The worst thing is they brainwash kids into believing it. I’ve told people in their 20s and 30s how much worse the environment was when I was young and they look at me like I’m crazy. Like, the air was so bad in LA that you couldn’t see 3 blocks sometimes, and the Ohio river actually caught on fire. It’s been cleaned up to the extent that the environmental groups had to claim CO2 is pollution to stay in business. They had literally never heard any of that before.
They need to claim an emergency to remain relevant.
For some reason, pessimism (gloom and green) is seen as a mark of intelligence, or a “progressive” mindset; while optimism is seen as a mark of naivety or a tendency to drag one’s knuckles while walking. You especially see that amongst the young hipsters, who dwell in coffee shops; or the brainwashed idealists on campuses everywhere.
It’s not just the young — even many people, who also lived through the changes you describe, refuse to believe that anything is getting better. It’s not just confined to the environment — this negativity encompasses every aspect of life. It’s a large part of the reason that disaster movies are perennially among the biggest Hollyweird block-busters.