This is the fallacy of counting the set of things that don't happen (I don't know if there's a technical term for it). The rivers aren't on fire anymore, the air is clean, the skies are safe - things are just about as good as they've ever been (despite a few outliers). That's all thanks to voting and common-sense regulations.

So to answer your question directly, "pretty much constantly but it's easy to miss since by definition they're successfully being prevented."