wˈʌn θˈɪŋ ɪz fɔːɹ sˈɜːʔn̩: pˌiːˌɛmsˈiːz ɑːɹ ʃˈeɪpt baɪ ðə mˌiːɾɪoːɹˈɑːlədʒi ʌvðə mˈɛsəsfˌɪɹ, wˌɪtʃ dˈʌz ɐpˈɪɹ təbi tʃˈeɪndʒɪŋ.
One thing is for certain: PMC's are shaped by the meteorology of the mesosphere, which does appear to be changing.