Via AGU, and the “science is settled” department, once again we learn things we didn’t know about climate.
In most cases, the annual East Asian Monsoon brings heavy rains and widespread flooding to southeast China and drought conditions to the northeast. At various points throughout history, however, large volcanic eruptions have upset the regular behavior of the monsoon.
Sulfate aerosols injected high into the atmosphere by powerful eruptions can lower the land-sea temperature contrast that powers the monsoon circulation. How this altered aerosol forcing affects precipitation is not entirely clear, however, as climate models do not always agree with observations of the nature and scale of the effect.
Using two independent records of historical volcanic activity along with two different measures of rainfall, including one 3,000-year long record derived from local flood and drought observations, Zhuo et al. analyzes how large volcanic eruptions changed the conditions on the ground for the period 1368 to 1911. Understanding the effect of sulfate aerosols on monsoon behavior is particularly important now, as researchers explore aerosol seeding as a means of climate engineering.
The authors find that large Northern Hemispheric volcanic eruptions cause strong droughts in much of eastern China. The drought begins in the north in the second or third summer following an eruption and slowly moves southward over the next 2 to 3 years. They find that the severity of the drought scales with the amount of aerosol injected into the atmosphere, and that it takes 4 to 5 years for precipitation to recover. The drying pattern agrees with observations from three large modern eruptions.
China’s northeast is the country’s major grain-producing region. The results suggest that any geoengineering schemes meant to mimic the effect of a large volcanic eruption could potentially trigger devastating consequences for China’s food supply.
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The paper:
Proxy evidence for China’s monsoon precipitation response to volcanic aerosols over the past seven centuries
http://onlinelibrary.wiley.com/doi/10.1002/2013JD021061/abstract
Abstract
The effect of volcanic aerosols on China’s monsoon precipitation over the past 700 years has been studied using two independently compiled histories of volcanism combined with the Monsoon Asia Drought Atlas. For both reconstructions, four categories of eruptions are distinguished based on the character of their Northern Hemisphere (NH) injection; then Superposed Epoch Analysis (SEA) with a 10,000 Monte Carlo resampling procedure is undertaken for each category and also each individual grid. Results show a statistically significant (at 90% confidence level) drying trend over mainland China from year 1 to year 4 after the eruptions, and the more sulfate aerosol that is injected into the NH stratosphere, the more severe this drying trend. In comparison, a minor wetting trend is observed in the years following Southern Hemisphere-only injections. Results from spatial distribution of the SEA show (1) a southward movement of the significant dry areas in eastern China from year 0 to year 2 after volcanic perturbations that are either equal to or double the size of the 1991 Mount Pinatubo eruption (15 T sulfate aerosols in NH) and (2) northeast and northwest China experienced substantial droughts in years 2 to 5. These results are in good agreement with a SEA analysis of the Chinese Historical Drought Disaster Index compiled from historical meteorological records. Our findings illustrate the important role stratospheric aerosols have played in altering China’s precipitation during the summer monsoon season and can shed new light on the possible effects that stratospheric geoengineering may have on China’s precipitation.
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From Wikiepdia:
A volcanic winter from an eruption in the late 17th century BCE has been claimed by some researchers to correlate with entries in Chinese records documenting the collapse of the Xia dynasty in China. According to the Bamboo Annals, the collapse of the dynasty and the rise of the Shang dynasty, approximately dated to 1618 BCE, were accompanied by “yellow fog, a dim sun, then three suns, frost in July, famine, and the withering of all five cereals”.
Source: Foster, KP, Ritner, RK, and Foster, BR (1996). “Texts, Storms, and the Thera Eruption”. Journal of Near Eastern Studies 55 (1): 1–14. doi:10.1086/373781.
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I did a long search of historical drought / famine a while back. Essentially, it happens during cold phases. Some modest, some dramatic; always the same cycles…
China tends to get it bad in cold times. Every “long time” of about 1000 to 1500 years (but with some 750 year minor points and even a 1/2 that about 360-375 year pattern) we get cold bad times. Especially Egypt gets whacked on the long cycle. The fall of the Akkadian Empire along with the Old Kingdom / New Kingdom transition.
