It is a claim he carefully lays out and in my mind, proves up , in his 2006 book of that title.
If you are a boomer and fear for this planet's climate, I strongly urge you to read and re-read Steinhorn's book.
But, not unexpectedly, I wish Professor Steinhorn had written another book on this subject.
Basically, I want to see him answer this question :
Was the baby boom (the unexpected blip upwards in births from 1941-1966 against a century and a half of decline) caused by postmodernity, or did it itself cause postmodernity, or were the two simultaneous events (the coming of age of boomers and of postmodernity) mere coincidences in time?