Home run? I count it as a five-bagger.
Of course for the keptocrats and those who feed them the problem isn’t that warnings go unheeded, but that they are heeded. :smack:
Oh my.
It may be a vain hope, but I think scare tactics are more effective when they’re firmly grounded in reality.*
I am tired of ignorant media reports trumpeting climate change on the basis of a single temperature record or severe storm (“See! There’s your proof!! These are gonna be a lot more common!!!”). Instead of singling out isolated events, take the trouble to explain how such things are already on the increase (at least in some areas) and where the trends are as of right now. I can see changes in my neck of the woods just from looking at the times of first autumn frost logged in my garden journal (on average about a week later than it was in 2001). I’m not going to be impressed if told that gosh, frost was a week later than the 30-year average this year. Year to year variance is not a big deal - show us the pattern over an extended period of time.
*I hear antivaxers moaning about “scare tactics”. A series of preventable disease outbreaks has a way of getting people to focus. 
Actually the most accurate answer was subtly included almost by accident, right in the opening post:
the answer is sneakily in the boy-who-cried-wolf story.
There’s really only one thing that makes a warning effective (if you assume basically competent formulation of the message, of course). That one thing, is the same answer as what makes plants grow: fertile ground.
What makes any warning work, is that the particular person or people getting the warning, can believe it. The boy-who-cried-wolf, caused the "ground" he was trying to "seed" with his message to become "infertile" by his repeated fake warnings. But in other cases, perhaps most common, is simply the the person or people being warned, can't conceive of what they are being told.
People were warned for hundreds of years, that pollution could destroy even the largest rivers, but until the first people actually found that all the fish were dead, and the water was poisonous, they couldn’t imagine that the warnings were valid. After all they’d spent hundreds of years, throwing all kinds of crap into the river, and it just moved off downstream, and all was well.
Most small children don’t understand warnings THEY get from parents, simply because they don’t know enough about the world yet. Even if their parents always told them the truth, some warnings will still fail, because the kids don’t have any way to comprehend what they are hearing.
So that’s it, really. What makes a warning work, is that the person who gets it, understands and believes it. No matter how clear and urgent, and no matter how obviously important or how well phrased the warning is, unless the people it’s aimed at are ready and willing to hear it, it will fail.