Tonga eruption will not contribute much to global cooling

The Hunga Tonga-Hunga Ha’apai (HTHH) undersea volcano, located close to the Tonga Islands in the Pacific Ocean, erupted violently on January 15, 2022, raising widespread public concern about its effect on global warming. Usually, the sulfur dioxide (SO₂) reaching the stratosphere after volcanic eruptions is oxidized and transformed into sulfate aerosols, which linger in the air for one or two years, reducing solar radiation, and contributing to a short period of global cooling. 

Unfortunately, a new analysis of the potential cooling effect of the Tonga eruption has concluded that the impact will be much smaller than initially thought, and will not succeed in offsetting the longer-term global warming tendency of our planet.

The largest volcanic eruption of the last 500 years – that of Mount Tambora in Indonesia in April 1815 – caused the so-called “year without summer” in many parts of the world, with a reduction of average surface temperature over the tropics and the northern hemisphere by 0.4 to 0.8°C. However, the Tambora volcano emitted 53 to 58 terrograms (Tg) of SO_2.  

Compared to this, HTHH’s 0.4 Tg sulfur dioxide emissions will most probably have a significantly smaller impact, regardless of the initial estimate that global surface air temperatures may decrease by 0.03 to 0.1°C over the next one to two years as a result of the Tonga eruption. 

“This reported initial estimate may have overestimated the impact as it did not take into account the location where the eruption occurred, which alters the spatial distribution of stratospheric sulfate aerosols – a variable that can alter results substantially,” explained study co-author Tianjun Zhou of the Institute of Atmospheric Physics at the Chinese Academy of Sciences.

“This is because southern hemisphere volcanic eruption emissions are largely confined to circulating in the same hemisphere and the tropics, with less of an impact on the northern hemisphere. This in turn leads to a weaker global cooling than those of northern hemispheric and tropical volcanoes.”

By comparing the Tonga eruption with several other major historical eruptions, Professor Zhou and his colleagues showed that, in the first year after the HTHH eruption, the global mean surface temperature will decrease by only 0.004°C. The eruption’s cooling effect will be stronger in the southern hemisphere, with a decrease of 0.01°C occurring in parts of Australia and South America.

However, if HTHH will erupt again, the situation may change dramatically. Such an event is quite possible, since this volcano has already erupted many times over the past century. “As a result, we should keep monitoring the activity of HTHH in the coming days, months, and years,” concluded Professor Zhou.

The study is published in the journal Advances in Atmospheric Sciences.

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By Andrei Ionescu, Earth.com Staff Writer