of several hundred years ago… so maybe:
At any rate, along the way I ran into a site that looked to have a very well researched paper on the topic. Being completely unfamiliar with the site (as it was a google based stumble upon) I clicked up to the home page where it self describes as a “Conservative Think Tank” founded by a Senator. (1994 – US Senator Malcolm Wallop). It is named “Frontiers Of Freedom”. I think I’ll have to learn more about them.
(I’m generally a bit skeptical of “think tanks” set up by politicians, but the work looks to be well laid out and properly referenced. I don’t know any reputations of the authors, though, so can’t properly evaluate it.)
At any rate, I’m going to quote one of their papers and add a comment or two. Just bear in mind that this is a “think tank” document and of unknown motivation.
The Dark Ages Cold Period
This is a chronology of the weather and climate shifts of The Dark Ages Cold Period. What I find intriguing about it is that it once again confirms the idea that a cold half cycle is also wet (presumably as heat is dumped off planet) and a hot half cycle is dry (as less moisture carries heat to altitude, to condense and fall as rain).
Dark Ages Cold Period (North America) – Summary
Noting that “knowledge of natural climatic variability is essential for evaluating possible human impacts on recent and future climate changes,” Hu et al. (2001) “conducted multiproxy geochemical analyses of a sediment core from Farewell Lake in the northwestern foothills of the Alaska Range,” obtaining what they describe as “the first high-resolution quantitative record of Alaskan climate variations that spans the last two millennia.” The team of five scientists say their results “suggest that at Farewell Lake SWT [surface water temperature] was as warm as the present at AD 0-300 [during the Roman Warm Period], after which it decreased steadily by ~3.5¡C to reach a minimum at AD 600 [during the depths of the Dark Ages Cold Period].” From that point in time, they say “SWT increased by ~3.0¡C during the period AD 600-850 and then [during the Medieval Warm Period] exhibited fluctuations of 0.5-1.0¡C until AD 1200.” Completing their narrative, they say that “between AD 1200-1700, SWT decreased gradually by 1.25¡C [as the world descended into the depths of the Little Ice Age], and from AD 1700 to the present, SWT increased by 1.75C,” the latter portion of which warming initiated the Modern Warm Period.
First off, that link listed at the top is a dead link. Don’t know what it was, or what it was for. Each of the “Foo et.al” references is a similarly dead link to “co2science.org” which does still exist, so perhaps this is just an old copy of one of their papers and they’ve had a site map reorg. More things to check “someday”…
But it’s on the content level that I find this interesting. It reports research done on things like sediment cores, pollens, and soil carbon. Real science, not computer models and simulations. ( I’m a “computer guy” by profession, so my skepticism of the validity of “models” as predictors of reality comes from actual experience.) I like Real Science ™ done on the ground and in the lab.
So what do they find? A cyclical process with about a 600 year period (300 year half period). There are some non-trending times like 900-1200 A.D. and then a 500 year drop. So there are some quasi-cyclical influences to be worked out. But watching for things to change at the 300 year point from the last inflection ought to be ‘fruitful’ more often than not. (Yeah, too small a sample to say for sure, but the pattern is there.) And where are we now? Roughly 300 years into a ‘warming trend’. That would say to watch out for a reversal. And not just a 60 year PDO cycle reversal, a 600 year cycle reversal.
A 1500 Year Perspective in Carbon
Dropping down to the central part of the conterminous United States, Follett et al. (2004) “used 13C:12C ratio (δ13C) and 14C dating to evaluate relationships and changes in warm (C4) versus cool season (C3) plant signatures with age of soil organic carbon” across “three soil temperature regimes and three soil moisture regimes within the historic grasslands [of the] US Great Plains and Western Corn Belt” for the entire period of the current interglacial or Holocene. They report that their data “indicate a change from C4 plants to increasing C3 plant dominance (as a surrogate of cooler temperature) at ~1,500 yr BP.” More specifically, they say that “the yr BP when δ13C was least negative was 1560,” and that “δ13C was more negative before or after that time,” which puts this significantly colder interval of time right in the middle of the Dark Ages Cold Period, as delineated by the results of the 30-plus other reports of this cold phase of earth’s millennial-scale oscillation of climate that we have reviewed and archived in the various Dark Ages Cold Period subsections of our Subject Index.
OK, I’ve seen that 1500 +/- number before. That’s the Bond Event period. So we’ve got an inflection 1560 years ago. (The period is 1470 +/- 100 or two, so it’s in the error band). This inflection comes just BEFORE the volcano of about 540 AD, as it comes in about 440 AD. Well… Kind of makes that whole ‘blame it all on the volcano’ a bit hard to swallow. Looks more like the volcano is the icing on the cake after a 100 year cooling trend into the inflection in the 1500 year cycle.
Sigma C13 / C12
Here we have an interesting study using C12 vs C13 as a temperature marker. The thesis being that C3 plants (that make a 3 carbon intermediate on the way to sugar as a first step) have a different affinity for C13 when compared to C4 plants (that make a 4 carbon starter unit). Hmmm…. So perhaps part of the C12 vs C13 signature in the CO2 today has to do with our dramatic cutting down of wild C3 plants and farming the area with loads of things like corn (maize) that’s a C4 plant which is more happy to pull C13 out of the air. (BTW, there are also C4 diatoms discussed at the C4 link above and some plants can swap from C3 to C4 as needed. So if they can change the C12 / C13 ratio they use, that will have interesting implications for attributing C12 / C13 ratio changes to people.)
This paper: http://www.plantphysiol.org/cgi/reprint/36/2/133.pdf talks about how that ratio changes with different plants and different parts of plants.
