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Column [Submarine volcanic eruption in Tonga]

- Can the Tonga submarine volcanic eruption affect the climate? -

SEKIYA Takashi, Researcher,
Earth Surface System Research Center (ESS),
Research Institute for Global Change (RIGC)

The Hunga Tonga-Hunga Haʻapai volcano has had repeated multiple sporadic eruptions since 2009. Recent volcanic activities began in late December 2021, and a large-scale eruption occurred on January 14, 2022. A larger-scale eruption occurred on January 15, and air vibrations and tide level increase occurred in the Pacific coast area. It is known that such types of volcanic eruption release various materials into the atmosphere that have impacts on short-term climate change. This column explains what possible impacts such large-scale volcanic eruptions, including the Hunga Tonga-Hunga Haʻapai volcano, have on climate change.

A large-scale volcanic eruption and climate change

A large-scale volcanic eruption is considered to affect the climate for several years after its occurrence. In a recent case, due to the Pinatubo volcanic eruption in June 1991, it was observed that the global average surface air temperature fell by approximately 0.5°C at maximum in the following year. Going further back into the past, Mount Tambora in Sumbawa island, Indonesia, erupted on the most significant scale on record in 1815. The next year 1816, there was an unprecedentedly cold summer, known as the “year without summer” in Northern Europe, northeastern America, and eastern Canada partly due to the volcanic eruption, with a serious crop failure.

Then, how does a large-scale volcanic eruption cause a decrease in air temperature? The sulfur dioxide (SO2) released into the stratosphere (higher than approximately 10 to 15 km altitude) by eruption forms sulfuric acid aerosol (droplet) with a particle size of less than 0.5 μm (*1) by an oxidation chemical reaction in the atmosphere. The sulfuric acid aerosol scatters solar light, resulting in a decrease in the energy reaching the ground. That is the main mechanism for the decline in air temperature (Fig. 1). The sulfuric acid aerosol, which also exists in the troposphere (from the ground to approximately 10 to 15 km altitude) where we live, is also one of the major components of PM2.5. However, the sulfuric acid aerosol stays in the air for only approximately two weeks on average since it is washed away by rain. On the other hand, the sulfuric acid aerosol stays in the stratosphere over several years without being washed away in the stratosphere. Therefore, a large-scale volcanic eruption significantly impacts short-term climate change.

Fig. 1
Schematic diagram of the mechanism in which a volcanic eruption affects climate. (Left) the condition before a volcanic eruption, (right) the condition after eruption. The orange arrow means solar light.

The fine particles of volcanic ash released by eruption, which contain larger particles (particle size of approximately 6 to 9 μm) than that of the sulfuric acid aerosol (particle size of less than 0.5 μm), also scatter solar light, and most of them are considered to drop into the troposphere within several days to several months. Therefore, the possibility of affecting climate change over several years is considered to be low.

Monitoring sulfur dioxide from space

Compared to the year 1991, when the Pinatubo volcanic eruption occurred, the current satellite observation network for atmospheric composition from space has significantly advanced. Currently, multiple satellites of the National Aeronautics and Space Administration (NASA) and European Space Agency (ESA) are globally monitoring sulfur dioxide, which allows quick evaluation of the released amount of sulfur dioxide. The sensor TROPOMI on board the Sentinel-5 Precursor, one of such observation satellites, observed highly concentrated sulfur dioxide near the Hunga Tonga-Hunga Haʻapai volcano on January 16, 2021, approximately one day after the large eruption (Fig. 2). Also, the observation results integrating information from the observation by such multiple satellites are published in near real-time on the NASA global SO2 monitoring WEB page (*2), for example. The initial result based on satellite observation estimates the released amount of sulfur dioxide due to the volcanic eruption on January 15, 2021, to be approximately 400,000 tons. The released amount, equivalent to 2.3% of the released amount (approximately 17,000,000 tons) of sulfur dioxide due to the Pinatubo volcanic eruption, is about the same level as mid-scale volcanic eruptions, such as the Calbuco, Chile volcanic eruption in 2015.

On the other hand, the highly concentrated aerosol layer is reported to have been observed at a high altitude of approximately 30 km (*3). While the information estimates that the released amount of sulfur dioxide due to the Hunga Tonga-Hunga Haʻapai volcanic eruption was small, it suggests that the scale of the eruption was significant.

Fig. 2
The vertically integrated amount (air column amount) of sulfur dioxide from the ground to the upper end of the atmosphere observed by TROPOMI, the sensor mounted on a satellite, on January 16, 2022. The TROPOMI satellite observation data was obtained from the Copernicus Open Access Hub (https://scihub.copernicus.eu).

The impact of the Hunga Tonga-Hunga Haʻapai volcanic eruption on climate and future development of study

As mentioned above, the released amount of sulfur dioxide due to the Hunga Tonga-Hunga Haʻapai volcanic eruption is estimated to be significantly less than that of the Pinatubo at this moment. The speculation based on such initial information suggests that the impact of the Hunga Tonga-Hunga Haʻapai volcanic eruption on climate is restrictive compared to the decline in air temperature after the Pinatubo volcanic eruption.

However, since this is only the initial estimation and the speculation based on it, the impact of volcanic eruption on climate needs to be examined accurately and quantitatively in the future. An accurate estimation of the impact of volcanic eruptions on climate is also important to understand the impact of human activities in observed global warming. JAMSTEC is promoting the research and development of the “atmospheric composition data assimilation system,” which allows back calculation of the released amount of material from satellite observation data, and the “earth system model,” which can deal with ecosystem activities and carbon circulation. We intend to effectively use such systems and models to evaluate the impact of volcanic eruptions on climate and the global environment in more detail.

1 μm is one millionth the length of 1 m.
Global Sulfur Dioxide Monitoring Home Page (https://so2.gsfc.nasa.gov)
NASA Earth Observatory

The Copernicus Sentinel data [2022] processed by ESA was used for the TROPOMI SO2 air column amount.