The cooling effect of the concentration of sulfur dioxide pumped into the air by the volcano is ‘disappointing’.

In early January, a submarine volcano near the island nation of Tonga in the Pacific Ocean erupted violently. The eruption caused an enormous shock wave that even reached the Netherlands. The eruption of the Hunga Tonga-Hunga Ha’apai volcano not only caused a huge ash plume and tsunamis, part of the island even sank. It was thought that the immense eruption could cause a sharp drop in global temperatures. But the influence of the mighty volcanic eruption on our climate turns out to be smaller than expected, researchers write in the journal Advances in Atmospheric Sciences†

Volcanic eruptions and the climate

It is known that large volcanic eruptions sometimes affect the temperature of the earth. That’s because huge amounts of sulfur dioxide (SO2) are spewed out and pumped into the atmosphere during immense eruptions. Once in the atmosphere, this is converted into so-called sulphate aerosols. These particles can then remain there for one or two years and block sunlight, causing the Earth’s temperature to plummet.

Eruption of the Tambora volcano
An example of a volcanic eruption that had far-reaching effects on the climate was the eruption of the Tambora volcano in 1815. The eruption has gone down in the books as the largest volcanic eruption in the past 500 years. With a volcanic explosivity index of 7, this was the largest eruption ever described by humans. The following year, the eruption caused the so-called ‘year without a summer’ in many parts of the world. In Northern Europe and the northeastern United States, the summer months of that year were unusually cold. The average surface temperature in the tropics and the northern hemisphere decreased by 0.4 to 0.8 degrees Celsius.

Satellite images of the eruption of the Hunga Tonga-Hunga Ha’apai volcano – which, incidentally, has erupted several times over the past century – showed that the volcanic ash reached a height of 30 kilometers. It is estimated that about 0.4 terrogram (Tg) of sulfur dioxide has been emitted. It was therefore thought that the volcanic eruption could significantly affect our climate in the next one to two years, which could lead to a drop in global temperatures between 0.03 and 0.1 degrees Celsius.

Cooling effect

A new research group is really questioning this conclusion. According to them, the impact of the Hunga Tonga-Hunga Ha’apai volcano on the climate will be much smaller than initially thought. “The impact may have been overestimated,” said researcher Tianjun Zhou. “In fact, the location where the eruption occurred was not taken into account – something that changes the spatial distribution of stratospheric sulfate aerosols.”

Location

And the exact spot where volcanic eruptions take place is very important for their influence on the climate. “Emissions from volcanic eruptions in the southern hemisphere are largely confined to the same hemisphere and the tropics,” explains Zhou. “These eruptions therefore have less impact on the Northern Hemisphere. This, in turn, leads to a weaker global cooling than volcanic eruptions that occur in the northern hemisphere or in the tropics.”

Climate change

It means that the cooling effect of the eruption of the Hunga Tonga-Hunga Ha’apai volcano is ‘disappointing’. For example, the researchers calculate that the average global temperature will drop by only 0.004 degrees Celsius in the first year after the eruption. This falls within the scope of the internal variability of the climate system. And so the recent eruption of the Tonga volcano is also unable to save our climate and reverse the current trend of global warming.

However, the researchers do have an important caveat. They are based on a one-time eruption of the Hunga Tonga-Hunga Ha’apai volcano. The volcano has been quiet since January. However, according to the researchers, it could well be that the volcano will be heard again in the future, as the volcano has erupted many times in the past 100 years. If that does happen, the volcano could indeed have a major climate impact. “We will need to continue to monitor Hunga Tonga-Hunga Ha’apai’s activity closely in the coming days, months and years,” concluded Zhou.