How Climate Change Caused the World’s First Empire to Collapse

Not one smoke stack, vehicle, or petroleum of any form was mentioned in this scientific article. However, there does appear to be an assumption of rhythmic cycles.

Gol-e-Zard Cave lies in the shadow of Mount Damavand, which at more than 5,000 meters dominates the landscape of northern Iran. In this cave, stalagmites and stalactites are growing slowly over millennia and preserve in them clues about past climate events. Changes in stalagmite chemistry from this cave have now linked the collapse of the Akkadian Empire to climate changes more than 4,000 years ago.

Akkadia was the world’s first empire. It was established in Mesopotamia around 4,300 years ago after its ruler, Sargon of Akkad, united a series of independent city states. Akkadian influence spanned along the Tigris and Euphrates rivers from what is now southern Iraq, through to Syria and Turkey. The north-south extent of the empire meant that it covered regions with different climates, ranging from fertile lands in the north which were highly dependent on rainfall (one of Asia’s “bread baskets”), to the irrigation-fed alluvial plains to the south.

It appears that the empire became increasingly dependent on the productivity of the northern lands and used the grains sourced from this region to feed the army and redistribute the food supplies to key supporters. Then, about a century after its formation, the Akkadian Empire suddenly collapsed, followed by mass migration and conflicts. The anguish of the era is perfectly captured in the ancient Curse of Akkad text, which describes a period of turmoil with water and food shortages: “… the large arable tracts yielded no grain, the inundated fields yielded no fish, the irrigated orchards yielded no syrup or wine, the thick clouds did not rain.”

Drought and dust

The reason for this collapse is still debated by historians, archaeologists and scientists. One of the most prominent views, championed by Yale archaeologist Harvey Weiss (who built on earlier ideas by Ellsworth Huntington), is that it was caused by an abrupt onset of drought conditions which severely affected the productive northern regions of the empire.

Weiss and his colleagues discovered evidence in northern Syria that this once prosperous region was suddenly abandoned around 4,200 years ago, as indicated by a lack of pottery and other archaeological remains. Instead, the rich soils of earlier periods were replaced by large amounts of wind-blown dust and sand, suggesting the onset of drought conditions. Subsequently, marine cores from the Gulf of Oman and the Red Sea which linked the input of dust into the sea to distant sources in Mesopotamia, provided further evidence of a regional drought at the time.

Many other researchers viewed Weiss’s interpretation with skepticism, however. Some argued, for example, that the archaeological and marine evidence was not accurate enough to demonstrate a robust correlation between drought and societal change in Mesopotamia.

A new detailed climate record

Now, stalagmite data from Iran sheds new light on the controversy. In a study published in the journal PNAS, led by Oxford palaeoclimatologist Stacy Carolin, colleagues and I provide a very well dated and high resolution record of dust activity between 5,200 and 3,700 years ago. And cave dust from Iran can tell us a surprising amount about climate history elsewhere.

Gol-e-Zard Cave might be several hundred miles to the east of the former Akkadian Empire, but it is directly downwind. As a result, around 90% of the region’s dust originates in the deserts of Syria and Iraq.

That desert dust has a higher concentration of magnesium than the local limestone which forms most of Gol-e-Zard’s stalagmites (the ones which grow upwards from the cave floor). Therefore, the amount of magnesium in the Gol-e-Zard stalagmites can be used as an indicator of dustiness at the surface, with higher magnesium concentrations indicating dustier periods, and by extension drier conditions.

The stalagmites have the additional advantage that they can be dated very precisely using uranium-thorium chronology. Combining these methods, our new study provides a detailed history of dustiness in the area, and identifies two major drought periods which started 4,510 and 4,260 years ago, and lasted 110 and 290 years respectively. The latter event occurs precisely at the time of the Akkadian Empire’s collapse and provides a strong argument that climate change was at least in part responsible.

The collapse was followed by mass migration from north to south which was met with resistance by the local populations. A 180km wall – the “Repeller of the Amorites” – was even built between the Tigris and Euphrates in an effort to control immigration, not unlike some strategies proposed today. The stories of abrupt climate change in the Middle East therefore echo over millennia to the present day.

JUST IN: Researchers Find Deep Ocean Getting Colder

A pair of researchers, one with the Woods Hole Oceanographic Institution, the other Harvard University, has found evidence of deep ocean cooling that is likely due to the Little Ice Age. In their paper published in the journal Science, Jake Gebbie and Peter Huybers describe their study of Pacific Ocean temperatures over the past 150 years and what they found.

