The violent eruption last January sent a large amount of sulfur into the atmosphere
In April 1815, the Mount Tambora volcano (Indonesia) erupted. Its force was such that all the sulfur dioxide is injected into the atmosphere led to a drop in temperatures that caused the so-called ‘Year without a summer in many parts of the world. When the submarine volcano Hunga Tonga-Hunga Ha’apai, in the South Pacific, woke up on January 15, it was feared that a similar effect would occur, although on a smaller scale. Could it even affect climate change? According to a new study published in the journal Advances in Atmospheric Sciences, not as much as first thought, though its authors add some important caveats.
In very violent eruptions, the ejected sulfur dioxide is injected into the stratosphere.
This then oxidizes into sulfate aerosols, which remain there for a year or two. In that time, they create a ‘screen’ effect that reduces the solar radiation that enters the Earth. And this causes a brief period of global cooling, like the one that occurred half a century ago, when temperatures in the tropics and the northern hemisphere dropped by an average of 0.4 to 0.8 °C.
Early estimates from the Tonga volcano assumed a reduction in global surface air temperature of between 0.03 and 0.1°C over the next one to two years. However, this prediction could be ‘bloated’: the Tambora eruption emitted 53-58 teragrams (Tg) of sulfur dioxide. But satellite measurements of the Tonga eruption showed that its volcanic ash reached an altitude of 30 kilometers in the stratosphere, with a total mass of only about 0.4 Tg. And, in addition, other factors would contribute to the consequences not being so acute.
“This initial estimate may have overestimated the impact as it did not take into account where the eruption occurred, which alters the spatial distribution of stratospheric sulfate aerosols, a variable that can substantially alter the results,” explains Tianjun Zhou, from the Institute of Atmospheric Physics at the Chinese Academy of Sciences. “This is because emissions from southern hemisphere volcanic eruptions are largely confined to circulating in the southern hemisphere and the tropics, with less impact in the northern hemisphere. This in turn leads to weaker global cooling than that of tropical and Northern Hemisphere volcanoes.”
Modeling eruptions in the southern hemisphere
The most challenging part for the researchers was accounting for the latitude of the sulfate aerosol release, as there are few southern volcanic eruptions similar to Tonga’s undersea volcano. Fortunately, climate model simulations using large southern eruptions in the last millennium generally provided a useful reference. In this way, the researchers found a significant correlation between the intensity of 70 selected volcanic eruptions over the last millennium and the global mean surface temperature response in the first year after the eruption.
They then selected and modeled six particularly large tropical eruptions and scaled the surface temperature response in line with the intensity of the 1991 Mount Pinatubo eruption, which ejected 20 Tg of sulfur dioxide. The results of the simulations were very similar to what actually happened, which indicated that the models were correct.
The next step was to model the Tonga eruption, with its stratospheric injection of 0.4 Tg of sulfur dioxide. The final results showed that the global mean surface temperature will decrease by only 0.004 °C in the first year, which will not be very different from the predictions already stipulated for the climate system. The eruption will not be strong enough to overcome the long-term global warming trend.
Warnings for the future
However, the researchers caution that all of this data is based on a single eruption; Although no more similar to those of January 15 have been detected, its reactivation could change the panorama. And the Tonga volcano has erupted many times in the last 100 years. “We must continue to monitor the activity in the coming days, months, and years,” said Professor Zhou.
