I am unable to actually find an sort of source for the statistic that "Adjuncts now make up well over 50 percent of the faculty at colleges and universities."
It seems to go back to the SEIU, a group that is attempting to unionize adjunct positions. I have seen it quoted in a number of ways, including "50% of part time faculty at universities are adjunct." and "50% of teaching positions at universities are adjunct."
I would like to see some sort of actual report that shows the source of that. My (very limited, anecdotal) experience seems to indicate much fewer than 50% of professors are adjunct. It all depends on how you count these things.
In 1975, 45% of teaching staff was tenure or tenure-track, 34% non-tenure-track (full or part time), and 21% grad students. In 2011, it's 24% tenure or tenure track, 57% non-tenure-track, and 19% grad students.
Now, part-time employees may make up a smaller proportion of actual teaching time than full time, but remember also that tenure track professors and grad students spend time doing research as well, not all of their time is spent teaching.
How many of your professors did you know the status of? I know that that certainly wasn't something I kept close tabs on when I was in college; there were a few professors who I knew well enough to know their status as tenured, tenure track, or not tenure track, but for many I didn't pay attention. Many of the adjunct professors are likely teaching intro-level classes that everyone is required to take; your freshman English or writing or math requirements.
Also recall that the more prestigious the school, the less likelihood that they will rely heavily on adjunct professors. Smaller state schools, community colleges, and for-profit schools may use them more often. Edit to add: the AAUP has another report that breaks down the faculty by school, and you can clearly see that these kind of non-tenure track and part time professorships are much more common at community colleges, smaller less prestigious schools, and for-profit schools, with some of them having 100% contingent (non-tenure track) faculty: http://www.aaup.org/sites/default/files/files/AAUPContingent...
And further, they may be named different things, but be roughly equivalent in job security, prestige, and benefits. Lecturer, instructor, visiting professor, visiting lecturer, assistant or associate teaching professor, etc.
Nonetheless, the AAUP document seems to show that even at US public doctoral and research universities, in 2005 non-tenure-track employees made up about a quarter of the full-time faculty and about 40% of all faculty if you include the part-timers (p. 18). There's also the issue of graduate students who teach or do research work. The numbers apparently included teaching grad. students, but only those which had been self-reported by their institutions as "employees" rather than recipients of valuable teaching/research experience (p. 10): it's not hard to imagine some under-reporting there.
According to the report, [tenure and tenure-track] positions now make up only 24 percent of the academic work force, with the bulk of the teaching load shifted to adjuncts, part-timers, graduate students and full-time professors not on the tenure track.
The report was published by Center for the Future of Higher Education in 2012. Link: [2]
From the executive summary from this 2010 publication by the American Federation of Teachers [3]:
Altogether, part-time/adjunct faculty members account for 47 percent of all faculty, not including graduate employees. The percentage is even higher in community colleges, with part-time/adjunct faculty representing nearly 70 percent of the instructional workforce in those institutions.
It seems to go back to the SEIU, a group that is attempting to unionize adjunct positions. I have seen it quoted in a number of ways, including "50% of part time faculty at universities are adjunct." and "50% of teaching positions at universities are adjunct."
I would like to see some sort of actual report that shows the source of that. My (very limited, anecdotal) experience seems to indicate much fewer than 50% of professors are adjunct. It all depends on how you count these things.