Undersea volcanic eruption in Tonga was a "once-in-a-lifetime event," scientists believe

Scientists are still trying to decipher the effects of January's underwater volcano eruption in Tonga.

Hunga Tonga-Hunga Ha'apai, the volcano responsible for the study published on Thursday in Science, is said to have released millions of tonnes of water vapor into the atmosphere.

Scientists believe the eruption, which was far more potent than the atomic bomb on Hiroshima, increased the amount of water in the stratosphere (the second layer of the atmosphere, high above the range where humans live and breathe) by about 5%.

Scientists are currently attempting to predict how much this water will affect the atmosphere and whether or not it will cause global warming in the coming years.

According to the primary author and climatologist at Colorado's National Center for Atmospheric Research, Holger Voemel: "This was a once-in-a-lifetime event."

Earth generally cools after significant eruptions. The majority of volcanoes spew massive quantities of sulfur into the sky, which blocks the sun's rays, according to Matthew Toohey, a climate researcher at the University of Saskatchewan who was not involved in the study.

The Tongan explosion was much wetter than average as it began its life beneath the sea and sent a plume of water into the air at a much higher concentration than usual. Since water vapor is a greenhouse gas that traps heat, Toohey predicts that the eruption will have the opposite effect of what was hoped for: a rise in global temperatures.

The extent to which the climate may warm is unknown.

N.O.A.A. climate scientist Karen Rosenlof, who was not involved in the study, said she anticipates the effects to be minor and transient.

This increase "could warm the surface a modest bit for a short time," Rosenlof wrote in an email.

According to scientists who reported this in August, it injected enough water vapor to fill 58,000 Olympic-sized swimming pools, setting a new "all-time record" since satellites began capturing such data.

Toohey predicted it would take several years for the water vapor to descend from the upper into the lower atmosphere. Meanwhile, Rosenlof added, the additional water may hasten ozone depletion in the atmosphere.

However, since experts have never witnessed an eruption quite like this one, it is difficult to determine for sure.

According to Voemel, the stratosphere is the region about 7.5 and 31 miles above Earth, where the air is typically relatively dry.

Voemel's group used a system of devices dangling from weather balloons to calculate the size of the volcano's plume. Voemel said that typically, such instruments are incapable of detecting even trace amounts of water in the stratosphere.

Scientists from another organization kept an eye on the explosion via a NASA satellite. Their analysis, released earlier this summer, suggested that the eruption was much more massive, adding roughly 150 million metric tonnes of water vapor to the stratosphere. This is three times as much as Voemel's study found.

Based on the research results, experts have concluded that the great plume may have a short-term impact on Earth's global average temperature.

Voemel conceded that the satellite imagery could have seen features of the plume that the balloon instruments missed, increasing the accuracy of its assessment.

As he put it, the Tongan blast was unlike anything witnessed in recent history, and researching its aftermath could reveal hitherto unknown aspects of our environment.