Highest ever volcanic plume may have warmed Earth’s climate
The Hunga Tonga volcanic eruption that sent shockwaves through Earth in January 2022 generated the highest volcanic cloud since at least the 1883 Krakatoa eruption, a new study reports. And the amount of water the volcano injected into Earth’s atmosphere may have warmed the planet’s climate.
The Volcanic Eruption That Tore Up the Polynesian Island Tonga-Hunga Sa’apai on Jan 15 was a disaster locally, but it has also turned out to be a scientific gift that continues to give. The previously modest underwater volcano in a remote region of the South Pacific exploded with unprecedented force in full view of three weather satellites. These satellites enabled scientists around the world to observe the mind-boggling explosion in real time and study its aftermath in unprecedented detail.
Among the researchers fascinated by the mushroom of water vapor and mineral ash that burst into the sky on that fateful Sunday evening was Simon Proud, an Earth observation scientist at STFC Rutherford Appleton Laboratory and the University of Oxford in the UK.
Proud, the lead author of a new study analyzing the plume, quickly realized that the Hunga Tonga eruption was rather unusual. For example, temperature measurements from Earth observation satellites suggested that the volcanic cloud must have reached an unprecedented height.
“When [the cloud] was developing, we looked at the temperatures based on the satellite data,” Proud told Space.com. “It went through the troposphere, where the temperature decreases with altitude, and then it got cooler, even though the atmosphere around it was is getting warmer.”
Scientists usually estimate the height of atmospheric phenomena by measuring their temperature using satellite infrared sensors and comparing these measurements to the temperature of the surrounding atmosphere. In the troposphere, the layer of the Earth’s atmosphere closest to the surface of the planet, the temperature decreases with altitude according to known physical rules. But these rules no longer apply in the stratosphere, the atmospheric layer that extends from 9 miles to 30 miles (15 to 50 kilometers) altitude, where the ozone layer absorbs the ultraviolet radiation emitted from the Sun, causing the temperature to rise. As the temperature of the Hunga Tonga cloud continued to drop, Proud realized that estimating height more accurately would require a more ingenious approach.
Because three different weather satellites observed the eruption from three different positions in geostationary orbit, an orbit at about 36,000 km altitude where objects appear to hover over a fixed spot on Earth, Proud managed to calculate the height of the cloud’s top using using a method known as parallax.
Parallax allows researchers to calculate the distance to an object using the apparent distances as observed from at least two different locations. It is often used to calculate distances from starsand Proud previously used it to calculate the height of the Chelyabinsk meteor that exploded over Russia in 2013.
“We were really lucky to be able to cover the area with three satellites,” Proud said. “[The calculation] delivered really nice results; it worked very well for such a high volcano. We’ve never seen everything so high.”
The calculation revealed that the Hunga Tonga cloud not only burst through the troposphere, but also rose through the entire stratosphere, only a plateau at an altitude of 57 km, well into the frigid and dry layer known as the mesosphere. This makes the Hunga Tonga volcanic cloud the tallest ever observed and most likely the tallest in over a century.
“The last [volcanic eruption] who could have reached this height was Krakatoa in 1883,’ said Proud [eruptions] like [the 1991 eruption of] Mount Pinatubo, and we think we underestimated its height, but not to the same extent.”
Ash from Mount Pinatubo’s eruption was detected at altitudes of nearly 25 miles (40 km (opens in new tab)). Proud believes that if there were better satellites in orbit at the time, traces of the cloud would have been seen even 10km higher, but still not below 35 miles from Hunga Tonga.
The Pinatubo axis in the stratosphere Earth’s climate cooled by 1 degree Fahrenheit (opens in new tab) (0.6 degrees Celsius) due to the presence of sulfur dioxide in the volcanic material. Sulfur dioxide reflects radiation and is often studied as part of potential geoengineering interventions designed to slow down climate change.
When Hunga Tonga exploded, scientists thought the eruption could trigger a similar effect (which, in Pinatubo’s case, was observable for two years). However, later measurements showed that the Hunga Tonga cloud contained only about 2% of the sulfur dioxide generated by Pinatubo, not enough to affect the climate measurably. However, Proud says the amount of water sprayed into the stratosphere by the explosion could actually warm the climate.
“This volcano has brought a lot of water into the stratosphere and some into the mesosphere,” Proud said. “Water in the stratosphere generally warms the Earth’s surface. So this could actually contribute to some warming of the Earth’s surface in the coming years. We have very good temperature data for the lower atmosphere, so that’s something we should be able to figure out pretty quickly.” .”
A study published earlier this year found that Hunga Tonga has an equivalent of 58,000 Olympic-size swimming pools in the Earth’s atmospherepotentially increasing the amount of water vapor in the stratosphere by 5%.
The effects on the mesosphere, Proud said, may be more subtle and accompanied by rather intriguing side effects.
“Mesosphere is usually the driest layer of the atmosphere, and if we put extra water there, we can get more polar mesospheric clouds,” Proud said. “These clouds are becoming more common anyway, probably due to climate change, so I want to look at satellite data and see if I can see an increase after this eruption.”
Polar mesospheric clouds, also known as nocturnal clouds due to their ability to glow at night, they form over the polar regions during the summer months at elevations from 47 miles to 53 miles (76 to 85 km). These clouds popped up regularly Space shuttle launchesthat emit huge amounts of water vapor into their rocket exhaust.
The mesosphere, Proud said, is rather unexplored because it’s too low for satellites to fly through, but too high for balloons to reach. The eruption of Hunga Tonga could therefore provide a unique incentive for scientists to look at the chemical processes that take place in this region.
Researchers are far from done with the Hunga Tonga eruption. Many questions remain unanswered, including its exact effect on Earth’s climate and why it exploded with such force after centuries of lukewarm activity.
The new study (opens in new tab) was published online today in the journal Science (Nov. 3).
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