Climate and civilisation
Have changes in climate had a hand in the collapse of civilisations?
During human history, civilisations have come and gone. Many theories have been proposed to account for their collapse – including changes in climate. The idea is that worsening climate affects agriculture, lowering crop yields and promoting social turmoil.
Evidence comes from a 2008 analysis of an ancient stalagmite from a cave in northern China. Chemical analysis of layered deposits in the stalagmite provided an exceptionally detailed record of rainfall – summer monsoons – over the past 2,000 years. When compared with Chinese history, there was a striking correlation between periods of low rainfall and the collapse of three major dynasties (the Tang, the Yuan and the Ming).
Conversely, the period of wettest summer monsoons coincided with the ‘golden age’ of the Northern Song dynasty.
Remarkably, the Asian monsoon data correlate closely with the advance and retreat of Alpine glaciers and climate data from Central and South America. Notably, the final days of the Tang dynasty coincide with the end of the Mayan classic period in Central America.
Part (but not all) of the climate change seems to be linked to variations in solar activity. Indeed, analysis of sediments from a Mexican lake suggested that Central America suffered a severe drought at the same time as the Mayan collapse, with 200-year-long climate cycles suggestive of a link to periodic variations in solar activity.
Climate change has been suggested as a factor in the decline of other civilisations, including the Akkadian Empire of Mesopotamia, the Old Kingdom of Egypt and others that collapsed around 4,000 years ago. Even the fall of the Roman Empire may in part have been driven by a drop in temperatures across Europe.
Not everyone is convinced. Droughts do not inevitably lead to social disintegration and something as complex as the collapse of a civilisation is likely to have multiple causes.
Might current circumstances be part of another ‘natural cycle’? The authors of the stalagmite paper suggest not. Over the 2,000 years, warmer weather has been associated with stronger monsoons. Around 1960, though, this trend disappears – presumably because of the impact of atmospheric greenhouse gases and particulate pollution.Lead image:
Theresia Hofer/Wellcome Images CC BY NC ND
- Dry spells spelled trouble in ancient China
- Climate change and the collapse of the Akkadian Empire: evidence from the deep sea (2000) [PDF]
- Climate and drought lessons from ancient Egypt
- Climate change during and after the Roman Empire: reconstructing the past from scientific and historical evidence (2012) [PDF]
- Climate variability and climate change: what is the difference [PDF]