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Guest essay by Eric Worrall

If you block the sun, you hurt food production. There’s even a study. But this terrifying problem has not stopped climate enthusiasts from pushing forward with an attempt to recreate the end of the dinosaur age, to “save” us from 1C of global warming.

Before geoengineering to mitigate climate change, researchers must consider some fundamental chemistry

By  University of Pennsylvania
NOVEMBER 22, 2021

It’s a tempting thought: With climate change so difficult to manage and nations unwilling to take decisive action, what if we could mitigate its effects by setting up a kind of chemical umbrella—a layer of sulfuric acid in the upper atmosphere that could reflect the sun’s radiation and cool the Earth?

According to a new study in the Journal of the American Chemical Society, a collaboration among Penn scientists and two groups in Spain, atmospheric conditions in the stratosphere pose a challenge to generating sulfuric acid, making its production less efficient than might have previously been expected. Thus more groundwork exploring the chemistry of how sulfuric acid and its building blocks will react in the upper atmosphere is required in order to confidently move forward with this climate geoengineering strategy, the researchers say.

“These fundamental insights highlight the importance of understanding the photochemistry involved in geoengineering,” says Joseph S. Francisco, an atmospheric chemist in Penn’s School of Arts & Sciences and a co-corresponding author on the study. “That’s critically important and it’s something that’s been ignored.”

Using sulfuric acid to blunt the sun’s rays as a means of curbing climate changeimpacts is based on a natural phenomenon: When volcanoes erupt, the sulfur they emit creates localized—or sometimes even far-reaching—cooling clouds that filter the sun. But those clouds emerge in the troposphere, which ranges from the Earth’s surface to about 10 kilometers up. Geoengineering using sulfuric acid would happen a good deal higher, in the stratosphere, from about 10 to 20 kilometers above the planet.

“One of the implications of this finding is, if you put sulfur dioxide up there, it’s going to just be recycling around,” Francisco says. “So it opens the door to whether we have a full understanding of atmospheric sulfur chemistry up in the stratosphere.”

The findings also highlight the need for a Plan B if the atmospheric chemistry doesn’t play out as expected. “It raises a fundamentally important question,” Francisco says. “If we put the sulfur dioxide in, can we get it out of the stratosphere?

Read more: https://phys.org/news/2021-11-geoengineering-mitigate-climate-fundamental-chemistry.html

The abstract of the study which discusses what geoengineering could do to plant growth;

Estimating global agricultural effects of geoengineering using volcanic eruptions

Published: 08 August 2018

Jonathan Proctor, Solomon Hsiang, Jennifer Burney, Marshall Burke & Wolfram Schlenker

Nature (2018)

Solar radiation management is increasingly considered to be an option for managing global temperatures, yet the economic effects of ameliorating climatic changes by scattering sunlight back to space remain largely unknown. Although solar radiation management may increase crop yields by reducing heat stress, the effects of concomitant changes in available sunlight have never been empirically estimated. Here we use the volcanic eruptions that inspired modern solar radiation management proposals as natural experiments to provide the first estimates, to our knowledge, of how the stratospheric sulfate aerosols created by the eruptions of El Chichón and Mount Pinatubo altered the quantity and quality of global sunlight, and how these changes in sunlight affected global crop yields. We find that the sunlight-mediated effect of stratospheric sulfate aerosols on yields is negative for both C4 (maize) and C3 (soy, rice and wheat) crops. Applying our yield model to a solar radiation management scenario based on stratospheric sulfate aerosols, we find that projected mid-twenty-first century damages due to scattering sunlight caused by solar radiation management are roughly equal in magnitude to benefits from cooling. This suggests that solar radiation management—if deployed using stratospheric sulfate aerosols similar to those emitted by the volcanic eruptions it seeks to mimic—would, on net, attenuate little of the global agricultural damage from climate change. Our approach could be extended to study the effects of solar radiation management on other global systems, such as human health or ecosystem function.

Read more (paywalled): https://www.nature.com/articles/s41586-018-0417-3

You can just imagine the scenario. Scientists pump a bit of sulfur into the atmosphere and nothing happens. Then they pump some more, the needle still doesn’t move. Then suddenly an extreme atmospheric event, like a large hurricane or a volcanic eruption, throws up some extra water vapour, and the entire sky goes black.

I’m glad at least one of them asked the obvious question, how to get the sulfur out of the atmosphere if it all goes wrong? But I’m guessing if the opportunity arose for a full scale test they would still probably want to try it out.

via Watts Up With That?

November 23, 2021