Link between volcanic eruptions, climate change unearthed from ice cores

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Researchers have established a link between large volcanic eruptions and climate variability and through a new study published in the journal Nature, an international team of scientists 18 universities and research institutions have come up with a reconstruction of the timing and associated radiative forcing of nearly 300 individual volcanic eruptions extending as far back as the early Roman period.

Led by Desert Research Institute (DRI), the team of 24 researchers have been able to show that large volcanic eruptions in the tropics and high latitudes were the dominant drivers of climate variability and have been responsible for numerous and widespread summer cooling extremes over the past 2,500 years.

Study’s lead author Michael Sigl, Ph.D., an assistant research professor at DRI and postdoctoral fellow with the Paul Scherrer Institute in Switzerland said that these cooler temperatures were cause by spread of volcanic sulfate particles injected into the upper atmosphere shielding the Earth’s surface from incoming solar radiation.

Through the study, researchers established that 15 of the 16 coldest summers that were recorded between 500 BC and 1,000 AD followed large volcanic eruptions – with four of the coldest occurring shortly after the largest volcanic events found in record.

Using more than 20 individual ice cores extracted from ice sheets in Greenland and Antarctica and analysing them for volcanic sulfate using DRI’s state-of-the-art, ultra-trace chemical ice-core analytical system, researchers were able to come up with a year-by-year history of atmospheric sulfate levels through time. Additional measurements including other chemical parameters were made at collaborating institutions.

The new timescale was derived using a statistical algorithm and not by hand, said Mai Winstrup, Ph.D., a postdoctoral researcher at the University of Washington, Seattle. “Together with the state-of-the-art ice core chemistry measurements, this resulted in a more accurate dating of the ice cores.”

The authors of the study from United Kingdom, Switzerland, Germany, Denmark, and Sweden note that identification of new evidence found in both ice cores and corresponding tree rings allowed constraints and verification of their new age scale.

Researchers say that throughout human history sustained volcanic cooling effects on climate have triggered crop failures and famines and these events may have also contributed to pandemics and societal decline in agriculture-based communities.

Researchers translated and interpreted ancient and medieval documentary records from China, Babylon (Iraq), and Europe that described unusual atmospheric observations as early as 254 years before Common Era (BCE). These phenomena included diminished sunlight, discoloration of the solar disk, the presence of solar coronae, and deeply red twilight skies.

Researchers note in the study that tropical volcanoes and large eruptions in the Northern Hemisphere high latitudes (such as Iceland and North America) – in 536, 626, and 939 CE often caused severe and widespread summer cooling in the Northern Hemisphere by injecting sulfate and ash into the high atmosphere.

These particles also dimmed the atmosphere over Europe to such an extent that the effect was noted and recorded in independent archives by numerous historical eyewitnesses. Climatic impact was strongest and most persistent after clusters of two or more large eruptions.

Researchers are also optimistic that their findings could help shed light on an unsolved mystery as to the causes of one of the most severe climate crises in recent human history, starting with an 18-month “mystery cloud” or dust veil observed in the Mediterranean region beginning in March, 536, the product of a large eruption in the high-latitudes of the Northern Hemisphere.

The initial cooling was intensified when a second volcano located somewhere in the tropics erupted only four years later. In the aftermath, exceptionally cold summers were observed throughout the Northern Hemisphere.

This pattern persisted for almost fifteen years, with subsequent crop failures and famines – likely contributing to the outbreak of the Justinian plague that spread throughout the Eastern Roman Empire from 541 to 543 CE, and which ultimately decimated the human population across Eurasia.

“This new reconstruction of volcanic forcing will lead to improved climate model simulations through better quantification of the sensitivity of the climate system to volcanic influences during the past 2,500 years,” noted Joe McConnell, Ph.D., a DRI research professor who developed the continuous-flow analysis system used to analyze the ice cores.

“As a result,” McConnell added, “climate variability observed during more recent times can be put into a multi-millennial perspective – including time periods such as the Roman Warm Period and the times of significant cultural change such as Great Migration Period of the 6th century in Europe.”

This reconciliation of ice-core records and other records of past environmental change will help define the role that large climatic perturbations may have had in the rise and fall of civilizations throughout human history.

“With new high-resolution records emerging from ice cores in Greenland and Antarctica, it will be possible to extend this reconstruction of volcanic forcing probably all the way back into the last Ice Age,” said Sigl.