Could Mount Agung’s latest eruption cool the planet?

Nearly 60,000 travelers have been stranded after yesterday’s eruption of Mount Agung in Bali. The volcano has been threatening a major eruption since earlier this year. In September, residents within a six-kilometer radius of the crater were told to evacuate for their own safety. Some did and have not returned, while others returned daily to feed and care for their livestock.

Yesterday’s eruption was the second in a week. According to reports, it spewed “ash 13,000 feet (4,000 meters [or nearly 2.5 miles]) into the atmosphere, and created plumes as high as 3.7 miles (6,000 meters).” The alert for the area has been raised, and people within 10 kilometers of the crater have been told to evacuate due to fears of a larger eruption to come.

Mount Agung map

Google Map showing Mount Agung’s location in Bali, Indonesia.

Bali is a small island in Indonesia, north of Western Australia. It’s proximity to the equator and mild weather make it a popular tourist destination for holiday travelers. It also gives Mount Agung the potential to affect weather on a global scale after a massive eruption.

If yesterday’s eruption is the worst of this round, then the weather in the region will be affected only in the near term. Ash contains sulfur dioxide, which when combined with water forms sulfuric acid aerosols. Those aerosols can “reflect incoming sunlight and influence cloud formation.” Australia’s Bureau of Meteorology predicts the weather could return to normal within a few weeks if the current wind direction continues.

If a larger eruption occurs – large enough to send ash into the stratosphere (18,000 meters) – the entire planet could be cooled for a year or more. While that sounds impressive, we’re really only talking about an estimated one degree Fahrenheit or less (0.55 degree Celsius or less).  Considering the upward global temperature trend in recent years, that much of a temperature drop would only take us back to 2014’s average temperature according to a report published by Carbon Brief back in October.

There have been major volcanic eruptions in the past that affected the earth’s temperature on a grand scale. Mount Tambora’s eruption in 1815 – just a few small islands east of Bali – may have caused the “year without a summer” as it is referred to in historical records in North America and Europe in 1816.

On their website longrangeweather.com, Climatologist Cliff Harris and Meteorologist Randy Mann have graphed global temperature swings over the past 4,500 years and correlated times of cooling to low solar activity and high volcanic activity. Alternately, periods of higher warming tend to be associated with peaks in solar activity and fewer eruptions. They also point out that El Nino and La Nina also play a role in global temperatures on smaller time scales.

Currently, we are seeing La Nina conditions in the Pacific, which is often associated with cooler-than-average global temperatures. If we were to add a major volcanic eruption to the mix, we could easily see that drop scientists are hypothesizing of a degree or more in the next year. It definitely bears watching, even from the other side of the world.