UK researchers have begun to unravel the complex relationship between volcanic eruptions and climate change, showing that the temperature of the atmosphere affects how ash and gas spread.
One of the most massive volcanoes eruptions of the 20th century was that of Mount Pinatubo in the Philippines. When it blew its top in 1991, it spewed clouds of gas and dust more than 30 kilometres up into the atmosphere, putting more particulate matter into the stratosphere than any eruption since Krakatoa in 1883.
This created a hazy layer that wrapped around the world, prevented some sunlight from reaching the Earth’s surface and ultimately causing a drop in global temperatures by 0.5 degrees Celsius between 1991 and 1993.
Now, a team of researchers from the University of Cambridge and the UK Meteorological Office have investigated current climate effects on such eruptions.
“We wanted to look at the question from the opposite angle: how could a warming climate affect the cooling from volcanic eruptions?” says Thomas Aubry from the University of Cambridge.
Aubry is the first author of a study published in Nature Communications, which used a combination of global climate models and volcanic plume models to answer this question.
The team found that a warmer atmosphere will cause the plumes of gas and dust from large eruptions to rise even higher, and aerosols will also spread quicker from the tropics to the higher latitudes. The combined effect will block more sunlight and result in temporary cooling, with the effect amplified by 15%. The study also notes that as the ocean warms, cooling may further increase.
However, the team also looked at small and medium eruptions, and found in a high-end emissions scenario, climate change could actually reduce the cooling effects by up to 75%. As the atmosphere warms, the tropopause (the boundary between the troposphere and stratosphere) is predicted to rise in altitude and make it more difficult for plumes to reach the upper atmosphere and circulate around the globe.
Smaller eruptions are more frequent than larger ones, which only occur once or twice in a century, but it’s unclear whether we would see a net warming or cooling effect – the team hasn’t crunched the numbers on that yet.
It’s a complex field of study, but one that we need to address, they say.
“Climate change isn’t something that’s coming – it’s already here, as clearly demonstrated by this week’s IPCC report,” say co-author Anja Schmidt, also from Cambridge.
“The effects of climate change and some of the feedback loops it can cause are becoming more obvious now. But the climate system is complex: getting a grasp of all these feedback loops is critical to understanding our planet and making accurate climate projections.”
Aubry adds: “The new feedback loops between climate and volcanic eruptions that we highlight in this work are currently unaccounted for by IPCC. It could shed new light on the evolution of future volcanic influences on climate. Even if volcanoes have a limited influence on climate compared to human greenhouse gas emissions, they are an important part of the system.”
Interestingly, as ice sheets melt in places like Iceland, the size and frequency of eruptions may increase; there is some evidence that melting ice at the end of the last ice age triggered an acceleration of volcanic activity. Plus, events like wildfires and extreme precipitation are also changing the atmosphere, with unknown consequences for volcanic eruptions.
“As we continue to emit greenhouse gases, the way that volcanic emissions interact with the atmosphere will continue to change and it is important to quantify these interactions in order to fully understand climate variability,” says Schmidt.