LC12C. Stay Current—Climate & Culture

Life and Climate book cover

Staying current for Chapter 12

{ Life and Climate Contents }

2023-09-13. Eclipse Records Pin Dates of 12th and 13th Century Eruptions. [] By Kate Evans, Eos/AGU. Excerpt: …ancient observations of rare dark lunar eclipses have recently taken on new importance after scientists used the records to date notable volcanic eruptions that occurred nearly a thousand years ago. The findings, published in Nature, could help answer some big questions about volcanism and climate change. …University of Geneva paleoclimatologist Sébastien Guillet …had been poring over hundreds of medieval manuscripts, searching for records of lunar eclipses that described the color of the Moon in totality. …The 12th and 13th centuries were among the most volcanically active of the past 2,500 years. Scientists know from telltale sulfate layers in Greenland and Antarctic ice cores that there were seven significant volcanic eruptions between 1108 and 1286. But only one of them—the eruption of Samalas on the island of Lombok in Indonesia in 1257—has been linked to a specific volcano or location. “These eruptions are very interesting because they happen at a quite critical moment,” Guillet said: the transition from the warm Medieval Climate Anomaly to the much colder Little Ice Age. “Did they contribute to this transition? And if so, to what extent? …The beauty of eclipses is that we know exactly when they occurred. And crucially, the color of the Moon during totality turns out to be a good proxy for whether there’s been a massive volcanic eruption lately. …Records of dark lunar eclipses showed up in 1110, 1172, 1229, 1258, and 1276, contemporaneous with five of the seven largest volcanic sulfate signals recorded in polar ice cores. …Medieval chroniclers recorded not just dark moons, but frosts, crop failures, and famines, she said. The eclipse records help to link these disruptions to large volcanic eruptions. If there is enough volcanic dust in the stratosphere to turn the eclipsing Moon black, there’s likely enough to cool the climate—something scientists can corroborate by checking tree rings for years of poor growth. …That knowledge may also help scientists to predict the effects of future volcanoes….

2022-12-17. For Planet Earth, This Might Be the Start of a New Age. [] By Raymond Zhong, The New York Times. Excerpt: The official timeline of Earth’s history — from the oldest rocks to the‌ dinosaurs to the rise of primates, from the Paleozoic to the Jurassic and all points before and since — could soon include the age of nuclear weapons, human-caused climate change and the proliferation of plastics, garbage and concrete across the planet. In short, the present. …a panel of scientists on Saturday took a big step toward declaring a new interval of geologic time: the Anthropocene, the age of humans. Our current geologic epoch, the Holocene, began 11,700 years ago with the end of the last big ice age. The panel’s roughly three dozen scholars appear close to recommending that, actually, we have spent the past few decades in a brand-new time unit, one characterized by human-induced, planetary-scale changes that are unfinished but very much underway. “If you were around in 1920, your attitude would have been, ‘Nature’s too big for humans to influence,’” said Colin N. Waters, a geologist and chair of the Anthropocene Working Group, the panel that has been deliberating on the issue since 2009. The past century has upended that thinking, Dr. Waters said….

2022-10-24. Oldest British DNA reveals mass immigrations after last ice age. [] By Andrew Curry, Science Magazine. Excerpt: Genetic material recovered from two caves suggests climate change brought into new cultures and lifestyles. …reindeer hunters etched designs onto human bones and drank out of carved human skulls about 15,000 years ago. A few hundred kilometers to the north, people living just a few hundred years later lived on freshwater fish and marine animals, laying their dead to rest in a cavern with decorated horse bones and bear-tooth pendants. Archaeologists had long thought these cultural shifts reflected people developing new tools and beliefs after the last ice age 18,000 years ago. But new evidence from the oldest known DNA from the British Isles shows the two sets of cave dwellers had dramatically different ancestry. These sweeping cultural changes weren’t signs of Great Britain’s first postglacial people adapting—they were signs of entirely new people altogether. …As the climate warmed, open tundra quickly gave way to thick forests. Melting ice sheets opened up new areas for human habitation, including what is today Great Britain, which was then connected by a land bridge to mainland Europe. A genetic analysis from two English caves, published today in Nature Ecology & Evolution suggests that as the landscape changed, populations shifted, too, with groups bringing new cultural practices, diets, and hunting strategies with them while replacing or pushing out previous populations.…

