How do volcanoes affect the weather and what's going on with the Hunga Tonga Hunga Ha'apai eruption?
Close to an eruption there is a huge impact as the volcano releases moisture, ash, and gases into the atmosphere.
Within the volcanic plume, electrical charges can build to trigger lightning and the aerosols can seed rain.
Volcanoes can even produce "mud rain" if the conditions are right.
When that rain hits the surface it can then do more damage in the form of a lahar, where volcanic ash flows in a deadly mudslide.
Then there is a phenomena known as "vog," volcanic fog, when harmful gases linger near the surface.
But it is when the plume gets further up into the atmosphere that it can start having global effects.
Volcanoes can cool the planet
According to Blair Trewin, senior research scientist at the Bureau of Meteorology, the major global-scale effect of volcanoes is that the bigger eruptions can temporarily cool the atmosphere by releasing sulphur dioxide.
It blocks the incoming light from the sun and acts as a kind of global shade.
But to hang around and have long term affects, the sulphur dioxide needs to get up above the troposphere.
If it remains in the troposphere, where our day-to-day weather takes place, it will be quickly rained back down to the surface.
The plume from the Tongan volcano is estimated to have reached approximately 35 kilometres high, well up into the stratosphere.
Emissions from the tropics have a much better chance of spreading over both hemispheres, rather than being stuck in one.
So two ticks.
But based on initial estimates, it is not looking like the latest Tongan eruption has released enough sulphur dioxide to cause significant cooling.
"The estimates I've seen so far suggest somewhere around 0.1-0.2 megatonnes [million tonnes] of sulphur dioxide has been emitted," Dr Trewin said.
The last volcano which did have a global cooling effect, Mount Pinatubo in 1991, released significantly more sulphur dioxide.
"Mount Pinatubo emitted about 15 to 20 megatonnes, so somewhere in the order of 100 times more than what the Tongan volcano has."
Mr Trewin said there could be local cooling around the volcano where significant ash is being generated.
Dr Trewin does not expect any significant effects on Australian weather form the Tongan volcano.
"Not really, apart from attractive sunsets in some places," he said.
Andrew Tupper of Natural Hazards Consulting and a former manager of the Darwin Volcanic Ash Advisory Centre is likewise not predicting weather interruptions in Australia.
According to Dr Tupper, the volcanic cloud is now travelling out over the Indian Ocean, having crossed Australia.
But because it has travelled around 35km up, it is not affecting our weather.
"The normal rain that we get, even in the summer, the maximum height of thunderstorms is around 16 or 17 kilometres in the tropics, and usually a bit lower in the mid-latitudes," he said.
"So they are just not interacting with that volcanic cloud."
Could there still be more to come?
The question remaining is if any more sulphur dioxide could be released in follow-up eruptions.
Heather Handley, volcanologist and adjunct associate professor at Monash University, said it depended on how much of the gas has been lost previously and how much is stored.
Her work on samples from the same volcano in 2009 showed the magma that formed rocks at the surface had travelled quickly and retained a lot of its gas.
"So there is potential that if there are larger scale eruptions it could contribute significant sulphur dioxide into the atmosphere," Dr Handley said.
"But we just don't know at this stage what the next steps for the volcano are.
World-cooling volcanoes
As mentioned, the last volcano to have a significant impact on the global climate was Mount Pinatubo in the Philippines in 1991.
According to Dr Trewin it was one of three eruptions in the last century which had a major effect on global climate — the others being El Chichón in Mexico in 1982 and Mount Agung in Bali in 1963.
The biggest eruption in recorded human history was Mount Tambora in 1815 in Indonesia.
Its cooling effects led to 1816 being know as the year without a summer.
According to Dr Handley, it affected different areas of the planet in different ways.
"[Researchers] linked that to things like a more successful polar bear breeding season because of the cool air, but then it affected a lot of crops in the northern hemisphere and led to famine," she said.
"So there were much wider reaching impacts of these larger scale volcanic eruptions that impact the climate."
Preparing for disaster
"One thing which I think's really cool in this context is that there was a major eruption in 1808 which is known about, both from it's climatic impact — from some of the deposits — and also from things like sunsets," Dr Trewin said.
But no one knows where the volcano was.
Seriously.
It is referred to as the "mystery eruption".
"The most prominent theory is that it was an undersea volcano somewhere in the South Pacific and whatever island it was on was destroyed by the eruption, never to be seen again," Dr Trewin said.
So climate-changing eruptions have certainly happened before and will certainly happen again.
For Dr Tupper, the Tongan eruption acts as a reminder that natural disasters often reach beyond one type of hazard or field of science.
"Over the last two years we've been dealing with COVID and some of the other stuff has has taken a back seat," he said.
