(Inside Science) – Secrets hidden within stalagmites in an Iraqi cave are now shedding light on how climate change influenced both the rise and fall of the Neo-Assyrian Empire, once the most powerful empire of its time, a new study finds.
The Neo-Assyrian Empire (912-612 B.C.) emerged from the remnants of the earlier Middle Assyrian Kingdom. With the first armies to use iron weapons on a large scale and an ideology of conquest, at its height the Neo-Assyrian Empire spanned the whole of Mesopotamia and parts of Anatolia, Egypt and the Levant, making it the largest empire of its era. However, the empire plummeted from its zenith (about 670 B.C.) to complete political collapse (about 609 B.C.) in roughly 60 years.
Previous explanations for the speed of the empire's collapse focused on the role of imperial overexpansion, political instability, and military defeat at the hands of the combined armies of the Babylonians and Medes. The study's lead author Ashish Sinha, a paleoclimatologist at California State University, Dominguez Hills in Carson, and his colleagues suggested that climate may have also played a role in the empire's fall. The empire ranged over an area that still remains vulnerable to droughts and crop failures because rainfall there can vary greatly year to year, typically by 40% to 60%.
The researchers noted that the role climate played in shaping the empire's history has largely been overlooked due to a lack of high-resolution ancient climate records from the region. Now, they reveal, they have uncovered millennia of rainfall data recorded within stalagmites that help explain the role climate change played on the rise and fall of the empire.
The scientists investigated Kuna Ba Cave on the western flank of the Zagros Mountains in the Kurdistan portion of northern Iraq, which is located about 180 miles from Nineveh (now Mosul), the ancient capital of the Neo-Assyrian Empire in the seventh century B.C. Iraqi and European caving groups discovered Kuna Ba in the early 2000s, exploring its length to nearly a third of a mile.
The researchers focused on two stalagmites from the cave -- one about 6 inches long, the other roughly 15 -- which nonprofit group Nature Iraq collected, along with other samples and data from inside the cave. Stalagmites rise from the floors of caves, forming from mineral-rich water dripping from cave ceilings. Analyzing carbon and oxygen isotopes from these stalagmites yielded a precisely dated record of rainfall over the past 4,000 years.
The researchers discovered a number of anomalously wet "megapluvial" periods in this record, the most significant of which coincided with the two centuries of the empire's rise. Back then, rainfall levels during the cool seasons were 15% to 30% higher than during the modern 1980 to 2007 period.
However, they found that during a "megadrought" in the seventh century B.C. that lasted decades rainfall levels during the cool seasons may have fallen below those needed for productive farming. "The megadrought affected the core region of Neo-Assyrian Empire, what is now present-day northern Iraq and Syria," Sinha said.
The fertile years of the empire's rise may have helped drive its unsustainable growth to an unwieldy size, Sinha said. Once the megadrought began, the resulting frequent crop failures may have exacerbated political unrest within the empire and inflamed tensions the empire had with conquered peoples such as the Babylonians and Medes, he added.
"It's just amazing to me how good the match is between the climate record and the political and social history of the region," said paleoclimatologist Michael Griffiths at William Paterson University in Wayne, New Jersey, who did not take part in this research. "It just adds weight to the story of how vulnerable humans are to big changes in the environment."
The historical megadroughts parallel more modern droughts in this region, such as severe drops in rainfall from 1999 to 2001 and 2007 to 2008, when crop failures and widespread livestock die-offs were pervasive.
"Much of the Middle East and the eastern Mediterranean region is already in the grips of a centurylong drying trend, which seems to be accelerating since the 1980s," Sinha said. "Most climate model projections suggest that the drying trend is likely to continue into the future. I may even dare to suggest that we may already have entered into the early stages of a megadrought, and we know from the proxy records that these droughts can last for a very long time. This is not good news for a politically volatile and water-stressed region."
The scientists detailed their findings online Nov. 13 in the journal Science Advances.