In 1991, the Pinatubo volcano eruption was a disaster for the Philippines and the effects were noticed across the world - it threw tons of ash and other particles into the atmosphere, which caused less sunlight to reach the Earth's surface. Global temperatures dropped by half a degree for years after that.

Clearly, volcanic eruptions can have a strong short-term impact on climate but a group of researchers are delighting doomsday believers by contending climate change will have an impact on volcanic eruptions. The researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel and Harvard University say they have strong evidence by using models of major volcanic eruptions around the Pacific Ocean over the past 1 million years.

For over 10 years the Fluids and Volatiles in Subduction Zones (SFB 574) project has been exploring volcanoes of Central America. "Among others pieces of evidence, we have observations of ash layers in the seabed and have reconstructed the history of volcanic eruptions for the past 460,000 years," says lead author and GEOMAR volcanologist Dr. Steffen Kutterolf. They noticed particular patterns. "There were periods when we found significantly more large eruptions than in others."

They compared those patterns with climate history and found that the periods of high volcanic activity followed fast, global temperature increases and associated rapid ice melting. They then studied other cores from the entire Pacific region. These cores had been collected as part of the International Integrated Ocean Drilling Program (IODP) and its predecessor programs and record more than a million years of the Earth's history. "In fact, we found the same pattern from these cores as in Central America," says co-author and geophysicist Dr. Marion Jegen from GEOMAR.

They then used geological computer models to affirm their beliefs. "In times of global warming, the glaciers are melting on the continents relatively quickly. At the same time the sea level rises. The weight on the continents decreases, while the weight on the oceanic tectonic plates increases. Thus, the stress changes within in the earth to open more routes for ascending magma," says Jegen.

The rate of global cooling at the end of the warm phases is much slower, so there are less dramatic stress changes during these times. "If you follow the natural climate cycles, we are currently at the end of a really warm phase. Therefore, things are volcanically quieter now. The impact from man-made warming is still unclear based on our current understanding," says  Kutterolf.

The next step is to investigate shorter-term historical variations to better understand implications for the present day.

 Published in Geology