2022-08-04. Evidence of Drought Provides Clues to a Viking Mystery. [] By Korena Di Roma Howley, Eos/AGU. Excerpt: …Why, after more than 450 years, did a colony of medieval Norse farmers disappear from their remote Greenland settlement? In attempting to uncover what may have happened, researchers have returned again and again to climate—and to a seemingly obvious scenario. Having turned up on the island during the centuries-long Medieval Warm Period, the settlers were then gradually ushered out by the arrival of the Little Ice Age in the 14th century. But a new study has found that drought, not plunging temperatures, may have pushed an already fragile community to its breaking point. …Around 985 CE, at the height of the Viking era, a group led by exiled explorer Erik the Red sailed west from Iceland and established the first European settlement on Greenland. The Norse farmed the land and hunted walrus for the ivory trade. …Though they inhabited Greenland concurrently with Indigenous Dorset and Thule populations, archaeological findings show that the Norse never adopted effective Indigenous sea ice hunting practices or tools. Other evidence indicates conflict between the two populations. According to radiocarbon dating, by 1450, the Norse settlers were gone. The Little Ice Age, a period of cooling temperatures, began around 1300 and affected different parts of the globe at different times until the mid-19th century. …researchers have tended to extrapolate Little Ice Age climate effects in western Europe and Iceland and, perhaps erroneously, relate them to the fate of the Norse in North America. …In looking at both temperature and hydroclimate, the researchers made two surprise findings. “We were expecting to see this dramatic temperature drop at the end of the Norse settlement period, if temperature was indeed the main factor that caused them to leave,” Castañeda said. Instead, the leaf waxes revealed that Greenland had experienced a relatively wet period just before the settlers arrived, and conditions became drier over time, peaking in the century after the Norse abandoned the site. According to study authors, this long-term drying trend would have decreased summer grass yields, a critical source of winter fodder for livestock.…

2022-01-11. Did Volcanoes Accelerate the Fall of Chinese Dynasties? By Tim Hornyak, Eos/AGU. Excerpt: After analyzing ice cores and historical documents, researchers found a link between eruptions and political change in China over the past 2 millennia. Researchers in China, Europe, and the United States …have found that volcanic eruptions (as well as conflict) may have contributed to dynastic collapse because they cooled the climate and affected agricultural production.… []

2021-11-29. How one society rebounded from ‘the worst year to be alive’. By Michael Price, Science Magazine. Excerpt: It was the worst time to be alive, according to some scientists. From 536 C.E. to 541 C.E., a series of volcanic eruptions in North and Central America sent tons of ash into the atmosphere, blocking sunlight, chilling the globe, and destroying crops worldwide. Societies everywhere struggled to survive. But for the Ancestral Pueblo people living in what today is the U.S. Southwest, this climate catastrophe planted the seeds for a more cohesive, technologically sophisticated society, a new study suggests. …Although there’s no way to perfectly reconstruct how the Ancestral Pueblo people’s social systems broke down and reformed, Sinensky thinks it may have happened something like this: As crops continued to fail, the small, disparate groups eventually had to band together to survive. They shared technology and growing techniques and built villages. Then, as rain and warmth returned, this cohesion persisted. Chaco Canyon emerged as a major cultural center for a resilient, restructured society. The findings speak to the ability of humans to reorganize in response to even extreme climate changes, Sinensky adds. “Ancestral Pueblo people restructured … and thrived with this reorganized economic and political structure,” he says. “We should take some solace in knowing that it’s possible to reorganize, to change, even deeply rooted aspects of societies.”… []

2021-03-17. Drawing A Line In The Mud: Scientists Debate When ‘Age Of Humans’ Began. By Rebecca Hersher, National Public Radio. Excerpt: Humans have changed the Earth in such profound ways that scientists say we have entered a new geological period: the Anthropocene Epoch. But when did the new epoch officially begin? …Teams are studying 11 locations on five continents, looking for a place where rock, mud or ice perfectly capture the global impact of humans. …ultimately only one site will be crowned the “golden spike” location for the Anthropocene: the place on Earth where a line in the rock, mud or ice exemplifies the unique markers of the age of humans. …For example, there is a line of pollen and dust in a specific ice core from Antarctica that is the official reference point for the beginning of the Holocene epoch, which commenced when the last ice age ended about 12 thousand years ago. The golden spike location for the end of the age of dinosaurs about 66 million years ago is a line in a cliff in Tunisia, where global debris from a meteor impact is clearly visible. …”There are some people who see an old Anthropocene that goes all the way back to when we see humans controlling and using fire, a hundred thousand years ago” …Others point to the dawn of agriculture as the moment that humans began to have large-scale impacts on the planet. Still others…point to colonialism as the turning point. …But the geologists on the Anthropocene Working Group disagree with the idea that the age of humans began hundreds or even thousands of years ago. They argue that industrialization and the nuclear age are the best geological markers of the new epoch. Specifically, scientists on the golden spike teams are zeroing in on a period in the 1940s and 1950s when some humans began detonating nuclear bombs…. [

