Ancient Arabic manuscripts have provided a clue to scientists about past climate, a study reveals.
Scientists from the Universidad de Extremadura, Spain, have turned to Arabic documentary sources from the 9th and 10th centuries (3rd and 4th in the Islamic calendar) to analyse the writings of scholars, historians and diarists in Iraq.
"Climate information recovered from these ancient sources mainly refers to extreme events which impacted wider society such as droughts and floods," said Fernando Dominguez-Castro, who led the study, from Extremadura.
"However, they also document conditions which were rarely experienced in ancient Baghdad such as hailstorms, the freezing of rivers or even cases of snow," added Dominguez-Castro, according to a university statement.
Baghdad was a centre for trade, commerce and science in the ancient Islamic world. In 891 AD Berber geographer al-Ya'qubi wrote that the city had no rival in the world, with hot summers and cold winters, climatic conditions which favored strong agriculture.
While Baghdad was a cultural and scientific hub, many ancient documents have been lost to a history of invasions and civil strife. However, from the surviving works of writers including al-Tabari (913 AD), Ibn al-Athir (1233 AD) and al-Suyuti (1505 AD) some meteorological information can be rescued.
When collated and analysed the manuscripts revealed an increase of cold events in the first half of the 10th century. This included a significant drop of temperatures during July 920 AD and three separate recordings of snowfall -- in 908, 944 and 1007.
In comparison the only record of snow in modern Baghdad was in 2008, a unique experience in the living memories of Iraqis.
"These signs of a sudden cold period confirm suggestions of a temperature drop during the tenth century, immediately before the Medieval Warm Period," said Dominguez-Castro.
"We believe the drop in July 920 AD may have been linked to a great volcanic eruption but more work would be necessary to confirm this idea," he added.