In AD 1204, Constantinople fell. That year, tens of thousands of Latin crusaders on their way to conquer Muslim-controlled Jerusalem made a side trip to the Eastern Roman Empire, or Byzantium, where they had made a deal to help prince Alexios IV become emperor. The Byzantine elite at Constantinople, not happy with these backroom wheelings and dealings, rebelled, and Alexios was strangled to death.
At least that’s the story that the history books tell you. What’s not really been explored is how much the increasingly arid weather contributed to Constantinople’s unrest during this time.
Just over 800 years later, neighbouring Syria is seeing similar societal unrest, exacerbated by drought. It begs the question: What might we learn from the way climate affected Byzantine political, economic and social systems so that we can better manage similar conditions today?
A recent study led by Elena Xoplaki in Quaternary Science Reviews examines ancient texts, excavated materials, lake sediments and climate models to provide one of the most comprehensive historical understandings of what really happened 800 years ago. And it suggests that Constantinople may have been better at weathering drought and heat than some scientists thought.
“Complex medieval societies, economic systems and political structures were actually relatively resilient in the face of climate change impacts,” says Xoplaki, a professor of geography at Justus-Liebig-University of Giessen in Germany.
“With today’s increased knowledge and technology, you may presume that we should be more capable with adapting to the impacts of climate change than the Byzantine society. However, we saw that when environmental crises are combined with political instability or other types of crisis, handling the impacts of climate change might become difficult.”
What happened to Constantinople?
The period AD 1081 to 1180 was a time of great prosperity in Byzantium – a time of population expansion; prolific wheat, barley and olive crops; political stability and a blossoming art and literary culture. An aristocratic elite emerged.
“This is a period when there were not large pressures from outside Byzantine society, such as invasions from external enemies. This was mainly an agricultural society, although very complex for a preindustrial society,” Xoplaki says. “And this complexity seemed to have supported the society in adapting to changing climatic conditions.”
But it wasn’t a time of climatic stability: climate models show that during this period, Constantinople and its surroundings saw less rainfall, overall warmer temperatures and colder winters. Scientists call this the “Medieval Climate Anomaly,” which was followed by a “Little Ice Age.”
Scientists aren’t yet sure what caused these shifts. Researchers have also long debated whether the Medieval Climate Anomaly was as warm as the current climate. “However, the climate changes that we saw then are not really similar to today, particularly the pace of change we are seeing now,” Xoplaki says.
Still, for an agrarian society whose whole economy is based on the trade of agricultural products and services, these climate extremes could have sharpened competition for resources between elites and government, says Adam Izdebski, a historian from Jagiellonian University in Krakow and co-author of the paper.
Scientists have frequently connected political unrest throughout history to this sort of competition — take Japan invading Manchuria in 1931 over food security concern, or the abandonment of Mexico’s Chaco Canyon, called the “Stonehenge of North America,” around AD 1130 due to a 50 year-long drought.
The same, however, may not have happened in Constantinople, Izdebski says. “While there was substantial disruption to the system, and while the empire more-or-less broke down in the face of local corruption, there is no societal collapse more broadly. Peasant cultivators continued to till their lands and produce crops with which to pay taxes and rents,” he says.
“So the break-down of the state in this region seems more intimately connected with shifts in power-relations between local elites and the centre than anything else.”
The history books, in other words, may not have been too far off.
Time to tread carefully
This year, a global analytic group called Verisk Maplecroft published an analysis of political risk, finding that 2016 will see little respite from the political instability, civil unrest, economic volatility, security crises and geopolitical rivalries that defined 2015.
Nowhere is that turbulence starker than in Syria. Since 1998, long droughts have reduced crop yields and pushed many farmers to the cities. This in itself did not caused the civil war that has wracked the country in recent years, just as the Medieval Climate Anomaly didn’t cause the collapse of the Byzantine Empire, says Joel Guiot. He is Director of Research at the French National Center for Scientific Research and the European Centre of Research and Teaching in Environmental Geosciences.
“If the political system is already declining, climate may amplify the problems. But finally it is an ensemble of environmental, cultural and political factors which are responsible of tensions. If one factor occurs, resilience is possible. If several factors co-occur, this is more difficult,” he says.
Joseph Manning, an ancient historian from Yale University, points out that we are currently focused on slow trends of climatic change but not as much on sudden shocks, such as volcanic eruptions. Such disasters can have extreme, and quick, effects on the Earth’s climate. That could be a problem, especially if the behaviour of countries doesn’t change.
“We are increasingly well prepared. We have a lot of data, a lot of science and now we have a lot of history that essentially confirms the science and gives us a window on how past human societies dealt with this,” he says.
“But there will inevitably be big shocks, like volcanic eruptions that this paper clearly shows will be harder to weather if our political and economic systems are strained.”
This research was part of the Past Global Changes (PAGES) project, a research project of Future Earth. You can read more about recent findings from PAGES here and here.