Is the idea that many people seem unable to detect gradual but deadly trends in modern civilization an example of the Hawthorne Effect?

No, the idea that many people are unable to detect gradual but deadly trends in modern civilization is not an example of the Hawthorne Effect. The Hawthorne Effect refers to changes in behavior that occur when people know they are being observed. In this case, the issue is related to awareness and perception of long-term trends, rather than the impact of observation on behavior.