Here's the plot of Neal Stephenson's 2021 novel "Termination Shock":
The book is about a solar geoengineering project conceived by a Texas oil-industry billionaire named T.R. Schmidt. Schmidt builds a launcher on the Texas-Mexico border to fire sulfur into the air, a form of stratospheric aerosol injection intended to cool the planet by reflecting sunlight into space. This technique replicates the effects of volcanic eruptions that inject sulfates into the atmosphere and produce global cooling, such as the 1991 Mount Pinatubo eruption.
Somebody is doing this now and nobody's quite sure what impact it will make:
An American startup firm has admitted to releasing reactive particles into the atmosphere in an attempt to alter the climate. The move has attracted widespread criticism, and marks a potentially dangerous new stage in the intensifying response to Earth’s “climate crisis”.
Just before Christmas 2022, the firm ‘Make Sunsets’ acknowledged it had launched weather balloons containing sulfur dioxide into the stratosphere. The launches took place in April 2022, in Baja California, Mexico, months before the company was even incorporated.
When quizzed about it, the company’s CEO, Luke Iseman, was unrepentant. “It’s morally wrong, in my opinion, for us not to be doing this”, he said, adding that it’s important “to do this as quickly and safely as we can,” because of the threat of man-made climate change.
In the book, the Indian government sends a military squad to destroy the sulfur launching site because the monsoon period was delayed.