Volcanic Eruptions Can Reduce Global Average Temperature (Credit: UCAR and Meteorology Today by C. Ahrens)
Volcanic eruptions have the potential to change the global average temperature and have done so in the past. There are just two important factors that can make this happen. These eruptions have to be massive and the spewed contents need to have a significant amount of sulfur dioxide and ash. One evident example of this is what is famously known as “The year without a summer”.
The year 1816 was notoriously known for its cold and gloomy summer, where overcast skies and rain was frequent. In order to explain the cold summer event, scientists researched global climatic changes and events over the past year. It was discovered that this massive eruption became the main cause of 1816’s chilly summer. On April 5th, 1815, Mt. Tambora in Indonesia erupted. The build up, however, took a staggering four months as ash and dust spewed high into the atmosphere, blocking out the sun. Based on its duration and magnitude, this eruption was dubbed the largest in recorded history. As the ash spewed into the air, debris that didn’t fall back to the ground was picked up by the trade winds and circulated around the world; a process that takes months. By the time the summer of 1816 came around, the global average temperature had decreased by about three degrees Celsius.
The small particles of ash from the eruption travel around the globe becoming perfect condensation nuclei for water vapor. Condensation nuclei is a term to explain how the particles of ash act as an object the water vapor in the air can easily attach to. The process of collision continues to grow the piece of ash into a water droplet. This occurs when more droplets of water continue to attach to the particle by colliding into it as it gets pushed around by the movement of air. Eventually, all the ash in the air will collect into a bigger droplet of vapor and form a cloud. With more ash in the air, this process increases cloud cover in the atmosphere and leads to increased precipitation. Clouds are notorious for blocking out the sun. In the case of the year 1816, this is exactly what happened. Most of the summer was cloudy and rainy.
Sulfur Dioxide, a gas released during volcanic eruptions, also combines with water vapor in the atmosphere. When this happens the chemicals react and the droplets of water vapor become droplets of sulfuric acid. Sulfuric acid is a great sunlight reflector. Naturally in our atmosphere, Sulfuric Acid is known as a coolant, contributing to the cooling of the earth's surface. With an increased amount of Sulfuric Acid in the atmosphere, the more likely it is to increase the cooling process. With the 1815 eruption, Mt. Tambora caused a significant amount of Sulfuric Acid to form. It takes about three years for Sulfuric Acid to collect into rain droplets and rain out of the atmosphere. So, with the highest content of sulfuric acid in the atmosphere the following year along with the increased cloud cover from the microparticles, the global average temperature decreased.
Another example of volcanic eruption that changed global average temperature occurred in 1991. Mt. Pinatubo in the Philippines spewed an estimated 20 million tons of Sulfur Dioxide into the atmosphere. Model predictions were in agreement that the global average temperature had dropped by 0.5 degrees Celsius and the following two years recorded below average temperatures around the world. This eruption was not nearly as big as the eruption of Mt. Tambora. However, it was still a large eruption that had a significant effect on the global average temperature.
It is very interesting how much one large eruption has an effect on our atmosphere. The effect made by Mt. Tambora was certainly the largest in recorded history. Although uncertain and difficult to predict, it is possible that another eruption could occur at some point in the future which may also have an effect on the global average temperature. There are still plenty of active volcanoes to this day that record seismic activity and/or spew lava and ash on occasion. Even after blowing its top in 1815, Mt. Tambora is one of the few/many volcanoes still active to this day.
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© 2019 Meteorologist Alexandria Maynard