Hunga Tonga! Could A Volcano That Spewed 150 Million Tons of Water Into the Stratosphere Cause Heat Waves? You Bet!

Note: We had to republish this as the original got accidentally deleted!

Judith Curry has performed a magnificent public service by giving Javier Vinós a platform to put forth his science on the subject of global warming. He has posted another outstanding article addressing the causes of our current spat of heat waves.

Read the whole thing, but here’s the part I found most fascinating (emphasis added):

Just over a year before the abrupt warming, in January 2022, an extremely unusual volcanic eruption took place in Tonga. How unusual? It was an eruption of VEI 5 explosivity, capable of reaching the stratosphere, which occurs on average every 10 years.

Figure 12. Time and cone elevation of VEI ≥5 volcanic eruptions of the past 200 years, their distribution by altitude (yellow bars), and the suggested depth for a submarine eruption capable of projecting a large amount of water to the stratosphere (red line).

There have been a number of eruptions with VEI 5 or higher in the last 200 years, although not all of them have affected the global climate. This figure shows with dots the date they occurred and the elevation at which the volcanic cone was located. The yellow bars show the distribution of eruptions in 500 m elevation bins. The Tonga eruption was a submarine explosion at very shallow depths, about 150 m below the sea surface. It ejected 150 million tons of water into the stratosphere.

In our 200 years of records there is only one other submarine eruption with VEI 5, which occurred in 1924 off the Japanese island of Iriomote at a depth of 200 m and did not affect the atmosphere. Only surface effects were observed. NASA scientists believe that the Tonga explosion occurred at the right depth to project a lot of water into the stratosphere.[vi] This depth is indicated by the red line. So, the Tonga eruption is a once in 200-year event, probably less than once in a millennium. Science was very lucky. We are not so lucky.

We know that strong volcanic eruptions, capable of reaching the stratosphere, can have a very strong effect on the climate for a few years, and that this effect can be delayed by more than a year. The eruption of Mount Tambora in April 1815 had a global effect on the climate, but it took 15 months for the effect to develop, during the year without a summer of 1816. These delayed effects coincided with the appearance of a veil of sulfate aerosols in the Northern Hemisphere atmosphere due to seasonal changes in the global stratospheric circulation.

Figure 13. Stratospheric water vapor anomaly at 45°N.

In this image on the vertical axis, we observe the water vapor anomaly in the stratosphere between 15 and 40 km altitude with ocher tones for negative values and greenish for positive ones. The measurement takes place at 45° latitude in the northern hemisphere. On the horizontal axis is the date, and we can see that the large anomaly created by the Tonga eruption does not appear in the Northern Hemisphere until one year later, in 2023, when the warming occurred. Thus, there are dynamical events in the stratosphere that have the appropriate time lag to coincide with the abrupt warming in 2023.

Because the Tonga eruption is unprecedented, there is much about its effects that we do not understand. But we do know that the planetary greenhouse effect is very sensitive to changes in stratospheric water vapor because, unlike the troposphere, the stratosphere is very dry and far from greenhouse saturation.

As a group of scientists showed in 2010, the effect of changes in stratospheric water vapor is so important that the warming between 2000 and 2009 was reduced by 25% because it decreased by 10%.[vii] And after the Tonga eruption, it increased by 10% because of the 150 million tons of water released into the stratosphere, so we could have experienced much of the warming of an entire decade in a single year.

Figure 14. Global water vapor anomaly above 68hPa.

The stratosphere has already begun to dry out again, but it is a slow process that will take many years. In 2023 only 20 million tons of water returned to the troposphere, 13%.[viii]

On the one hand, we have an absolutely unprecedented abrupt warming that the models cannot explain and that has scientists scratching their heads. Such anomalous warming cannot logically respond to the usual suspects, El Niño, reduced sulfur emissions, or increased CO₂, which have been going on for many decades.

On the other hand, we have an absolutely unprecedented volcanic eruption, the effects of which we cannot know, but which, according to what we know about the greenhouse effect, should cause significant and abrupt warming.

Of course, we cannot conclude that the warming was caused by the volcano, but it is clear that it is by far the most likely suspect, and any other candidate should have to demonstrate its ability to act abruptly with such magnitude before being seriously considered.

So why do scientists like Gavin Schmidt argue, without evidence or knowledge, that the Tonga volcano could not have been responsible? If the effect were cooling, the volcano would be blamed without a second’s hesitation, but significant natural warming undermines the message that warming is the fault of our emissions.

A narration of the article can also be watched here:

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