Climate Shocks and the Fate of Empires (and of World Religions)

I have been describing the astonishing success of Buddhism across much of Southern and Eastern Asia in the first millennium AD, and how that movement suffered grave setbacks from the ninth century onward. Although Buddhism continued to be a vital cultural force, its loss of influence in India and, to a lesser extent, China, was a real setback. So why did this happen? I will argue that this resulted from the failure of the great empires that had hitherto either supported or tolerated that faith. Underlying that shift was a climate disaster on a transcontinental scale.

In my 2021 book Climate, Catastrophe and Faith, I described how episodes of sudden climate shock wreaked havoc on societies, by causing droughts, famines, and the plagues that commonly followed such horrors. Some of these events, like the aftermath of the Tambora volcano of 1815, are well known and have been much studied. A couple of years ago, at this site, I described how a huge volcanic eruption in 626 AD effectively shattered the Persian empire, and opened the door for the emergence of Islam on the global stage. It was a very good time indeed for a religion preaching doomsday and judgment. A climate catastrophe remade the world’s great empires, and its religions.

In my Buddhist story, the ninth century marked a critical turning point, with political chaos and disintegration in India and China, and similar events would undoubtedly have occurred much further afield, if our sources allowed us to see them in detail. Climate change can make empires, and it can ruin them. If it is lengthy and severe enough, then drought, in particular, can be an empire-slayer.

In China, the great Tang dynasty had enjoyed immense wealth and power from the seventh century onward, but signs of trouble were accumulating by the 840s. Large areas were falling out of imperial control, as pirates and bandits became ever more daring. The emperors sought a convenient scapegoat in the form of supposedly foreign creeds such as Buddhism and what they thought was the sectarian offshoot of that faith, Christianity. Zoroastrians and Manicheans also suffered. In the early 840s, the Emperor Wuzong launched a stern persecution that was in part designed to claw back resources that had been poured into the monasteries, in an effort to buttress crumbling imperial finances. Heavily dependent on the monasteries and their sizable landed estates, Buddhism was a luxury that an increasingly strained Chinese society could no longer afford.

Matters grew still worse for China in the 870s, with a historic famine that provoked major rebellions. The harvest of 873 was a catastrophe. According to the worldview of the time, these events showed that the dynasty had lost the Mandate of Heaven, and local aristocrats and warlords duly seized power in their particular regions. The dynasty collapsed in 906, to be followed by over fifty years of fragmentation and disruption, the time of the Five Dynasties.

Although Indian conditions are nothing like as well recorded, we know that the powerful Pala Empire faced grave crises and multiple defeats in these same years. This was very bad news for Indian Buddhism, for which the Palas were the principal patrons and support. Although the Pala Empire achieved some degree of recovery, India, like China, faced an era of smaller competing states. There would never again be a great Indian Buddhist empire of the kind that for centuries had done so much to promote the well-being and expansion of the faith.

European historians might experience a certain sense of déjà vu here. The great Frankish Empire founded by Charlemagne was suffering similar disasters in these very same years, to the point that the mid-ninth century is sometimes called a Second Dark Age. This was partly a matter of the multiple foreign invaders cross-crossing the continent in these years – Vikings, Magyars, and Muslim Saracens – but the fact that those groups were able to cause so much havoc was as much a consequence of imperial weakness as its cause. Not until the tenth century did European polities reorganize on something like the familiar model of later centuries, with a new France and a German Empire. It is almost as if some external force were imposing its baleful influence on these very diverse societies in such different parts of the world …