2021-01-28.  Drought, Not War, Felled Some Ancient Asian Civilizations. By Richard J. Sima, Eos/AGU. Excerpt: Radiocarbon dating, luminescent sand grains, and climate records point to drought as the reason for the civilizations’ demise. When we read about the fall of ancient civilizations in history books, we may think of warfare and other struggles on the human stage as leading causes for a culture’s decline. But climate change also accounts for many a society’s ruin. Such seems to be the case for the central Asian civilizations of the Otrār oasis located at the junction of the Syr Darya and Arys Rivers in what is now southern Kazakhstan. In a new study published in the Proceedings of the National Academy of Sciences of the United States of America, an interdisciplinary team of researchers report that the Otrār oasis had already been in a prolonged period of decline long before the Mongols invaded. …The clues lie in irrigation canals that the ancient civilizations of Transoxania relied on for agriculture. …Transoxania’s canals were previously thought to have been destroyed by the Mongols during their invasion, helping to precipitate decline in Transoxania. But Macklin and his colleagues were able to determine that much to their surprise, the canals fell into disrepair before Mongols ever set foot in the region. They used a combination of radiocarbon dating and a technique called optically stimulated luminescence (OSL), which dates the last time that sand was exposed to sunlight. …The researchers also reconstructed climate records in the region over the past 2,000 years, which revealed that the canals were abandoned during periods of prolonged drought that both weakened the civilizations before the Mongols arrived and stunted their recovery afterward. Archaeological records further corroborated the coincident timing of the region’s cultural decline…. []

2020-08-24. Ancient megadrought may explain civilization’s ‘missing millennia’ in Southeast Asia. By Charles Choi, Science Magazine. Excerpt: A megadrought that lasted more than 1000 years may have plagued Southeast Asia 5000 years ago, setting up dramatic shifts in regional civilizations, suggests a new study of cave rocks in northern Laos. The researchers believe the drought began when the drying of the distant Sahara Desert disrupted monsoon rains and triggered droughts throughout the rest of Asia and Africa. For years, archaeologists studying mainland Southeast Asia—an area encompassing modern-day Cambodia, Laos, Myanmar, Malaysia, Thailand, and Vietnam—have been puzzled by what they call “the missing millennia,” a period from roughly 6000 to 4000 years ago with little evidence of human settlements. University of Pennsylvania archaeologist Joyce White, a co-author on the new paper, says she and others long thought this was because researchers hadn’t yet pinpointed where people of the era lived. Now, she believes the settlements could be missing because a megadrought devastated their populations and drove them to find water elsewhere. To re-create the climate of that time, White and her colleagues investigated stalagmites in Tham Doun Mai, a cave in northern Laos…. []2020-06-22. Ancient Rome Was Teetering. Then a Volcano Erupted 6,000 Miles Away. By Katherine Kornei, The New York Times. Excerpt: Scientists have linked historical political instability to a number of volcanic events, the latest involving an eruption in the Aleutian Islands. …This eruption was one of the largest of the last few millenniums, Dr. McConnell and his collaborators concluded, and the sulfate aerosols it created remained in the stratosphere for several years. These tiny particles are particularly good at reflecting sunlight, which means they can temporarily alter Earth’s climate. “They’ve created, for a short term, global cooling events,” said Jessica Ball, a volcanologist at the California Volcano Observatory, who was not involved in the research. …There’s good evidence that the Northern Hemisphere was colder than normal around 43 B.C. Trees across Europe grew more slowly that year, and a pine forest in North America experienced an unusually early autumn freeze. Using climate models to simulate the impact of an Okmok eruption, Dr. McConnell and his collaborators estimated that parts of the Mediterranean, roughly 6,000 miles away, would have cooled by as much as 13.3 degrees Fahrenheit…. [] See also New York Times article [] “We can absolutely say this volcanic eruption generated extreme climate,” says Joseph McConnell, a glaciologist at the Desert Research Institute and the study’s lead author. If the eruption did indeed contribute to famine and other disruptions, it could have helped the Roman Empire consolidate its control, McConnell says. “The end of the republic happened during these two extreme years of climate,” he says. “It’s a possible coincidence, but it doesn’t seem likely.”….

2020-01-15. Megadrought Helped Topple the Assyrian Empire. By Mary Caperton Morton, Eos/AGU. [] Excerpt: Paleoclimate records shed light on the ancient civilization’s meteoric rise and catastrophic collapse….

2019-12-31. A warning from ancient tree rings: The Americas are prone to catastrophic, simultaneous droughts. By Paul Voosen, Science Magazine.  [] Excerpt: For 10 years, central Chile has been gripped by unrelenting drought. With 30% less rainfall than normal, verdant landscapes have withered, reservoirs are low, and more than 100,000 farm animals have died. The dry spell has lasted so long that researchers are calling it a “megadrought,” rivaling dry stretches centuries ago. It’s not so different from the decadelong drought that California, some 8000 kilometers away, endured until this year. By analyzing tree ring records, scientists have now found evidence that such tandem droughts are more than a coincidence: They are surprisingly common over the past 1200 years, and they may often share a common cause—an abnormally cool state of the eastern Pacific Ocean known as La Niña. …Nor is it clear how the drought patterns will change as climate warms. A warming atmosphere alone seems certain to make megadroughts more frequent, especially in the Southwest. But scientists remain divided on how climate change will affect the El Niño-La Niña cycle. Models suggest El Niño will dominate, but in the past few decades, La Niña has seemed to be more frequent. …As bad as the drought in Chile is today, it barely qualifies as a megadrought when compared with the medieval ones, which were longer and more severe. Clearly, there was something about that period that switched off in recent centuries, Cook says. If that pattern somehow came back, with greenhouse warming amplifying it, Cook says, “then things could get quite catastrophic.”….

