Mount Etna’s Restless Slumber: Understanding Volcanoes and Their Atmospheric Influence

Mount Etna, Europe's most active and largest volcano, has once again made its presence known with recent eruptive activity in early June 2025. While these latest paroxysms on the Sicilian volcano have, so far, been relatively contained, they serve as a potent reminder of the dramatic and far-reaching ways volcanoes can interact with our weather and climate. Understanding these interactions is crucial, not just for those living in the shadow of these geological giants, but for grasping the complexities of our global atmospheric system.

Volcanic eruptions, whether the effusive lava flows sometimes seen at Etna or more explosive, ash-rich events, release a variety of substances into the atmosphere. These include vast quantities of gases – primarily water vapour, carbon dioxide (CO2​), and sulphur dioxide (SO2​) – along with particulate matter, most notably volcanic ash. The altitude these materials reach, and their chemical composition, largely determine their subsequent effects on weather and climate.

Immediate, Localised Weather Effects

The most immediate and often dramatic impacts of a volcanic eruption are on local and regional weather patterns.

• Ash Fall and Air Quality: Dense plumes of volcanic ash can blanket vast areas, posing significant risks. This ash consists of fine, sharp rock fragments and glass. It can cause respiratory problems, contaminate water supplies, and damage infrastructure, including buildings and power lines. The recent activity at Mount Etna, for instance, led to the issuance of red alerts for aviation, a common precaution as ash can severely damage jet engines. Fine ash particles also reduce visibility and can impact local air quality significantly. Tracking ash dispersion is vital, and services providing detailed air quality forecasts, such as those offered by OpenWeather, become invaluable for communities downwind of an eruption.
• Changes in Precipitation: The injection of large amounts of fine particles (ash and aerosols) into the atmosphere can act as condensation nuclei. This can sometimes lead to increased local rainfall, or even "volcanic rain" which can be acidic if it incorporates significant amounts of sulphur dioxide or hydrogen chloride. In some instances, if the eruption is powerful enough to inject a lot of material into the drier upper troposphere or lower stratosphere, it can also lead to localised decreases in precipitation by altering cloud formation processes.
• Volcanic Smog (Vog): When sulphur dioxide and other volcanic gases react with oxygen, moisture, and sunlight in the atmosphere, they can form volcanic smog, or "vog." Vog can cause hazy conditions, reduce visibility, and lead to respiratory issues, similar to those caused by urban smog.
• Temperature Fluctuations: Locally, heavy ash clouds can block sunlight, leading to a temporary cooling effect at the surface directly beneath the plume. Conversely, the heat released during an eruption can sometimes create localised thermal anomalies.

Broader Climatic Implications

While local weather effects are often immediate and apparent, the impact of volcanoes on the broader climate system is more complex and typically unfolds over longer timescales, particularly after very large eruptions.

The most significant climate impact comes from the injection of sulphur dioxide (SO2​) into the stratosphere, the atmospheric layer above the troposphere where our weather occurs. In the stratosphere, SO2​ undergoes chemical reactions to form tiny sulphate aerosol particles. These aerosols are highly reflective and can persist in the stratosphere for several years, spreading globally.

By reflecting incoming solar radiation back into space, these sulphate aerosols can lead to a net cooling effect on the Earth's surface. Historic eruptions provide clear evidence of this cooling effect. For example, the 1991 eruption of Mount Pinatubo in the Philippines, which injected about 20 million tonnes of SO2​ into the stratosphere, caused a global average surface cooling of around 0.5∘C (0.9∘F) for about two years. The colossal 1815 eruption of Mount Tambora in Indonesia led to the infamous "Year Without a Summer" in 1816, with widespread crop failures and unseasonably cold conditions across parts of Europe and North America.

It is important to note that while volcanic eruptions release carbon dioxide, a greenhouse gas, the amount released by individual eruptions, even large ones, is dwarfed by human emissions. The long-term warming effect of volcanic CO2​ is negligible compared to the shorter-term cooling effect of sulphate aerosols from major eruptions.

Monitoring and Forecasting in Volcanic Events

The recent activity at Mount Etna highlights the critical need for continuous monitoring of active volcanoes and the atmospheric conditions surrounding them. Satellite imagery, ground-based sensors, and sophisticated weather models all play a role. Understanding wind patterns at various atmospheric levels, along with precipitation levels, for example, is essential for forecasting the dispersion of ash plumes and gaseous emissions. Historical weather data such as the OpenWeather Historical Products Collection and the Current Weather and Forecasts Collection can be instrumental for emergency planners and authorities in predicting the trajectory and potential impact zones of volcanic emissions. This data aids in making informed decisions to protect lives and minimise disruption.

While eruptions like the recent ones at Mount Etna are a stark reminder of the Earth's powerful internal forces, they also provide invaluable opportunities to study and understand the intricate connections between geology and the atmosphere. By carefully observing these events and utilising advanced weather data, we can better prepare for their impacts and deepen our knowledge of the complex systems that shape our planet's weather and climate.