So why were empires stumbling and collapsing in these same years? Climate factors were playing a potent role, with drought as the key factor. The evidence comes from multiple sources, including the silent records of changing conditions preserved in stalagmites and (above all) tree rings. But the data all speak to similar and consistent conclusions. In the ninth century, the Uighur people of Central Asia were vital to the commerce and trade routes of the time. They suffered a drought that lasted an incredible seven decades, from 783 through 850. A historian describing the Byzantine Empire in the year 813 noted “For there were now famines and droughts and burning sun, now earthquakes and eruptions; and at other times darts of fire, so it seemed, in the air and, from another side, civil uprisings threatened the most extreme dangers.” (That is from the Continuation of the Chronicle of Theophanes). The reign of the Emperor Theophilos (829-842) is described thus:

By about 840, the Emperor Theophilos in the West could have had some interesting conversations with his Chinese counterpart, Wuzong. For other regions, the worst conditions came somewhat later, with the ghastly 870s as a uniquely dreadful period.

Although the exact sequence of causation is debated, the main element was probably a sharp decline in solar energy, which would have its impact on the cycles of the oceans and the El Niño cycles that can transform conditions around the world. (I discuss these processes at length in my Climate, Catastrophe, and Faith). Adding to the global impact of El Niño cycles is their intimate connection with the monsoon system. The Asian monsoon is arguably “the Earth’s largest and most important climate phenomenon,” in that it presently influences the livelihood of over 60 percent of the human population. If the exact share of population differed somewhat several centuries ago, it was always very substantial. Across much of Asia, rice-based agriculture was critically dependent on irrigation systems and on water regulation, so periods of very high or low rainfall were uniquely perilous. At its most damaging, El Niño could threaten famines on a frightful scale, and that is the fate that befell the Tang dynasty, and likely the Pala Empire. When the seas warmed in later centuries, that in turn created the Medieval Warm Period. That laid the foundation for the phenomenal success of China’s Song Empire, which Chinese historians usually value as the greatest and most successful of all the dynasties.

I just raise one mystery here. Climate shocks often correlate closely with very large volcanic eruptions. In the modern history of Earth’s volcanoes, one of the real giants occurred with the eruption of Paektu Mountain on the border of Korea and China, which scored a terrifying 7 on the Volcanic Explosivity Index, the VEI. To put that in context, that was a one in 500 years event, and possibly even a once in a millennium. The date of that particular very big bang is much debated, and it is commonly placed at 946 AD. In terms of the possible observed effects around the world, it would have been far more plausible if it occurred some decades earlier, in time to contribute to the nightmares of the 870s. I am not a volcanologist, but I do just raise that non-scientific and somewhat plaintive cry against the 946 dating for Paektu.

Whatever the causation, I do stress the effects of that devastating climate event in the mid-late ninth century, and on a global scale. That would have included a megadrought in the Americas, which (controversially) was instrumental in provoking the collapse of the Classic Maya civilization and the ruin of Maya cities. The disaster apparently sparked a whole new religious movement.  Those Maya regions have a very high concentration of caves, which were regarded as gateways to the underworld, Xibalba, the “place of fear.” These were moreover sacred to the rain god Chac. During the ninth century, those caves became the setting for extensive ritual deposits of cherished goods and ceramics, and also witnessed large-scale sacrifices, of human beings as well as animals. In the vast majority of those instances, the sacrificial remains date to the era of megadrought, suggesting a mass collective ritual and even a sweeping new religious movement.

That, as we say, is another story. To return to my original point, a climate shock on a vast scale caused a fundamental political reorientation in many parts of the world. In Asia, the major casualty was the Buddhism that had benefited so greatly from the empires of preceding centuries.

For the ninth century megadrought as it affected the US southwest and northern Mexico, see A. Park Williams, Benjamin I. Cook & Jason E. Smerdon, “Rapid Intensification of the Emerging Southwestern North American Megadrought in 2020–2021,” Nature Climate Change (2022), at https://doi.org/10.1038/s41558-022-01290-z

Full Disclosure: Theories about what brought down the Classic Maya civilization are fiercely debated, and so, specifically, is the role of drought. The issue is not whether massive droughts persisted for many years – they did – but rather the exact mechanisms by which they could have caused such ruin to the society.