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Robert Roy Britt of Live Science reports on the research of a team led by University of Wisconsin-Madison professor John Valley that shows increased dryness in the Eastern Mediterranean between 100 and 700 of the Common Era (CE), with dramatic dips in rainfall in 100 CE and 400 CE. It raises questions about whether climate is somehow implicated in the decline of the Roman Empire (traditionally considered to have fallen in 476 CE) and the weakening of the Byzantine Empire in the 600s-700s CE.

Britt does not mention that the 600s were the era in which the Orthodox Caliphs of Islam took greater Syria and Egypt away from Byzantium; these lands were later ruled by the Umayyad Empire. Indeed, within the first century after Islam was founded, its adherents spread out with lightning speed to take over the southern third of the old Roman Empire, as well as the entirety of the Sasanid Empire of Iran. The Muslim conquests after 632 CE are rivaled in history for their speed and extent only by the 13th-century Mongol expansion. The Muslim empire, however, retained its civilizational identity and it was adopted by the conquered, whereas the Mongols were absorbed.

Since the Arab Muslims were from desiccated Western Arabia, they may have been better at dealing with a dry climate; Muslim water-management techniques were superior to those of other civilizations in that era. They may also have had advantages in logistics and fighting technique. The Bedouin tribesmen of Arabia that were the core of the Arab Muslim army had been used to raiding across arid territory. Camels need less water than horses and can cover more territory per day, so in dry conditions a camel cavalry has advantages over a horse cavalry. Bedouin had been probing Byzantine defenses in Syria all along; why were they suddenly able to over-run Damascus in 634 CE? Many historians have focused on the esprit de corps and unifying ideology they derived from the new religion of Islam, but other explanations should continue to be considered.

Institutions and social arrangements–how people deal with climate change– are more important than the change itself. Note that pastoral nomads, who take their herds to pasturage wherever it pops up, have advantages over farming peasants in dry eras. Peasants and urban people defect to tribes, or engage in migrations to regain access to water. Since the Bedouin were such an important social element in early Islam, a shift in social and economic power toward pastoralists would have benefited the new religion.

Britt writes:

‘ The work involved geochemical analysis of a stalagmite from Soreq Cave in the Stalactite Cave Nature Reserve near Jerusalem. Rain flushed organic matter from the surface into the cave, and it was trapped in mineral deposits that formed layers on the stalagmite. Geology graduate student Ian Orland determined annual rainfall levels for the years the stalagmite was growing, from approximately 200 B.C. to 1100 A.D. ‘

A lot of climate history is done from tree ring analysis, but it has been difficult to pursue in the Middle East because the arid conditions there are not conducive to long-lived trees like the California redwoods. Some analysis has been done for medieval Turkey by using antique wooden, from surviving buildings, churches and ships, but getting a long data series that has wide implications has been difficult.

Richard Bulliet at Columbia University has used rainfall data for Mongolia in trying to understand medieval Iran’s climate history. But obviously Middle Eastern data would be preferable where it can be gotten.

Some scientists have suggested that rainfall can be a proxy for temperature, but that relationship is not accepted by everyone(warm weather might be associated with dry periods, cold weather with increased rainfall).

Climate history enjoyed a vogue a hundred years ago in areas like Roman history, but became discredited because its practitioners tried to explain too much by it and discounted other important explanations. We should avoid these temptations as new climate information allows another run at weather explanations in history.