Complex sentence: The CFC ban of the early 1990s was implemented by international treaty (see Montreal Protocol), after some scientists advanced the theory that CFC emissions were depleting the ozone layer, which (they predicted) would allow harmful ultraviolet radiation to reach the earth's surface.
Split into simpler sentences: The CFC ban of the early 1990s was implemented by the Montreal Protocol, an international treaty. The ban came after some scientists advanced the theory that CFC emissions were depleting the ozone layer, which they predicted would allow harmful ultraviolet radiation to reach the earth's surface.