I came across the following statement:
People have either ignored or neglected these effects because...
I think there must be some subtle differences between the two bold words. Anyone could point out it? You are appreciated.
one is actively not paying any attention, on purpose
She ignored his advances until he left her alone.
The referee ignored the crowd's screaming for a penalty.
one may have forgotten about, or not been aware of a critical situation for something one was supposed to take care of or oversee
Their electricity bill was very high since they neglected to turn off the lights.
The plant was never watered and died of neglect.
Your example sentence would be more correct as
People have either ignored or neglected...
However, neglect also has a meaning that implies a sense of responsibility:
[3.] to be remiss in the care or treatment of
So, the word ignore suggests that the people are aware of the effects, but do not give it much thought or do anything about it. It is possible that they are not obligated to take any action. On the other hand, using the word neglect, the author suggests that the people have a responsibility to do something about these effects, like remedy them, record them, report them, etc.
Note, there is a matter of "People has". As I understand it, the word people is plural. So I think it should be People have, unless there is a good reason it should be otherwise that has been omitted.