The scientist's groundbreaking research could ______ the way we understand climate change and its effects on the environment.

The context of the sentence indicates that the scientist's groundbreaking research has the potential to change or modify our understanding of climate change and its effects on the environment. "Alter" means to change or modify, which fits perfectly with the idea of changing our understanding. "Prevent" suggests stopping something from happening, which does not apply in this context. "Ignore" means to disregard or overlook, which is the opposite of enhancing understanding. "Delay" means to postpone or slow down, which is not relevant to changing understanding.