Standard climate projections are likely underestimating the cooling effect that volcanic eruptions have on Earth’s surface temperature by a factor of two and possibly even by a factor of four, according to research.
The researchers, led by the University of Cambridge, claim that small-magnitude eruptions are responsible for as much as half of all sulfur gases emitted by volcanoes into the upper atmosphere, despite the fact that this effect is insufficient to offset the effects of global temperature rise caused by human activity.
According to the findings, which are published in the journal Geophysical Research Letters, enhancing the representation of volcanic eruptions of all magnitudes will increase the robustness of climate projections.
Volcanoes aren’t something humans can control, but they play a significant role in the global climate system in terms of where and when they erupt. Sulfur gases can spew into the upper atmosphere when volcanoes erupt, forming tiny aerosols that reflect sunlight back into space. The volume of volcanic aerosols is so large during extremely large eruptions, like Mount Pinatubo in 1991, that it causes a drop in global temperatures on its own.
“Compared to the greenhouse gases emitted by human activity, the effect of volcanoes on global climate is relatively minor, but it is critical that we include them in climate models in order to accurately assess temperature changes in the future,”
May Chim, a Ph.D. candidate in the Yusuf Hamied Department of Chemistry.
However, the majority of small-magnitude eruptions occur every year or two, and these large eruptions only occur a few times per century.
First author May Chim, a Ph.D. candidate in the Yusuf Hamied Department of Chemistry, stated, “The effect that volcanoes have on the global climate is relatively minor compared to the greenhouse gases emitted by human activity; however, it’s important that we include them in climate models in order to accurately assess temperature changes in the future.”
Standard climate projections, such as the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), ignore the effects of small-magnitude eruptions and assume that explosive volcanic activity will remain the same between 2015 and 2100.
According to Chim, “These projections mostly rely on ice cores to estimate how volcanoes might affect the climate; however, smaller eruptions are too small to be detected in ice-core records.” In order to fill the void and account for eruptions of all magnitudes, we wanted to make better use of satellite data.”
Chim and her colleagues from the University of Exeter, the German Aerospace Center (DLR), the Ludwig-Maximilians University of Munich, Durham University, and the UK Met Office created 1,000 distinct scenarios of future volcanic activity by utilizing the most recent satellite and ice-core data. Using the UK Earth System Model, they selected scenarios that represented low, median, and high levels of volcanic activity, and then they carried out climate simulations.
According to their simulations, current climate projections significantly underestimate the likely future level of volcanic activity, which results in underestimating the impacts of volcanic eruptions on climate variables like global surface temperature, sea level, and sea ice extent.
They discovered that, in the median future scenario, climate projections are underestimating the effect of small-magnitude eruptions on the effect of volcanoes on the atmosphere—known as volcanic forcing—by up to 50%.
“We found that small-magnitude eruptions are actually responsible for as much as half of all volcanic forcing,” Chim stated. “Not only is volcanic forcing being underestimated,” Individually, these eruptions of small magnitude may not have any discernible impact, but taken together, they have a significant impact.
“I was astonished to see exactly how significant these little emissions are—we realized they made a difference, yet we didn’t realize it was so enormous.”
The researchers emphasize that while volcanoes’ cooling effect is underestimated in climate projections, it is not comparable to human-generated carbon emissions.
According to Chim, volcanic aerosols in the upper atmosphere typically remain in the atmosphere for one or two years, whereas carbon dioxide remains in the atmosphere for much, much longer. Regardless of whether we had a time of remarkably high volcanic movement, our recreations show that halting an Earth-wide temperature boost wouldn’t be sufficient. It’s similar to a passing cloud on a sunny, hot day: It only lasts for a short time.”
The researchers claim that climate projections can be strengthened by fully accounting for the impact of volcanoes. They are now using their simulations to see if future volcanic activity could impede the repair of the Antarctic ozone hole and, consequently, keep the Earth’s surface at relatively high levels of harmful ultraviolet radiation.
More information: Man Mei Chim et al, Climate Projections Very Likely Underestimate Future Volcanic Forcing and Its Climatic Effects, Geophysical Research Letters (2023). DOI: 10.1029/2023GL103743