The model showed that the Pacific Ocean cooled over the course of the 20th century at depths of 1.8 to 2.6 kilometers. The amount is still not precise, but the researchers suggest it is most likely between 0.02 and 0.08° C. That cooling, the researchers suggest, is likely due to the Little Ice Age, which ran from approximately 1300 until approximately 1870. Prior to that, there was a time known as the Medieval Warm Period, which had caused the deep waters of the Pacific to warm just prior to the cooling it is now experiencing.

Prior research has suggested that it takes a very long time for water in the Pacific Ocean to circulate down to its lowest depths. This is because it is replenished only from the south, which means it takes a very long time for water on the surface to make its way to the bottom – perhaps as long as several hundred years. That is what Gebbie and Huber found back in 2012. That got them to thinking that water temperature at the bottom of the Pacific could offer a hint of what surface temperatures were like hundreds of years ago.

To find out if that truly was the case, the researchers obtained data from an international consortium called the Argo Program – a group of people who together have been taking ocean measurements down to depths of approximately two kilometers. As a comparative reference, the researchers also obtained data gathered by the crew of the HMS Challenger – they had taken Pacific Ocean temperatures down to a depth of two kilometers during the years 1872 to 1876. The researchers used the data from both projects to build a computer model meant to mimic the circulation of water in the Pacific Ocean over the past century and a half.

Super Grand Solar Minimum Hypothesis Considered

Professor Valentina Zharkova gave a presentation of her Climate and the Solar Magnetic Field hypothesis at the Global Warming Policy Foundation in October, 2018.

Zharkova models solar sunspot and magnetic activity. Her models have run at a 93% accuracy and her findings suggest a Super Grand Solar Minimum could begin in 2020.

A Super Grand Solar Minimum would have four magnetic fields out of phase. There was about 40-60 years of cold weather 350 years ago. This was a Maunder Minimum of lower solar activity. The historical cold weather had two magnetic fields out of phase.

Zharkova is predicting a cooling effect that is 2.5 to 4 times larger than the Maunder minimum. Zharkova’s analysis shows an 8 watts per square meter decrease in TSI (Total Solar Irradiance). A 2015 Nature study looked at 2 watts per square meter decrease causing a 0.13-degree celsius effect. A four times larger effect would be 0.5-degree celsius.

Zharkova believes the warming models are including the warming effect of increased solar activity. If she is correct there would be cooling and the warming models would be wrong.

Numerous studies have identified links between past climate and solar variability. During the Maunder Minimum (1645-1715), very few sunspots were seen despite regular observations. If the past relationships between TSI and ultraviolet irradiance and sunspots are the same as are observed for modern solar variability, then a decline in both TSI and ultraviolet for this period can be assumed.

The Maunder Minimum coincided with more severe winters in the UK and continental Europe and many reconstructions suggest atmospheric conditions were broadly comparable with the regional effects on European atmospheric circulation found here. Some modeling studies also support the idea that similar regional cooling and circulation changes occurred during this period.

Earth’s Magnetotail: First-Ever Views Of Elusive Energy Explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving “magnetic reconnection” — the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion — in the Earth’s magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can have — sparking auroras and possibly wreaking havoc on power grids in the case of extremely large events — but they haven’t completely understood the details. In a study published in the journal Science, the scientists outline the first views of the critical details of how this energy conversion process works in the Earth’s magnetotail.

“This was a remarkable event,” said Roy Torbert of the Space Science Center at UNH and deputy principal investigator for NASA’s Magnetospheric Multiscale mission, or MMS. “We have long known that it occurs in two types of regimes: asymmetric and symmetric but this is the first time we have seen a symmetric process.”

Magnetic reconnection occurs around Earth every day due to magnetic field lines twisting and reconnecting. It happens in different ways in different places, with different effects. Particles in highly ionized gases, called plasmas, can be converted and cause a single powerful explosion, just a fraction of a second long, that can lead to strong streams of electrons flying away at supersonic speeds. The view, which was detected as part of the scientists’ work on the MMS mission, had enough resolution to reveal its differences from other reconnection regimes around the planet like the asymmetric process found in the magnetopause around Earth which is closer to the sun.

“This is important because the more we know and understand about these reconnections,” said Torbert, “the more we can prepare for extreme events that are possible from reconnections around the Earth or anywhere in the universe.”

