Newswise — A recent study has revealed that the impact of volcanic eruptions on cooling Earth's surface temperature is probably underestimated by a factor of two, and potentially even by a factor of four, in standard climate projections.
Although this phenomenon alone falls short of counterbalancing the global temperature increase resulting from human activities, scientists led by the University of Cambridge assert that minor volcanic eruptions contribute up to 50% of all sulphur gases released into the upper atmosphere by volcanoes.
According to a report published in the journal Geophysical Research Letters, the findings indicate that enhancing the portrayal of volcanic eruptions across different scales will enhance the reliability of climate projections.
The occurrence and timing of volcanic eruptions are beyond human control; however, volcanoes do have a significant impact on the global climate system. During eruptions, volcanoes release sulphur gases into the upper atmosphere, creating minuscule particles known as aerosols. These aerosols have the ability to reflect sunlight back into space. In the case of extremely large eruptions like Mount Pinatubo in 1991, the sheer volume of volcanic aerosols is substantial enough to induce a global temperature decrease on its own.
Nonetheless, such large-scale eruptions occur only a few times within a century. On the other hand, smaller eruptions of lesser magnitude take place more frequently, typically happening every year or two.
"Although the impact of volcanoes on the global climate is relatively insignificant when compared to greenhouse gas emissions from human activities, it is crucial to incorporate them into climate models to precisely evaluate future temperature changes," explained May Chim, a PhD candidate in the Yusuf Hamied Department of Chemistry and the first author of the study.
In standard climate projections, such as the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report, it is assumed that the level of explosive volcanic activity between 2015 and 2100 will remain consistent with that observed during the period from 1850 to 2014. However, these projections tend to overlook the impacts of small-magnitude eruptions.
"Most of these projections heavily depend on ice cores to estimate the climate impact of volcanoes. However, smaller eruptions are often too minute to be detected in ice-core records," explained Chim. "Our aim was to utilize satellite data more effectively to bridge this gap and account for eruptions of varying magnitudes."
Leveraging the most up-to-date ice-core and satellite data, Chim and her team, comprising researchers from the University of Exeter, the German Aerospace Center (DLR), the Ludwig-Maximilians University of Munich, Durham University, and the UK Met Office, developed 1000 distinct scenarios to depict future volcanic activity. These scenarios encompassed various levels of volcanic activity, including lower, median, and high ranges. Subsequently, they conducted climate simulations employing the UK Earth System Model.
The simulations conducted by the researchers indicate that the effects of volcanic eruptions on climate, such as global surface temperature, sea level, and sea ice extent, are underestimated due to the prevailing climate projections inadequately considering the potential magnitude of future volcanic activity.
In the case of the median future scenario, the researchers discovered that the influence of volcanoes on the atmosphere, referred to as volcanic forcing, is underestimated by up to 50% in climate projections. This substantial underestimation is primarily attributable to the impact of small-magnitude eruptions.
Chim emphasized, "Our findings indicate that not only is volcanic forcing being underestimated, but small-magnitude eruptions are actually accountable for up to 50% of the volcanic forcing. Although these individual eruptions may not have a discernible impact, their cumulative effect is substantial."
"I was taken aback by the significance of these small-magnitude eruptions. While we were aware of their impact, we had no idea it was of such magnitude," Chim expressed her surprise.
While the cooling effect of volcanoes is indeed underestimated in climate projections, the researchers emphasize that it pales in comparison to the carbon emissions generated by human activities.
Chim clarified, "Volcanic aerosols present in the upper atmosphere generally persist for a year or two, whereas carbon dioxide remains in the atmosphere for significantly longer periods. Even if we were to experience an extended period of remarkably high volcanic activity, our simulations demonstrate that it would not be sufficient to halt global warming. It is akin to a passing cloud on a scorching, sunny day, where the cooling effect is only temporary."
The researchers emphasize that incorporating the complete impact of volcanoes can significantly enhance the reliability of climate projections. Presently, they are utilizing their simulations to explore the potential risk of future volcanic activity jeopardizing the recovery of the Antarctic ozone hole. They aim to assess whether such volcanic activity could lead to the persistence of elevated levels of harmful ultraviolet radiation at the Earth's surface.
The research was supported in part by the Croucher Foundation and The Cambridge Commonwealth, European & International Trust, the European Union, and the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI).
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