Bali’s Mount Agung could erupt at any moment – and when it does, climate watchers may notice a slight shift from the seemingly endless global temperature rise. Ever so slightly, global temperatures will drop in the wake of the eruption. While this may sound like good news, it will only serve to temporarily cool down the planet. If Mount Agung’s most recent eruption offers any insight, the global temperature drop from the imminent volcanic activity should be approximately 0.1-0.4 degrees Celsius, as it was in 1963. Although this may not seem like much, even a small change in global temperature can make a significant difference on climate. For example, during the most recent Ice Age, the planet’s global temperature was only 5 degrees Celsius cooler than it is today.
The significant cooling that should follow Agung’s eruption is the result of its spewing ash and sulfur dioxide into the air. When the sulfur dioxide reacts with the water vapor in the atmosphere, it becomes sulfuric acid. Accumulation of these droplets creates an atmospheric haze, which blocks the Sun’s ultraviolet rays from reaching the Earth, which causes the global cooling. Though the haze can remain in the atmosphere for years, its effects are short lived. “They’re small enough that they can stay up there for a while … but eventually they get rained out,” said Richard Arculus, Emeritus Professor in geology at the Australian National University. “These are short-term effects, not like the enduring, year after year injection of carbon dioxide by burning fossil fuels — which keeps accumulating.”
Though the cooling effects may be significant, and brief, you are unlikely to notice any major temperature change on the ground. However, it is not unheard of for volcanic eruptions to cause disruptive changes to the planet’s climate. For example, the 1815 eruption of Mount Tambora in Indonesia resulted in what has become known as the Year Without Summer, during which Europe and the Northeast United States suffered from major crop losses due to unseasonable frost and lack of sunlight sufficient for plants.