Was the Medieval Warm Period the Result of AGW?

[bbr2314]

It has been difficult/impossible to find anything specific relating to this, but wondering -- could it be possible that the "Medieval Warm Period" was in fact the result/after-effect of peak emissions from the Roman period through the time of Genghis Khan & the Black Death?

Current theory seems to blame solar/other influences but it seems oddly coincidental that the "Little Ice Age" would follow the only widely-established human population decline in the last several thousand years.

Does anyone have any information on Roman-era carbon output? From this account it would seem it got to about where we were in 1750 or so. And while the popular narrative says AGW only began recently, the ongoing extinctions of megafauna/etc would argue that perhaps the impacts of AGW began *far* long ago, and we may actually be able to look at the Medieval Warm Period & ensuing Little Ice Age as an example of what happens when carbon emissions see a relatively rapid rise and decline (although not absolute, the derivative of output surely decreased as societies in Europe/Asia fell apart from ~1250-1500, and importantly, the end of this timeframe is when the Americas genocide occurred).

With industrial output only reaching levels it attained back in 0-200AD in ~1650 or so, that = a cooldown in human GDP output for approximately 400 years... which is perhaps not coincidentally approximately the length of the "little ice age."

www.independent.co.uk/news/uk/ice-pack-reveals-romans-air-pollution-1450572.html

IF this is anywhere near valid or true (and it could be completely off-base), then is it possible that the derivative annual change of our carbon addiction is more important to the direction global climate state than its actual figure?

I would think the explanation for this would be that the planet has an extraordinary capacity for absorbing CO2, and as we have seen, we have been surprised by the uptake of the deep oceans/everything else considering how much pollution humans have spewed.

Once industrial output begins to decline/carbon emissions decrease, that leaves the planet with its newfound "infrastructure" of expanded carbon sinks, and then these work to dissolve/distribute the excess CO2 at a pace that then surpasses humanity's inputs. These processes are particularly obvious to us over areas like the North Atlantic, and it could be possible that some variation of AMOC shutdown was responsible for the LIE over Europe as well.

Obviously modern output/sheer volume would potentially induce a sharper reaction both in terms of warming and cooling, assuming the warming does not run out of control. Is this insane or possible?

(this paper also a great read! http://www2.sci.u-szeged.hu/eghajlattan/akta03/005-015.pdf)

[Neven]

bbr2314, your question reminds me of the work of William Ruddiman. See his book, Plows, Plagues and Petroleum: How Humans Took Control of Climate, published 10 years ago. Or see this Nature article from a couple of years ago:

The 8,000-year-old climate puzzle

Models bolster case for early human effect on greenhouse-gas levels.

Scientists have come up with new evidence in support of the controversial idea that humanity's influence on climate began not during the industrial revolution, but thousands of years ago. Proposed by palaeoclimatologist William Ruddiman in 2003, the theory says that human influences offset the imminent plunge into another ice age and helped create the relatively stable climate that we are familiar with today. It has been repeatedly panned as implausible by palaeoclimate researchers, but eight years on, Ruddiman and others say that they have the data to support early anthropogenic climate change.

The argument centres on a curious trend in atmospheric carbon dioxide and methane levels since the last ice age ended about 11,000 years ago and the current Holocene epoch began. In previous interglacial periods, CO2 levels spiked early and then gradually declined until the globe went into another ice age. The Holocene began by following this trend, but then CO2 levels changed course and began to rise around 8,000 years ago. The same thing happened with methane levels around 5,000 years ago. These trends align with the expansion of human agriculture, and Ruddiman, of the University of Virginia in Charlottesville, argues that it is no coincidence — the clearing of land and expansion of irrigation released huge amounts of greenhouse gases into the atmosphere.

Critics say that human populations were probably too small to support such a hypothesis, and recent studies have raised serious questions about early anthropogenic carbon and methane emissions. But rather than backing down, Ruddiman and several other researchers will present their supporting evidence in a series of papers scheduled for publication in a special issue of The Holocene journal later this year. Researchers presented some of the work this week at the American Geophysical Union's Chapman Conference on Climates, Past Landscapes and Civilizations in Santa Fe, New Mexico.

"I'm of course hopelessly biased, but this year is going to be a good year for the early anthropogenic influence hypothesis," Ruddiman said as he presented his overview study.