This isn’t just supported by history books. It is supported by sand / dust layers in the dirt. By layers of death in the ground.
So this paper finds a specific: Volcanoes cool things, and China has drought.
Now generalize….
Things COOL, and lots of folks get drought, leading to famine, death, and economic collapse, followed by political upheaval and the fall of dynasties. It has happened repeatedly throughout history. Some major (like the Old Kingdom / New Kingdom transition) and some minor (like a famine in China). Some others major, but not quite fully taking down the major Empire. In 535 AD a cold dark cycle hit. The Western Roman Empire fell and the Dark Ages began. In the east, the Eastern Roman Empire surived (eventually to become Byzantium). They made it all the way to the Little Ice Age …
Why am I, a person of mixed English, German and Irish ancestry over here in North America? Because during an early cold fall, my Saxon ancesters moved to England. During another, my Irish ancesters abandonded a cold and starving Europe and moved here. And in another, my German ancesters moved south from the coast, then off to the west. Each time leaving cold and starvation behind, and moving to warmth and plenty.
The Migration Era Pessimum was called that due to it being a pessimistic time due to the cold. ( The Wiki has now been purged of the name ‘pessimum’ after it was pointed out…) The folks on those Asian steppes always run south and west when the cold returns. That is why Hungarians are in the middle of Europe. That is why Ostrogoths wandered past Rome and on as Visigoths headed down to Spain (and on to North Africa).
In warm times, people expand north and east in Eurasia. In cold times, they run south and west. It pulses all through history. (Though the Slavs moved north and east, then hung onto the land as the cold came). For America, that movement got on boats and came to a new continent. It contiued even here. In “The Year WIthout A Summer” or “1800 and Froze To Death”, farms in New Endland were abandoned as folks headed south and west into Oklahoma in a great land rush. My family ended up in Iowa in slighly warmer times and stayed through the Dust Bowl hot times… then ‘moved on’ to California a bit after the Grapes Of Wrath …
That the folks who preach catastrophic unprecidented “Climate Change” seem clueless about this is a bit daft of them… We are in unprecidented stable and pleasant times. What historically was called an “Optimum”. A warm optimum. (And a lot of Mexicans are moving north and east…) It is not the warmth that is a problem. It is when the cold returns. As it always does…
One thing to do in life is visit Santorini and enjoy the view on the ancient crator rim as you sip the local wine (Boutari) . But go in late spring and early summer. I also recommend visiting Crete to imagine how the Minoans lived in an agreeable warm climate before Thera blew and destroyed their civilization. One can look further back in human history when the Indonesian supervolcano erupted and changed the destiny of mankind. It just shows us how the dynamic earth may decide to burp in the future and once again have an destructive effect on mankind. And we are worrying about a degree or so temperature rise over a century. How pathetic we are.
Steve Mosher
Do you not understand the posted study?
It puts cooling as the cause of crop failure/famine. What do you think? Should this be rejected? It has great implications for the whole school that adheres to the viewpoint “CO2 is bad” If this is right then you are not.
John nice post. Actually there is a bit of controversy about when and how the Minoan civilization collapsed, as there discrepancies in the archaeological record. One thing for sure though, is Thera was the main hub for trading and an earthquake did a lot of damage decades before the eruption, they were rebuilding then. I’ve passed Crete on my way to Cyprus in the sixties. It has very high mountains. The time of the eruption would depend on the month. As the Cretan fleet only went out at times when the same men were not required for agriculture and inter-trade items. So the fleet may have been else where or just harbored. There was little ash deposits, and only on the side of the island facing Thera and was not deep. It would have killed off seedlings but would not have harmed fully grown crops or trees. (Olives, fruit etc). It seems, that Thera eruption was four times the force of Krakatoa, but depending on the wind the ash cloud may have largely missed Crete and other nearby land falls. There is evidence that some sea did go inland though, but Knossis is placed very high and maybe not effected by the Tsunami directly. But all sea life in the area would have been effected. But it would have left the main hub for trading under the sea. And maybe they switched to Mycenia as their main trading posts.