To accompany my post on back close rounded vowels here is another dangerous prediction about the future of General British English pronunciation. At some date in the future, maybe not too distant, GBE will have no centring diphthongs. /ɪə eə ʊə/ are doomed to extinction. They will go the way of /ɔə/, which I reckon is dead.
/ʊə/ is hanging on by its fingertips, I think, but has for most people (1) merged with /ɔ:/ OR (2) merged with /ɜ:/ OR (3) become a new phonological unit which we could symbolise as /ʊ:/. I don’t think we can exclude the possibility that combinations of (1), (2) and (3) occur in some people’s speech. I don’t know if anyone has done any empirical studies on the various fates of /ʊə/, but I reckon it would a worthwhile project.
/eə/ is pretty sickly looking too. It is my impression that increasingly people are using a long monophthong [ɛ:]. The same sort of fate is overtaking /ɪə/, which now turns up as [ɪ:] in all environments for many younger speakers.
|The situation with the last two is interesting in NZ English too. For a long time now, the /ɪə/ – /eə/ distinction has been lacking for many, probably most, NZ speakers. However, a change has taken place relatively recently. Initially, it seems that word pairs like bear/beer were homophones in NZE, both being produced with [eə]. However, there has been a switch and now, for younger speakers, both have [ɪə].|