Could Tonga’s major volcanic eruption produce global climate change?

An underwater volcanic eruption near Tonga is visible in this image taken by the Himawari weather satellite and posted on the Japan Meteorological Agency website.

TOKYO – Major volcanic eruptions have often resulted in temporary climate changes on a global scale. The eruption of Mount Pinatubo in the Philippines in 1991 would have caused a drop in average temperatures in the northern hemisphere. So is it also possible that the recent eruption of Hunga Tonga Hunga Ha’apai, an undersea volcano in Tonga that has caused tsunamis in Japan and other parts of the world, is producing global climate change?

A chemical compound ejected during an eruption that is feared to affect the climate is sulfur dioxide (SO2). The SO2 that is released into the atmosphere gradually undergoes a chemical change and turns into tiny particles of “sulphate aerosols”. When the sulfate aerosol reaches the stratosphere (an altitude of 10 to 50 kilometers), it floats there for several years, partially reflecting sunlight, which has the effect of lowering the temperature on the Earth’s surface. Therefore, when a large amount of SO2 is ejected during an eruption, there is a good chance that it will trigger a drop in temperatures.

During the eruption of Mount Pinatubo, considered the largest eruption of the 20th century, the amount of SO2 emitted would have reached some 20 million metric tons. Following the eruption, the temperature in the northern hemisphere dropped. Japan experienced a summer of record cold temperatures in 1993, with temperatures between June and August dipping 2 degrees Celsius below the average for that period in some areas.

In addition, due to the lack of sunshine caused by the long-term stagnation of the seasonal rain front over the Japanese archipelago and other reasons, many crops, including rice plants and vegetables, suffered badly. behaved. The shortage of rice, in particular, was severe, and the Japanese government resorted to emergency imports from Thailand and other countries. This caused what was known as the “Heisei (era) rice riots”, characterized by the formation of queues in stores by people looking for rice.

The eruption of Mount Pinatubo is not the only one to have triggered a global drop in temperatures. Large-scale events such as the Indonesian eruptions of Krakatoa in 1883 and Mount Agung in 1963, and El Chichon in Mexico in 1982 also caused global temperature drops. Following the eruption of Mount Tambora in 1815 – considered the largest on record in human history – the world was blanketed in sulfate aerosols and the following year, 1816, became known as of “year without summer” around the world.

However, the effect of such eruptions on the climate does not last for years. Professor Toshihiko Takemura of Kyushu University, who specializes in meteorology and atmospheric environment, commented: “Sulphate aerosols that have reached the stratosphere stay there for one or two years and then fall from the stratosphere due to gravity, and their cooling effect is lost. It is clear from history that temperature drops from major eruptions only last for a year or two.”

This photo taken in Towada city, Aomori prefecture, shows a paddy field on October 23, 1993. Poor harvests of rice and other crops due to a cool summer that year prompted some farmers to harvest early in fields that produced virtually no crop. (Mainichi)

So what about the latest eruption, which happened in the southern hemisphere?

Based on data from an Earth observation satellite, Simon Carn of the Michigan Technological University in the United States posted estimates on social media that the Tonga eruption released up to 400 000 tons of SO2 in the atmosphere.

Zeke Hausfather, director of climate and energy at the Breakthrough Institute, an American environmental think tank, told the Mainichi Shimbun that according to the institute’s estimates, the amount of SO2 released was around one-fortieth to one. fiftieth of that of the eruption of Mount Pinatubo. He said the volcanic eruption in Tonga seemed unlikely to significantly affect the climate, even in the southern hemisphere. It therefore appears that the effects of the eruption on the climate will be limited.

It was pointed out that the reason the amount of SO2 emitted was low was that it was an underwater volcano. Volcanologist Masato Koyama from Shizuoka University pointed out: “SO2 has the property of easily dissolving in water and is contained in the hot water of the crater. It is possible that the amount dissolved in the water of sea ​​has decreased the amount released into the atmosphere of the same degree.”

However, volcanic ash from the eruption could eventually affect the climate. Koyama noted that the volcanic ash emitted during the latest eruption is characterized by its thinness, and when it reaches the stratosphere, it does not fall easily. Because of this, it could remain in the stratosphere for several months, and solar insolation in the southern hemisphere could be blocked for a short time. But in the long term it seems that the effects of the eruption will be limited.

In the meantime, keep in mind that global temperatures are rising primarily due to global warming. Carbon dioxide (CO2), a major greenhouse gas emitted from the burning of fossil fuels and other sources, remains in the atmosphere for a long time and its concentration continues to break records every year.

According to the United States National Oceanic and Atmospheric Administration, the annual average concentration of CO2 in the atmosphere recorded by the Mauna Loa Observatory in Hawaii was 355.7 parts per million (ppm) by volume in 1991, but in 2021, it had reached 416.45 ppm, which is about 1.5 times the level before the industrial revolution.

In a report published in August 2021, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) said for the first time that there was no doubt that human activity was a cause of global warming. . Temperatures have continued to rise at a rate not seen in the past 2000 years, and the average global temperature from 2010 to 2019 has increased by around 1.07 degrees Celsius compared to the average between 1850 and 1900.

According to Seita Emori, deputy director of the Earth System Division of the National Institute for Environmental Studies, an anomaly resembling the El Niño phenomenon – which is believed to be linked to abnormal weather conditions around the world following an increase in sea temperatures in the equatorial Pacific region off South America – would have had an influence on the onset of the cool summer of 1993.

Emori commented, “It is unnatural to say that the eruption alone was the cause of the cool summer. The following year in 1994, Japan had a scorching summer.” He added: “Even if a major eruption occurs, there is virtually no possibility that there will be a halt to global warming, which is caused by human activities. The importance of continuing to advancing countermeasures against global warming is unchanged.”

(Japanese original by Toshiyuki Suzuki and Mayumi Nobuta, Department of Science and Environmental News)