According to a study conducted by the National Center for Atmospheric Research (NCAR), proposals to offset global warming by artificially seeding the stratosphere with sulfate particles could do more harm than good by having a negative impact on Earth's protective ozone layer. Such a plan might not only delay recovery of the ozone hole currently situated over the Antarctic by as much as 30 to 70 years, it could also destroy anywhere from one-fourth to three-fourths of the ozone layer above the Arctic. This would affect a significant part of the Northern Hemisphere due to atmospheric circulation patterns.
The idea to artificially cool the Earth's surface by injecting large amounts of sun-blocking sulfate particles into the stratosphere was actually inspired by volcanoes. As history has shown, sulfur particles from volcanic eruptions have resulted in reduced surface temperatures on Earth. What the researchers also discovered, however, is that volcanic sulfates provide a surface on which chlorine gases in the cold polar lower stratosphere can become activated, causing chemical reactions that intensify the destruction of ozone molecules. In other words, although the sulfates themselves would not directly destroy ozone, they could be a catalyst.
To determine the relationship between sulfates and ozone loss, the researchers used a combination of measurements and computer simulations. They then estimated future ozone loss by looking at two geo-engineering schemes: one using volcanic-sized sulfates and one using much smaller injections. What they found was that injecting small particles over the next 20 years could reduce the ozone layer in the Northern Hemisphere by 100 to 230 Dobson Units. A Dobson Unit is equivalent to the number of ozone molecules that would create a layer 0.01 millimeters thick under conditions at Earth's surface.