Although volcanic eruptions are mostly known for their devastating impacts on land, they also influence the atmosphere in surprising ways. Particles that are catapulted into the sky by eruptions can alter the composition of clouds, cooling the surface below. Volcanic ash, as new research suggests, plays an unexpected role in cloud formation by manipulating ice crystals.

A new study published in Science Advances found that volcanic ash enables ice to take shape in clouds, a process that hasn’t been studied extensively before. The environmental effects — how volcanic ash contributes to radiation on Earth — are still up for debate, but a better understanding of cloud formation could inform geoengineering efforts that aspire to slow global warming. 

How Clouds and Volcanoes Impact Radiation

Clouds have a complex relationship with radiation. This is seen with their influence on Earth’s radiation budget, the balance between incoming shortwave radiation from the Sun and outgoing longwave radiation from Earth. Depending on the thickness and elevation of a cloud, it can either have an absorbing or reflecting effect. 

Lower, thicker clouds reflect more radiation coming from the Sun and cool the Earth’s surface. Higher, thinner clouds reflect less incoming solar radiation and even tend to absorb outgoing infrared radiation constantly emitted by Earth itself. Cirrus clouds — wispy, icy clouds that sit high in the atmosphere — generally have a net warming effect on Earth. 

Volcanoes also affect Earth’s radiation budget through the particles they eject. Scientists have mostly focused on sulfate aerosols, which form after sulfur dioxide is released into the atmosphere by an eruption. Although sulfate aerosols can deplete the ozone layer and produce acid rain, they also help cool Earth by reflecting solar radiation. 

Read More: Volcanic Eruption Warnings Are Now Possible With Fiber-Optic Cables

The Impact of Volcanic Ash

Volcanic ash hasn’t garnered as much attention as sulfate aerosols, but the new study proves that it also needs to be considered in climate discussions. 

In the study, researchers from the Lawrence Livermore National Laboratory (LLNL) gathered information on ice crystals in clouds by examining radar and lidar data from NASA’s Cloudsat and CALIPSO missions. 

The team found that ash-rich volcanic eruptions caused clouds to host fewer, but larger ice crystals. 

“At the beginning of the study, we did expect clouds affected by volcanic eruptions to look different from natural clouds, but not in the way we ultimately found,” said Lin Lin, a scientist at LLNL, in a statement. “We anticipated that volcanic aerosols would lead to an increase in the number of ice crystals in clouds. But to our surprise, the data showed the opposite.”

Dealing with Cirrus Clouds

The team initially thought that an eruption would cause homogenous nucleation, in which ice forms spontaneously without the need for a surface. They instead found that ash-heavy eruptions prompt an opposite reaction called heterogenous nucleation, in which ice needs an “impurity” like volcanic ash to form. After an eruption, water droplets stick to ash particles before they can get cold enough to freeze. 

By producing fewer and larger ice crystals, clouds that undergo heterogenous nucleation end up reflecting less solar radiation, but they also allow more radiation from Earth to escape into space. The team also determined that ash-rich eruptions led to a higher frequency of cirrus clouds. 

The researchers say volcanic ash needs to be implemented in more climate models to understand exactly how all of these factors influence Earth’s surface temperature. Further studies on volcanic ash could also guide plans for cirrus cloud thinning, a proposed idea for mitigating global warming. This process would involve spraying aerosols into the atmosphere to thin or eliminate cirrus clouds, allowing more longwave radiation to leave Earth.

Read More: The Planet-wide Problem That Is Solar Geoengineering

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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.