Climate change may cause volcanic eruptions to be far more devastating

CAMBRIDGE, United Kingdom — Climate change may make large volcanic eruptions even more devastating in the future, a new study predicts. Researchers from Cambridge University say as the atmosphere warms, plumes of ash and gas from big volcanic eruptions will rise ever higher.

Climate change will also accelerate the dispersal of volcanic material in the form of small, shiny droplets called volcanic sulfate aerosols – sending them to higher latitudes. For large eruptions, the combined effect will cause the haze created by volcanic aerosols to block more sunlight from reaching Earth’s surface. This may ultimately amplify the temporary cooling effect volcanic eruptions cause.

Study authors add that large-magnitude eruptions will have greater effects as the climate continues to warm. However, the cooling effects of small and medium-sized eruptions could shrink by as much as 75 percent.

“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 Dr. Anja Schmidt, a lecturer in Climate Modelling, in a university release.

Past eruptions have cooled the planet

When Mount Pinatubo in the Philippines erupted in 1991, the effects had a worldwide impact. The plume from the eruption – the second largest of the 20th century – reached more than 18 miles into the sky, forming a layer of global haze. In 1992, this haze caused global temperatures to drop by about one degree Fahrenheit. In comparison, human activities have warmed global temperatures by over two degrees since 1850. However, the effect of volcanic aerosols only hang around for one or two years, while greenhouse gases will affect 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,” says Dr. Thomas Aubry from Cambridge’s Department of Geography.

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

Volcanic plumes rise like hot air balloons. They keep rising to a height where they’re naturally buoyant. The researchers looked at how high in the atmosphere these plumes can rise and travel globally under different warming scenarios. Using global climate models combined with volcanic plume models, the team simulated how climate change may affect the aerosols emitted by volcanic eruptions.

The study finds that for large eruptions like Mount Pinatubo, which typically occur once or twice per century, climate change will cause the plumes to rise higher and the aerosols to spread faster over the globe, resulting in a cooling effect amplified by 15 percent.

What’s happening in the atmosphere?

Scientists expect changes in ocean temperatures to further amplify the cooling. Additionally, the melting of ice sheets is also projected to increase volcanic eruptions frequency and size in places such as Iceland. However, for moderate-sized eruptions such as the 2011 Nabro eruption in Eritrea, which typically occur on a yearly basis, the effect will be reduced by about 75 percent under a high-end warming scenario.

This is because the height of the tropopause – the boundary between the troposphere and the lowest level of Earth’s atmosphere – and the stratosphere above it is predicted to increase. This will make it harder for volcanic plumes to reach the stratosphere. Aerosols from volcanic plumes confined to the troposphere are washed out by precipitation in a matter of weeks, making their impact relatively minor and much more localized.

The effects of climate change and some of the feedback loops it can cause are becoming more obvious now,” Dr. Schmidt says. “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.”

“Even if volcanoes have a limited influence on climate compared to human greenhouse gas emissions, they are an important part of the system,” Dr. Aubry adds.

“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,” Schmidt concludes.

The results of the study appear in the journal Nature Communications.

South West News Service writer William Janes contributed to this report.

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