University of Iowa engineers investigating the deadly 2022 Hunga Tonga–Hunga Haʻapai volcano in the South Pacific Ocean – the largest underwater explosion ever recorded – discovered key differences in how volcanoes in the ocean affect Earth’s climate compared to landlocked volcanoes.

Volcanic eruptions release particles into the upper atmosphere that block sunlight, causing surface cooling on Earth. The particles also absorb radiation from the Sun and Earth, heating the surrounding atmosphere.

In contrast, the Hunga-Tonga volcano, which triggered a tsunami resulting in at least six deaths, unleashed a different phenomenon when it injected unprecedented water vapor high into the stratosphere, 6- to 30 miles above Earth's surface. The mid-stratosphere cooled by about 7 degrees Fahrenheit (4 degrees Kelvin) for over a year while the lower stratosphere warmed by approximately 2.7 degrees Fahrenheit (1-2 degrees Kelvin), according to satellite observations analyzed in the study.

“This study develops analytical models constrained by satellite observations to quantify the contribution of water vapor to the rapid formation and growth of aerosol particles through different processes, as well as the disparate roles of water vapor in perturbing the stratospheric temperature over time and altitude,” said Xi Chen, an assistant research scientist in the Atmospheric and Environmental Research Lab (AER) at the Iowa Technology Institute (ITI), a research center within the College of Engineering.

The findings were published in npj Climate and Atmospheric Science, a scholarly journal from Nature, in May. Chen is the lead author.

Water vapors and other gases in the lower atmosphere where humans live absorb or trap heat being radiated away from Earth, creating a warming effect often referred to as global warming or the greenhouse gas effect.

In the stratosphere, water vapor behaves differently. An increase of water vapor enhances emissions of energy, pushing heat further up into space and back toward earth, while cooling the surrounding atmosphere.

The study also found that the large amount of water vapor caused sulfuric oxide to form and grow into larger sulfate particles via a condensation and nucleation process in the middle levels of the stratosphere. The large sulfate particles eventually descended via gravitational pull into the lower stratosphere where they absorbed infrared solar radiation, leading to warming in the lower part of stratosphere.

“This study provides a comprehensive understanding and new insights of how volcanic eruptions from the ocean have a different and unique impact on our climate as compared to the those over land with much less injection of water vapor into the atmosphere,” said Jun Wang, Lichtenberger Family Chair in Chemical and Biochemical Engineering, director of the AER Lab and assistant director of ITI. “Such studies would not be possible without satellite observations, especially those data collected through the Stratospheric Aerosol and Gas Experiment or SAGE aboard the International Space Station.”

Wang serves as the science team lead for SAGE. He is also a professor and DEO of chemical and biochemical engineering.

The Iowa team collaborated with Luke Oman and Ghassan Taha at the NASA Goddard Space Flight Center and Lyatt Jaegle at the University of Washington. The collaboration benefits from their joint efforts to develop the Stratosphere Troposphere Response using Infrared Vertically-resolved light Explorer (STRIVE) mission, a proposed NASA satellite to observe how the water vapor, temperature, aerosols, and other chemical compounds are changing the upper part of atmosphere in the 2030s.