Climate change may prevent cooling by volcanic eruptions

November 16, 2016
Image: 
Comic by science writer JoAnna Wendel.

New research by PhD student Thomas Aubry shows that climate change may hamper the ability of large volcanic eruptions to cool down the planet.

Large volcanic eruptions produce plumes containing sulfuric gases that can reach 10 – 15 kilometers high, reaching a layer of Earth's atmosphere known as the stratosphere. There the gases react with water to form aerosols, tiny suspended particles that reflect incident sunlight away from the Earth thereby cooling the planet. Aerosol particles linger in the stratosphere for 1 – 2 years; aerosols that form in the lower level of the atmosphere, the troposhere, are short lived because they are purged by precipitation. Historic large volcanic eruptions have directly coincided with some of the coolest global temperatures in human history, and the rate of global warming has slowed over the last 10 – 15 years in part to volcanically generated sulfuric aerosols.

“Volcanic eruptions tend to counteract global warming. But as the planet warms and our atmosphere changes, we’ve found that less eruptions may reflect back the Sun's radation,” said Thomas “It will be harder for the volcanic gases to reach high enough into atmosphere to help cool the planet.”

Thomas combined a of volcanic plumes with published global climate models to determine their interaction. He discovered that two effects of climate change will raise the bar on the intensity of a volcanic eruption required to for the plume to reach the stratosphere. First, increased carbon dioxide concentrations in the atmosphere increases the density gradient of the atmosphere through which the plume travels, causing the volcanic plume to stabilize and spread at lower altitudes. Second, the volume of the troposphere itself will expand, shifting the troposphere–stratosphere boundary higher. As a result, the average input of sulfuric gas input to the stratosphere is modeled to decrease anywhere from 2 – 12% over the next century, and by as much as 25% within the next two centuries.

Just how those changes will impact Earth's surface temperature is a subject of further study. Thomas' supervisor, Mark Jellinek, notes that this “new positive feedback has provocative implications for understanding climate variability in Earth’s past. In particular, this mechanism may have contributed to Earth’s entry into a protracted global glaciation around 700 Million years ago (Snowball Earth).”

Thomas' results are published today in an article entitled Impact of global warming on the rise of volcanic plumes and implications for future volcanic aerosol forcing in the Journal of Geophysical Research: Atmospheres. Thomas' results were also covered in the American Geophysical Union's blog Geospace, where science writer and artist JoAnna Wendel documented Thomas' research as a colourful comic.

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