What is a primary cause for the thinning of the ozone layer over Antarctica?

The primary cause for the thinning of the ozone layer over Antarctica is the use of chlorofluorocarbons (CFCs). These are human-made compounds that were commonly used in refrigeration, air conditioning, foam blowing, and aerosol propellants. When CFCs are released into the atmosphere, they eventually rise to the stratosphere, where they are broken down by ultraviolet radiation, releasing chlorine atoms.

These chlorine atoms react with ozone (O₃) molecules, leading to a significant reduction in ozone concentration. The peculiar atmospheric conditions over Antarctica, including extreme cold and the presence of polar stratospheric clouds, enhance this process. These clouds provide a surface for reactions that release more chlorine from CFCs, making the ozone depletion particularly pronounced over this region during the Southern Hemisphere's spring months.

Other options do not primarily contribute to the depletion of the ozone layer in the same manner. Burning fossil fuels primarily leads to increased carbon dioxide and other greenhouse gases, while the atmospheric testing of nuclear weapons has various environmental impacts but is not a direct cause of ozone depletion. The release of methane from farm animals contributes to global warming rather than specifically affecting ozone levels.