If hearing the word concerning used as an adjective to mean “causing anxiety” gives you a chalkboard moment, you may as well get used to it. The usage has yet to make its way into all the dictionaries, but it has hit the mainstream and it won’t be turned back.
For about 200 years, concerning has been functioning quite happily as a preposition to mean any of the following:
with reference to
with regard to
with respect to
on the subject of
in connection with
Supporters of the adjectival use of concerning point to the definition in the OED: “that gives cause for anxiety or distress.” The one citation given for this usage is from Pamela (1740), the overwrought epistolary novel by Samuel Richardson. Pamela is a virtuous young maidservant resisting the overtures of her employer. Here is the passage in which concerning means “anxiety-producing.” The words not in quotations belong to Pamela’s narration:
“Well,” said he, “if you won’t eat with me, drink at least with me.”
I drank two glasses by his over-persuasions, and said, “I am really ashamed of myself.”
“Why, indeed,” said he, “my dear girl, I am not a very dreadful enemy, I hope! I cannot bear any thing that is the least concerning to you.”
Elsewhere, Richardson uses concerning conventionally, as a preposition:
“Mrs. Jewkes has directions concerning you.”
I hope, whatever be your honour’s intention concerning her, you will not be long about it.
Have mercy on me, and hear me, concerning that wicked woman’s usage of me.
To perform a Google Ngram search, I used the phrase “very concerning” to get an idea of the adjectival use of concerning. The phrase is effectively flat-lined in American English until 1972; it begins to take off in the late 1980s. My guess is that political writers and other media manipulators rediscovered adjectival concerning as a useful euphemism for words that might frighten voters or consumers. Compare:
Increased juvenile drug use is disturbing.
Increased juvenile drug use is concerning.
The possibility of more terroristic attacks is a cause for concern.
The possibility of terroristic attacks is concerning.
The rise in global temperatures is troubling.
The rise in global temperatures is concerning.
It seems to me that concerning has the effect of distancing a perceived threat by making it seem to be a matter to be watched, but perhaps not one to get too excited about for the present.
Whatever the reasons for the current popularity of concerning as an adjective to describe anything that causes concern, it has certainly caught on in American speech.
If you find yourself looking for an alternative, here’s a list of possibilities: