grammar - What is the grammatical function of the NP (or clause?) in this sentence?

I just came across this sentence in a newspaper:

The mill ceased production in 1982, an early warning of another revolution on a global scale.

I know it is a perfectly grammatical sentence and I've seen a lot of similar ones. But I'm wondering what grammatical function the latter NP (or clause?) plays. It looks like a relative clause without "which is", right? Does this grammatical role have a name?