Magnetic reconnection also happens on the sun and across the universe — in all cases forcefully shooting out particles and driving much of the change we see in dynamic space environments — so learning about it around Earth also helps us understand reconnection in other places in the universe which cannot be reached by spacecraft. The more we understand about different types of magnetic reconnection, the more we can piece together what such explosions might look like elsewhere.

For the first reported asymmetrical event on October 16, 2015, and now this symmetrical event on July 11, 2017, NASA’s MMS mission made history by flying through magnetic reconnection events near the Earth. The four MMS spacecrafts launched from a single rocket were only inside the events for a few seconds, but the instruments which UNH researchers helped to develop were able to gather data at an unprecedented speed of one hundred times faster than ever before. As a result, for the first time, scientists could track the way the magnetic fields changed, new electric fields presented, as well as the speeds and direction of the various charged particles.

Could Yesterday’s Earth Contain Clues For Making Tomorrow’s Medicines?

Several billion years ago, as the recently formed planet Earth cooled down from a long and brutal period of heavy meteor bombardment, pools of primordial muck began to swirl with the chemical precursors to life.

Today, scientists are devising chemical reactions that mimic early Earth not only to learn about how life developed, but also to unlock new capabilities for modern medicine.

“If you can get chemistries that encode information, then maybe you can design new drugs,” says John Yin, a professor of chemical and biological engineering at the University of Wisconsin-Madison.

In a paper published recently in the journal Origins of Life and Evolution of Biospheres, Yin and colleagues described initial steps toward achieving chemistries that encode information in a variety of conditions that might mimic the environment of prehistoric Earth.

“I view this as systems chemistry,” says Yin. “How do we take store-bought chemicals and combine them in such a way that they display emergent properties like the ability to store information or copy themselves?”

The compounds the researchers combined were molecules called amino acids, which are the molecular building blocks for the proteins that perform much of the structural and chemical work inside living cells. There are 20 different amino acids that combine to form the essential proteins for life, but Yin and colleagues focused on just two: alanine and glycine, which are among the simplest examples of these molecules.

Also in the mix was an energy molecule called triphosphate, believed to be available on early earth.

The researchers “cooked” together the mixture over a range of different temperatures and variously acidic conditions. In mixtures without the energy molecule, amino acids only joined together under the most hot and harsh conditions. When triphosphate was present, however, short chains of alanine and glycine formed at more moderate temperatures.

“Triphosphate facilitates reactions in conditions where most life is found to occur,” says Yin.

Intriguingly, the alanine and glycine did not combine at random. Instead, the amino acids linked up into chains with specific sequences, depending on temperature and pH.

“What we have shown is that you are a product of your environment,” says Yin.

Key to the study was the ability to determine the composition of different amino acid chains with sophisticated analytical chemistry. For the molecular characterizations, Yin collaborated with Lingjun Li, a UW-Madison professor of pharmacy and chemistry.

“People have been cooking amino acids since 1940 or so,” says Yin. “But now we can identify what’s actually in there.”

What they identified hints at the first glimmers of information storage that arose so many billions of years ago.

The scientists speculate that, with increased “cooking” time, even greater complexity might appear. Their reactions only proceeded for 24 hours — a mere blink of an eye compared to the history of the planet. Additionally, the scientists plan to add a greater variety of molecules into the mixture.

Eventually, they hope to create mixtures where complicated molecules spontaneously come together from simpler components and create self-driving chemical reactions that interact and feed off of each other.

Those reactions could contain the keys to creating new drugs or synthesizing existing compounds more efficiently.

“We’ll figure out how to close the loop,” says Yin.

Scientists Develop A New Way To Remotely Measure Earth’s Magnetic Field

Researchers in Canada, the United States and Europe have developed a new way to remotely measure Earth’s magnetic field—by zapping a layer of sodium atoms floating 100 kilometres above the planet with lasers on the ground.

The technique, documented this week in Nature Communications, fills a gap between measurements made at the Earth’s surface and at much higher altitude by orbiting satellites.

“The magnetic field at this altitude in the atmosphere is strongly affected by physical processes such as solar storms and electric currents in the ionosphere,” says Paul Hickson an astrophysicist at the University of British Columbia (UBC) and author on the paper.

“Our technique not only measures magnetic field strength at an altitude that has traditionally been hidden, it has the side benefit of providing new information on space weather and atomic processes occurring in the region.”

