• Reuters

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Climate scientists are tracking an erupting volcano on the Indonesian holiday island of Bali for clues about a possible shortcut to curb global warming by injecting sun-dimming chemicals high above the Earth.

Volcanoes are emerging as natural geoengineering labs, adding a veil of sulfur dioxide high above the planet and creating artificial sunshade to curb man-made global warming.

Ash and smoke ejected by Mount Agung, which has been erupting in recent days, has not been plentiful enough in the atmosphere to cool world temperatures. But scientists are studying what would happen if the volcano has a repeat of a far bigger eruption in 1963.

Jim Haywood, professor of atmospheric science at the University of Exeter, said he has been simulating Bali eruption scenarios.

He estimated that Agung spewed 8 million tons of sulfur dioxide into the stratosphere in 1963, which is about 10-15 kilometers above the Earth’s surface and enough to trim world temperatures for months. The eruption killed more than 1,000 people in Bali.

“Many scientists are keeping an eye on the Agung eruption in Bali,” said Alan Robock, a professor of climate science at Rutgers University. “Volcanic eruptions serve as an analog for the idea of humans creating such a cloud.”

Satellite measurements of eruptions have only recently become precise enough to exploit volcanoes as models for geoengineering.

That was impossible in the Philippines, for instance, when Mount Pinatubo erupted in 1991 and blew about 20 million tons of sulfur dioxide into the stratosphere, the second biggest eruption of the 20th century after a 1912 eruption in Alaska.

Mount Pinatubo had a cooling effect on the Earth because sun-dimming sulfur spread worldwide.

“Since Pinatubo we’ve got a lot better” at measuring the effects of big eruptions, said Matthew Watson of the University of Bristol. “We’re waiting for something to happen on a scale where we can start thinking about what it means for geoengineering.”

He estimated that the Agung volcano has probably ejected only about 10,000 tons of sulfur dioxide in the latest eruption, and not as high as the stratosphere.

Governments agree they should focus most on cutting greenhouse gas emissions according to the 2015 Paris agreement rather than on science-fiction-like shortcuts to limit the rising temperatures, which is blamed for causing more heat waves, floods and rising sea levels.

But current policies put the world on track to overshoot the Paris goal of limiting rising temperatures to “well below” two degrees Celsius (3.6 Fahrenheit) above pre-industrial times.

U.S. President Donald Trump, who doubts man-made emissions are the prime cause of warming, also plans to pull out of the Paris deal and promote the U.S. fossil fuel industry, further weakening the Paris plan.

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