Archaeology is the only discipline that can identify past instances of climate change, and then assess the impact on human societies, and I have been involved for some time in one such case, that of the civilisation of Angkor.
In 1590s, Portuguese missionaries encountered in northwest Cambodia, the remnants of a great stone city overtaken by the jungle. But for 11 months in 1296-7, the Chinese diplomat Zhou Daguan lived there, and in his memoire he described a thriving city, teeming with life.
He watched a procession by King Indravarman III, riding a massive elephant and holding the sword of state. He noted the busy market, people bathing in the heat of the day and the number of great temple mausolea for ancestral kings.
What happened between 1296 and 1590?
Angkor was dependent on the rice harvest. Perennial streams issuing from the Kulen upland to the north were diverted into reservoirs, the biggest measuring 8 by 2 kilometres. Each had a temple in the centre that linked the king with the success of the rice harvest. Water was fed into the rice fields below the city to supplement dry episodes during the monsoon period rains.
We now know from tree rings that from about 1400, there was a sharp deterioration in the vital monsoon climate. Very dry years interspersed with catastrophic rains. Forest clearance north of Angkor as the city expanded brought huge loads of sediment down in rivers that burst their banks as the canals choked and the rice withered.
The god kings of Angkor had for centuries been seen as intermediaries with the Hindu gods. When they died, they assumed a new name and joined their deities. Essentially, the kings built the reservoirs, and were responsible for the success of the rice harvest. For them, climate change was a catastrophe.
During the 15th century, life at Angkor, once the largest dispersed urban complex in the word, became untenable and the court moved to a new capital near the Mekong River. The jungle began to encroach on the abandoned city and the first Portuguese came to ruins as they said, punctuated only by the sound of wild animals.
