The Tonga volcano eruption isn't going to cool the planet



The Jan. 15 explosion of the Hunga Tonga Hunga Ha'apai volcano in Tonga caught climate scientists' attention since major eruptions throughout history have temporarily cooled the globe.

Why it matters: Large volcanic eruptions are one of the main natural control knobs that can slow the pace of human-caused global warming. Studies have shown that tropical volcanoes, such as in Tonga, tend to be particularly effective at injecting sunlight-reflecting material.

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The backstory: The last volcano to put a sizable dent in the pace of global warming was Mt. Pinatubo, which erupted in the Philippines in 1991. It lowered global temperatures by about 0.5°C, or about 1°F, in 1992, Alan Robock, a meteorologist at Rutgers University, told Axios in an email.

How it works: Robock said volcanic eruptions cause a net cooling if sufficient quantities of tiny droplets of sulfuric acid (or sulfate) aerosols penetrate the stratosphere, where they reflect sunlight. These droplets spread out globally over time, Robock said.

But for a measurable temperature response to occur, a volcano has to vault a huge quantity of material, on the order of at least 5 Teragrams (Tg), which is equivalent to 5 million tons of sulfur dioxide, said Simon Carn of Michigan Tech.

What they found: Scientists investigating the Tonga eruption used satellite sensors to measure the emissions plume. Their estimates showed the volcano emitted only about 0.4 Tg of sulfur dioxide, or about one-fiftieth the size of Pinatubo, which emitted about 15 Tg of SO2, Carn said.

What they're saying: "This was certainly a very large, powerful eruption with some devastating local impacts in Tonga due to the associated tsunami and volcanic ash fall," Carn said. "However, satellite measurements indicate that the eruption will not have significant climate impacts."

"We have an unprecedented ability to analyze volcanic eruptions and assess the potential impacts in near real-time," he said.

Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, said if another eruption with more climate-altering potential occurs in Tonga or elsewhere, researchers would respond with a "massive, mobilized effort" to learn more about it, deploying aircraft and other assets.

NASA has a rapid response plan for such an occasion.

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