2019-12-05. How a volcanic eruption helped create modern Scotland. By Sid Perkins, Science Magazine. [] Excerpt: Over seven terrible years in the 1690s, crops failed, farming villages emptied, and severe famine killed up to 15% of the entire population of Scotland. The so-called Scottish ills (named after the biblical plagues) ushered in an era of crippling economic conditions. Soon after, the formerly independent nation joined Great Britain. Now, researchers suggest volcanic eruptions thousands of kilometers away may have helped spark this political transformation. Scientists have long known that volcanoes can alter Earth’s climate. During large eruptions, light-scattering droplets of sulfuric acid reach the stratosphere and spread around the globe, reflecting some of the Sun’s radiation back into space and cooling the planet. Such cold spells can last from several months to several years—and they can help trigger droughts and crop failures. The clues to such events are often locked away in the rings of tree, whose growth slows with wild shifts in temperature and precipitation. But until recently, researchers didn’t have any tree-ring records from northern Scotland, where the worst effects of the famine took place. That all changed 2 years ago, when scientists stitched together a complete record of the local climate from 1200 to 2010. They used data from still-living trees and logs that had fallen into lakes, where they were preserved for centuries. …Their analysis reveals that the second-coldest decade of the past 800 years stretched from 1695 to 1704. Summertime temperatures during this period were about 1.56°C lower than summertime averages from 1961 to 1990, the team will report in a forthcoming issue of the Journal of Volcanology and Geothermal Research. All of this coincides with two major volcanic eruptions in the tropics: one in 1693 and an even larger one in 1695. The one-two punch likely sent Scotland into a deep chill that triggered massive crop failures and famines for several years, the team speculates…. 

2019-08-16. ‘Mystery’ volcano that cooled the ancient world traced to El Salvador. By Katherine Kornei, Science Magazine. [] Excerpt: The sixth century was a rough time to be alive: Lower-than-average temperatures in the Northern Hemisphere triggered crop failure, famine, and maybe even the onset of bubonic plague. The ultimate culprit, scientists say, were two back-to-back volcanic eruptions—one in 536 C.E. and another around 540 C.E. The first likely happened in Iceland or North America. But the location of the second one has remained a mystery—until now. Researchers studying ancient deposits from El Salvador’s Ilopango volcano knew that a massive eruption had taken place there sometime between the third and sixth centuries. That event, dubbed Tierra Blanca Joven (TBJ), or “white young earth,” sent a volcanic plume towering nearly 50 kilometers into the atmosphere….

2019-07-24. Ancient global climate events rippled unevenly across the globe. By Sid Perkins, Science Magazine.  [] Excerpt: In the past 2000 years, Earth has drifted in and out of extended periods of warmer- and cooler-than-normal climate, including the so-called Medieval Warm Period and the Little Ice Age. Scientists long thought that during these hot and cold spells, temperatures rose and fell in sync across the globe. In fact, Earth warmed and cooled unevenly, with different regions reaching peak high and low temperatures at different times, two new studies suggest. The one exception: Since the mid–19th century, warming trends have covered some 98% of the globe. Widespread networks of weather stations that could accurately record local temperatures didn’t exist until the last half of the 1800s. But scientists can estimate past temperatures using a variety of natural proxies. These “paleothermometers” include the widths of tree rings and the proportions of isotopes—forms of atoms such as oxygen that contain different numbers of neutrons—in glacial ice, corals, clam shells, cave deposits, and even lake sediments. …the Little Ice Age (which most scientists say began between 1350 and 1450 before being overtaken by warming in the 1800s) was undoubtedly the longest and deepest cool spell of the past 2 millennia. Most scientists had presumed that the Little Ice Age unfolded pretty much the same everywhere, Neukom says. But his team’s new analyses, reported in Nature, reveal that’s not the case. In the central and eastern Pacific Ocean, the coldest decades of the Little Ice Age fell during the 15th century. In northwestern Europe and the southeastern United States, the deepest cold occurred during the 17th century. For the rest of the world, the strongest chill didn’t occur until the mid–19th century, almost at the very end of this colder-than-normal interval. …The results show the current global warming is unusual not only in magnitude, but also in terms of its geography, says Scott St. George, a paleoclimatologist at the University of Minnesota in Minneapolis…. “No matter where you go, you can’t avoid the dramatic march toward warmer temperatures.”….