Notably, it also has a table in it that shows “ocean carbonate” with a very positive sigma C13 / C12 along with the values (as ranges) for various oils, coal, and plants. I find it intriguing that this implies either the ratio was very different in the past, or the formation of marine limestone or ocean carbonate will preferentially use C13, thus leaving more C12 behind. Oddly, while the chart shows “marine limestone’ as a positive sigma C13/C12 compared to air, the text says that “limestone” (unqualified) is about the same as air. Something different seems to be happening with ocean limestone. (Which implies we need to know more about limestone creation and destruction and the types of limestone – or the chart is wrong…) The creation of marine carbonate would imply it removes C13, giving the same signature as people burning fossil fuels… It looks to me like we need a very good understanding of ocean carbonate and limestone creation and destruction (and on an isotopic basis…) or we are clueless about what changes in atmospheric C13 / C12 ratios might mean. (It’s also possible that the Marine Limestone is made at, for example, mid-ocean ridges and that source of CO2 is enriched in C13. In that case it implies we can’t know much about our impact on C13 / C12 ratios as we don’t now how mid-ocean ridge CO2 production changes over time. It all just looks to me like a big “we don’t know” on where the two isotopes come from and go to. But the paper does show how plants use them. Further, the chart implies that cutting down a load of forest (as we’ve done world wide) has the same signature as burning fossil fuels…
Wet Pollen and Dinoflagellates in the Water
Meanwhile, back at the first link / paper:
Moving to the east coast of the United States, Willard et al. (2003) “examine[d] the late Holocene (2300 yr BP to present) record of Chesapeake Bay and the adjacent terrestrial ecosystem in its watershed through the study of fossil dinoflagellate cysts and pollen from sediment cores.” They report that “several dry periods ranging from decades to centuries in duration are evident in Chesapeake Bay records.” The first of these periods of lower-than-average precipitation, which spanned the period 200 BC-AD 300, occurred during the Roman Warm Period. The next such period (~AD 800-1200) “corresponds to the ‘Medieval Warm Period’, which has been documented as drier than average by tree-ring (Stahle and Cleaveland, 1994) and pollen (Willard et al., 2001) records from the southeastern USA.” In addition, they note that “mid-Atlantic dry periods generally correspond to central and southwestern USA ‘megadroughts’, described by Woodhouse and Overpeck (1998). Hence, it would appear that the intervening Dark Ages Cold Period was a time of relatively greater wetness throughout much of the United States.
So this gives us confirmation of the thesis that precipitation is a pretty good proxy for heat gain vs loss with warming periods being a time of low precipitation and cooing periods times of high precipitation.
Given that right now we’re getting drenched everywhere AND the talk was all of droughts up until 1998, I think this holds up in our present regime. Further, this implies that we’re headed to cold “right quick”. This also implies that the Salt Lake proxy for hot / cold cycling ought to work just fine. OK, time to start collecting that list of salt lakes and periodic lakes from the comments on the Great Salt Lake Barometer posting and gather data. If Lake Chad starts coming back, I think we’ll have a poster child for cooling… I’d also be wary of buying property near the Great Salt Lake ;-)
Sand Grains and Water Flow
A similar pattern of alternating multi-century wet and dry regimes was found by Campbell (2002), who analyzed the grain sizes of sediment cores obtained from Pine Lake, Alberta, Canada to provide a high-resolution record of climate variability for this part of North America over the past 4000 years. Periods of both increasing and decreasing grain size (moisture availability) were noted throughout the 4000-year record at decadal, centennial and millennial time scales. The most prominent of the major dry periods once again occurred during the Roman Warm Period (abut 900-100 BC) and Medieval Warm Period (about AD 700 to 1300), while the major wet periods occurred during the Dark Ages Cold Period (about 100 BC to AD 700) and Little Ice Age (about AD 1500 to 1900).
In conclusion, throughout many parts of the United States and some of Canada, it would appear that the Dark Ages Cold Period was a time of both relative coolness and wetness, much like the Little Ice Age was in this part of the world.
And following that are a bunch of references that look like peer reviewed journals to me.
So this part finds. from looking at grain sizes in cores. that there are decadal, centennial, and millennial scale events. Well, we know there’s a 11 year sun spot cycle. We know there is a 176-208 year solar quasi cycle (and three of them would be a 600 year quasi cycle). And we know there are 1500 year Bond Events.
Again the conclusion that “warm is dry” and “cold is wet”. Makes that 1930′s Dust Bowl and the 1934 record hot look more like a matched set…
Also note that this is in North America, so confirms that the Dark Ages Cold Period was at least hemispheric and probably global in scope as was the Little Ice Age.
All very nicely done.
Somehow I get the feeling I’m going to be spending a while digging through those 2 sites to see what else they have squirreled away.
It’s time to start a big “dig here” into global precipitation data looking for a confirmation with temperatures (and if it diverges in, oh, 1990, we’ve got a major issue with the thermometer station changes then).
It’s time to start a tracking system for various selected cyclical lakes globally. And if they diverge from the instrumental record about 1990, well, that’s going to be a problem too.
If you cook the temperature record (or re-cook it in “adjustments”) you are going to have to cook the precipitation records and the lake levels as well. And, I suspect, retroactively… Oh, and don’t forget the pollen and dinoflagellates too ;-)
It also looks like we are not only at a cold inflection of the 60 year PDO cycle, but also a cold inflection of the 600 year quasi cycle AND a cold inflection of the 1500 year cycle. If that’s in fact the case, we’ve got a big problem. It would explain the high peak in 1998 as all three reached a high roughly together, but it also implies a big plunge right after it. Very “Not Good”.