LONDON, United Kingdom (AFP) — Climate change could magnify the atmospheric cooling effects of once-in-a-century volcanic eruptions, but also lessen the impact of smaller eruptions, according to new research released Thursday.

Scientists at the University of Cambridge and the UK Met Office examined how rising temperatures are likely to affect the ash and gases shot into the atmosphere by volcanoes.

The emerging “feedback loops” between the changing climate and eruptions were not accounted for in this week’s landmark scientific report by the UN’s Intergovernmental Panel on Climate Change (IPCC), said lead author Thomas Aubry of Cambridge’s Department of Geography.

“It could shed new light on the evolution of future volcanic influences on climate,” he said of the study.

“Even if volcanoes have a limited influence on climate compared to human greenhouse gas emissions, they are an important part of the system.” 

The research, published in the journal Nature Communications, used climate and volcanic plume models to project future changes. 

It also looked back at the worldwide impact of Mount Pinatubo’s eruption in the Philippines in 1991, the second largest of the 20th century.

The giant plume of ash and gas generated a layer of haze that caused global temperatures to drop by as much as 0.5 degrees Celsius the following year. 

– ‘Relatively minor’ climate impact-

The study found that climate change, by warming the atmosphere, will allow future Pinatubo-sized plumes to rise even higher — blocking more sunlight, dispersing aerosols faster and heightening the cooling effect worldwide by up to 15 per cent.

“However, the effect of volcanic aerosols only persists for one or two years, while anthropogenic greenhouse gases will affect the climate for centuries,” the researchers said.

And for smaller outbursts such as the 2011 Nabro eruption in Eritrea, which tend to occur annually, the cooling effect will be reduced by about 75 per cent under a high-end warming scenario. 

“This is because the height of the tropopause — the boundary between the troposphere and the stratosphere above it — is predicted to increase, making it harder for volcanic plumes to reach the stratosphere,” the scientists said.

“Aerosols from volcanic plumes confined to the troposphere are washed out by precipitation in a matter of weeks, making their climatic impacts relatively minor and much more localised.” 

Human activities have already warmed global temperatures by more than 1.0 degree Celsius since 1850 and under the IPCC projections, the world is on course to reach 1.5C of warming around 2030, a decade sooner than previously forecast.

That assumes there is no major volcanic eruption in the next decade, the UN report said, while stressing that any cooling effects would be temporary.