Global Cooling? Bali Volcano Could (Temporarily) Reverse Global Warming

Mount Agung in Bali erupting this week. So far, the
eruptions have not been strong enough to have any
effect on global climate, but that could change. 

The Mount Agung volcano on the Indonesian island of Bali continues to barf ash as high as two and a half miles into the sky.

More than 100,000 people have been evacuated, tourists were stranded and Bali's airport was closed because all that ash in the air would wreck aircraft engines.

The wind shifted yesterday, allowing the ash to clear, flights to resume and tourists to leave. But the threat remains.

So far, the Mount Agung eruption is a rather local disaster, but it's possible it could eventually have worldwide effects. In short, it could cause global cooling. That is, if Mount Agung really blows its top.

Global warming is the big concern everywhere, of course, as increasing levels of CO2 in the atmosphere, mostly from us humans burning fossil fuels, is raising the temperature. The three years ending 2016 were the hottest for the world on record, and 2017 is going to make a run at the top three hottest.

What Mount Agung does next will determine in large part how much warmer than normal the world's temperature will be for the next few years.

So far, Mount Agung's eruptions have not been nearly big enough to have any effect on the world climate. But if it really blows, which many scientists expect, the volcano could temporarily cool the Earth's climate.

We're not talking about a new Ice Age here. Still, global temperatures would slip if Mount Agung erupted violently, which is a strong possibility. Vox quoted climate researcher Zeke Hausfather this way:

"This projection, which is based on the historical relationship between volcanic eruptions and temperature, suggests than an Agung eruption would reduce global temperatures between 0.1 and 0.2 Celcius in (the) period from 2018 to 202, with temperatures mostly recovering back to where they otherwise would be by 2023"

A worldwide temperature drop of 0.2 degrees does not sound like much, but it would be at least vaguely noticeable.

Throughout history, volcanoes have caused temporary bouts of planetary cooling. The last time this was really noticeable was in 1991, when Mount Pinatubo in the Philippines erupted, cooling the Earth by as much as 0.4 degrees Celcius in 1992 and 1993 before temperatures recovered in 1994.

This chart shows global temperature trends, rising due
to global warming. The blue dip is a projection of
the temporary cooling Mount Agung could cause
if it erupts violently. The dips in the middle of the
graph show the cooling effects of the eruptions of
El Chichon in 1982 and Pinatubo in 1991. 

That cooling was likely enough to help make a couple winters unusually  harsh in parts of the Northern Hemisphere in 1992 to 1994. (Here in Vermont, we had record cold in February, 1993 and January, 1994, but it's hard to tease out to what extent, if any, Pinatubo had on those winters.)

More notably, in 1815, Mount Tambora erupted in a much more violent fashion than Pinatubo, killing 90,000 people.

This eruption poured so much stuff into the atmosphere that the world cooled a fair amount, contributing to the 1816 "Year Without A Summer in New England, crop failures and epidemics in Europe, and more crop failures in China and Tibet.

The 1816 Year Without a Summer here in Vermont produced frost every month of the year, and snow in June, drifting to up to 20 inches deep in Danville.

Even if Mount Agung erupts terribly, we won't get another 1816. But how much the world cools from an eruption, if it does at all, depends on a few factors. The strength of the eruption is one of them. A stronger eruption would eject more ash and sulpher dioxide high into the atmosphere.

Sulfer dioxide is the stuff that would contribute most to global cooling. Sulfer dioxide particles, if ejected into the stratosphere, would reflect sunlight (much more than ash, which falls back to Earth quite quickly) and cause the world to cool.

Some volcanic eruptions pour out more sulpher dioxide than others, so how much sulpher dioxide would be in a new Mount Agung eruption would determine how much the world cools. When El Chichon erupted in Mexico in 1982, the explosion wasn't nearly as big as the one that would come from Pinatubo a decade later.

But El Chichon emitted an enormous amount of sulpher dioxide, so the world temporarily cooled after that eruption.

The vivid sky colors in Edvard Munch's
"The Scream" might have been inspired
by brilliant sunsets caused by sulpher
dioxide swept through the worldwide
atmosphere by the eruption of
Krakatoa in 1883. 

The fact that Mount Agung is near the Equator would help spread sulpher dioxide particles to both the southern and northern hemispheres which would make the volcano more efficient at cooling the Earth than volcanoes further north or south.

Volcanoes that erupt closer to the poles aren't as good at spreading their emissions worldwide, so they have less effect on climate that equatorial volcanoes.

By the way, another side effect of lots of sulpher dioxide going into the upper atmosphere, besides global cooling, is spectacular sunsets and sunrises. The particles scatter the low-angled sun light, causing brilliant reds and oranges.

The famous painting "The Scream" by Edvard Munch, with its swirling red colors in the sky, might have been inspired by the aftermath of the Indonesian Krakatoa eruption in 1883, which also temporarily cooled the planet and helped cause striking red worldwide sunsets.

Regardless of what happens with Mount Agung, global warming is not revoked. The sulpher dioxide released by the volcano will fall back to earth within a few years, but the excess carbon dioxide we continue to pump into the atmosphere will stay put.

Once the volcanic material from Mount Agung dissipates, global warming will come roaring back.