This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Volcanic eruptions are known for their spectacular visual displays of vivid lava, as well as the devastating impacts they can have on the environment and the communities who live nearby. But they can also have far-reaching impacts across the globe.
Explosive eruptions release vast quantities of sulfur dioxide gas into the upper atmosphere (stratosphere), where it reacts with water vapor and oxygen to form tiny aerosol droplets of sulfuric acid. These droplets scatter and reflect incoming solar radiation from the sun back out to space, reducing the warming energy reaching Earth's surface and therefore helping to keep the planet cooler for multiple months or even years. A famous example of this is when Mount Tambora in Indonesia erupted in 1815, leading to the "year without a summer" in 1816.
Mary Shelley spent much of that time indoors due to the poor weather and wrote the literary classic "Frankenstein" in Switzerland and England—a curious cultural connection to a seemingly unrelated event far away. New research, published in Geophysical Research Letters, has now explored whether a volcano's location makes a difference in the amount of cooling experienced in the Northern Hemisphere. Zachary McGraw, of Columbia University, and colleagues report that previous studies have found volcanic eruptions in the middle latitudes between 30° and 70° (known as the extratropics) produced greater cooling than tropical eruptions of similar magnitude.
To test this, the researchers used a NASA climate model to simulate the difference between tropical and extratropical eruptions that released different amounts of sulfur gas across eruptions in summer and winter. However, the team found no clear indication of increased Northern Hemisphere cooling based on an erupting volcano's location—at most, an extratropical eruption increased cooling by twice as much, not the 7.5 times found in previous studies. They identified that there could be some enhanced cooling from extratropical eruptions as a result of the microscopic aerosols being concentrated within just the Northern Hemisphere, whereas aerosols from tropical eruptions are moved into both hemispheres by wind patterns to distribute the reflective cooling effects of aerosols more evenly.
This is the only mechanism that they say could create increased cooling in the extratropics, and there is no known process that could amplify cooling to 7.5 times. To consider this in real terms, McGraw and the team tested this theory against ancient climate records to see how past tropical and extratropical eruptions had influenced weather. One of these so-called paleoclimate proxies is tree rings.
The annual growth rings of trees can become wider during wet or warm seasons and narrower during dry or cold years when they're experiencing more environmental stress. They therefore considered tree ring data associated with historical records of extratropical eruptions from 1783 CE in Iceland, 536 CE somewhere in the mid-latitudes and 43 BCE in Alaska, as well as simulating 100,000 similar eruptions and subsequent cooling periods due to a lack of modern extratropical eruptions. This was compared to numerous post-750 CE tropical eruptions to identify patterns in weather following an eruption and validate whether modeling can accurately represent climate patterns seen in historical records.
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