How January’s Hunga Tonga volcanic eruption is potentially causing spectacular sunsets in Johannesburg

Picture by Chris Stewart via AP.

Picture by Chris Stewart via AP.

Published Mar 5, 2022

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Johannesburg - There has been something different about Joburg’s sunsets of late.

New colours have filled the sky as the sun slips below the horizon.

Projected across the sky in those last rays of light have been shades of pink and splashes of deep magenta.

It is unusual enough from some Joburgers to stop and notice. Others, wondering what is behind all this, have uploaded pictures and asked on social media if anyone knows what is up with these strange sunsets.

Ask around and it is a mystery that is hard to solve.

“Nice sunsets, na, that is not our department,” chuckled one weather forecaster, when asked if they knew what was causing those strange sunsets.

But this phenomenon is not just casting a strange glow across the Jozi skyline, thousands of kilometres away in Australia, they are having almost identical sunsets, and it is here where the clue to the mystery lies.

The suspicion is that the cause of these spectacular sunsets and sunrises, too, has to do with the Hunga Tonga volcanic eruption that happened on January 15.

The eruption occurred way out in the Pacific ocean, but the magnitude of this event that has been described as being hundreds of times more powerful than the atom bomb blast in Hiroshima, is having a global impact.

"I wouldn't be surprised if it is behind the sunsets. It's particles that get distributed throughout the earth. And it's a commonly known phenomenon that when you have a big volcanic eruption, it affects the atmosphere, and produces these spectacular sunsets,” explained Professor Lewis Ashwal of the School of Geosciences, University of the Witwatersrand.

The eruption, which has been called the largest in the 21st century, spewed particles 58 km up into the mesosphere – a part of the atmosphere that usually only sees the odd low orbiting space craft.

These particles contain sulphur dioxide that when they react with the atmosphere form sulphate aerosols. Together with ash these aerosols scatter the sun’s rays that in turn paints those sunsets.

There is nothing new about this. With the volcanic eruptions of the past, it was the artists that usually noticed the change of colours in the sky and tried to capture it on canvas.

Artist Joseph Mallord William Turner was known for his paintings of sunsets. When scientists measured and analysed some of his paintings they came to the conclusion that what he was capturing in some of them was a sky changed by the Tambora volcanic eruption in Indonesia in 1815.

It is believed that Edvard Munch painted the banded red blue and orange sky in The Scream after he noticed the oddly coloured sunsets following Krakatoa’s eruption in 1883.

“Suddenly the sky turned blood red – I paused, feeling exhausted, and leaned on the fence...” is how Munch described his inspiration for the painting.

Just as Joburg is thousands of kilometres from the site of the Hunga Tonga volcanic eruption, Munch was watching the blood red sunset in Norway, a world away from Indonesia, the site of the Krakatoa volcano.

A Jozi sunset photographed on February 22 with spectacular hues. Picture: Kashiefa Ajam

Those mega volcanic eruptions don’t just leave pretty sunsets, their deadly reach can span continents, as was seen with the Tambora eruption in 1815.

This eruption ushered in the “year without a summer,” that was caused by a drop in global temperatures. The average temperature across the tropics and the northern hemisphere is believed to have fallen by 0.4 to 0.8 degrees Celsius.

Crops failed and there were global famines. Large numbers of people died of starvation.

The Hunga Tonga eruption is not expected to cause such temperature drops.

Initially it was estimated that the eruption might reduce the global surface air temperature at between 0.03 and 0.1 degrees Celsius over the next one to two years.

“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 sulphate aerosols — a variable that can alter results substantially,” said Tianjun Zhou of the Institute of Atmospheric Physics at the Chinese Academy of Sciences, in a statement.

“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,” it said.

The estimate now is that the mean surface temperature will decrease by only 0.004°C in the first year after the eruption.

So the lasting global effect of the Hunga Tonga volcanic eruption is likely to be those sunsets that for a while at least, will create fiery backdrops for picture perfect photos of the Jozi skyline.