The Testimony of Trees: How Volcanic Eruptions Shaped 2000 Years of World History

Related Articles

Related Articles

Researchers have shown that over the past two thousand years, volcanoes have played a larger role in natural temperature variability than previously thought, and their climatic effects may have contributed to past societal and economic change.

The researchers, led by the University of Cambridge, used samples from more than 9000 living and dead trees to obtain a precise yearly record of summer temperatures in North America and Eurasia, dating back to the year 1 CE. This revealed colder and warmer periods that they then compared with records for very large volcanic eruptions as well as major historical events.

Crucial to the accuracy of the dataset was the use of the same number of data points across the entire 2000 years. Previous reconstructions of climate over this extended period have been biased by over-representation of trees from more recent times.

 

The results, reported in the journal Dendrochronologia, show that the effect of volcanoes on global temperature changes is even greater than had been recognised, although the researchers stress that their work in no way diminishes the significance of human-caused climate change.

Instead, the researchers say, the study contributes to our understanding of the natural causes and societal consequences of summer temperature changes over the past two thousand years.

“There is so much we can determine about past climate conditions from the information in tree rings, but we have far more information from newer trees than we do for trees which lived a thousand years or more ago,” said Professor Ulf Büntgen from Cambridge’s Department of Geography, the study’s lead author. “Removing some of the data from the more recent past levels the playing field for the whole 2000-year period we’re looking at, so in the end, we gain a more accurate understanding of natural versus anthropogenic climate change.”

Comparing the data from tree rings against evidence from ice cores, the researchers were able to identify the effect of past volcanic eruptions on summer temperatures.

Large volcanic eruptions can lower global average temperatures by fractions of a degree Celsius, with strongest effects in parts of North America and Eurasia. The main factor is the amount of sulphur emitted during the eruption that reaches the stratosphere, where it forms minute particles that block some sunlight from reaching the surface. This can result in shorter growing seasons and cooler temperatures, that lead in turn to reduced harvests. Conversely, in periods when fewer large eruptions occurred, the Earth is able to absorb more heat from the Sun and temperatures rise.

“Some climate models assume that the effect of volcanoes is punctuated and short,” said Büntgen. “However, if you look at the cumulative effect over a whole century, this effect can be much longer. In part, we can explain warm conditions during the 3rd, 10th and 11th centuries through a comparative lack of eruptions.”

Reconstructed summer temperatures in the 280s, 990s and 1020s, when volcanic forcing was low, were comparable to modern conditions until 2010.

Compared with existing large-scale temperature reconstructions of the past 1200-2000 years, the study reveals a greater pre-industrial summer temperature variability, including strong evidence for the Late Antique Little Ice Age (LALIA) in the 6th and 7th centuries.

Then, working with historians, the scientists found that relatively constant warmth during Roman and medieval periods, when large volcanic eruptions were less frequent, often coincided with societal prosperity and political stability in Europe and China. However, the periods characterised by more prolific volcanism often coincided with times of conflict and economic decline.

“Interpreting history is always challenging,” said Dr Clive Oppenheimer, the lead volcanologist of the study. “So many factors come into play – politics, economics, culture. But a big eruption that leads to widespread declines in grain production can hurt millions of people. Hunger can lead to famine, disease, conflict and migration. We see much evidence of this in the historical record.

“We knew that large eruptions could have these effects, especially when societies were already stressed, but I was surprised to see the opposite effect so clearly in our data – that centuries with rather few eruptions had warmer summers than the long-term average.”

The new temperature reconstructions provide deeper insights into historical periods in which climactic changes, and their associated environmental responses, have had an outsized impact on human history. This has clear implications for our present and future. As climate change accelerates, extreme events, such as floods, drought, storms and wildfires, will become more frequent.

“Humans have no effect on whether or not a volcano erupts, but the warming trend we are seeing right now is certainly related to human activity,” said Büntgen. “While nothing about the future is certain, we would do well to learn how climate change has affected human civilisation in the past.”

UNIVERSITY OF CAMBRIDGE

Header Image Credit : Public Domain

Download the HeritageDaily mobile application on iOS and Android

More on this topic

LATEST NEWS

Camulodunum – The First Capital of Britannia

Camulodunum was a Roman city and the first capital of the Roman province of Britannia, in what is now the present-day city of Colchester in Essex, England.

African Crocodiles Lived in Spain Six Million Years Ago

Millions of years ago, several species of crocodiles of different genera and characteristics inhabited Europe and sometimes even coexisted.

Bat-Winged Dinosaurs That Could Glide

Despite having bat-like wings, two small dinosaurs, Yi and Ambopteryx, struggled to fly, only managing to glide clumsily between the trees where they lived, according to a new study led by an international team of researchers, including McGill University Professor Hans Larsson.

Ancient Maya Built Sophisticated Water Filters

Ancient Maya in the once-bustling city of Tikal built sophisticated water filters using natural materials they imported from miles away, according to the University of Cincinnati.

New Clues Revealed About Clovis People

There is much debate surrounding the age of the Clovis - a prehistoric culture named for stone tools found near Clovis, New Mexico in the early 1930s - who once occupied North America during the end of the last Ice Age.

Cognitive Elements of Language Have Existed for 40 Million Years

Humans are not the only beings that can identify rules in complex language-like constructions - monkeys and great apes can do so, too, a study at the University of Zurich has shown.

Bronze Age Herders Were Less Mobile Than Previously Thought

Bronze Age pastoralists in what is now southern Russia apparently covered shorter distances than previously thought.

Legio IX Hispana – The Lost Roman Legion

One of the most debated mysteries from the Roman period involves the disappearance of the Legio IX Hispana, a legion of the Imperial Roman Army that supposedly vanished sometime after AD 120.

Popular stories

Legio IX Hispana – The Lost Roman Legion

One of the most debated mysteries from the Roman period involves the disappearance of the Legio IX Hispana, a legion of the Imperial Roman Army that supposedly vanished sometime after AD 120.

The Secret Hellfire Club and the Hellfire Caves

The Hellfire Club was an exclusive membership-based organisation for high-society rakes, that was first founded in London in 1718, by Philip, Duke of Wharton, and several of society's elites.

Port Royal – The Sodom of the New World

Port Royal, originally named Cagway was an English harbour town and base of operations for buccaneers and privateers (pirates) until the great earthquake of 1692.

Matthew Hopkins – The Real Witch-Hunter

Matthew Hopkins was an infamous witch-hunter during the 17th century, who published “The Discovery of Witches” in 1647, and whose witch-hunting methods were applied during the notorious Salem Witch Trials in colonial Massachusetts.