Bali's fiery volcano could end up temporarily cooling the entire planet

On the Indonesian island of Bali, a volcano called Mount Agung is spewing ash 2.5 miles into the sky, causing flights to be canceled and trapping thousands of tourists and locals on the island, even as the potential for a bigger eruption looms.

This is the second straight day authorities have closed Bali’s international airport for fear of ash damage to aircraft engines. More than 100,000 people near the volcano were told to evacuate as explosions were heard more than 7 miles away.

You can watch the eruption of Mount Agung in this live stream:

Indonesia’s National Disaster Management Authority (BNPB) warned yesterday that the eruptions are increasing and declared the highest alert level for the volcano. An Indonesian government scientist said a larger eruption is possible, but also that the current levels of lava, ash, sulfur, and carbon dioxide emissions could continue for weeks. (You can see ongoing volcanic activity in Indonesia on this live map.)

As Denison University volcanologist Erik Klemetti noted on Twitter, no one knows how the current eruption will pan out.

The eruption at #Agung in Indonesia has been relatively small so far, but with lava at the summit crater, it is anyone’s guess how it proceeds from here: https://t.co/1rOS1u9UAW
— Erik Klemetti (@eruptionsblog) November 27, 2017

Bali has a tragic history with Mount Agung, as you can see in this old-timey newsreel (complete with offensive tropes about the indigenous population):

In 1963, Mount Agung’s eruption killed more than 1,600 people on the island over several months — and that was merely a “moderate” eruption, Diana Roman, a geologist at the Carnegie Institution of Washington, told the Washington Post. So locals are understandably unnerved.

But beyond the threat of local devastation, the current eruption of Mount Agung has the potential to impact the entire world.

Scientists have long understood that volcanic eruptions can nudge the planet’s thermostat for months, as millions of tons of gases and particles spread through the atmosphere.

How much the needle moves, however, depends on what’s being erupted, as NASA climate scientist Chris Colose pointed out:

If these conditions are met, the eruption cools the surface/troposphere and warms the stratosphere, the opposite of both patterns associated with CO2 increases. But both are very short-lived (~years).
— Chris Colose (@CColose) November 27, 2017

Volcanoes emit carbon dioxide, which traps heat, but they also spray out ash particles and gases like sulfur dioxide, which form compounds that reflect sunlight, thereby cooling the planet. (The amount of carbon dioxide volcanoes emit overall is trivial compared to the amount from human activities.)

How much a volcanic eruption cools the planet depends on the amount of material it erupts and the composition of that material. Eruptions can also change global rainfall patterns.

Scientists are also toying with the idea of imitating volcanoes to keep global warming in check, a strategy known as geoengineering. This includes deliberately seeding clouds or spraying sulfuric acid into the stratosphere to offset some of humanity’s impacts on the world’s climate.

We don’t know yet whether the ongoing eruption will pump out enough gas and ash to have a measurable impact on the climate, but we do know that the 1963 eruption of Mount Agung knocked down global temperatures between 0.1 and 0.2 degrees Celsius for a year.

Over at Carbon Brief, climate researcher Zeke Hausfather graphed what would happen to global temperatures if the current eruption were to reach the same scale as the last one.

Global mean surface temperatures from Berkeley Earth (black dots), major volcanoes (shaded areas), and estimated temperatures based on human and natural radiative forcing (red) with a 1963-size Agung eruption in mid-2017 (blue). The baseline period is 1961-’90.

“This projection, which is based on the historical relationship between volcanic eruptions and temperature, suggests that an Agung eruption would reduce global temperatures between 0.1C to 0.2C in period from 2018 to 2020, with temperatures mostly recovering back to where they otherwise would be by 2023,” Hausfather wrote.

However, locals are more concerned about the next few days, keeping an uneasy eye on their backyard volcano and wearing surgical masks to ward off the ash. Despite evacuation orders, they are wary of leaving their homes without alternative jobs and housing in place, so if the eruption suddenly gets worse, many will likely remain in harm’s way.

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