Could Mount Agung cause global cooling effects lasting for years?

By Jennifer Fabiano, AccuWeather staff writer
December 01, 2017, 11:21:50 AM EST

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Mount Agung is experiencing an ongoing eruption, with the first occurring on Nov. 21.

Scientists are not able to predict if or when Mount Agung will have a major eruption, according to AccuWeather Senior Meteorologist Brett Anderson.

If a major eruption occurs, there could be some dramatic effects on Earth’s climate, including global cooling periods that can last from months to a couple of years. When Mount Agung last erupted in 1963, it eventually caused a 0.1 to 0.2 of a degree Celsius drop in the global temperature.

During the 1963 eruption, there were fluxes in activity resulting in three eruptions, each about a month apart, according to AccuWeather Senior Meteorologist Eric Leister.

“A more significant eruption can have more of a wide range of impacts beyond Bali and the immediate parts of Indonesia,” said Leister “Whether that happens is pretty much just speculation at this point.”

Indonesia Volcano

Mount Agung volcano spews smoke and ash in Karangasem, Bali, Indonesia, Tuesday, Nov. 28, 2017. Mount Agung volcano on Bali has erupted for the first time in more than half a century, forcing closure of the Indonesian tourist island's busy airport as the mountain gushes huge columns of ash that are a threat to airplanes. (AP Photo/Firdia Lisnawati)

Three factors determine if a volcanic eruption will have a major effect on Earth’s climate: sulfur dioxide levels, location and eruption intensity.

When a volcano erupts, it emits many different types of materials, including sulfur dioxide, which will sometimes pass into the stratosphere, according to Brian Toon, a professor of atmospheric and oceanic sciences at the University of Colorado Boulder.

Sulfur dioxide will transform into sulfate aerosols, which are minute particles suspended in the atmosphere, according to NASA.

The sulfate aerosols block the sun’s energy and instead of passing through the Earth’s atmosphere, the energy will be reflected back out to space.

As a result, there is a decrease in the sun’s energy reaching the Earth’s surface, which causes a cooling effect on temperatures. The more sulfur dioxide that is emitted from a volcano, the more sunlight will be blocked out thus resulting in a greater impact on the climate.

The second factor determining impact on climate is location of the volcano. Volcanic eruptions that take place closer to the equator will have a more significant impact on climate. At the equator, there is more sunlight to reflect, so sulfur aerosols will have a bigger impact.

The last factor is the intensity of the eruption. The eruption must be strong enough that the cloud on top of the volcano passes through the troposphere and into the stratosphere, according to Daniel Swain, a climate scientist at the University of California, Los Angeles.

The stratosphere, which is a layer of the atmosphere, is located at an altitude of 65,000 feet near the equator and as low as an altitude of 23,000 feet near the poles, according to the University Corporation for Atmospheric Research (UCAR).

The sulfur dioxide will stay in the stratosphere for long periods of time, causing the cooling to last for months, even up to a few years. In contrast, sulfur dioxide in the lower atmosphere would fall in just a few weeks.

“This volcano in Indonesia is relatively close to the equator, so it has the potential to check all three boxes, but we don’t yet know if it’s going to,” Swain said.

Mt. Agung

This Monday, Nov. 27, 2017, file photo, shows Mount Agung volcano erupting in Karangasem, Bali, Indonesia. Mount Agung volcano on Bali has erupted for the first time in more than half a century, forcing closure of the Indonesian tourist island's busy airport as the mountain gushes huge columns of ash that are a threat to airplanes. (AP Photo/Firdia Lisnawati, File)

Mount Agung is currently producing sulfur dioxide and has emitted it in large amounts in past eruptions, according to Swain.

“What we haven’t seen yet, and what we don’t know if we’ll see, is an eruption big enough to get that sulfur all the way up into the stratosphere,” Swain said.

According to Darwin Volcanic Ash Advisory Centre, ash from Mount Agung eruptions thus far in November have reached as high as 26,000 feet in the sky, which is not high enough to cause impacts to longer-term weather trends.

Without a larger eruption, there will not be significant impacts on the global temperature.

The most notable example of this effect was in 1815 when Mount Tabora erupted, emitting large amounts of sulfur dioxide into the stratosphere. Labeled “the year without a summer,” there was snow in every month of the year in New England in 1816, according to Michael Mills, an atmospheric scientist at the National Center for Atmospheric Research.

The eruption of Mount Pinatubo in 1991 also caused global cooling the following year. In addition to a 0.6 of a degree drop in global temperature, there were also brilliant red sunsets due to particles high in the stratosphere, according to Anderson.

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Global cooling due to volcanic eruptions does not put up a long-lasting fight against global warming, according to Swain. Once the sulfate aerosols have left the stratosphere, the global temperature will spring right back up to where it would have been without the eruption.

“It’s not just that the effect is temporary, but it’s also that it's only masking the warming that’s already going on,” Swain said.

According to Swain, this phenomenon is like if you had a furnace heating your home and turned on the air conditioner at the same time. The air conditioner will mask that the furnace is on high, but as soon as you turn it off, your house temperature will continue to rise to the level it was at before.

“You have both a warming and a cooling effect, but the warming effect is both larger and more persistent,” Swain said. “And it’s going to win out.”

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