Tonga explosion's weather effects probably small

The weather in many regions of the world has been particularly noteworthy recently. But what's behind it?

Some have pointed to the violent Hunga Tonga-Hunga Ha’apai (HTHH) eruption on 15th January this year which was the largest explosion ever recorded by modern instruments – far larger than any nuclear test. It was the most powerful explosion since the 1883 Krakatoa event.

Producing the highest known eruption column in history, its effects reached the mesosphere. Because the volcano was 150 metres below sea level the explosion injected water vapour as high as 53 km. Large amounts of water ended up in the stratosphere, surpassing anything we have seen since satellite observation of such events commenced in the 1970s.

Image: NOAA

According to an assessment of the event researchers said it, “ranks it among the most remarkable climatic events in the modern observation era, with a range of potential long-lasting repercussions for stratospheric composition and climate”. 

Observations from NASA’s Aura satellite estimates that the explosion may have added 10% of the typical amount of water vapour into the stratosphere. Water vapour is a powerful greenhouse gas because it traps heat over a wider range of the infra-red spectrum than carbon dioxide. This effect is short-lived though as it soon enters the natural water cycle.

However unlike previous eruptions it may not cool the surface but warm it. This is because it released little in the way of sunlight-reflecting aerosols. The effect could be quite small, or it might not. One estimate suggests 0.035°C over the next 5 years which is within the “noise” of variability. So HTHH is likely to have only a small effect -- as far as we know at present. Jucker at al on the other hand suggest the effect could be long-term winter warming in the northern hemisphere and cooling over Australia in winter.

The recent warmth has also been attributed to El Nino; but it is currently still rather weak, although strengthening.

Thus is seems unlikely that these events have significantly affected recent weather, though we should heed the words of Agatha Christie who once wrote: "Any coincidence is worth noticing. You can throw it away later if it is only a coincidence."

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