Guest essay by Eric Worrall
A study published in the Journal of Geophysical Research claims that global warming will impede the ability of volcanoes to push sulphur compounds into the stratosphere, which will in turn reduce the cooling effect of volcanic eruptions.
Climate change may prevent volcanoes from cooling the planet
When an eruption is powerful enough, volcanoes spew sulfur gasses high into the atmosphere, reaching a layer called the stratosphere, about 10 to 15 kilometres above Earth’s surface. Here, gasses react with water to form aerosol particles that linger in the stratosphere for one or two years, reflecting sunlight and heat from the sun, and cooling the planet. On average, there are anywhere from three to five eruptions that reach the stratosphere every year.
Previous research has shown that as the planet warms, the lower layers of the atmosphere will expand, making it much harder for the gasses to reach the stratosphere. At lower levels, in the troposphere, the gasses quickly get turned into aerosols and clouds and precipitate back down to earth as rain or snow.
“Volcanic eruptions tend to counteract global warming but as the planet heats up and our atmosphere changes, we’ve found that fewer eruptions will be able to reflect the sun’s radiation,” said Thomas Aubry, a PhD student studying climate and volcanoes. “It will be harder for the volcanic gasses to reach high enough into atmosphere to help cool the planet.”
The abstract of the study;
Impact of global warming on the rise of volcanic plumes and implications for future volcanic aerosol forcing
Thomas J. Aubry ,A. Mark Jellinek, Wim Degruyter, Costanza Bonadonna, Valentina Radić, Margot Clyne, Adjoa Quainoo
Volcanic eruptions have a significant impact on climate when they inject sulfur gases into the stratosphere. The dynamics of eruption plumes is also affected by climate itself, as atmospheric stratification impacts plumes height. We use an integral plume model to assess changes in volcanic plume maximum rise heights as a consequence of global warming, with atmospheric conditions from an ensemble of global climate models (GCM), using three representative concentration pathways (RCP) scenarios. Predicted changes in atmospheric temperature profiles decrease the heights of tropospheric and lowermost stratospheric volcanic plumes and increase the tropopause height, for the RCP4.5 and RCP8.5 scenarios in the coming three centuries. Consequently, the critical mass eruption rate required to cross the tropopause increases by up to a factor 3 for tropical regions, and up to 2 for high-latitude regions. A number of recent lower stratospheric plumes, mostly in the tropics (e.g., Merapi, 2010), would be expected to not cross the tropopause starting from the late 21st century, under RCP4.5 and RCP8.5 scenario. This effect could result in a ≃5 − 25% decrease in the average SO2 flux into the stratosphere carried by small plumes, which frequency is larger than the rate of decay of volcanic stratospheric aerosol, and a ≃2 − 12% decrease of the total flux. Our results suggest the existence of a positive feedback between climate and volcanic aerosol forcing. Such feedback may have minor implications for global warming rate but can prove to be important to understand the long-term evolution of volcanic atmospheric inputs.
Read more (paywalled): http://onlinelibrary.wiley.com/doi/10.1002/2016JD025405/full
I don’t have access to the full study, but the obvious question – why did the researchers base their study on a model?
Why not send a few weather balloons through volcanic plumes at different latitudes and different times of year, to actually measure the impact of different atmospheric conditions on the formation of volcanic stratospheric aerosols?
The atmosphere is much thicker at the equator than at the poles – the troposphere is only around 4 miles thick at the poles during winter, but reaches 12 miles thick in equatorial regions.