In cases where science has been brought to bear on ghosts the best that can be ascertained, AFAIK, are fields of "energy" that persist where certain deceased people existed prior to assuming room temperature. There are many accounts of some kind of plasma that is visible in places attested as "haunted." At any rate, what reason is there to assume, if we should be able to put scientific terms on a phenomenon, that the phenomenon is now "natural" when prior to our understanding it was considered "supernatural?"
It wouldn't be science that has done that, although it might be guys with fancy looking ghostbuster stuff.