The consequences of the Earth’s changing climate may be very grave. It is essential to understand past climate change so that we can anticipate future changes. This week, That’s Maths in The Irish Times ( TM047 ) is about the chronology of the Middle East. Surprisingly, this has important implications for our understanding of climate change.
The Greek geometer Pythagoras, whose theorem is familiar to every student of mathematics, lived around 500 BC but the theorem was known to the Babylonians much earlier. The Babylonians used a numbering system based on sixty. We find a residue of this in our own measurement of time and of angles. They also invented the place value system, where one symbol has different meanings in different positions. We enjoy the benefits of this system today: the 5 in 53 is not the same as in 35.
We know of the ancient Middle-East mainly through a vast collection of clay tablets with cuneiform inscriptions. Cuneiform is one of the earliest writing systems, with wedge-shaped marks made by a stylus in the soft clay, which is then baked dry. Laws, letters, accounts, stories and mathematics were all impressed on clay tablets.
Irish clergyman Edward Hincks, a Fellow of Trinity College and Member of the Royal Irish Academy, achieved one of the earliest decipherments of cuneiform. He studied a tablet originally found in Nineveh, the Assyrian capital, and now in the British Museum. He determined that it was in the Akkadian language and described Venus as a morning or evening star on specific dates. The dates were in the Assyrian lunar calendar and their precise interpretation was uncertain.The Reign of Hammurabi
The Code of Hammurabi is amongst the first written legal systems in history. Hammurabi, the sixth king of Babylon, flourished in the eighteenth century before Christ, but the exact dates of his reign are uncertain.
When did Hammurabi reign? The precise dates are uncertain. Disagreements abound on the chronology of Mesopotamia: estimates extend over more than two centuries, with the so-called middle chronology fixing his reign to 1792–1750 BC.
In a recent discourse at the Royal Irish Academy, Professor Werner Nahm revisited some century-old scholarship and found that the date when Hammurabi first reigned could be fixed, by known astronomical events, to one of four years. Nahm, director of the School of Theoretical Physics of the Dublin Institute for Advanced Studies, is also expert in reading and interpreting ancient cuneiform script.
Nahm examined digitally-enhanced images of a newly-found tablet now in Ankara and was able to establish the first year of Ammizaduqa, the great-great-grandson of Hammurabi. A reference to a solar eclipse in the Assyrian year 127, when Puzur-Ishtar was governor, enabled him to establish the dates for Hammurabi precisely. There were 195 years between the solar eclipse and the first year of Ammizaduqa. Genealogical records then showed the beginning of Hammurabi’s reign to be 1784 BC.
Pinning down dates like this is important. Potentially grave consequences of the changing climate loom before us. Such changes, both short and long-term, have occurred before. The Mesopotamian civilization declined after Hammurabi, and many cities were abandoned. Babylon itself lay in ruin for some time. While military decline was one factor, there were others. The simultaneous collapse of the Egyptian civilization, a thousand miles away, lends support to a major perturbation of the climate.
The inscription on one tablet describes a period when Venus, which should have been prominent, was unobserved. This may well have been due to the obscuring effect of volcanic dust. Volcanic events are known to cause crop failure and famine for a year or more.
Evidence of a climate downturn around the year 1627 BC is found in the tree-rings of Irish bog oak, analysed by Mike Baillie of Queens University in Belfast . A possible link to the eruption of Santorini, which wiped out the Minoan Empire in Crete, is intriguing but, to date, unproven.
Irish tree rings, Santorini and volcanic dust veils. Nature 332, 344 – 346. doi:10.1038/332344a0
 Teije de Jong: Astronomical Fine-tuning of the Chronology of the Hammurabi Age. Academia.edu. PDF
 O. Neugebauer, 1941: The Chronology of the Hammurabi Age. Journal of the American Oriental Society. Available on JSTOR
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