2019-02-05. Before Global Warming, Humans Caused Global Cooling, Study Finds. By Niraj Chokshi, The New York Times. [] Excerpt: When they arrived in the Americas centuries ago, European colonists brought pestilence and death. Their arrival was so devastating, in fact, that it may have contributed to a period of global cooling, according to a new study. The research, to be published in the March issue of the journal Quaternary Science Reviews [], represents an ambitious attempt to show that, through a series of events, human activity was affecting the climate long before the industrial revolution and global warming. The authors found that disease and war wiped out 90 percent of the indigenous population in the Americas, or about 55 million people. The earth, they argue, then reclaimed the land that these populations left behind. The new vegetation pulled heat-trapping carbon dioxide from the atmosphere and into the land, contributing to what scientists refer to as the “Little Ice Age.”…

2018-11-15. Why 536 was ‘the worst year to be alive’. By Ann Gibbons, Science Magazine. [] Excerpt: Ask medieval historian Michael McCormick what year was the worst to be alive, and he’s got an answer: “536.” Not 1349, when the Black Death wiped out half of Europe. Not 1918, when the flu killed 50 million to 100 million people, mostly young adults. But 536. …A mysterious fog plunged Europe, the Middle East, and parts of Asia into darkness, day and night—for 18 months. “For the sun gave forth its light without brightness, like the moon, during the whole year,” wrote Byzantine historian Procopius. Temperatures in the summer of 536 fell 1.5°C to 2.5°C, initiating the coldest decade in the past 2300 years. Snow fell that summer in China; crops failed; people starved. The Irish chronicles record “a failure of bread from the years 536–539.” Then, in 541, bubonic plague struck the Roman port of Pelusium, in Egypt. What came to be called the Plague of Justinian spread rapidly, wiping out one-third to one-half of the population of the eastern Roman Empire and hastening its collapse, McCormick says. …the middle of the sixth century was a dark hour in what used to be called the Dark Ages, but the source of the mysterious clouds has long been a puzzle. Now, an ultraprecise analysis of ice from a Swiss glacier by a team led by McCormick and glaciologist Paul Mayewski at the Climate Change Institute of The University of Maine (UM) in Orono has fingered a culprit. …a cataclysmic volcanic eruption in Iceland spewed ash across the Northern Hemisphere early in 536. Two other massive eruptions followed, in 540 and 547. The repeated blows, followed by plague, plunged Europe into economic stagnation that lasted until 640, when another signal in the ice—a spike in airborne lead—marks a resurgence of silver mining, as the team reports in Antiquity this week….

2018-08-02. Severe Drought May Have Helped Hasten Ancient Maya’s Collapse. By Jenessa Duncombe, Eos/AGU. Excerpt: Chemical signatures from sediments in lake cores reveal that the centuries-long drought during the fall of Classic Maya civilization was worse than researchers had imagined. …From about 250 to 900 CE, the Maya thrived in what’s known as its Classic period. During this time, the Maya built cities with plazas and multistory temples, devised a complex calendar system, and housed an urban population density that rivals Los Angeles County today. But then, sometime between the 8th and 9th centuries, many of the bustling Maya cities fell silent. By around 900 CE, a number of the grand cities had been abandoned. Scholars have many theories about what went wrong. …A study unveiled today in Science offers …another answer: a severe drop in rainfall that coincided with the Maya downfall. At the end of the Classic period in the northern reaches of the Maya civilization, “rainfall decreased on average by about half and up to 70% during peak drought conditions,” lead author Nick Evans, a Ph.D. candidate at the University of Cambridge, told Eos. Given the finding, “our research provides another piece of the puzzle for understanding the Maya collapse,” he said. …If drought did help lead to the Maya downfall, could it be an alarm bell for severe droughts that humans face today? …Depending on how society copes with environmental changes, outcomes can be very different. …in an abstract sense, there are lessons to be learned about the sensitivity and resilience of society to climate change….

2017-10-23. Volcanic Woes May Have Contributed to Ancient Egypt’s Fall. By JoAnna Wendel, Eos/AGU. Excerpt: Ice cores and ancient river records suggest that volcanic eruptions may have reduced the flow of the Nile River. Failures of the Nile floods that usually irrigated Egypt’s farms could have fed social unrest. …In a new paper in Nature Communications, the researchers present a raft of evidence—from climate modeling and ice core and Nile River hydrological records to ancient Egyptian chronicles—indicating that a series of eruptions may have caused sharp drop-offs in the summer rainfall usually brought by the African monsoon. The loss of monsoon precipitation would have depleted the headwaters of the Nile River and deprived Egyptian civilization of the annual Nile flooding that it depended on to sustain its agriculture. As food became scarce, insurrections may have followed, including one known as the Theban revolt, which rose against the ruling Macedonian Ptolemies starting in 207 BCE. “The Ptolemies lost control over huge areas of Egypt for almost 2 decades” during the Theban revolt, said Francis Ludlow, a coauthor of the study and a climate historian at Trinity College in Dublin, Ireland. It “was a very destructive revolt, with damage to temples and huge losses of tax revenues for the state.”…

