NASA shares an interesting article that will warm the climate at least temporarily by water vapor, a greenhouse gas. The eruption of Hunga Tonga-Hunga Ha'apai, a submarine caldera in the Tonga archipelago, sent massive amounts of water vapor into the stratosphere, which also holds the earth's ozone. Previous eruptions can also send water vapor into the stratosphere. Still, the Tonga eruption was unprecedented, primarily due to the location of the caldera, several hundred feet below the surface of the southern Pacific.
Not only was the consequence of the eruption unprecedented at the size of the plume of water vapor, the violence of the eruption sent a sonic boom that circled the globe not once but twice, along with a tsunami that barreled across the earth. Few people in the archipelago were swept away by the tsunami; two women in Peru also vanished in the waves.
Volcanic eruptions rarely inject much water into the stratosphere. In the 18 years that NASA has been taking measurements, only two other eruptions – the 2008 Kasatochi event in Alaska and the 2015 Calbuco eruption in Chile – sent appreciable amounts of water vapor to such high altitudes. But those were mere blips compared to the Tonga event, and the water vapor from both previous eruptions dissipated quickly. The excess water vapor injected by the Tonga volcano, on the other hand, could remain in the stratosphere for several years.
This extra water vapor could influence atmospheric chemistry, boosting certain chemical reactions that could temporarily worsen depletion of the ozone layer. It could also influence surface temperatures. Massive volcanic eruptions like Krakatoa and Mount Pinatubo typically cool Earth’s surface by ejecting gases, dust, and ash that reflect sunlight back into space. In contrast, the Tonga volcano didn’t inject large amounts of aerosols into the stratosphere, and the huge amounts of water vapor from the eruption may have a small, temporary warming effect, since water vapor traps heat. The effect would dissipate when the extra water vapor cycles out of the stratosphere and would not be enough to noticeably exacerbate climate change effects.
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The sheer amount of water injected into the stratosphere was likely only possible because the underwater volcano’s caldera – a basin-shaped depression usually formed after magma erupts or drains from a shallow chamber beneath the volcano – was at just the right depth in the ocean: about 490 feet (150 meters) down. Any shallower, and there wouldn’t have been enough seawater superheated by the erupting magma to account for the stratospheric water vapor values Millán and his colleagues saw. Any deeper, and the immense pressures in the ocean’s depths could have muted the eruption.
The MLS instrument was well situated to detect this water vapor plume because it observes natural microwave signals emitted from Earth’s atmosphere. Measuring these signals enables MLS to “see” through obstacles like ash clouds that can blind other instruments measuring water vapor in the stratosphere. “MLS was the only instrument with dense enough coverage to capture the water vapor plume as it happened, and the only one that wasn’t affected by the ash that the volcano released,” said Millán.
Space writes about the likely damage to the ozone layer, which protects us from the sun's ultraviolet radiation. Also, the plumes affect methane in the stratosphere.
The researchers also pointed out that such a sharp increase in water vapor could decrease the amount of ozone in the stratosphere, thus potentially weakening the ozone layer that protects life on Earth from damaging ultraviolet radiation from the sun. Stratospheric water, or H2O, can break down into OH ions over time. Those ions could react with ozone, which is made of three oxygen atoms, to create water and oxygen. However, it is unclear how this will affect the ozone layer as a whole, researchers wrote.
However, the researchers also think the increased water vapor could decrease the amount of methane in the atmosphere, which is one of the main greenhouse gases responsible for climate change. The same OH ions that react with ozone can also react with methane to produce water and a methyl radical (methane with one less hydrogen atom), which traps much less heat in the atmosphere than methane. Hopefully, this potential reduction in methane might offset some of the warming caused by the water vapor, researchers wrote.
However, the study authors think it's still too early to predict the exact climatic effects of the Tonga eruption. "It is critical to continue monitoring volcanic gases from this eruption and future ones to better quantify their varying roles in climate," the researchers wrote.
This looks like so much fun.