No, Hunga-Tonga eruption won’t slow global warming

It produced an ash cloud spanning hundreds of square kilometres – but scientists say it’s unlikely Hunga-Tonga’s big blow will put any dent in global warming.

Saturday’s Tongan volcano eruption was so massive that it could clearly be seen from space. The eruption created an enormous cloud of ash that spanned approximately 260km.

Major eruptions in the past have been able cool the planet’s climate by releasing large amounts of dust and sulphate aerosols.

While larger ash particles are more likely to fall from the atmosphere quickly, they form smaller clouds in the troposphere.

The eruption of Mt Tambora in Indonesia in 1815 caused an estimated 100-kilometre ash cloud to enter the atmosphere. This resulted a global drop in temperature that was as high as 3C in 1816. It also influenced the famous “year without summer” in North America.

2020 Study found six major eruptions – including Krakatoa in 1883, Tarawera in 1886 and Mt Pinatubo in 1991 – had their own fleeting footprint on New Zealand’s climate over the last 150 years.

These events had led to mean temperatures about 0.3C to 0.5C lower compared with several seasons before – and often an increase in southwesterly winds.

Climate scientist Professor Jim Salinger, who co-authored the study, said Hunga-Tonga’s eruption was big enough to send 0.4 teragrams – equivalent to 0.4 megatons – of sulphur dioxide (SO2) into the stratosphere.

He stated that although it would not likely have any global effect on climate, it could have a regional one.

“What we’ll probably see in the next two months is rather magnificent sunsets as the sulfuric acid mist slowly descends from the stratosphere – but I’d also expect cooling in our region to amount to a few tenths of a degree, maximum.”

Salinger stated that any climate effect would likely take several months to manifest, as it took time for these tiny particles over the Southern Hemisphere to disperse.

Professor James Renwick, climate scientist from Victoria University, agreed.

He stated that while it is certain that the local climate has been affected, it is unlikely to have an impact on the global one.

“Sure, it’s cutting a bit of sunlight reaching that particular part of the tropics, and what’s in the aerosol cloud will spread out in the stratosphere – but that’s not going to lead to significantly cooler temperatures.”

By contrast, Mt Pinatubo’s eruption – the second-largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in Alaska – pushed down global temperatures by 0.5C.

This was due to the volume of SO2 it ejected into space: approximately 15 million tonnes, more than any other eruption since Krakatoa in1883.

Niwa stated that early signs of the Tonga eruption didn’t show high levels of SO2 in stratosphere.

Niwa said that although more data is needed and other eruptions are possible it appears unlikely that this eruption event will have a significant impact upon global climate or alter the direction of the global heat trend.

However, some SO2 was wrapped in Cyclone Cody east of New Zealand.

“SO2” is a toxic, invisible pollutants, so Tonga residents could be exposed to short-term health risks, such as acid rain and ‘volcanic Smog’.

While volcanic eruptions may also have released carbon dioxide (CO2) in the past, it has never been detected as a cause of global warming.

Studies have shown that the world’s volcanoes emit less than 1% of the CO2 currently produced by human activities.

A new analysis by Salinger found that the New Zealand region had its third-warmest year in 2021. This is behind 2016 and 2019.

The sea surface temperatures averaged 14.15C in the region last year, while the mean temperatures on land were at 13.56C was a record setting temperature.

The average temperature in the “Zealandia”, as Salinger called it collectively, was 14.11C.

Along with the influence of climate change, Salinger said last year’s warmth was because of a mix of factors, including warmer seas and the effect of La Niña, which faded but then returned.

The tripolar index is a separate climate indicator that spent much of the year in a negative phase. This encouraged La Ninas to increase and sea surface temperatures to be above average around New Zealand.

Still, Salinger said the result again drove home the fact that climate change was continuing – and he urged leaders to take bold action to slow it.

“We urgently need to move.”