[S.Pansa]

As I have just finished Ruddimans recent book "Earth Transformed", I wanted to add two figures that might be relevant to your question.
The first image illustrates what Neven has cited above - the core of Ruddimans hypothesis/theory (While in the last interglacials GG-concentrations gradually declined, in the Holocene they suddenly started to grow again - and that was us, says Ruddiman).
The second figure shows the greenhouse-gas-concentrations (CO2, CH4) during the last 2.000 years and compares them to big depopulation events in China, Europe and the Americas. According to Ruddiman, especially the killing of 50m people in the late 16th century, after the "discovery" of America,  did contribute to the LIA.

And is a video of Ruddiman summarizing the latest science on his theory (AGU Meeting 2014).

[bbr2314]

TY for the responses!

Neven: last night I actually found him, and did some research on his UVA homepage which has some good links to his recent work.

www.evsc.virginia.edu/ruddiman-william-f/

While his work is absolutely fantastic, it unfortunately seems to focus primarily on the impact of agricultural contributions vs. something more comprehensive that would take industry into account. Not that I would fault him for this, but perhaps it begs questions --

1) Is it easier to see the impact of agriculture on AGW than it is to examine industry's impact? I think it is a foregone conclusion that initial human transformation of the planet (farmland/etc) had a huge effect, and if we are now making even larger changes through industrial output (that we are only now "officially" noticing), then why would it be a stretch to assume industrial output may have been equally or partially as impactful 1000-2000 yrs ago, at its advent?

2) Does the impact of industry have a "shorter" but more impactful signature than agriculture? Are we just missing it in some places still? Could we be missing the "peaks" in emissions in the data from the last 2000 years, and could our current estimates of the maximum previous outputs of global CO2 be missing some of the higher data points from what was evidently the last cycle of obvious AGW?

[Neven]

What industry are you thinking of? Metallurgy? I don't think that comes even close to the level of industry in modern times. I'd think that deforestation for agriculture is the most significant factor, land use changes rather than greenhouse gases. But I know nothing of the subject.

[jai mitchell]

I have long suspected that the increased AMOC during this period, and the resulting warmer temperatures in the north atlantic region was the result of massive deforestation of the amazon by the mayan culture.  There has been recent observations of ancient agriculture there that showed a population that rivaled that of europe during the same period. 

a deforestation led drought and reduction in DMS would produce the observed drought of the period and significant reductions in regional rainfall could lead to an increased salinity of the tropical atlantic which would increase the rate of downwwelling of the AMOC at the north atlantic.

[JMP]

Mayan deforestation yes, perhaps but don't think they got quite so far South   (of course you meant what is now Mexico and the Yucatan Peninsula?)  Maya = fascinating.

 

There seems to be evidence that the warming was not uniformly global, that the Southern Hemisphere didn't warm simultaneously (?)
   
 (sadly can only get to the abstract) http://www.nature.com/nature/journal/v346/n6283/abs/346434a0.html

...we introduce a new millennial ensemble reconstruction of annually resolved temperature variations for the Southern Hemisphere based on an unprecedented network of terrestrial and oceanic palaeoclimate proxy records. In conjunction with an independent Northern Hemisphere temperature reconstruction ensemble5, this record reveals an extended cold period (1594–1677) in both hemispheres but no globally coherent warm phase during the pre-industrial (1000–1850) era. The current (post-1974) warm phase is the only period of the past millennium where both hemispheres are likely to have experienced contemporaneous warm extremes.

Or, at least there was lack of uniform warming with relative cooling in the Tropical Pacific.  It's complicated.  
Interesting information here:

Support for global climate reorganization during the ‘‘Medieval Climate Anomaly’’  http://shadow.eas.gatech.edu/%7Ekcobb/pubs/graham10.pdf

[bbr2314]

I think the problem seems to be that we humans are incapable of piecing together all the historical pieces, and our Western culture/upbringing leaves us with 90% of typical historical education focusing on relatively modern times, and then further back, it only really centers on Rome (and a bit of Greece, its predecessor). While Asia is typically acknowledged, human influence on the Americas is usually ignorantly dismissed as a bunch of people in teepees when in fact they were at pretty much the same level as the Europeans, at least in terms of CO2 output.

So if people are even educated about events like the Native American genocide at all, they don't think of these people as having lived in cities/etc. And that's ignoring the tremendous output that was happening in Asia prior to Genghis Khan/Black Death, too!

When you look at these events from a global rather than a regional perspective they seem to fit into our recorded temperature measurements to a tee.

Neven: I was extremely surprised to discover that the Romans did in fact have a tremendous industrial output, partially because their smelting methods were much dirtier and released significantly more amounts of gas.

http://historum.com/blogs/guaporense/959-rise-fall-ancient-economy-part-1.html

Copper, lead, etc, all of these things were produced by the Romans at levels unseen again til about 1750 (besides things beyond their tech at that point -- which relatively speaking in terms of filthy GHG producing energy sources, wasn't that much).



