Scientists have found that volcanic cooling affects Earth’s climate, with surface temperatures likely influenced more than once or twice, and perhaps even four times, beyond what standard forecasts show. While this cooling helps temper warming trends, it does not erase the overall rise in global temperatures observed today.
Researchers led by the University of Cambridge in England have shown that human activity drives the most significant part of the volcanic signal. Smaller eruptions release sulfur gases into the upper atmosphere, where they help cool the planet by reflecting sunlight. Although sizable eruptions produce a pronounced temporary cooling, these events are relatively rare, occurring only a few times per century, while smaller eruptions happen regularly about every one to two years.
The study, published in Geophysical Research Letters, argues that better understanding eruptions of all sizes will strengthen climate projections. Improving knowledge about how volcanic activity interacts with the atmosphere can lead to more robust forecasts of future temperatures.
Volcanic activity cannot be controlled by humans, but its role in the climate system is important. When volcanoes erupt, they release sulfur gases and aerosols that reflect sunlight back into space. For an eruption with the volume of aerosols seen in Mount Pinatubo’s 1991 event, global temperatures can drop significantly. The image below shows an example of a recent eruption that drew attention to the power of volcanic activity in the climate system.
Major eruptions are rare. The more common, smaller explosions occur routinely and collectively contribute a substantial portion of the volcanic forcing that shapes climate trends.
First author May Chim notes that, compared with human-made greenhouse gases, volcanic influences are smaller in total impact. Yet including them in climate models is essential to accurately gauge potential temperature changes in the future.
The impact of small eruptions
Traditional climate projections, such as those in the IPCC Sixth Assessment Report, often assume that explosive volcanic activity from 2015 to 2100 will resemble that of the period 1850-2014 and tend to overlook small eruptions. These estimates have relied heavily on ice-core records, which miss many smaller events. The researchers aimed to better use satellite data to capture eruptions of all sizes.
Using up-to-date satellite records along with ice-core data, the team created 1,000 scenarios for future volcanic activity. These scenarios span low, medium, and high levels of activity and were run in climate simulations with the UK Earth System Model to assess potential outcomes for temperature, sea level, and sea ice.
Their results indicate that the climate impact of volcanic eruptions has been underestimated in many projections, largely because small eruptions have not been fully accounted for. For mid-century scenarios, volcanic forcing appears underestimated by as much as 50 percent, driven in part by smaller explosions that add up over time.
Chim emphasizes that while small eruptions collectively matter, they are not a substitute for reducing human carbon emissions. Volcanic aerosols usually persist for one to two years, whereas carbon dioxide remains in the atmosphere for much longer. Even a period of heightened volcanic activity would not halt global warming, but it can act as a temporary cooling influence, like a passing cloud on a sunny day.
The researchers hope that fully accounting for volcanic effects will make climate projections more robust. They are now using their simulations to explore how future volcanic activity might affect the Antarctic ozone hole and the resulting ultraviolet radiation reaching Earth’s surface.
Reference work: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL103743
Notes from the environment research team emphasize that the cooling influence of volcanic activity should be considered alongside other climate drivers to improve model reliability and future scenario planning.