Volcanic eruptions will lose their cooling effects on a warmer planet

Climate change will alter the way that volcanic eruptions interact with the atmosphere, according to a new study from the University of Cambridge. These changes will compromise the cooling effects of most volcanoes.

“Due to more frequent and more intense wildfires, as well as other extreme events, the composition of the upper atmosphere is changing in front of our eyes, and so is our understanding of the consequences of these changes,” said study co-author Dr. Anja Schmidt.

“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.”

The experts report that the cooling effects of large-magnitude eruptions will be enhanced by global warming. On the other hand, the cooling effects of small- and medium-sized eruptions will decrease by up to 75 percent. 

Considering that smaller eruptions are much more common, it is especially important to understand their overall influence on the climate. 

In a warming atmosphere, plumes of ash and gas ejected by large volcanic eruptions will rise increasingly higher. In addition, the transport of volcanic sulfate aerosols will be accelerated.

When it comes to large eruptions, these aerosols will block more sunlight from reaching Earth’s surface, which will ultimately amplify the temporary cooling effect.

In 1991, Mount Pinatubo erupted in the Philippines, and the effects were felt worldwide. The plume from the eruption was ejected more than 30 kilometres into the sky. The resulting layer of haze moved across the planet, causing temperatures to drop by as much as 0.5 degrees Celsius in 1992.

Human activities have warmed global temperatures by over one degree Celsius since 1850. The major difference is that volcanic aerosols only persist for one or two years, but greenhouse gases influence the climate for centuries.

“Beyond the data we have from recent eruptions like Pinatubo, we can also see the cooling effect of volcanoes going back two thousand years from the information contained in tree rings,” said study first author Dr. Thomas Aubry.

“However, we wanted to look at the question from the opposite angle: how could a warming climate affect the cooling from volcanic eruptions?”

To investigate, the researchers looked at how high in the atmosphere volcanic plumes can rise and be transported under different warming scenarios.

The study showed that for large eruptions like Mount Pinatubo, climate change will cause the plumes to rise higher and the aerosols to spread faster across the globe, amplifying the overall cooling effects by 15 percent.

For moderate-sized eruptions, however, the cooling effect will be reduced by about 75 percent under a high warming scenario. This is because the height of the tropopause is predicted to increase, making it harder for volcanic plumes to reach the stratosphere. 

When aerosols are confined to the troposphere, they are washed out by precipitation in a matter of weeks. The subsequent climatic impacts are relatively minor and much more localized, according to the researchers.

“Climate change isn’t something that’s coming – it’s already here, as clearly demonstrated by this week’s IPCC report,” said Dr. Schmidt. 

“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.”

“The new feedback loops between climate and volcanic eruptions that we highlight in this work are currently unaccounted for by IPCC,” said Dr. Aubry. “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.”

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer