Hunga Tonga Volcanic Eruption Part II: Is that volcanic eruption actually warming the atmosphere?

September 19, 2022

As written in an earlier blog post from ForecastWatch, measurements indicated that not enough dioxide was injected into the atmosphere to have any type of significant cooling effect on the atmosphere, as most powerful volcanic eruptions do, despite being the largest eruption since Mount Pinatubo erupted in 1991. In fact, an earlier study this spring indicated it was likely as powerful as the 1883 Krakatoa eruption in Indonesia with hurricane-force winds that even reached space.

But more recent data from a NASA satellite indicate that this volcanic eruption, unlike most, might actually temporarily warm the Earth’s surface, not cool. How can that be?

The Hunga Tonga volcano was mostly underwater, which means this eruption was an underwater eruption, which essentially is why there were limited amounts of sulfur dioxide injected high into the atmosphere. What there was a lot of, however, was water.

Recent measurements from the NASA Aura satellite indicated that enough water vapor was sent into the atmosphere that if condensed into liquid water, would be enough water to fill 58,000 Olympic swimming pools – 146 trillion grams of water. That amount of water is equal to 10% of the amount of water that already existed in the stratosphere – a layer of the atmosphere that is cold enough to support much less water vapor than the troposphere, the lowest part of the atmosphere where nearly all weather on Earth occurs. The 1991 Mount Pinatubo eruption only sent about 35 trillion grams of water vapor into the atmosphere.

Unlike ash and sulfur dioxide, which typically reflect solar radiation into space – or absorb solar radiation during chemical reactions – water vapor is a greenhouse gas. It allows solar radiation to mostly pass through and then absorbs outgoing infrared radiation from Earth before radiating energy back toward earth in a phenomenon resembling a greenhouse – making Earth’s surface warmer. The amount of water vapor sent into the air by the Hunga Tonga eruption may stay in the atmosphere for several years, enhancing the current warming trend on Earth’s surface during that time, even though the warming effect due to this water vapor itself is expected to be small.

As always, ForecastWatch will continue to monitor forecasts in the years to come, although it is likely this expected temporary warming will be difficult to discern from the underlying trend of globally increasing temperatures.

For more information on this injection of record amounts of water vapor into the atmosphere by Hunga Tonga’s eruption, see CNN’s articles, Tonga eruption blasted 58,000 Olympic pools into the Earth’s atmosphere, NASA says and Tonga volcanic eruption the most powerful in more than a century, as well as the research published in Geophysical Research Letters in July 2022.

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