Climate change to dampen cooling effects of moderate volcanic eruptions

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The ongoing transformation of Earth’s atmosphere, fueled by runaway greenhouse gas emissions, will shrink the cooling effects of small- and medium-sized eruptions by as much as 75 percent, according to new research. Conversely, the study — published Thursday in the journal Nature Communications — suggests the cooling effects of larger eruptions will be amplified by global warming. In 1991, the massive plume from the eruption of the Philippines’ Mount Pinatubo, the second largest of the 20th century, reached 18 miles into the atmosphere and spread out in all directions, forming a thick layer of haze that caused global temperatures to drop by as much as 0.5 degrees Celsius. By comparison, human-caused global warming has raised global temperatures by more than 1 degree Celsius since 1850. But whereas the cooling effects of volcanic eruptions dissipate after a couple of years, greenhouse gases persist in the atmosphere for hundreds of years. “Beyond the data we have from recent eruptions like Pinatubo, we can also see the cooling effect of volcanoes going back two thousand years from the information contained in tree rings,” first author Thomas Aubry said in a press release. “However, we wanted to look at the question from the opposite angle: how could a warming climate affect the cooling from volcanic eruptions?,” said Aubrey, a geophysicist ans research fellow at Cambridge University in Britain. For the new study, scientists looked at how the atmosphere’s shifting composition and characteristics will influence the buoyancy of rising volcanic plumes. For large eruptions, the models showed plumes are likely to rise faster and spread out more quickly, amplifying the haze’s cooling effects by 15 percent. However, simulations suggest the cooling effects of more moderately sized eruptions — which happen more frequently than large eruptions — are likely to decline by as much as 75 percent under a high-end warming scenario. That’s because the troposphere is expected to expand as the planet warms, pushing the troposphere-stratosphere boundary higher and higher. When volcanic ash is unable to reach the stratosphere, plumes are more easily washed out by precipitation patter in just a few weeks, limiting an eruption’s ability to block out sunlight for long periods of time. “Climate change isn’t something that’s coming – it’s already here, as clearly demonstrated by this week’s IPCC report,” co-author Anja Schmidt said in the release. “The effects of climate change and some of the feedback loops it can cause are becoming more obvious now. But the climate system is complex: getting a grasp of all these feedback loops is critical to understanding our planet and making accurate climate projections,” said Schmidt, a geochemist and interdisciplinary lecturer in climate modeling at Cambridge. Researchers suggest the feedback loops identified in their latest paper remain unaccounted for in the climate models used by the IPCC. Scientists predict the structure and composition of the atmosphere will continue to change as wildfires burn with greater frequency and greenhouse gas emissions continue unabated. As a result, scientists must continue to reassess and model the ways volcanic eruptions interact with the atmosphere,50634257.html

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