How volcanic eruptions cooled the planet 800 years ago

Volcanic eruptions are known to blast heat and ash into the sky but, oddly, they can also cool the planet. Now, scientists have found fresh evidence of this effect hidden in Antarctic ice. 

A new analysis of polar ice cores detected signals from five major volcanic eruptions that occurred in the 13th century. It turns out that, while volcanoes burn hot in the moment, their lasting impact can be chilling.

Jihong Cole-Dai, lead author of the study, is an expert in the Department of Chemistry, Biochemistry, and Physics at South Dakota State University.

How volcanic eruptions affect the climate

When a volcano erupts, it emits particles and gases into the atmosphere. These substances do not just vanish. They alter the properties of the atmosphere, including the critical energy balance, which is the equilibrium between the incoming solar radiation and outgoing infrared rays.

One of the most important gases released during volcanic eruptions is sulfur dioxide. In the atmosphere, it reacts with water to form tiny droplets called sulfate aerosols. They scatter the incoming sunlight away from the Earth, reducing the solar energy that reaches its surface. 

This can lead to temporary global cooling. That is why volcanoes are seen as powerful agents of natural climate change. Records of past climatic shifts and volcanic eruptions help scientists understand this volcano-climate connection.

So, how do we uncover these ancient eruptions and their climatic footprints? The answers lie buried in ice. That is where the frozen archives of the polar regions come in, offering a timeline of global volcanic history.

Ice cores reveal five volcanic eruptions

Volcanic particles can spread globally through atmospheric circulation. When they fall to the ground in polar regions, they get stuck in the snow. As the snow piles up, year after year, these particles become buried. 

Over time, the snow compacts into ice. This forms distinct layers called strata, which preserve these particles.

The five volcanic eruptions identified in the study were classified as Large or Very Large, depending on the amount of sulfate they deposited. Large eruptions deposited 914 to 2,740 ounces of sulfate per square mile, while deposits from Very Large eruptions exceeded 2,741 ounces per square mile. 

Eruptions with a strong cooling effect

The study showed that the strongest volcanic eruption signal appeared in 1259. This matches the massive 1257 Samalas eruption in Indonesia. Because volcanic aerosols from tropical eruptions take time to travel to the poles, the ice core signal can appear one to two years after the eruption itself.

The unusually high sulfate levels found in the ice indicate that these eruptions likely had a strong cooling effect. Only the Samalas eruption has been definitively linked to a specific volcano. The remaining four eruptions remain unattributed, and identifying their sources could help clarify their climate impact.

But it was not just one volcanic eruption shaking up the climate. What stood out was how close together these events occurred.

A rare cluster cooled the Earth

The scientists also got an idea about the timing of the eruptions. Surprisingly, four of the five eruptions happened just a decade apart, suggesting a rare burst of volcanic activity.

This kind of decadal pacing of large eruptions is unusual. Even the 19th century, with eruptions like Tambora (1815) and Krakatau (1883), did not have such closely spaced events.

In the ice cores, the sulfate signals lasted between two and four years, depending on snowfall rates and sampling resolution. In some cases, slower snowfall and shifting particles stretched these signals even further.

Volcanic particles can only last in the atmosphere for up to two or three years. But in this case, since a cluster of eruptions happened, the cooling effects were compounded, which led to lasting climate changes. 

Why the 13th century matters 

Researchers analyzed ice cores, cylindrical ice samples drilled out of ice sheets or glaciers, from both Antarctica and Greenland, to confirm the scale of these ancient eruptions. They measured the levels of sulfur compounds, such as sulfates and sulfuric acid, which are the fingerprints of past eruptions.

The ice core records show that the 13th century had the highest frequency of massive eruptions in the past 1,000 years. This makes it a key period for understanding the past climate changes due to natural phenomena and how they compare with the modern climate changes due to human influence.

These findings highlight how natural forces can drive major shifts in the climate. By studying past events, scientists gain valuable context for understanding today’s climate changes and what might lie ahead.

The full study was published in the journal Atmosphere.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–