2016-07-28. How Irrigation in Asia Affects Rainfall in Africa. By Sarah Stanley, EoS Earth and Space News, AGU. Excerpt: Agricultural irrigation is so widespread that it accounts for about 4% of the total evapotranspiration of water from Earth’s surface. Scientists have known for some time that water vapor from irrigation affects regional and global climates. Now, for the first time, researchers have shown that irrigation in one region can directly affect the climate of another region thousands of kilometers away. De Vrese et al. used the Max Planck Institute for Meteorology’s Earth System Model to simulate the fate and impact of water used for irrigation in South Asia from 1979 to 1999. In the simulations, early spring winds carried water vapor from irrigation in South Asia across the Arabian Sea and into East Africa, increasing humidity there. By late spring, when irrigation in the Middle East, Turkmenistan, and Afghanistan is in full swing, wind transported water vapor into Africa, increasing humidity as far west as Nigeria. …The simulations show that water vapor transport from South Asian irrigation increases springtime rainfall in Africa by up to 1 millimeter per day. Increased rainfall and cloud cover may cool the surface by up to 0.5 kelvin. In the arid parts of East Africa, as much as 40% of the total yearly rainfall may be attributed to irrigation in Asia….

2016-06-17. Rising temperatures and humans were a deadly combo for ancient South American megafauna. By Lizzie Wade, Science. Excerpt: If you’re fossil hunting in Patagonia you might find some weird creatures: giant jaguars, 3-meter-tall sloths, and bears 10 times the size of grizzlies. The southern part of South America was once crawling with these great beasts, collectively known as megafauna. But around 12,000 years ago, they suddenly disappeared from Patagonia and many other parts of the Americas. What caused the mass extinction? A new study suggests it was a one-two punch: rapid climate warming and humans. …Alan Cooper, an evolutionary biologist at the University of Adelaide in Australia, radiocarbon dated nearly 100 fossils from Patagonia and sequenced their mitochondrial DNA, genes found in the power plants of cells and passed down only from the mother. When he lined up their ages with global climate records, he noticed a pattern: Many species of megafauna seemed to disappear during a period of extreme warming around 12,300 years ago, Cooper and his team write today in Science Advances. …Patagonia warmed by about 2°C over 1000 years, and the effects were devastating: All but one of the species Cooper studied went extinct. …Last year, Cooper spotted a similar pattern in North America, with megafauna going extinct during ancient warming events (which occurred at slightly different times in the Northern Hemisphere). The existence of complementary data from the two continents “is as close as you’re going to get to a replicated experiment,” he says….

2016-01-19. Early Agriculture Has Kept Earth Warm for Millennia. By Sarah Stanley, Earth & Space News (EoS; AGU). Excerpt: Ice core data, archeological evidence, and other studies suggest humans had a significant influence on Earth’s preindustrial climate. Modern human activity is known to drive climate change, but global temperatures were already affected by farmers millennia before the Industrial Revolution. For years, scientists have been debating about the size of preindustrial warming effects caused by human activities. Now, according to Ruddiman et al., new evidence confirms that early agricultural greenhouse gas emissions had a large warming effect that slowed a natural cooling trend. Earth’s climate has cycled between warmer interglacial and cooler glacial periods for 2.75 million years as a result of cyclic variations in the Earth’s orbit. The current Holocene epoch, which began about 11,700 years ago, is an interglacial period. In an earlier study, Ruddiman compared Holocene trends with data from previous interglacial periods over the past 350,000 years. Instead of slowly decreasing—as observed early in previous interglacial periods—carbon dioxide levels began to rise 8000 years ago, and methane levels started increasing 5000 years ago. These increases correspond with the onset of early agriculture, which, Ruddiman hypothesized, may have produced enough greenhouse gases to slow the normal cooling trend. Now Ruddiman and 11 colleagues have more thoroughly compared the Holocene with past interglacial periods.  …The team also reviewed archaeological and paleoecological evidence. Studies show that the spread of rice irrigation is likely responsible for much of the increase in atmospheric methane between 5000 and 1000 years ago. The spread of livestock across Asia, Africa, and Europe—as well as other agricultural activities like burning weeds and crop residues—contributed as well. Deforestation that accompanied early agriculture could be responsible for the carbon dioxide increase that began nearly 7000 years ago….

2015-07-08. Timing and climate forcing of volcanic eruptions for the past 2,500 years. M. Sigl et al, Nature. Excerpt: Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. …Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing….