Also, the article linked in the first post (again below) gives a fantastic overview of ancient industrial output.

http://www2.sci.u-szeged.hu/eghajlattan/akta03/005-015.pdf

Outside the Roman Empire, important copper production occurred in Southwest
Asia and in Far East, too. When the Han dynasty (206 B.C. –220 A.D.) extended its
influence to Southwest Asia, copper production of China was about 800 tons/year. In the
medieval age, most part of the world production came from China (during the rule of the
northern Sung dynasty). In this period, the Chinese production reached its maximum of
13,000 tons/year and this resulted in the peak of the world production of 15,000 tons/year in
1080s A.D. Most part of copper was used for minting (Archaometallurgy Group, Beijing
University of Iron and Steel Technology, 1978). During some hundred centuries after this
period, the production suddenly dropped (about 2,000 tons/year in the 14th century) and
then started to increase again from the industrial revolution till recently. (A comparison: the
total copper production of the world was 10,000 tons/year at the beginning of the industrial
revolution.)

...importantly

Emissions concerning the production, in connection with a significant technological
development, have considerably changed during the past 7,000 years. In the ancient times,
due to the primitive smelting procedures, the emission factor was about 15 %. At the
beginning, several steps of processing of sulphide ores (roasting, smelting, oxidation,
cleaning) were performed in open furnaces. Emission has been taken out of consideration
until the industrial revolution. From this time on, more developed furnaces and more recent
metallurgical procedures have spread. Since the middle of the 19th century, the processing
procedure has reduced to five steps. These technological developments have resulted in
significant decrease of the emission factor. In the 20th century, this factor has only been 1 %
and later, with introducing further modifications, it became a mere 0.25 % (Hong et al.,
1996a; 1996b).

According to the ice samples in Greenland, comparing production data with
emission factors, atmospheric copper emission culminated twice in the period before the
industrial revolution. The first peak occurred in the golden age of the Roman Empire about
2,000 years ago with a mass of some 2,300 tons/year, when use of metal coins spread in the
Ancient Mediterranean. The second peak appeared in the golden age of the northern Sung
dynasty (960-1279 A.D.) in China, at about 1080 A.D. with a mass of some 2,100
tons/year, when the Chinese economy was extensively developing and copper production
increased. Since smelting technology was primitive at that time, about 15 % of the smelted
copper got into the atmosphere. Though the total copper emission of the Roman and Sung
times was about a tenth of that in the 1990s, copper production did not reach even a
hundredth of that in the recent period. Hemispheric copper pollution caused by copper
emissions has more than 2,500 years old history and copper emissions of the Roman and
Sung times were so high than never before 1750 (Hong et al., 1996b).

[bbr2314]

I have long suspected that the increased AMOC during this period, and the resulting warmer temperatures in the north atlantic region was the result of massive deforestation of the amazon by the mayan culture.  There has been recent observations of ancient agriculture there that showed a population that rivaled that of europe during the same period. 

a deforestation led drought and reduction in DMS would produce the observed drought of the period and significant reductions in regional rainfall could lead to an increased salinity of the tropical atlantic which would increase the rate of downwwelling of the AMOC at the north atlantic.

This would make sense, though I would think it would have occurred on the "other" side of the forest from where deforestation is most prevalent today, i.e. on the Andes-facing side vs. the Brazilian coast? Maya mentioned above, but Incas were equally competent...

[johnm33]

Roman palaces were mostly kept warm by underfloor heating, and these furnaces alone led to massive deforestation both locally and increasingly around the Med. wherever ships could access.
I can't remember where i read it but iirc a Portugese agronomist calculated that a sustainable population of 65m could have lived in the amazon basin area using the farming methods they had. So he suspected the actual number would be higher than the 16m max of then current estimates, which would go some way to explain why tribes now reduced to 2-300 claim ancestral rights to areas the size of France, his thought not mine.
It's worth a look at  https://en.wikipedia.org/wiki/Mound_Builders these people were accidently wiped out by the French, whilst trading had had very little impact as soon as the French began to bring children over all the diseases of childhood came with them and frequently only a core of the most robust young adults in a society, as little as 5%, survived an epidemic, which were diverse and came in waves, so over a couple of generations many whole cultures disintegrated. I'm deeply sceptical of the claim they were hunter gatherers, and suspect they cleared vast areas of forest for agriculture, which grew back long before the Louisianna purchase.