Science

The decline of the Mayans: a warning signal

That’s Maths: We can learn from climate variations of the past

Indigenous women take part in the prayer for rain ceremony on the shore of Chicabal Lagoon in San Martin Sacatepequez, Guatemala. Photograph: Johan Ordonez/AFP

Peter Lynch
Thu Dec 21 2023 - 06:00

The rising temperatures of today’s climate are being linked to extreme weather, droughts, floods and intense storms, and global food and water supplies are coming under severe stress. While these changes are unprecedented in their rapidity, climate variations in the past have had devastating consequences. What can we learn from them?

The Mayan civilisation flourished in Central America between the third and 10th centuries AD. Although isolated from other centres of mathematical activity, the Mayans achieved remarkable results in numeration and calendar construction. The Mayan numeration system, with 20 as base, was used mainly for calendar computations. Only three symbols were required: dots and bars, sometimes formed using pebbles and sticks, were used for one and five, and a shell symbol stood for the numeral (but not the number) zero.

The Mayans had three kinds of calendar: a sacred calendar for religious rituals; a civil calendar based on the solar cycle, with 20 months of 18 days and five extra days; and a special calendar used for extended timespans and employing a mixed-base numeration. George G Joseph, in his book The Crest of the Peacock, on the non-European roots of mathematics, describes these in some detail.

Mayan astronomy achieved a remarkable degree of accuracy, which is amazing considering the Mayans never employed fractional quantities or decimals. The Mayan estimates of the length of a solar year and the duration of a lunar month were in excellent agreement with our current best estimates.

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Catastrophic droughts

All advanced societies require dependable water supplies as well as annual weather variations predictable enough to ensure a steady food supply. Climate changes can disrupt these supplies to the point of collapse. The regular summer rainfall on the fertile land of the Yucatán Peninsula allowed the Mayan civilisation to flourish for centuries. However, between 800 and 1000 AD the civilisation went into serious decline, apparently as a consequence of sustained drought, and the population plummeted.

By the time of the Spanish conquest in 1520 the glorious days of the Mayans were far in the past. To understand what happened, we need a detailed historical rainfall record for the Yucatán region. In the absence of direct rainfall measurements, proxy data must be used.

There are two naturally-occurring isotopes of oxygen in rainfall water, O-18 and O-16. Their relative proportions vary with rainfall intensity. Heavy rainfall produced from cold high clouds contains a lower proportion of the heavier isotope O-18. This permits a reconstruction of the rainfall climatology from analysis of stalagmites, rock formations formed from the residue of rainwater dripping from cave ceilings.

Dr Medina-Elizalde and his team at the University of Massachusetts, Amherst, have reconstructed the rainfall record of the Yucatán Peninsula over the past 1,500 years. Through mass spectrometric analyses of tiny stalagmite samples, they found that, during the decline of the Maya, the Yucatán Peninsula experienced a succession of drought events with a 40 per cent reduction in annual rainfall.

[ A link between physics, maths and the Mayans ]

There are ineluctable similarities between the climate stress suffered by the ancient Maya and the weather anomalies we see today. A fuller understanding of past climate should help us to anticipate, and hopefully prevent, threats to our society and ecosystem.

Peter Lynch is emeritus professor at the School of Mathematics & Statistics in University College Dublin. He blogs at thatsmaths.com

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