2015-01-27. Long dry spell doomed Mexican city 1,000 years ago. By Robert Sanders, UC Berkeley News Center. Excerpt: …Archaeologists continue to debate the reasons for the collapse of many Central American cities and states, from Teotihuacan in Mexico to the Yucatan Maya, and climate change is considered one of the major causes. …A UC Berkeley study sheds new light on this question, providing evidence that a prolonged period of below-average rainfall was partly responsible for the abandonment of one such city, Cantona, between A.D. 900 and A.D. 1050. At its peak, Cantona, located in a dry, volcanic basin (La Cuenca Oriental) east of today’s Mexico City, was one of the largest cities in the New World, with 90,000 inhabitants. The area was a major source of obsidian, and the city may have played a military role alongside an important trade route from the Veracruz coast into the highlands. …UC Berkeley geographers … found evidence of a 650-year period of frequent droughts that extended from around A.D. 500 to about A.D. 1150. This was part of a long-term drying trend in highland Mexico that started 2,200 years ago, around 200 B.C. The climate became wetter again in about A.D. 1300, just prior to the rise of the Aztec empire. “The decline of Cantona occurred during this dry interval, and we conclude that climate change probably played a role, at least towards the end of the city’s existence,” said lead author Tripti Bhattacharya, a UC Berkeley graduate student….

2012-11-09. Development and Disintegration of Maya Political Systems in Response to Climate Change | by Douglas J. Kennett et al, Science Magazine: Vol. 338 no. 6108 pp. 788-791.  Editor’s description: Climate has affected the vitality of many different societies in the past, as shown by numerous records across the globe and throughout human history. One of the most obvious and spectacular examples of this is from the Classic Maya civilization, whose advanced culture left highly detailed records of all aspects of their existence between 300 and 1000 C.E. Kennett et al. (p. 788; see the cover) present a detailed climate record derived from a stalagmite collected from a cave in Belize, in the midst of the Classic Maya settlement. The fine resolution and precise dating of the record allows changes in precipitation to be related to the politics, war, and population fluctuations of the Mayans. -|- Abstract:  The role of climate change in the development and demise of Classic Maya civilization (300 to 1000 C.E.) remains controversial because of the absence of well-dated climate and archaeological sequences. We present a precisely dated subannual climate record for the past 2000 years from Yok Balum Cave, Belize. From comparison of this record with historical events compiled from well-dated stone monuments, we propose that anomalously high rainfall favored unprecedented population expansion and the proliferation of political centers between 440 and 660 C.E. This was followed by a drying trend between 660 and 1000 C.E. that triggered the balkanization of polities, increased warfare, and the asynchronous disintegration of polities, followed by population collapse in the context of an extended drought between 1020 and 1100 C.E. Read the full article:[subscription needed] 

2010 Dec 6. Did Climate Change Drive Prehistoric Culture Change? By Michael Balter, Science.  Excerpt: A new study finds a strong correlation between changing climate and changing culture in the prehistoric United States…
…The team found that nearly all of the transitions between one cultural period and the next occurred at times of ecological and environmental changes…
…The authors don’t claim that climate change directly drove cultural change, but they do argue that prehistoric humans periodically “adjusted their tool kits” in response to climate changes…

2009 November 2. In the Mediterranean, Killer Tsunamis From an Ancient Eruption. By William J. Broad, The NY Times. Excerpt: The massive eruption of the Thera volcano in the Aegean Sea more than 3,000 years ago produced killer waves that raced across hundreds of miles of the Eastern Mediterranean to inundate the area that is now Israel and probably other coastal sites, a team of scientists has found.
The team, writing in the October issue of Geology, said the new evidence suggested that giant tsunamis from the catastrophic eruption hit “coastal sites across the Eastern Mediterranean littoral.” Tsunamis are giant waves that can crash into shore, rearrange the seabed, inundate vast areas of land and carry terrestrial material out to sea.
The region at the time was home to rising civilizations in Crete, Cyprus, Egypt, Phoenicia and Turkey.
For decades, scholars have suggested that the giant eruption, just 70 miles from Crete, might have brought about the mysterious collapse of Minoan civilization at the peak of its glory….

2009 July 24. An Amazon Culture Withers as Food Dries Up. By Elisabeth Rosenthal, The NY Times. Excerpt: XINGU NATIONAL PARK, Brazil — As the naked, painted young men of the Kamayurá tribe prepare for the ritualized war games of a festival, they end their haunting fireside chant with a blowing sound — “whoosh, whoosh” — a symbolic attempt to eliminate the scent of fish so they will not be detected by enemies. For centuries, fish from jungle lakes and rivers have been a staple of the Kamayurá diet, the tribe’s primary source of protein.
But fish smells are not a problem for the warriors anymore. Deforestation and, some scientists contend, global climate change are making the Amazon region drier and hotter, decimating fish stocks in this area and imperiling the Kamayurá’s very existence. Like other small indigenous cultures around the world with little money or capacity to move, they are struggling to adapt to the changes.
…The Intergovernmental Panel on Climate Change says that up to 30 percent of animals and plants face an increased risk of extinction if global temperatures rise 2 degrees Celsius (3.6 degrees Fahrenheit) in coming decades. But anthropologists also fear a wave of cultural extinction for dozens of small indigenous groups — the loss of their traditions, their arts, their languages….