Sodium atoms are continually deposited in the mesosphere by meteors that vaporize as they enter Earth’s atmosphere. Researchers at the European Southern Observatory (ESO), the University of Mainz and UBC used a ground-based laser to excite the layer of sodium atoms and monitor the light they emit in response.

“The excited sodium atoms wobble like spinning tops in the presence of a magnetic field,” explains Hickson. “We sense this as a periodic fluctuation in the light we’re monitoring, and can use that to determine the magnetic field strength.”

Hickson and UBC Ph.D. student Joschua Hellemeier developed the photon counting instrument used to measure the light coming back from the excited sodium atoms, and participated in observations conducted at astronomical observatories in La Palma.

The ESO team, led by Bonaccini Calia, pioneered world-leading laser technology for astronomical adaptive optics used in the experiment. Project lead Felipe Pedreros and Dmitry Budker (Johannes Gutenberg University), Simon Rochester and Ronald Holzloehner (ESO), experts in laser-atom interactions, led the theoretical interpretation and modeling for the study.

A Wrench In Earth’s Engine

Researchers at CU Boulder report that they may have solved a geophysical mystery, pinning down the likely cause of a phenomenon that resembles a wrench in the engine of the planet.

In a study published today in Nature Geoscience, the team explored the physics of “stagnant slabs.” These geophysical oddities form when huge chunks of Earth’s oceanic plates are forced deep underground at the edges of certain continental plates. The chunks sink down into the planet’s interior for hundreds of miles until they suddenly—and for reasons scientists can’t explain—stop like a stalled car.

CU Boulder’s Wei Mao and Shijie Zhong, however, may have found the reason for that halt. Using computer simulations, the researchers examined a series of stagnant slabs in the Pacific Ocean near Japan and the Philippines. They discovered that these cold rocks seem to be sliding on a thin layer of weak material lying at the boundary of the planet’s upper and lower mantle—roughly 660 kilometers, or 410 miles, below the surface.

And the stoppage is likely temporary: “Although we see these slabs stagnate, they are a fairly recent phenomena, probably happening in the last 20 million years,” said Zhong, a co-author of the new study and a professor in CU Boulder’s Department of Physics.

The findings matter for tectonics and volcanism on the Earth’s surface. Zhong explained that the planet’s mantle, which lies above the core, generates vast amounts of heat. To cool the globe down, hotter rocks rise up through the mantle and colder rocks sink.

“You can think of this mantle convection as a big engine that drives all of what we see on Earth’s surface: earthquakes, mountain building, plate tectonics, volcanos and even Earth’s magnetic field,” Zhong said.

The existence of stagnant slabs, which geophysicists first located about a decade ago, however, complicates that metaphor, suggesting that Earth’s engine may grind to a halt in some areas. That, in turn, may change how scientists think diverse features, such as East Asia’s roiling volcanos, form over geologic time.

Scientists have mostly located such slabs in the western Pacific Ocean, specifically off the east coast of Japan and deep below the Mariana Trench. They occur at the sites of subduction zones, or areas where oceanic plates at the surface of the planet plunge hundreds of miles below ground.

Slabs seen at similar sites near North and South America behave in ways that geophysicists might expect: They dive through Earth’s upper mantle and into the lower mantle where they heat up near the core.

But around Asia, “they simply don’t go down,” Zhong said. Instead, the slabs spread out horizontally near the boundary between the upper and lower mantle, a point at which heat and pressure inside Earth cause minerals to change from one phase to another.

To find out why slabs go stagnant, Zhong and Mao, a graduate student in physics, developed realistic simulations of how energy and rock cycle around the entire planet.

They found that the only way they could explain the behavior of the stagnant slabs was if a thin layer of less-viscous rock was wedged in between the two halves of the mantle. While no one has directly observed such a layer, researchers have predicted that it exists by studying the effects of heat and pressure on rock.

If it does, such a layer would act like a greasy puddle in the middle of the planet. “If you introduce a weak layer at that depth, somehow the reduced viscosity helps lubricate the region,” Zhong said. “The slabs get deflected and can keep going for a long distance horizontally.”

Stagnant slabs seem to occur off the coast of Asia, but not the Americas, because the movement of the continents above gives those chunks of rock more room to slide. Zhong, however, said that he doesn’t think the slabs will stay stuck. With enough time, he suspects that they will break through the slick part of the mantle and continue their plunge toward the planet’s core.

The planet, in other words, would still behave like an engine—just with a few sticky spots. “New research suggests that the story may be more complicated than we previously thought,” Zhong said.