A team of scientists led by the National Center for Atmospheric Research (NCAR) has developed a new method to measure how smaller volcanic eruptions are affecting the atmosphere and found that satellite observations are often missing more than half of the particles that result from volcanic eruptions.
It is known that volcanoes have a cooling effect on the world's climate. They are doing this by spitting gases into the atmosphere that form sunlight-blocking particles. But NCAR scientists warn that satellite observations may be failing to detect aerosols at lower levels of the atmosphere, which means that the computer models used by climate scientists may also be underestimating their cooling effects.
Through an innovative combination of computer modeling and observations, both from the ground and from satellites, they found that satellites are often missing more than half of the sulfates and other aerosols that result from volcanic eruptions.
This indicates that standard climate models, which depend on satellite observations to simulate the effect of eruptions, are underestimating the role of volcanoes. And it could help explain why global warming appeared to temporarily slow down early this century, as volcanic activity has increased.
“In light of these results, the impact of volcanoes on reducing the rate of global average temperature increases since the year 2000 should be revisited,” said NCAR scientist Michael Mills, the lead author of the new study published in the Journal of Geophysical Research: Atmospheres.
Most climate models rely on analyses of satellite measurements to represent volcanic aerosol. While satellites can globally monitor stratospheric aerosol, they have trouble measuring aerosol in the lowermost stratosphere, where clouds interfere with measurements. As a result, models are failing to include volcanic aerosols below about 15 km (9 miles), thereby missing the majority of volcanic aerosol outside of the tropics.
To determine how much is being overlooked by satellites, Mills and his co-authors compiled a database of emissions from 171 volcanic eruptions from 1990 to 2014. They drew on measurements from an array of satellites and databases, such as the Smithsonian Global Volcanism Program and NASA’s Global Sulfur Dioxide Monitoring website, which monitor eruptions but do not measure the resulting aerosols.
They then produced a series of simulations of the gases that would likely have been lofted into the atmosphere by the eruptions, as well as the resulting chemical reactions that would have generated aerosols. For the simulations, they turned to an advanced computer model, the NCAR-based Whole Atmosphere Community Climate Model, which enables scientists to study the atmosphere from Earth’s surface all the way up to 140 kilometers (87 miles).
Credit: @UCAR. Scientific visualization by Michael Mills, NCAR.
“This is the first time that this many volcanic eruptions occurring over the past quarter century have been simulated interactively from sulfur emissions in a global climate model,” Mills said.
The research showed that satellites are missing 50-95 percent of stratospheric aerosols at middle and higher latitudes, where cloud cover makes it more difficult for satellites to observe that low in the atmosphere. Volcanic aerosols also impact depletion of the ozone layer, and the authors show that models have been failing to account for 60 percent of that effect.
To verify the accuracy of the simulations, the study team used measurements taken with ground-based lidars and balloon-borne instruments. They found that the model simulations corresponded remarkably well with these observations, which show a significant increase in volcanic aerosol since 2005.
“This represents an important new capability for climate modeling,” Mills said. “It can greatly advance our understanding of how volcanic eruptions influence the climate system.”
- Global volcanic aerosol properties derived from emissions, 1990-2014, using CESM1 (WACCM) - Michael J. Mills, Anja Schmidt, Richard Easter, Susan Solomon, Douglas E. Kinnison, Steven J. Ghan, Ryan R. Neely III, Daniel R. Marsh, Andrew Conley, Charles G. Bardeen, Andrew Gettelman - 2016, Journal of Geophysical Research: Atmospheres - 121, DOI: 10.1002/2015JD024290
- Volcanic emissions: More than meets the eye? New method estimates climatic influence of eruptions - Article published by NCAR/UCAR (Accessed March 15, 2016)
Featured image: Aerosols from Nyamuragira eruption in December 2006. Credit: NCAR/UCAR