2008 November 7. Rise and Fall of Chinese Dynasties Tied to Changes in Rainfall. By David Biello, Scientific American. Excerpt: In the late ninth century a disastrous harvest precipitated by drought brought famine to China under the rule of the Tang dynasty. By A.D. 907—after nearly three centuries of rule—the dynasty fell when its emperor, Ai, was deposed, and the empire was divided. According to the atmospheric record contained in a stalagmite, one of the causes of that downfall may have been climate change.
“We think that climate played an important role in Chinese history,” says paleoclimatologist Hai Cheng of the University of Minnesota, a member of the scientific team that harvested and analyzed the stalagmite from Wanxiang Cave in Gansu Province in northwest China. The stalagmite reveals, for example, that the vital rains of the Asian monsoon weakened at the time of the downfalls of the Tang, Yuan and Ming dynasties over the past 1,810 years.
…Composed of calcium carbonate leached from dripping water, the 4.6-inch- (11.7-centimeter-) long stalagmite preserves a record of rainfall in this region, which is on the edge of the area impacted by the Asian monsoon. The region gets less rainfall when the monsoon is mild and more when it is strong…
These periods of strong and weak rains, when compared with Chinese historical records, coincide with periods of imperial turmoil or prosperity….
In fact, the collapse of the Tang Dynasty coincides with that of the Mayan civilization—both due to extreme drought. “We have demonstrated that the cave record correlates well with many other records, including the Little Ice Age in Europe, temperature changes [across the] Northern Hemisphere, and major solar variability,” Cheng notes….

2008 August 31. For the first time in human history, the North Pole can be circumnavigated.By Geoffrey Lean, The Independent. Excerpt: Open water now stretches all the way round the Arctic, making it possible for the first time in human history to circumnavigate the North Pole… New satellite images, taken only two days ago, show that melting ice last week opened up both the fabled North-west and North-east passages, in the most important geographical landmark to date to signal the unexpectedly rapid progress of global warming.
Last night Professor Mark Serreze, a sea ice specialist at the official US National Snow and Ice Data Center (NSIDC), hailed the publication of the images…as “a historic event”, and said that it provided further evidence that the Arctic icecap may now have entered a “death spiral”. Some scientists predict that it could vanish altogether in summer within five years, a process that would, in itself, greatly accelerate.
…scientists…have long regarded the disappearance of the icecap as inevitable as global warming takes hold, though until recently it was not expected until around 2070.
Many scientists now predict that the Arctic ocean will be ice-free in summer by 2030 – and a landmark study this year by Professor Wieslaw Maslowski at the Naval Postgraduate School in Monterey, California, concluded that there will be no ice between mid-July and mid-September as early as 2013….

Summer 2007. Forest Magazine. Thirsting for Water. By Allen Best. Excerpt: …The dust traveled far, even to New York City. In Kansas, Oklahoma, Texas and Colorado, where the Dust Bowl was most severe, the roiling clouds were deadly. The young and old, even the formerly robust, succumbed to pneumonia. The luckier ones, the quitters, abandoned the dryland farms … and migrated westward, ….
Several decades of wet weather had supported the widespread plowing of grasslands in a semi-arid climate. Then came drought, lasting the better part of the decade. In all, about a third of a million people left the Great Plains. It was, until Hurricane Katrina, the greatest population displacement in the United States caused by an environmental event.
The Dust Bowl, say climatologists, is unlikely to occur again. 
Farmers and government scientists learned much from the experience about how to farm the land-and where not to. But drought most certainly will return, perhaps even more harshly. And turning to the American Southwest, …experts say new evidence reveals a clearer picture of extended and sometimes severe droughts in the past 1,100 years that very well may reappear-this time with an overlay of hotter temperatures caused by increased levels of greenhouse gases. What effect these human-caused emissions will have on precipitation is still uncertain. On the matter of temperature, however, nearly all the computer models reach one conclusion: It will get hotter, much hotter, in places like Tucson, Colorado Springs and Reno. And hotter-even if precipitation stays the same-means drier. In other words, the “average” of the future will resemble what in the past we called drought.
…Climates of the past can be documented in various ways, but one of the most important methods is by studying tree rings, a scientific discipline called dendrochronology. …
What these tree rings say is that the Southwest was far more arid in the past. … A period from 800 to 1300 A.D. was generally more arid and punctuated by what paleoclimatologists call megadroughts. Some lasted thirty years. Archaeologists think that one of the final megadroughts, from about 1270 to 1300, may have partly caused the Ancestral Pueblo (also called the Anasazi) to vacate their cliff-dwelling communities at Mesa Verde in Colorado and Chaco Canyon in Arizona….