Will Tonga volcanic eruption affect global climate?

Will the underwater volcanic eruption that occurred in Tonga in the southern Pacific Ocean January 15, 2022, affect global climate? That is a question on the minds of many after the explosion spewed plumes of gases, steam and ash into the stratosphere.

The gases included sulphur dioxide (SO2), which is of particular interest because of its global cooling effect.

Extreme levels of SO2 have not been recorded in the stratosphere going by the early data. The Tonga volcanic cloud contains roughly 0.4 teragram (Tg) of SO2. It has reached an altitude of up to approximately 30 km, Simon A Carn, volcanologist at Michigan Technological University, explained in a tweet.

Compare that with the 1991 Mount Pinatubo explosion in the Philippines.

According to studies, Pinatubo spewed about 15 million tonnes of sulphur dioxide into the stratosphere. The total mass of SO2 in the volcanic cloud was 20 Tg.

Researchers recorded a 0.5 degrees Celsius (°C) drop in the average global temperature over large parts of the earth between 1992 and 1993.

“This means that the (Tonga) event appears unlikely to have a significant cooling effect on temperatures globally,” New Zealand’s National Institute of Water and Atmospheric Research (NIWA), which provides weather and climate updates, wrote in a tweet.

Daniel Swain, a climate scientist at the University of California, believes Tonga’s effects on climate are 10x lesser than Pinatubo’s. “So measurable global climate impacts seem unlikely at this point,” he wrote in a tweet.

However, experts pointed said it was still too early to draw conclusions as new data would emerge. Also, more eruptions were possible, they added.

Swain expects shorter-term and more regional weather impacts.

The Tonga event follows the Intergovernmental Panel on Climate Change report of 2021, which had suggested that an explosive volcanic eruption could occur in the 21st century.

This eruption could lower surface temperature and precipitation globally, especially over land, for one to three years. “If such an eruption occurs, it would therefore temporarily and partially mask human-caused climate change,” the report had added.

SO2 reacts with water to form sulphuric acid droplets, which become a part of aerosol particles. Aerosols are tiny liquid droplets suspended in the air. 

Mount Pinatubo recorded the largest SO2 cloud since 1978. It took about three weeks to spread around the world.

The sulphuric acid-rich aerosol particles induce cooling by reflecting the incoming sunlight into space. The particles from Mount Pinatubo remained in the stratosphere for three-four years after the explosion, according to a study.

The Tonga volcanic event of January 15 was violent, triggering a tsunami in Tonga, Fiji and Samoa. Shockwaves were recorded thousands of kilometres away, reaching as far as New Zealand about 2,000 km away. No casualties have been recorded so far.

The eruption damaged an undersea cable, severing the communication network. Australia and New Zealand sent flights on January 17 to assess damage in Tonga, according to reports.

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