Without the hyphen it could suggest that CC scientists are responsible for deadly weather. They may be responsible for the hype, but not the deadly weather. I'd have written "Scientists claim deadliest..." Probably too wordy for a headline. If word count a problem then the hyphen seems a reasonable compromise (to me).I know I misread what this was saying but not sure the hyphen makes it totally clear what was meant.
Better than my suggestion or a hyphen. Now why didn't I think of that?say scientists