When I was a girl, 50 years ago, we had very smoggy cities, wild bird eggs going too thin to hatch because of the use of DDT, pesticides that stay effective for 60+ years, and litter on the highways beyond belief. We had numerous species going extinct including whooping cranes, alligators, hawks, and eagles. Today, none of our cities are identified solely by their smog production. We have banned DDT. Pesitcides are, as a matter of course, strictly regulated. Litter on highways is way better, and all the species I've mentioned have made come-backs along with wolves, black bears, and a few others.
There's always room for improvement. We will always have work to do; but, from my perspective at almost 60, things look--and breathe--a whole lot better than they did so many years ago.